Anterior Vertebral Body Tethering for Adolescent Scoliosis with Growth Remaining: A Retrospective Review of 2 to 5-Year Postoperative Results

Growth modulation increases clinical success in vertebral body tethering

PURPOSE

The relationship between skeletal maturity and postoperative growth modulation (GM) in patients treated with Vertebral Body Tethering (VBT) is poorly understood. We aimed to: (1) identify preoperative skeletal maturity factors associated with GM, and (2) assess the relationship between GM and postoperative success in patients treated with VBT.

METHODS

We retrospectively reviewed radiographic data from 55 patients with a minimum follow-up of 2 years (2.6 ± 0.5). Changes in standing height and skeletal maturity (Sanders Stage [SS], Triradiate Cartilage [TRC], and Risser Stage [RS]) were assessed at all timepoints. Patients that exhibited GM were defined by ≥ 6° of deformity correction from first erect to any postoperative timepoint. Successful outcomes were defined by a Cobb Angle of ≤ 30° at latest follow-up.

RESULTS

We observed GM in 42% (23 of 55) of patients. GM was influenced by SS (p = 0.017) and TRC (p = 0.013), but not RS (p = 0.104). We observed a successful outcome in 91% of patients that exhibited GM compared to 44% of those that did not (p < 0.001; OR 12.9). No difference was identified in preoperative deformity magnitude or amount of initial correction achieved between patients that did and did not exhibit GM. Patients who exhibited GM had a higher revision rate (30.4%) than when compared to those who did not (3.0%, p = 0.005, OR 9.7).

CONCLUSION

Postoperative success after VBT is directly related to GM. Patients who modulate their deformity are 12.9 times more likely to exhibit a successful outcome and can be identified preoperatively based on SS or TRC.

Correction of L5 Tilt in 2-Row Vertebral Body Tethering Versus Posterior Spinal Fusion for Adolescent Idiopathic Scoliosis

STUDY DESIGN

Single-center retrospective cohort study.

OBJECTIVE

To compare the correction of fractional curve and L5 tilt in 2RVBT versus PSF with LIV in the lumbar spine.

SUMMARY OF BACKGROUND DATA

Vertebral body tethering, an AIS fusion-alternative, avoids rigid constructs, allowing for lower instrumented vertebra (LIV) selection. Single-tether constructs break, but mini-open thoracoscopic assistant double-row vertebral body tethering (2RVBT) reduces this. Limited comparative studies exist with posterior spinal fusion (PSF).

METHODS

Retrospective analysis of AIS correction surgeries with lumbar LIV using preoperative and minimum 2-year postoperative imaging. Patients were divided into 2RVBT or PSF groups. Data included age, Riser, UIV, LIV, instrumented levels, and revision rates. Radiographic analyses included preoperative and postoperative main curve Cobb (MCC), secondary curve Cobb (SCC), fractional curve Cobb (FCC), and L5 tilt.

RESULTS

Ninety-nine patients participated (49 in 2RVBT, 50 in PSF). Preoperatively, secondary CC differed significantly (2RVBT: 44.6±10.4 degrees vs. PSF: 39.5±11.8 degrees, P =0.026), but not L5 tilt, MCC, or FCC. Postoperatively, MCC (2RVBT: 25.7±12.3 degrees vs. PSF: 19.5±7.4 degrees, P =0.003) and SCC (2RVBT: 18.0±8.4 degrees vs. PSF: 14.5±6.6 degrees, P =0.012) varied. Preoperative to postoperative changes in MCC (2RVBT: -32.0±11.3 degrees vs. PSF: -37.2±13.3 degrees, P =0.044) and L5 tilt (-13.8±9.0 degrees vs. PSF: -8.1±6.8 degrees, P =0.001) differed. Revision rates were similar (2RVBT: 2.0%, PSF: 4.0%, P =0.57). In 2RVBT, 3 tethers broke, 1 revision occurred for a broken tether, and 1 pleural effusion needed thoracocentesis. In PSF, 1 superficial infection needed surgery, and 1 revision was for add-on phenomenon. After PSM for Lenke classification, 54 patients remained (27 in each group). At 2 years, 2RVBT showed less MCC correction (-30.8±11.8 degrees vs. -38.9±11.9 degrees, P =0.017), but greater L5 tilt correction (-14.6±10.0 degrees vs. -7.5±6.0 degrees, P =0.003).

CONCLUSIONS

This study with a minimum 2-year radiographic follow-up demonstrates that 2RVBT results in greater L5 tilt correction when compared with posterior spinal fusion after PSM for Lenke classification and similar rates of revision surgery.

LEVEL OF EVIDENCE

Level III.

Outcomes in patients with tether rupture after anterior vertebral tethering for adolescent idiopathic scoliosis: the good, the bad, and the ugly

INTRODUCTION

Though multiple studies have reported tether rupture rates after anterior vertebral tethering (AVT) as high as 50%, few have adequately analyzed the clinical significance of tether rupture and factors that potentially increase the likelihood of revision surgery. We reviewed 262 consecutive adolescent idiopathic scoliosis (AIS) patients after AVT with the goal of identifying early and late tether ruptures and categorizing these tether ruptures as inconsequential, consequential, problematic, or beneficial. Our hypothesis was that the tether rupture rate after AVT for AIS would be significant but only a small percentage of patients would require revision surgery.

METHODS

Charts, radiographs, and CT scans were reviewed for tether rupture in 262 consecutive AIS patients treated with AVT for thoracic and thoracolumbar/lumbar curves 33-77°. Early tether rupture occurred < 2 years and late tether rupture ≥ 2 years postoperatively. Tether rupture was further categorized as inconsequential (final curve < 40° and no pain), consequential (curve ≥ 40° and/or convex back pain), problematic (revision surgery required), or beneficial (improvement of overcorrection) at follow-up.

RESULTS

Of 262 consecutive AIS patients status post AVT (106 thoracic curves, 53 thoracolumbar curves, and 103 double curves), tether rupture was found in 45 patients with 66 curves (34 thoracic and 32 thoracolumbar/lumbar) treated at age 14.5 years and at Risser 2.6 and Sanders 4.7. Curves with tether rupture corrected from 50.3° preoperatively to 20.8° postoperatively, but lost 7.2° of correction with tether rupture settling at 28.0° final at 2.6 years (0-11 years). Early tether rupture occurred in 12/133 (9%) and late tether rupture in 33/129 (26%) patients with 2-11 year follow-up. Tether rupture was inconsequential in 67% (30/45) of patients, consequential in 13% (6/45), problematic in 16% (7/45), and beneficial in 4% (2/45). In those patients with tether rupture, 69% occurred in a thoracolumbar/lumbar curve and 47% demonstrated a rupture at L2,3. Revision surgery for a thoracolumbar/lumbar tether rupture involved tether replacement alone in 4 patients and thoracic fusion in 2 additional patients, 1 requiring thoracic fusion alone, and 1 requiring thoracic fusion with thoracolumbar/lumbar tether replacement (hybrid). Revision surgery for a thoracic tether rupture involved 1 tether replacement and 1 thoracic fusion. Revision surgery was unrelated to curve correction or loss of correction, but was related to multiple tether ruptures and convex back pain (p < 0.005).

CONCLUSION

This study demonstrated an early tether rupture rate of 9% and late tether rupture rate of 26% in a large series of patients treated with AVT for AIS over 14 years. While the majority of patients had inconsequential tether rupture (67%), with 7.2° loss of correction, a final curve < 40°, and no pain, a number of patients had consequential (13%) or problematic tether rupture (16%). These adversely affected patients had a final curve ≥ 40°, convex back pain, or required revision surgery. Additionally, a small number of patients (4%) actually benefitted from tether rupture by improvement in an area of impending overcorrection.

LEVEL OF EVIDENCE

IV.

Impact of growth on spinal biomechanics and tether force in VBT: a simulation study

PURPOSE

Vertebral Body Tethering (VBT) allows correction of scoliosis while preserving the spinal mobility. Despite an increasing availability of data on clinical experience and surgical techniques, there is still a lack of knowledge on the underlying biomechanics, specifically when considered in combination with growth. Therefore, the purpose of this study is to develop a growing flexible spine model to investigate spinal biomechanics after VBT surgery.

METHODS

A multi-body simulation approach was chosen. A growing, flexible thoracolumbar VBT spine model was developed to analyze the spinal biomechanics during various physiological movements and growth. The model includes a flexible spine with a VBT device and a musculoskeletal system. Therefore, the resulting tether tension and intervertebral compression force can be calculated with respect to the human anatomy and material properties of the VBT device.

RESULTS

During growth, the tether and compression forces increase continuously with the highest forces between L1 and L2. The highest tether force is measured at 50° lateral bend at 200 N pre-tension. The compression forces in a tethered spine are during adolescence up to twice higher than in a healthy spine.

CONCLUSION

The simulated biomechanical data provides insight into the forces exerted on the spine during various physiological movements and the remaining growth. They are consistent with previously published clinical data and underlie the finding that age at surgery or residual growth doesn't greatly affect tether forces. During growth, however, intervertebral compression forces increase.

The Fate of The Broken Tether: How Do Curves Treated With Vertebral Body Tethering Behave After Tether Breakage?

STUDY DESIGN

Retrospective, multicenter.

OBJECTIVE

The aim of this study was to assess curve progression and occurrence of revision surgery following tether breakage after vertebral body tethering (VBT).

SUMMARY OF BACKGROUND DATA

Tether breakage after VBT is common with rates up to 50% reported. In these cases, it remains unknown whether the curve will progress or remain stable.

MATERIALS AND METHODS

Adolescent and juvenile idiopathic scoliosis patients in a multicenter registry with ≥2-year-follow-up after VBT were reviewed. Broken tethers were listed as postoperative complications and identified by increased screw divergence of >5 degrees on serial radiographs. Revision procedures and curve magnitude at subsequent visits were recorded.

RESULTS

Of 186 patients who qualified for inclusion, 84 (45.2%) patients with tether breakage were identified with a mean age at VBT of 12.4±1.4 years and mean curve magnitude at index procedure of 51.8±8.1 degrees. Tether breakage occurred at a mean of 30.3±11.8 months and mean curve of 33.9±13.2 degrees. Twelve patients (12/84, 14.5%) underwent 13 revision procedures after tether breakage, including six tether revisions and seven conversions to fusion. All tether revisions occurred within 5 months of breakage identification. No patients with curves <35 degrees after breakage underwent revision. Revision rate was greatest in skeletally immature (Risser 0-3) patients with curves ≥35 degrees at time of breakage (Risser 0-3: 9/17, 53% vs. Risser 4-5: 3/23, 13%, P =0.01). Curves increased by 3.1 and 3.7 degrees in the first and second year, respectively. By 2 years, 15/30 (50%) progressed >5 degrees and 8/30 (26.7%) progressed >10 degrees. Overall, 66.7% (40/60) reached a curve magnitude >35 degrees at their latest follow-up, and 14/60 (23.3%) reached a curve magnitude >45 degrees. Skeletal maturity did not affect curve progression after tether breakage ( P >0.26), but time to rupture did ( P =0.048).

CONCLUSIONS

While skeletal immaturity and curve magnitude were not independently associated with curve progression, skeletally immature patients with curves ≥35 degrees at time of rupture are most likely to undergo additional surgery. Most patients can expect progression at least 5 degrees in the first 2 years after tether breakage, though longer term behavior remains unknown.

LEVEL OF EVIDENCE

Level III.

Two to five years pulmonary functions after thoracic, thoracolumbar and bilateral vertebral body tethering surgery

PURPOSE

Adolescent Idiopathic Scoliosis negatively impacts chest wall development. Bracing and fusion surgery have shown varied effects on pulmonary outcomes. Vertebral Body Tethering presents a growth-sparing alternative that might mitigate these effects by reducing biomechanical disruptions. Aim was to evaluate changes in pulmonary functions during the course of the follow-up after VBT surgery.

METHODS

Retrospective cohort study including patients who underwent Thoracic, Thoracolumbar and Bilateral VBT surgery with a minimum 24 months follow-up. Forced Vital Capacity (FVC%), Forced Expiratory Volume in the first second (FEV1%) and FEV1/FVC ratio were evaluated at multiple time points. Four groups were formed using main curve location and surgical technique. Analyses of variance were used to assess changes over time.

RESULTS

81 consecutive patients (76F, 5 M; 12.5 ± 1.6 years) with a mean follow-up 53.4 (24-105) months were included. Preoperatively, the median Sanders was 3 (1-7) and the median Risser was 0 (- 1-5). The mean MT curve of 50.8º ± 11.0º was corrected to 26.0º ± 7.3º at 6 weeks, which was modulated to 22.4º ± 13.4º. FVC%, FEV1%, and FEV1/FVC showed significant improvements over time for the entire cohort up to 2-3 years (p < 0.0005) where the curve type and surgical technique influenced improvement patterns. For patients with longer follow-up, values at 4-6 years did not differ from those at 2-3 years (p > 0.05, for all comparisons).

CONCLUSIONS

Thoracoscopic VBT surgery led to consistent increases in FVC%, FEV1%, and FEV1/FVC values across the entire cohort, which were sustained at longer follow-up in a subset of patients. Surgeries on thoracic curves showed more pronounced improvements compared to thoracolumbar curves.

KEY POINTS

Pulmonary function test results (FVC%, FEV1% and FEV1/FVC) improved following VBT surgery for AIS patients. Thoracic and thoracolumbar surgery for thoracic curves, and bilateral surgery resulted in more pronounced FVC% and FEV1% improvements. Improvement in FVC% and FEV1% values started earlier after Thoracic VBT. Thoracolumbar surgery for thoracolumbar curves displayed significant improvement only in FEV1/FVC results, as they had better preoperative pulmonary functions. Observed improvements in FVC%, FEV1% and FEV1/FVC were preserved at 4-6 and 7-8 years follow-up in a subset of patients, averaging a mean duration of 48.7 months for the whole cohort.

Compensatory thoracic curve correction in lumbar anterior vertebral body tether (VBT) versus lumbar posterior spinal fusion (PSF)

PURPOSE

Anterior vertebral body tethering (VBT) is a non-fusion surgical option for skeletally immature patients with idiopathic scoliosis. Prior studies demonstrated compensatory correction of the thoracic curve after lumbar posterior spinal fusion (PSF); however, no studies have examined thoracic curve correction after lumbar VBT.

METHODS

Patients with Lenke 5 + 6 lumbar scoliosis who underwent VBT and at least 2 years' follow-up were compared to matched lumbar PSF patients. Groups were compared for major lumbar (L) and compensatory thoracic (T) curve correction, coronal/sagittal balance, and complications.

RESULTS

24 AVBT and 24 PSF patients were matched 1:1 for skeletal maturity and curve flexibility. There were no significant differences between VBT and PSF for average pre-operative or 2 year post-operative major L or compensatory T curves. Average final L curve correction was 50% VBT and 60% PSF (p = 0.08); average T curve correction was 17% VBT and 20% PSF (p = 0.18). Compared to pre-operative flexibility radiographs, the final post-op thoracic curves were 6° (VBT) and 5° (PSF) larger. PSF had better coronal balance by average of 17 mm (p < 0.0001). There were seven (24%) reoperations in the VBT group: two overcorrections relaxed, two T adding-on (extended to T by PSF-1, VBT-1), one broken tether converted to PSF. There was one (4%) reoperation in the PSF group (10-year post-op extension).

CONCLUSION

Compensatory thoracic correction was achieved to a similar degree for lumbar VBT and PSF patients. There was little change in thoracic curve magnitude over time, and, on average, the correction did not reach the pre-operative flexibility curve measurement. There was better coronal balance by PSF, and a higher rate of re-operation in VBT patients.

LEVEL OF EVIDENCE

III.

Combined Anterior Thoracic Vertebral Body Tethering and Posterior Lumbar Tethering Results in Quicker Return to Sport and Activity Compared to Posterior Spinal Instrumented Fusion in Patients with Adolescent Idiopathic Scoliosis

STUDY DESIGN

Retrospective comparative study.

OBJECTIVE

To compare patient-reported physical activity between anterior thoracic vertebral body tethering and posterior lumbar spine tethering (ATVBT/PLST) and posterior spinal instrumentation and fusion (PSIF) with minimum 2 year follow-up.

METHODS

Consecutive skeletally immature patients with idiopathic scoliosis and a thoracic and lumbar curve magnitude ≥40° who underwent either ATVBT/PLST or PSIF from 2015-2019 were included. The primary outcome was rate of returning to sport. Secondary outcomes included ability to bend and satisfaction with sport performance as well as weeks until return to sport, school, physical education (PE) classes, and running.

RESULTS

Ten patients underwent ATVBT/PLST and 12 underwent PSIF. ATVBT/PLST patients reported significantly faster return to sport (13.5 weeks vs 27.9 weeks, P = .04), running (13.3 weeks vs 28.8 weeks, P = .02), and PE class (12.6 weeks vs 26.2 weeks, P = .04) compared to PSIF patients. ATVBT/PLST patients reported that they had to give up activities due to their ability to bend at lower rates than PSIF patients while reporting "no changes" in their ability to bend after surgery at higher rates than PSIF patients (0% vs 4% giving up activities and 70% vs 0% reporting no changes in bending ability for ATVBT/PLST and PSIF, respectively, P = .01). Compared to PSIF patients, ATVBT/PLST patients experienced less main thoracic and thoracolumbar/lumbar curve correction at most recent follow-up (thoracic: 41 ± 19% vs 69 ± 18%, P = .001; thoracolumbar/lumbar: 59 ± 25% vs 78 ± 15%, P = .02). No significant differences in the number of revision surgeries were observed between ATVBT/PLST and PSIF patients (4 (40%) and 1 (8%) for ATVBT/PLST and PSIF, respectively, P = .221).

CONCLUSIONS

ATVBT/PLST patients reported significantly faster rates of returning to sport, running, and PE. In addition, ATVBT/PLST patients were less likely to have to give up activities due to bending ability after surgery and reported no changes in their ability to bend after surgery more frequently than PSIF patients. However, the overall rate of return to the same or higher level of sport participation was high amongst both groups, with no significant difference observed between ATVBT/PLST and PSIF patients.

Achieving the Needed Correction in Vertebral Body Tethering: The Relationship Between Preoperative Flexibility, Intraoperative Correction, and First Erect Imaging

BACKGROUND

Vertebral body tethering (VBT) is a nonfusion surgical treatment for scoliosis. Recent data have shown that intraoperative correction is critical for successful curve correction over time. This study aims to evaluate the relationship between preoperative, intraoperative, and postoperative correction. We hypothesize that preoperative flexibility will match first erect imaging, intraoperative correction will overestimate postoperative correction, and correction has improved over time with increased surgeon experience.

METHODS

This study is a retrospective review of patients who underwent VBT at a single center between 2015 and 2023. Patient radiographs were reviewed preoperatively (standing and fulcrum bending), intraoperatively, and postoperatively first erect.

RESULTS

Our study included 157 patients: 127 females (81%) with a mean age of 13.2 years (range: 9 to 17) at surgery and a mean of 7.9 vertebrae instrumented (range: 5 to 12 vertebrae). Twenty-three had 2 curves instrumented (85% single curve). One hundred eight patients had thoracic curves (69%), 33 thoracolumbar (21%), and 16 lumbar (10%). Preoperative curve magnitude averaged 51 degrees (range: 36 to 72). The mean bending radiograph curve measurement was 24 degrees (53% correction). The mean intraoperative curve magnitude was 15 degrees (72% correction). Intraoperative curve magnitude and correction were significantly different between curve types, with increased correction in lumbar curves (7 degrees, 86% correction) and less correction in thoracic curves (16 degrees, 68% correction). On first erect postoperative imaging (mean 8 d post-op, range: 1 to 44), the curve magnitude was 26 degrees (49% correction). The R2 correlation of the first erect radiograph was 0.209 for preoperative bending and 0.554 for intraoperative measurements. The mean difference in first erect curve magnitude was +2 degrees from preoperative flexibility radiographs and +11 degrees from intraoperative radiographs. Pre-2020, the intraoperative curve averaged 18 degrees, and >2020 averaged 13 degrees ( P =0.001). Pre-2020, the first erect averaged 30 degrees, and >2020 improved to 24 degrees ( P <0.001), despite equivalent preoperative metrics (both 51 degrees curves, P =0.98, with 54 vs. 52% flexibility, P =0.31).

CONCLUSIONS

Our study indicates that preoperative bending films can provide a practical approximation of the correction on first erect imaging. Intraoperative correction has the strongest relationship and averages 11 degrees less than the postoperative standing curve magnitude. Further, our site's intraoperative and postoperative correction has improved over time with increased surgeon experience.

LEVEL OF EVIDENCE

Level III-retrospective cohort.

Apical stress redistribution during anterior vertebral body tethering for thoracic adolescent idiopathic scoliosis: a finite element analysis of a novel surgical technique

PURPOSE

Apical stress redistribution (ASR) is proposed to mitigate failure risks after anterior vertebral body tethering for adolescent idiopathic scoliosis. It consists in releasing set-screws at peri-apical levels following curve tensioning to redistribute stresses within the construct. This study determines the biomechanical impact and curve correction obtained with ASR.

METHODS

Finite element models of anterior vertebral body tethering were constructed for three typical scoliotic patients with Lenke 1 curves. ASR was simulated by releasing tension on the cable at the level of the three apical set screws (i.e. untightening three consecutive periapical set screws), followed by retightening of the set screws without further tensioning. Cable tension, implant forces and spine geometry were compared before and after performing ASR.

RESULTS

Periapical cable tension decreased post-ASR, and ASR also reduced the maximum tensions proximally and distally. Postoperative disc height was similar between conventional and ASR approaches. Apical intervertebral disc stresses were shifted from concave to convex compression intra and postoperatively, with a similar pattern between the conventional and ASR techniques. The ASR technique achieved scoliotic curve corrections of 54%, 68%, and 79%, while the conventional technique resulted in corresponding corrections (54%, 68%, and 80%) for subjects 1, 2, and 3. The periapical coronal curves exhibited similar patterns.

CONCLUSION

ASR demonstrated promising apical cable and implant forces re-equilibrium compared to the conventional approach. This novel technique did not impair immediate and postoperative curve correction, while maintaining similar apical intervertebral stress distribution. ASR shows potential to modulate growth while reducing maximum cable tension infra- and supra-apical.

How Do Patients Perceive Success and Satisfaction After Vertebral Body Tethering and Fusion for Adolescent Idiopathic Scoliosis? A Qualitative Study

BACKGROUND

Adolescent idiopathic scoliosis (AIS) is the most common spinal deformity among children. Although posterior spinal fusion (PSF) is a commonly used treatment for curves ≥ 45°, anterior vertebral body tethering (VBT) has recently gained traction as an alternative for some patients. Surgeons have established radiographic definitions of success for PSF, with similar efforts underway for VBT. However, these definitions may not align with patient perceptions of success or their satisfaction with achieved outcomes.

QUESTIONS/PURPOSES

To enhance patient-centered care and inform subsequent comparative effectiveness research, we asked: (1) How do patients who have undergone VBT or PSF define and perceive treatment success ≥ 3 years after surgery? (2) What are patients' perceptions of their outcomes, specifically regarding satisfaction with symptom relief, side effects, physical function, and physical appearance?

METHODS

Using an approach informed by concepts from phenomenology to capture patients' lived experiences, we conducted semistructured interviews using an interview guide. Inclusion criteria required patients to have (1) progressive AIS with moderate deformity (< 60°) at surgery, (2) undergone VBT or PSF with at least 3 years of follow-up, and (3) reached full skeletal maturity. Patients unable to communicate or schedule interviews were excluded. From 96 eligible patients (VBT n = 47, PSF n = 49), we recruited 40 (20 per cohort). The sample size was guided by qualitative studies in the field and aimed to achieve saturation, defined as the point at which minimal new information and no new coding categories were identified. Participants were treated at a single urban Midwest hospital by the same physician. The VBT cohort (median age 18 years [range 16 to 22]) was 85% women/girls, while the PSF cohort (median age 21 years [range 18 to 27]) was 70% women. Interviews were analyzed using a collaborative content analysis approach in which two researchers independently identified key ideas, assigned codes, and resolved discrepancies through consensus to develop themes and subthemes aligned with the research questions.

RESULTS

Patients from both cohorts defined success as achieving pain relief, maintaining physical function, improving appearance, ensuring long-term deformity correction, and alleviating concerns about future health risks. Patient priorities varied; some prioritized flexibility to swim competitively or play musical instruments, while others prioritized pain-free living or improved physical appearance. Overall, both groups expressed satisfaction with symptom relief, physical function, and appearance improvements despite ongoing pain, side effects, and physical limitations.

CONCLUSION

These findings may be used as a guide for preoperative counseling and highlight the importance of incorporating patient perspectives into preoperative counseling for AIS, emphasizing the need to set realistic expectations regarding pain relief, physical function, long-term stability, and emotional well-being. While patients frequently reported positive outcomes in pain reduction, mobility, and appearance, counseling should address potential residual discomfort, physical limitations, and body image concerns to improve satisfaction. Future research should prioritize developing nuanced, patient-centered outcome measures that capture specific priorities such as detailed pain characteristics, functional abilities, and appearance-related concerns. Comparative effectiveness studies should explore granular outcomes to provide evidence that supports shared decision-making and guides patients and clinicians in choosing between VBT and PSF based on individual goals. Additionally, examining how presurgery discussions about tradeoffs and long-term outcomes shape patient expectations and satisfaction can improve alignment between surgical practices and patient priorities.

LEVEL OF EVIDENCE

Level III, therapeutic study.

Defining the segmental tension generated in a vertebral body tethering system for scoliosis

Vertebral body tethering (VBT) uses a flexible tether affixed across the curve convexity with tension applied at each segment to treat scoliosis. Intraoperative tether tension may be achieved directly with a counter-tensioner or with an extension spring tube. The purpose of this study was to quantify the force generated with and without the extension spring tube using current FDA-approved VBT instrumentation, to understand the variation between surgeons using the same instrumentation, and to define the force range that is generated intra-operatively. Using a benchtop mechanical testing setup to simulate a spinal segment, we affixed the tether and applied tension using a tensioner and counter-tensioner alone (method T1) or by adding an extension spring tube (method T2). Eight orthopedic surgeons used T1 and T2 at six tensioner settings, and one surgeon completed three trials. A two-way ANOVA with a Tukey's HSD post hoc test (p < 0.05) compared the tensioner methods and testing levels. Inter- and intra-rater reliabilities were calculated using intraclass correlation coefficients (ICCs). Methods T1 and T2 exhibited linear tension-setting relationships, with high determination coefficients (R2 > 0.93). T2 consistently produced higher forces (increase of 62.1 N/setting), compared to T1 (increase of 50.6 N/setting, p < 0.05). Inter-rater reliability exhibited excellent agreement (ICC = 0.951 and 0.943 for T1 and T2, respectively), as did intra-rater reliability (ICC = 0.971).

Perioperative Outcomes Related to Thoracic and Lumbar Spine Exposure During Vertebral Body Tethering for Adolescent Idiopathic Scoliosis: A Large, Single-institution Retrospective Review

BACKGROUND

Vertebral body tethering (VBT) is a novel non-fusion technique for the management of scoliosis. Despite growing popularity, data concerning complications and thoracic surgery-related outcomes are lacking.

METHODS

A single-institution retrospective review was conducted of patients who underwent VBT with video-assisted thoracic surgical exposure from 1/1/2015-3/1/2022. Data obtained included demographics, comorbidities, hospital course, and outcomes.

RESULTS

106 patients (81 % female) were identified with a mean age at surgery of 12.7 ± 1.5 (range 9-16). Most patients underwent single curve tethering (n = 93, 87.7 %) with a mean number of vertebral bodies tethered of 8.0 (range 5-13). The mean operative time was 236 ± 96 min (range 129-661) minutes with an estimated blood loss of 165 ± 143 mL (range 20-750) and no patients required allogeneic blood transfusion. The extent of tethering was significantly associated with increased operative time, fluids received, and chest tube output. Excluding instrument-related complications, the complication rate was 13.2 %, mostly occurring within the first 30 days after surgery and pleural effusion being the most common event. Two patients experienced a postoperative hemothorax requiring reoperation. No patients experienced sequelae of spinal cord ischemia secondary to the division of intercostal and/or lumbar vessels during surgical exposure and no deaths occurred.

CONCLUSION

VBT is a seemingly safe alternative to spinal fusion in skeletally immature adolescents, however, there are notable complications of this procedure related to thoracic exposure. Our experience indicates clinically significant pulmonary complications are uncommon and the extent of vertebral body exposure/tethering was strongly associated with operative duration, fluids, and chest tube output.

LEVELS OF EVIDENCE

This original article represents a treatment study of Level IV evidence.

Where does the tether break in vertebral body tethering cases? Clinical insights from revision cases after tether breakage

PURPOSE

To evaluate the sites where the tether breaks in vertebral body tethering (VBT) cases.

METHODS

Intraoperative evaluation of broken tethers in patients who had anterior revision.

INCLUSION CRITERIA

anterior revision of VBT cases with explantation of the full implant and photo documentation. Eight patients met the inclusion criteria. The primary variable of interest was the location of tether breakage in relation to the vertebral curve and the tether-screw interface. Another variable of interest was to evaluate the difference in breakage rates between anterior and posterior tethers in double tether cases.

RESULTS

Sixty tethers bridging the intervertebral disc within this cohort of eight patients were found. Seven implants were removed from thoracolumbar curves and one implant from a thoracic curve. We identified 32 tether breakages. Double tethers were used in six patients. In these six cases, 15 breakages were found in the posterior tether and 13 in the anterior tether. Four cases (50%) exhibited breakages at the apex, eight cases (100%) at the lowest instrumented vertebra (LIV), and five cases (63%) at the uppermost-instrumented vertebra (UIV). Five tether breakages (in three cases with double tether) were observed at the screw sites, while the remaining 27 exhibited cord breakages near the intervertebral discs. In double tether systems, statistical analysis did not reveal any significant difference in breakage rates between anterior and posterior tethers.

CONCLUSIONS

In VBT cases, the tether breaks mostly at the level of the intervertebral disc, adjacent to the lowest instrumented vertebra.

LEVEL OF EVIDENCE

Level IV (Case series with no comparison group).

A comparative analysis of axial and appendicular skeletal maturity staging systems through assessment of longitudinal growth and curve modulation after VBT surgery

PURPOSE

Appendicular skeleton markers are commonly used for maturity assessment for Adolescent Idiopathic Scoliosis (AIS) patients. Traditionally, Risser has been a standard skeletal maturity assessment method. More recently, Sanders classification (SSMS), as a more comprehensive system, became popular, especially in decision-making for Vertebral Body Tethering (VBT). Thumb-Ossification Composite Index (TOCI), using ossification of thumb epiphyses, has been claimed to more accurately stage patients around their peak height velocity. However, growth peaks may occur separately at lower limbs and trunk. Hence, Cervical Vertebral Maturity (CVM), using cervical spine morphology, possesses a potential to better estimate spinal growth as it uses axial skeleton markers instead of appendicular skeleton markers. The aim of the study was to compare various axial and appendicular skeletal maturity assessment methods for longitudinal growth and curve modulation after VBT.

METHODS

A retrospective analysis of prospectively collected data was conducted. Skeletal maturity was determined using Risser, SSMS, TOCI and CVM for each patient. Crosstabulations of axial vs. appendicular markers were formed to analyze their concordance and discordance. Logistic and logarithmic regression models were run to assess longitudinal growth (postoperative height gain and leg-length growth) and curve modulation (follow-up instrumented Cobb correction after index operation), respectively. Models were compared using Akaike information criterion (AIC).

RESULTS

34 patients (32 F/2 M, mean age: 12.8 ± 1.5 years, mean follow-up: 47.7 (24-80) months) were included. The median preoperative maturity stages were: Risser: 1 (-1-4), SSMS: 4 (1-7), TOCI: 6 (1-8) and CVM: 4 (1-6). At latest follow-up, all patients reached skeletal maturity. Concordance and discordance were observed between axial vs. appendicular systems that demonstrated a range of possible distributions of CVM, where trunk peak height velocity occurred before, simultaneously with or after the standing height peak height velocity. R-squared values for Risser, SSMS, TOCI and CVM were 0.701, 0.783, 0.810 and 0.811, respectively, for prediction of final height; 0.759, 0.821, 0.831 and 0.775 for final leg-length, and 0.507, 0.588, 0.668 and 0.673 for curve modulation. Delta AIC values demonstrated that different skeletal maturity assessment methods provided distinctive information regarding follow-up height gain, leg-length growth and curve behavior.

CONCLUSIONS

Risser score provided considerably less information for all three outcome variables. TOCI and SSMS provided substantial information regarding remaining leg-length assessments, while in terms of assessment of total height gain and curve modulation after surgery, CVM and TOCI offered substantial information and SSMS offered strong information. Mutual use of axial and appendicular markers may provide valuable insight concerning timing of surgery and magnitude of surgical correction.

Accuracy of screw placement during vertebral body tethering using fluoroscopic guidance and anatomic landmarks

PURPOSE

To determine the accuracy of screw placement using fluoroscopy and anatomic landmarks during vertebral body tethering (VBT) surgery.

METHODS

Ten patients with 73 VBT screws were converted to posterior spinal fusion (PSF) after continued curve progression. The positions of each VBT screw were analyzed using intraoperative computed tomography (CT) scans performed for image guidance during VBT. Differences for screws placed using an open versus thoracoscopic approach were noted for the screw position in each vertebra, distance from the spinal canal, unicortical versus bicortical placement, the distance of screw tips from the thoracic aorta, and impingement of screws on adjacent rib heads.

RESULTS

Seventy three (73) screws in ten (10) patients were available for analysis. Only 21% of screws were placed traversing the middle one-third of the vertebral body, without spinal canal penetration, with the distal tip placed unicortically or bicortically as planned, and without touching the thoracic aorta. The rates of non-ideal screw placement were not significantly different for screws placed via thoracoscopic versus open approaches. Five (5) screws (6.8%) penetrated the spinal canal 1-2 mm, but without known clinical sequelae.

CONCLUSION

The majority of VBT screws available for analysis were placed in non-ideal positions, suggesting that accurate screw placement using intraoperative fluoroscopy and anatomic landmarks can be challenging, but without adverse clinical consequences.

Matched comparison of non-fusion surgeries for adolescent idiopathic scoliosis: posterior dynamic distraction device and vertebral body tethering

PURPOSE

Two non-fusion devices for adolescent idiopathic scoliosis (AIS) received HDE approval for clinical use in 2019: posterior dynamic distraction device (PDDD) and vertebral body tethering system (VBT). Although indications are similar, there is no comparative study of these devices. We hypothesize that curve correction will be comparable, but PDDD will have better perioperative metrics.

METHODS

AIS PDDD patients were prospectively enrolled in this matched multicenter study. Inclusion criteria were Lenke 1 or 5 curves, preoperative curves 35°-60°, correction to ≤30° on bending radiographs, and kyphosis <55°. Patients were matched by age, sex, Risser, curve type and curve magnitude to a single-center cohort of VBT patients. Results were compared at 2 years.

RESULTS

20 PDDD patients were matched to 20 VBT patients. Blood loss was higher in the VBT cohort (88 vs. 36 ml, p < 0.001). Operative time and postoperative length of stay were longer in the VBT cohort, 177 vs. 115 min (p < 0.001) (2.9 vs. 1.2 days, p < 0.001). Postoperative curve measurement and correction at 6 months were better in the PDDD cohort (15° vs. 24°, p < 0.001; 68% vs. 50%, p < 0.001). At 1-year, PDDD patients had improved Cobb angles (14° vs. 21°, p = 0.001). At 2 years, a correction was improved in the PDDD cohort, with a curve measurement of 17° for PDDD and 22° for VBT (p = 0.043). At the latest follow-up, 3 PDDD patients and 1 VBT patient underwent revision surgery.

CONCLUSION

Early results show PDDD demonstrates better index correction, reduced operative time, less blood loss, and shorter length of stay but higher rates of revision compared to a matched cohort of VBT patients at two-year follow-up.

LEVEL OF EVIDENCE

Level II, prospective cohort matched comparative study.

Vertebral Body Tethering in Skeletally Immature Patients: Results of a Prospective U.S. FDA Investigational Device Exemption Study

BACKGROUND

The purpose of this study was to report on 2-year results of vertebral body tethering (VBT), performed under a Food and Drug Administration protocol, to obtain insight into outcomes and complications.

METHODS

Forty prospectively enrolled patients with adolescent idiopathic scoliosis (AIS) who had a Sanders score of ≤4 or a Risser score of ≤2 underwent VBT for curves between 40° and 70°. Surgical, radiographic, and patient-reported outcomes were reviewed at a minimum 2-year follow-up.

RESULTS

Mean age at surgery was 13 (range, 10 to 16) years. The 40 patients were 90% female; 95% White, 2.5% other, and 2.5% unreported; and 92.5% non-Hispanic, 5% Hispanic, and 2.5% unreported. A mean of 8 (range, 5 to 12) levels were instrumented. Most patients were at Sanders 4 (65%) and Risser 0 (63%). Mean length of stay was 3 ± 1 days, estimated blood loss was 236 ± 158 (range, 25 to 740) mL, and operative time was 4.4 ± 1.4 hours. Mean correction of the major curve was 44% (range, 22% to 95%) on the 3-month standing radiograph, 49% at 1 year, and 46% (range, -10% to 93%) at 2 years. The mean major Cobb angle improved from 51° ± 8° (range, 40° to 70°) preoperatively to 27° ± 11° (range, 3° to 56°) at 2 years. Success at 2 years, defined by a Cobb angle of <35° and no reoperation, was seen in 30 patients (75%) and was associated with a mean Cobb angle of <35° on the first postoperative standing radiograph (p < 0.001). Twelve patients (30%) demonstrated improvement in the curve with growth. By 2 years, 2 (5%) of the patients underwent repeat surgery (1 release for overcorrection, 1 lumbar VBT for lumbar curve progression after thoracic VBT). The Scoliosis Research Society (SRS) satisfaction score improved 2 years following surgery (p < 0.001), but other SRS domains only remained stable over time. Beyond 2 years, 1 additional lumbar tether was required after thoracic VBT, 1 implant was removed, and 3 fusions were performed, for a 10% fusion rate and overall 20% reoperation rate at a mean of 3.8 ± 1.1 years of follow-up. The rate of cord breakage in the study population was 20%.

CONCLUSIONS

In skeletally immature patients treated in the U.S. under a prospective Investigational Device Exemption, there was a 75% rate of successful outcomes at 2 years. Most correction was obtained at the time of surgery, and inadequate intraoperative curve correction was associated with a higher Cobb angle on the first postoperative standing radiograph and failure by 2 years.

LEVEL OF EVIDENCE

Therapeutic Level II. See Instructions for Authors for a complete description of levels of evidence.

Anterior Vertebral Body Tethering (AVBT) in the Treatment of Adolescent Idiopathic Scoliosis: A Retrospective Study

Background/Objectives: Anterior Vertebral Body Tethering (AVBT) is a relatively novel minimally invasive surgical technique for the treatment of adolescent idiopathic scoliosis (AIS) that enables deformity correction of the spine diminishing vertebral motion reduction caused by the standard posterior spinal fusion approach. This paper reports the introduction of a new technical variant of AVBT, with the aim of evaluating its effectiveness on the correction of both axial and coronal spinal deformity. Methods: A single-centre single-surgeon retrospective cohort study was conducted. AVBTs were performed between 2020 and 2024. Radiographical values, surgical details, and complications of 67 patients affected by AIS were compared before surgery, immediately after surgery, and at the most recent follow-up. Results: Postoperative results have revealed a statistically significant coronal curve correction of 29.85% in the main thoracic (MT) curves (from mean preoperative width of 54.81 ± 11.86° to 38.45 ± 10.19°) and of 26.93% in the thoracolumbar (TL/L) curves (from 35.15 ± 11.83° to 25.69 ± 10.50°) in line with that obtained by the standard technique. Coronal correction at the most recent follow-up was maintained. Postoperative axial rotation reduction was found to be statistically significant in the main thoracic (MT) curves (from mean Nash-Moe value of 1.84 ± 0.71 to 1.36 ± 0.73), with a further decrease at the most recent follow-up compared with preoperative values. Improvement in other radiographical measures did not reach statistical significance and the complication rate was comparable to the standard technique. Conclusions: The extent of coronal correction in patients treated with the proposed modified AVBT technique is satisfactory and in line with results from studies testing the standard AVBT technique. The findings of this study seem to suggest that this technical variant of AVBT is effective in the correction of both axial and coronal deformity, with a surgical complication rate comparable to the standard technique.

Current Status of Vertebral Body Tethering for Adolescent Idiopathic Scoliosis: An Umbrella Review

Background

Adolescent idiopathic scoliosis (AIS) is a prevalent spinal deformity among teenagers worldwide. Vertebral body tethering (VBT) is an innovative, minimally invasive technique developed to address spinal curvature by modulating vertebral growth. However, the existing body of evidence regarding the effectiveness and safety of VBT in treating AIS is fragmented and requires thorough consolidation and critical assessment.

Methods

Six databases were thoroughly examined, yielding 11 relevant systematic reviews and meta-analyses. The methodological quality of the included studies was evaluated using the Joanna Briggs Institute's critical appraisal checklist. The key findings were encapsulated using a narrative synthesis approach.

Results

The reviews indicated notable improvements in coronal plane radiographic parameters, transverse plane clinical outcomes, and health-related quality of life scores following VBT. Nevertheless, the complication rates associated warrant attention. Additionally, the variability in methodological quality across the included reviews underscores the necessity for more robust and systematic investigations in this domain.

Conclusion

This umbrella review revealed promising results for VBT as a treatment option for AIS. However, further research is needed to address knowledge gaps and limitations, focusing on long-term outcomes, patient selection, standardized techniques, and comparison with traditional treatments.

A comparison of patients receiving vertebral body tethering for adolescent idiopathic scoliosis in the public and private hospital setting

PURPOSE

Vertebral body tethering (VBT) is a new growth-modulating surgery for adolescent idiopathic scoliosis (AIS) requiring a distinct skillset and intraoperative setup. We compared perioperative details and outcomes of VBTs performed in a public pediatric orthopedic hospital and a general private hospital setting.

METHODS

We identified all patients receiving VBT for AIS from 1/2020 to 12/2023 with ≥ 6 months post-operative follow-up, with surgeries performed by the same senior surgeons. Clinical, radiological, and surgical details were retrieved.

RESULTS

24 VBTs were performed in the private setting and 16 in the public setting. Average age at operation was 11.9 ± 1.1 at a Sanders staging of 3.8 ± 1.2 when the major curve Cobb angle was 50.5 ± 8.0°. Tethered curves were most often thoracic in location (23/40) followed by thoracolumbar/lumbar curves (10/40) and double curve tethers (7/40). Overall correction ratio of 68.0 ± 19.0% was achieved. Time from booking to operation (82.2 ± 39.2 vs 63.1 ± 34.4 days, p = 0.112) and operation time (310 ± 86.4 min vs. 289 ± 87.4 min, p = 0.054) were longer in the public and private setting respectively but failed to reach statistical significance. Time to chest drain removal (1.5 ± 0.8 vs. 3.5 ± 1.7 days, p < 0.001) and length of stay (4.3 ± 0.9 vs. 6.6 ± 1.8 days, p < 0.001) were significantly shorter in the private setting, whilst complication rates remained similar (7/24 vs. 3/16, p = 0.456).

CONCLUSION

Expertise, resource availability, and costs differ in the public and private healthcare setting. With regards to VBT, the conditions for referral and surgical outcomes remained similar. Earlier drain removal and discharge for patients managed in the private setting was not associated with an increase in complication rate.

Growth modulation response in vertebral body tethering depends primarily on magnitude of concave vertebral body growth

PURPOSE

There is variability in clinical outcomes with vertebral body tethering (VBT) partly due to a limited understanding of the growth modulation (GM) response. We used the largest sample of patients with 3D spine reconstructions to characterize the vertebra and disc morphologic changes that accompany growth modulation during the first two years following VBT.

METHODS

A multicenter registry was used to identify idiopathic scoliosis patients who underwent VBT with 2 years of follow-up. Calibrated biplanar X-rays obtained at longitudinal timepoints underwent 3D reconstruction to obtain precision morphological measurements. GM was defined as change in instrumented coronal angulation from post-op to 2-years.

RESULTS

Fifty patients (mean age: 12.5 ± 1.3yrs) were analyzed over a mean of 27.7 months. GM was positively correlated with concave vertebra height growth (r = 0.57, p < 0.001), 3D spine length growth (r = 0.36, p = 0.008), and decreased convex disc height (r = - 0.42, p = 0.002). High modulators (patients experiencing GM > 10°) experienced an additional 1.6 mm (229% increase) of mean concave vertebra growth during study period compared to the Poor Modulators (GM < - 10°) group, (2.3 vs. 0.7 mm, p = 0.039), while convex vertebra height growth was similar (1.3 vs. 1.4 mm, p = 0.91).

CONCLUSION

When successful, VBT enables asymmetric vertebra body growth, leading to continued postoperative coronal angulation correction (GM). A strong GM response is correlated with concave vertebral body height growth and overall instrumented spine growth. A poor GM response is associated with an increase in convex disc height (suspected tether rupture). Future studies will investigate the patient and technique-specific factors that influence increased growth remodeling.

A multibody simulation of the spine for objectification of biomechanical quantities after VBT: a proof of concept and description of baseline data

PURPOSE

Vertebral Body Tethering (VBT), an alternative treatment for adolescent idiopathic scoliosis, shows satisfactory post-operative results. However, the biomechanical quantities and consequences after VBT surgery remain largely unknown. Therefore, the aim of this study is to analyze the spinal biomechanics during different motions using a multibody simulation approach.

METHODS

The tether and intervertebral compression forces were simulated in a validated spine model during different physiological movements at different pre-tensions and screw positions, while considering the anatomical muscle and ligament properties.

RESULTS

The simulations showed that an augmentation of the pre-tension and an alteration of the screw position have both significant impact on the intervertebral compression and tether forces. The forces also vary depending on the movement performed, with the highest tether forces measured during lateral bending. In the upright position, with a pre-tension of 200 N, the maximum compression force increases by up to 157% compared to the untethered maximum compression force. The screw position can lead to large differences in the distribution of forces in the spine.

CONCLUSION

The biomechanical data provide a first impression of the forces that occur along the spine during various physiological movements and are consistent with published clinical data. Forces are not evenly distributed along the spine, with higher lumbar forces. The tether forces reach values during lateral bending that can potentially destroy the tether´s integrity and thus may explain the common post-operative complication, namely tether breakage. The results of the model can therefore have an impact on future directions for improved surgical VBT treatment.

Vertebral Body Tethering for Thoracolumbar Curvatures in Adolescent Idiopathic Scoliosis: Radiographic and Clinical Outcomes at 2-6-Year Follow-Up

Background: The gold standard treatment for adolescent idiopathic scoliosis (AIS) is posterior spinal fusion (PSF). However, long-term consequences of PSF can include reduced spinal flexibility, back pain, and intervertebral disc degeneration. Vertebral body tethering (VBT) is a non-fusion alternative that preserves motion. We investigated the outcomes of VBT for the treatment of thoracolumbar (TL) major AIS in the largest single-surgeon series with a minimum 2-year follow-up (FU). Methods: We performed a retrospective single-center review. Inclusion criteria were AIS, Lenke 5/6 curvature, and skeletally immature Variables were compared using Student's t-tests, Wilcoxon rank sum tests, Chi-square, and Fisher's exact tests. Results: A total of 37 consecutive patients, age 14.1 ± 1.6 years, 86.5% F, 35.9 ± 11.5-month FU, were examined. Overall, 27 patients (73%) had Lenke 5 and 10 (27%) had Lenke 6 curvatures. Instrumentation of the TL curve alone was performed in 59.5%, and thoracic (T) and TL in 40.5% of patients. Overall, 45.9% of patients had two tethers placed in the TL spine; no patients had double tethers placed at the main thoracic curves. The TL (51 ± 8° to 20 ± 11°; p < 0.0001) and T (37 ± 13° to 17 ± 10°; p < 0.0001) curvatures improved from baseline to the latest FU. Overall, 89% of patients achieved major Cobb < 35°; the three patients who did not experienced at least one cord breakage or required PSF. T5-T12 kyphosis increased (p = 0.0401) and lumbar lordosis was maintained (p = 0.9236). Both the TL inclinometer (16 ± 4º to 4 ± 2°; p < 0.0001) and T (6 ± 4° to 4 ± 3°; p = 0.0036) measurements improved. There was a 49% tether breakage rate as follows: 60% for single-cord TL constructs and 35% for double cords (p = 0.0991). There was an 8.1% re-operation rate as follows: one conversion to T PSF and revision of the TL tether; one release of the T tether and revision of the TL tether; one screw revision for radiculopathy. One patient was re-admitted for poor pain control. Conclusions: Patients with TL major curvature treated with VBT experienced a high rate of clinically successful outcomes with maintenance of lumbar lordosis and relatively low complication rates at the latest FU.

Anterior Vertebral Body Tethering: A Single-Center Cohort with 4.3 to 7.4 Years of Follow-up

BACKGROUND

Vertebral body tethering (VBT) is a well-recognized, non-fusion alternative for idiopathic scoliosis in children with growth remaining. To date, there have been almost no published outcome studies with postoperative follow-up of >2 years. We aimed to fill this gap by evaluating mid-term outcomes in our first 31 consecutive patients.

METHODS

We retrospectively assessed additional clinical and radiographic data (mean, 5.7 ± 0.7 years) from our first 31 consecutive patients. Assessments included standard deformity measures, skeletal maturity status, and any additional complications (e.g., suspected broken tethers or surgical revisions). Using the same definition of success (i.e., all residual deformities, instrumented or uninstrumented, ≤30° at maturity; no posterior spinal fusion), we revisited the success rate, revision rate, and suspected broken tether rate.

RESULTS

Of our first 31 patients treated with VBT, 29 (of whom 28 were non-Hispanic White and 1 was non-Hispanic Asian; 27 were female and 2 were male) returned for additional follow-up. The success rate dropped to 64% with longer follow-up as deformity measures increased, and the revision rate increased to 24% following 2 additional surgical revisions. Four additional suspected broken tethers were identified, for a rate of 55%, with only 1 occurring beyond 4 years. No additional patients had conversion to a posterior spinal fusion. We observed a mean increase of 4° (range, 2° to 8°) in main thoracic deformity measures and 8° (range, 6° to 12°) in thoracolumbar deformity measures.

CONCLUSIONS

With >5 years of follow-up, we observed a decrease in postoperative success, as progression of the deformity was observed in most subgroups, and an increase in the revision and suspected broken tether rates. No additional patients had conversion to a posterior spinal fusion, which may indicate long-term survivorship.

LEVEL OF EVIDENCE

Therapeutic Level III . See Instructions for Authors for a complete description of levels of evidence.

Anterior vertebral tethering for adolescent idiopathic scoliosis: our initial ten year clinical experience

BACKGROUND

Anterior vertebral tethering (AVT) is a minimally invasive alternative to fusion surgery for adolescent idiopathic scoliosis (AIS) that offers the potential for definitive scoliosis treatment with the possibility of preservation of the growth, motion, function and overall health of the spine. This study represents our first ten years using AVT to treat AIS.

METHODS

In this retrospective review we analyzed our first 74 AIS patients treated with AVT 2010-2020. Multiple Lenke curve types 33-70° were treated with skeletal maturity spanning Risser -1 to 5.

RESULTS

Of 74 consecutive AIS patients treated with AVT, 52 patients (47 female, 5 male) had sufficient 2-year follow-up for inclusion. Forty-six of these 52 patients (88%) with 65 curves (35T, 30TL/L) were satisfactorily treated with AVT demonstrating curve correction from 48.6° pre-op (range 33°-70°) at age 15.1 years (range 9.2-18.8) and skeletal maturity of Risser 2.8 (range -1 to 5) to 23.2° post-op (range 0°-54°) and 24.0° final (range 0°-49°) at 3.3 years follow-up (range 2-10 years). Curve corrections from pre-op to post-op and pre-op to final were both significant (p < 0.001). The 0.8° change from post-op to final was not significant but did represent good control of scoliosis correction over time. Thoracic kyphosis and lumbar lordosis were maintained in a normal range throughout while axial rotation demonstrated a slight trend toward improvement. Skeletal maturity of Risser 4 or greater was achieved in all but one patient. Four of the 52 patients (8%) required additional procedures for tether rupture (3 replacements) or overcorrection (1 removal) to achieve satisfactory treatment status after AVT. An additional 6 of the 52 patients (12%), however, were not satisfactorily treated with AVT, requiring fusion for overcorrection (2) or inadequate correction (4).

CONCLUSIONS

In this study, AIS was satisfactorily treated with AVT in the majority of patients over a broad range of curve magnitudes, curve types, and skeletal maturity. Though late revision surgery for overcorrection, inadequate correction, or tether rupture was not uncommon, the complication of overcorrection was eliminated after our first ten patients by a refinement of indications.

LEVEL OF EVIDENCE

IV.

Differential vertebral body growth is maintained after vertebral body tethering surgery for idiopathic scoliosis: 4-year follow-up on 888 peri-apical vertebrae and 592 intervertebral discs

PURPOSE

To radiographically evaluate if vertebral body tethering (VBT) can maintain differential peri-apical vertebral growth at medium-term follow-up of 4 years.

METHODS

A prospective, international, multicenter database was queried to identify idiopathic scoliosis patients treated with thoracic VBT. Concave vs. convex vertebral body height, vertebral wedging, and disc wedging of the 3 peri-apical vertebrae were measured by two independent observers at 5 timepoints (pre-operative to 4-year follow-up).

RESULTS

65 skeletally immature patients (60 female, mean 12.8 years old, 21 with open triradiate cartilages) met inclusion criteria. Mean pre-operative maximum scoliosis of 50 ± 8° decreased significantly post-operatively to 27 ± 9° (p < 0.001), which remained stable at 4-year follow-up 30 ± 17° (p = 0.38 vs. post-operative). Mean instrumented scoliosis was 21 ± 14° at 4-year follow-up, which was significantly different than 4-year maximum scoliosis (p < 0.001). Mean pre-operative kyphosis of 30 ± 12° did not significantly change post-operatively (p = 1.0) and remained stable at 4-year follow-up (35 ± 18°; p = 0.05). Mean individual convex vertebral height increased from 17.7 ± 1.9 mm to 19.8 ± 1.5 mm (p < 0.001), while mean individual concave height increased from 14.8 ± 1.9 mm to 17.6 ± 1.6 mm (p < 0.001). Summing the peri-apical heights, the difference in height from pre-operative to 4-year follow-up was greater on the concave (8.3 ± 4.7 mm) than on the convex side (6.2 ± 4.7 mm) (p < 0.001). Mean individual vertebral wedging decreased from 6 ± 2° at pre-operative to 4 ± 2° at 4-year follow-up (p < 0.001). Mean total vertebral and disc wedging started at 29 ± 7° pre-operatively, decreased to 16 ± 6° at post-operative (p < 0.001), then further decreased to 14 ± 8° at 4-year follow-up (p < 0.001). Patients with open triradiate cartilages at the time of surgery had a larger height change over the 4 years compared to those with closed triradiate cartilages (p < 0.001).

CONCLUSION

Patients with idiopathic scoliosis treated with VBT demonstrated differential vertebral growth which was maintained at minimum 4-year follow-up. This effect was more pronounced in patients whose triradiate cartilages were open at the time of surgery.

LEVEL OF EVIDENCE

III.

Three-dimensional vertebral shape changes confirm growth modulation after anterior vertebral body tethering for idiopathic scoliosis

PURPOSE

To evaluate three-dimensional (3D) vertebra and disk shape changes over 2 years following anterior vertebral body tether (AVBT) placement in patients with idiopathic scoliosis (IS).

METHODS

Patients with right thoracic IS treated with AVBT were retrospectively evaluated. 3D reconstructions were created from biplanar radiographs. Vertebral body and disk height (anterior, posterior, left and right) and shape (wedging angle) were recorded over the three apical segments in the local vertebral reference planes. Changes in height and wedging were measured through 2 years postoperatively. Change in patient height was correlated with changes in the spine dimensions.

RESULTS

Forty-nine patients (Risser 0-3, Sanders 2-4) were included. The mean age was 12.2 ± 1.4 years (range 8-14). The mean coronal curve was 51 ± 10° preoperatively, 31 ± 9° at first postoperative time point and 27 ± 11° at 2-year follow-up (p < 0.001). The mean patient height increased 8 cm by 2 years (p < 0.001). The left side of the spine (vertebra + disc) grew in height by 2.2 mm/level versus 0.7 mm/level on the right side (p < 0.001). This differential growth was composed of 0.5 mm/vertebral level and 1.0 mm/disk level. Evaluation of the change in disk heights showed significantly decreased height anteriorly (- 0.4 mm), posteriorly (- 0.3 mm) and on the right (- 0.5 mm) from FE to 2 years. Coronal wedging reduced 2.3°/level with 1.1°/vertebral level change and 1.2°/disk level. There was no differential growth in the sagittal plane (anterior/posterior height). Patient height change moderately correlated with 3D measures of vertebra + disk shape changes.

CONCLUSIONS

Three-dimensional analysis confirms AVBT in skeletally immature patients results in asymmetric growth of the apical spine segments. The left (untethered) side length increased more than 3 × than the right (tethered) side length with differential effects observed within the vertebral bodies and disks, each correlating with overall patient height change.

Analysis of three-dimensional spine growth for vertebral body tethering patients at 2 and 5 years post operatively

PURPOSE

Scoliosis can be treated with vertebral body tethering (VBT) as a motion-sparing procedure. However, the knowledge of how growth is affected by a tether spanning multiple levels is unclear in the literature. Three-dimensional true spine length (3D-TSL) is a validated assessment technique that accounts for the shape of the spine in both the coronal and sagittal planes. This study aimed to assess if 3D-TSL increases over a five-year period after VBT implantation in thoracic curves for idiopathic scoliosis.

METHODS

Prospectively collected radiographic data from an international pediatric spine registry was analyzed. Complete radiographic data over three visits (post-operative, 2 years, and 5 years) was available for 53 patients who underwent VBT.

RESULTS

The mean age at instrumentation of this cohort was 12.2 (9-15) years. The average number of vertebrae instrumented was 7.3 (SD 0.7). Maximum Cobb angles were 50° pre-op, which improved to 26° post-op (p < 0.001) and was maintained at 5 years (30°; p = 0.543). Instrumented Cobb angle was 22° at 5 years (p < 0.001 vs 5-year maximum Cobb angle). An accentuation was seen in global kyphosis from 29° pre-operative to 41° at 5 years (p < 0.05). The global spine length (T1-S1 3D-TSL) started at 40.6 cm; measured 42.8 cm at 2 years; and 44.0 cm at the final visit (all p < 0.05). At 5 years, patients reached an average T1-S1 length that is comparable to a normal population at maturity. Immediate mean post-operative instrumented 3D-TSL (top of UIV-top of LIV) was 13.8 cm two-year length was 14.3 cm; and five-year length was 14.6 cm (all p < 0.05). The mean growth of 0.09 cm per instrumented level at 2 years was approximately 50% of normal thoracic growth. Patients who grew more than 0.5 cm at 2 years had a significantly lower BMI (17.0 vs 19.0, p < 0.05) and smaller pre-operative scoliosis (48° vs 53°, p < 0.05). Other subgroup analyses were not significant for age, skeletal maturity, Cobb angles or number of spanned vertebras as contributing factors.

CONCLUSIONS

This series demonstrates that 3D-TSL increased significantly over the thoracic instrumented levels after VBT surgery for idiopathic scoliosis. This represented approximately 50% of expected normal thoracic growth over 2 years.

Early-term outcome of apical fusion with vertebral body tethering for thoracolumbar curves in adolescent idiopathic scoliosis: a preliminary study

INTRODUCTION

Vertebral body tethering (VBT) has become an alternative option for select patients with idiopathic scoliosis. However, studies have shown a high number of tether breakages, specifically after thoracolumbar (TL) VBT, that can have a negative impact on the outcome, when the breakage occurs within the first year after surgery. In order to overcome this problem, we have started to apply an apical fusion (AF) in combination with TL VBT for select patients. This study aims to analyze the outcome after AF plus VBT.

METHODS

This is a retrospective single surgeon's data analysis. All patients were included who have had TL VBT after January 2022 and a follow-up of 12 months. Patients were grouped based on whether they only had VBT or VBT + AF.

RESULTS

Twenty-five patients were analyzed (15 VBT, 10 VBT + AF). Both groups showed a significant curve correction for thoracic and TL curves. Minor loss of correction was observed in both groups. A significant difference was seen regarding early tether breakages, which were found in 60% of VBT patients and 10% of VBT + AF patients.

CONCLUSION

The preliminary data shows a significant reduction of early tether breakages when TL VBT is applied in combination with AF.

Vertebral body tethering for Lenke 1A curves: the lumbar modifier predicts less optimal outcomes

INTRODUCTION

The addition of the L4 "AR" and "AL" lumbar modifier for Lenke 1A idiopathic scoliosis (IS) has been shown to direct treatment in posterior spinal fusion; however, its utility in vertebral body tethering (VBT) has yet to be evaluated.

METHODS

A review of a prospective, multicenter database for VBT in IS was performed for patients with Lenke 1A deformities and a minimum of 2 years follow-up. Patients were categorized by their lumbar modifier (AR vs AL). Less optimal VBT outcome (LOVO) was defined as a final coronal curve > 35°, lumbar adding-on, or revision surgery for deformity progression or adding-on.

RESULTS

Ninety-nine patients met inclusion criteria (81% female, mean 12.6 years), with 55.6% being AL curves. Overall, there were 23 instances of tether breakage (23.3%) and 20 instances of LOVO (20.2%). There was a higher rate of LOVO in AR curves (31.8% vs 10.9%, P = 0.01). Patients with LOVO had greater preoperative deformity, greater apical translation, larger coronal deformity on first erect radiographs, and less coronal deformity correction. Failure to correct the deformity < 30° on first erect was associated with LOVO, as was LIV selection short of the last touch vertebra (TV). Independent risk factors for LOVO included AR curves (OR 3.4; P = 0.04) and first erect curve magnitudes > 30 degrees (OR 6.0; P = 0.002).

DISCUSSION

There is a 20.2% rate of less optimal VBT following VBT for Lenke 1A curves. AR curves are independently predictive of less optimal outcomes following VBT and require close attention to LIV selection. Surgeons should consider achieving an initial coronal correction < 30 degrees and extending the LIV to at least the TV to minimize the risk of LOVO.

Double major curvature treated with vertebral body tethering of both curves: how do outcomes compare to posterior spinal fusion?

PURPOSE

Vertebral body tethering (VBT) is a non-fusion alternative to posterior spinal fusion (PSF). There have been few reports on VBT of two curvatures. We aim to compare the radiographic outcomes between VBT and PSF in patients with double curvatures in which both curves were instrumented.

METHODS

29 AIS patients matched by Lenke, age (± 2 years), triradiate cartilage closure status, major Cobb angle (± 8°), and T5-T12 kyphosis (± 10°). Variables were compared using Wilcoxon rank-sum tests, Student's t tests, and chi-Square. Clinical success was defined as major curve < 35°.

RESULTS

Group baseline demographics were similar. Major thoracic (T) curve types had significantly better major (VBT 51.5 ± 7.9° to 31.6 ± 12.0° [40%] vs. PSF 54.3 ± 7.4° to 17.4 ± 6.5° [68%]; p = 0.0002) and secondary curve correction in the PSF group. 71% of major T VBT patients were clinically successful versus 100% of PSF. Major thoracolumbar (TL) curve types experienced comparable major (VBT 52.3 ± 7.0° to 18.3 ± 11.4° (65%) vs. PSF 53.0 ± 5.2° to 23.8 ± 10.9° (56%); p = 0.2397) and secondary curve correction. 92% of major TL VBT patients were clinically successful versus 75% in the PSF group. There was no difference in T5-12 kyphosis or lumbar lordosis between groups for any curve type. There were 4 patients (13.8%) with major complications in the VBT group compared to 0 (0%) in the PSF.

CONCLUSION

Patients with double major AIS who underwent VBT with major T curve types had less correction than PSF; however, those with major TL curves experienced similar radiographic outcomes regardless of procedure. Complications were greater for VBT.

Vertebral body tethering for adolescent idiopathic scoliosis: a review

PURPOSE

Adolescent Idiopathic Scoliosis (AIS) remains the most common type of pediatric scoliosis, mostly affecting children between ages 10 and 18. Vertebral body tethering (VBT) offers a non-fusion alternative to the gold standard spinal fusion that permits flexibility and some growth within instrumented segments. This article will serve as a comprehensive literature review of the current state-of-the-art of VBT in relation to radiographic and clinical outcomes, complications, and the learning curve associated with the procedure.

METHODS

A systematic literature review was conducted on PubMed, Scopus, and Web of Science from April 2002 to December 2022. Studies were included if they discussed VBT and consisted of clinical studies in which a minimum 2-years follow-up was reported, and series that included anesthetic considerations, learning curve, and early operative morbidity.

RESULTS

Forty-nine studies spanning the period from April 2002 to December 2022 were reviewed.

CONCLUSION

This article illustrates the potential benefits and challenges of the surgical treatment of AIS with VBT and can serve as a basis for the further study and refinement of this technique ideally as a living document that will be updated regularly.

The Impact of Anterior Vertebral Body Tethering on Pulmonary Function

STUDY DESIGN

Retrospective, single-center study.

OBJECTIVE

To examine pulmonary function tests (PFTs) in patients undergoing anterior vertebral body tethering (AVBT).

SUMMARY OF BACKGROUND DATA

The effect of AVBT on pulmonary status remains unclear.

MATERIALS AND METHODS

The authors examined preoperative and postoperative PFTs following AVBT in a retrospective, single-center cohort of patients. Outcomes were compared using percent predicted values as continuous and categorical variables (using 10% change as significant) and divided into categorical values based on the American Thoracic Society standards.

RESULTS

Fifty-eight patients with adolescent idiopathic scoliosis were included, with a mean age of 12.5±1.4 years and a follow-up of 4.2±1.1 years. The mean thoracic curve was 47°±9°, which improved to 21°±12°. At baseline, the mean forced expiratory volume in one second (FEV1%) and forced vital capacity (FVC%) values were 79% and 82%, respectively. Four patients had normal FEV1% (≥100%), 67% had mild restrictive disease (70%-99%) and the rest had worse FEV1%. Mean FEV1 improved from 2.2 to 2.6 L ( P <0.05) and FVC improved from 2.5 to 3.0 L ( P <0.05); however, % predicted values remained unchanged (FEV1%: 79%-80%; FVC%: 82-80%, P >0.05) with mean postoperative PFTs at 37±12 months postoperative. The use of miniopen thoracotomy was not associated with worsening PFTs, but extension of the lowest instrumented vertebra below T12 was correlated with decreasing FEV1% in the bivariate analysis ( P <0.05). Patients with worse preoperative FVC% (80±13% vs. 90±11%, P =0.03) and FEV1% (77±17% vs. 87±12%, P =0.06) also had a greater likelihood of declining postoperative FEV1%.

CONCLUSION

Pulmonary function in most patients undergoing AVBT remained stable (76%) or improved (14%); however, a subset may worsen (10%). Further studies are needed to identify the risk factors for this group, but worse preoperative PFTs and extension below T12 may be risk factors for worsening pulmonary function.

A New Look at Vertebral Body Tethering (VBT): Through the Modified Clavien-Dindo-Sink (mCDS) Classification

INTRODUCTION

Anterior vertebral body tethering (AVBT) is increasingly popular as an option for surgical treatment of idiopathic scoliosis (IS). While the technology remains new, it is important for families and patients to be able to compare it to the current standard of care, posterior spinal fusion (PSF). The purpose of this study is to describe the complication rate of AVBT in IS using the mCDS and to compare it to the recently reported complication rate of PSF in IS.

METHODS

A multicenter pediatric spine deformity database was queried for all idiopathic scoliosis patients who underwent vertebral body tethering. There were 171 patients with a minimum 9-month follow-up included in this study. Complications were retrospectively graded by 2 attending pediatric spine surgeons using the mCDS classification system.

RESULTS

Data from 171 patients with idiopathic scoliosis was available for analysis, with 156/171 (91%) of patients being female and an average age of 12.2 years old at surgery. There were 156 thoracic tethers (1 with an LIV below L2), 5 lumbar tethers, 9 staged double tethers, and only 1 patient with same-day double tether. Fifty-five (55) (32%) patients experienced a total of 69 complications. The most common complication type for VBT by mCDS was Grade IIIb, encompassing 29/69 (42%) of complications. The second most frequent complication grade was Grade I at 23/69 (33%). Thirty-four (34) out of 69 (49%) of the VBT complications reported required either procedural/surgical intervention or admission to the ICU.

CONCLUSIONS

This is the first study to directly compare the complication profile of VBT to PSF using the mCDS. Forty-nine percent (49%) of the VBT complications reported were at least Grade III, while only 7% of complications in the control PSF cohort from the literature were Grade III or higher. The mCDS complication classification brings light to the early learning experience of a new technique compared to the widely accepted standard of PSF for IS.

LEVEL OF EVIDENCE

III - Retrospective comparative study.

How Long Can You Delay? Curve Progression While Awaiting Vertebral Body Tethering Surgery

Background: The implications of delaying surgical intervention for patients with adolescent idiopathic scoliosis (AIS) wishing to undergo vertebral body tethering (VBT) have not yet been explored. It is important to understand how these delays can impact surgical planning and patient outcomes. Methods: This was a retrospective review that analyzed all AIS patients treated between 2015 and 2021 at a single tertiary center. Time to surgery from initial surgical consultation and ultimate surgical plan were assessed. Patient characteristics, potential risk factors associated with increased curve progression, and reasons for delay were also analyzed. Results: 174 patients were evaluated and 95 were scheduled for VBT. Four patients later required a change to posterior spinal fusion (PSF) due to excessive curve progression. Patients requiring PSF were shown to have significantly longer delays than those who received VBT. Additionally, longer delays, younger age, greater curve progression, and lower skeletal maturity were correlated with significant curve progression (≥5 degrees). Conclusions: Surgical delays for AIS patients awaiting VBT may lead to significant curve progression and necessitate more invasive procedures. Patients with longer delays experienced an increased risk of needing PSF instead of VBT. Of those requiring PSF, the majority were due to insurance denials. Optimizing surgical timing and shared decision-making among patients, families, and healthcare providers are essential for achieving the best outcomes.

Incidence of Tether Breakage in Anterior Vertebral Body Tethering

BACKGROUND

Thoracic anterior vertebral body tethering (TAVBT) is an emerging treatment for adolescent idiopathic scoliosis. Tether breakage is a known complication of TAVBT with incompletely known incidence. We aim to define the incidence of tether breakage in patients with adolescent idiopathic scoliosis who undergo TAVBT. The incidence of tether breakage in TAVBT is hypothesized to be high and increase with time postoperatively.

METHODS

All patients with right-sided, thoracic curves who underwent TAVBT with at least 2 and up to 3 years of radiographic follow-up were included. Tether breakage between 2 vertebrae was defined a priori as any increase in adjacent screw angle >5 degrees from the minimum over the follow-up period. The presence and timing of tether breakage were noted for each patient. A Kaplan-Meier survival analysis was performed to calculate expected tether breakage up to 36 months. χ 2 analysis was performed to examine the relationship between tether breakage and reoperations. Independent t test was used to compare the average final Cobb angle between cohorts.

RESULTS

In total, 208 patients from 10 centers were included in our review. Radiographically identified tether breakage occurred in 75 patients (36%). The initial break occurred at or beyond 24 months in 66 patients (88%). Kaplan-Meier survival analysis estimated the cumulative rate of expected tether breakage to be 19% at 24 months, increasing to 50% at 36 months. Twenty-one patients (28%) with a radiographically identified tether breakage went on to require reoperation, with 9 patients (12%) requiring conversion to posterior spinal fusion. Patients with a radiographically identified tether breakage went on to require conversion to posterior spinal fusion more often than those patients without identified tether breakage (12% vs. 2%; P =0.004). The average major coronal curve angle at final follow-up was significantly larger for patients with radiographically identified tether breakage than for those without tether breakage (31 deg±12 deg vs. 26 deg±12 deg; P =0.002).

CONCLUSIONS

The incidence of tether breakage in TAVBT is high, and it is expected to occur in 50% of patients by 36 months postoperatively.

LEVEL OF EVIDENCE

Level IV.

Evidence-based Indications for Vertebral Body Tethering in Spine Deformity

Posterior spinal fusion has long been established as an effective treatment for the surgical management of spine deformity. However, interest in nonfusion options continues to grow. Vertebral body tethering is a nonfusion alternative that allows for the preservation of growth and flexibility of the spine. The purpose of this investigation is to provide a practical and relevant review of the literature on the current evidence-based indications for vertebral body tethering. Early results and short-term outcomes show promise for the first generation of this technology. At this time, patients should expect less predictable deformity correction and higher revision rates. Long-term studies are necessary to establish the durability of early results. In addition, further studies should aim to refine preoperative evaluation and patient selection as well as defining the benefits of motion preservation and its long-term effects on spine health to ensure optimal patient outcomes.

Minimally Invasive Surgery for Adolescent Idiopathic Scoliosis: A Systematic Review

Background: Minimally invasive surgical (MIS) techniques have gained popularity as a safe and effective alternative to open surgery for degenerative, traumatic, and metastatic spinal pathologies. In adolescent idiopathic scoliosis, MIS techniques comprise anterior thoracoscopic surgery (ATS), posterior minimally invasive surgery (PMIS), and vertebral body tethering (VBT). In the current systematic review, the authors collected and analyzed data from the available literature on MIS techniques in AIS. Methods: The articles were shortlisted after a thorough electronic and manual database search through PubMed, EMBASE, and Google Scholar. Results: The authors included 43 studies for the review; 14 described the outcomes with ATS, 13 with PMIS, and 16 with VBT. Conclusions: While the efficacy of the ATS approach is well-established in terms of comparable coronal and sagittal correction to posterior spinal fusion, the current use of ATS for instrumented fusion has become less popular due to a steep learning curve, high pulmonary and vascular complication rates, implant failures, and increased non-union rates. PMIS is an effective alternative to the standard open posterior spinal fusion, with a steep learning curve and longer surgical time being potential disadvantages. The current evidence, albeit limited, suggests that VBT is an attractive procedure that merits consideration in terms of radiological correction and clinical outcomes, but it has a high complication and re-operation rate, while the most appropriate indications and long-term outcomes of this technique remain unclear.

Anterior Vertebral Body Tethering: A Review of the Available Evidence

Idiopathic scoliosis is a complex three-dimensional deformity of the spine with anterior overgrowth (hypokyphosis), coronal curvature, and axial rotation. Scoliosis treatment in the skeletally immature spine is therapeutically challenging because of growth and was commonly limited to observation, bracing treatment, or fusion. Fusion accomplishes powerful deformity correction at the expense of future growth and mobility of the involved segments, increasing the risk of adjacent segment degeneration and intervertebral disk disease later in life. Anterior vertebral body tethering is a motion-preserving technique that exploits the Hueter-Volkmann principle by applying compression at the anterior and convex aspects of the curve to stimulate differential vertebral growth for gradual deformity reduction without fusion. The appropriate timing, curve magnitude, tensioning, growth prediction, indications, and limitations of tethering are being refined as this technique becomes more prevalent. Early outcome studies show that growth modulation with vertebral body tethering is safe, can achieve good results, and preserve motion in select patients.

Results of posterior spinal fusion after failed anterior vertebral body tethering

PURPOSE

In patients with adolescent idiopathic scoliosis (AIS) undergoing anterior vertebral tethering (AVBT), some will subsequently require posterior spinal fusion (PSF). Limited data exist on clinical and radiographic outcomes of fusion after tether failure.

METHODS

490 patients who underwent AVBT were retrospectively analyzed. Twenty patients (4.1%) subsequently underwent conversion to PSF. A control group of patients with primary PSF (no previous AVBT) was matched for comparison. Data were compared using paired t-tests and Fisher Exact Tests.

RESULTS

There was a significant increase in estimated blood loss (EBL) (p = 0.002), percent estimated blood volume (%EBV) (p = 0.013), operative time (p = 0.002), and increased amount of fluoroscopy (mGy) (p = 0.04) as well as number of levels fused (p = 0.02) in the AVBT conversion group compared to primary fusion. However, no difference was found in implant density (p = 0.37), blood transfusions (p = 0.11), or intraoperative neuromonitoring events (p > 0.99). Both groups attained similar thoracic and lumbar percent correction (major coronal curve angle) from pre-op to the latest follow-up (thoracic p = 0.507, lumbar p = 0.952).

CONCLUSION

A subset of patients with AVBT will require conversion to PSF. Although technically more challenging, revision surgery can be safely performed with similar clinical and radiographic outcomes to primary PSF.

LEVEL OF EVIDENCE: 3

Automated measurements of interscrew angles in vertebral body tethering patients with deep learning

BACKGROUND CONTEXT

Vertebral body tethering is the most popular nonfusion treatment for adolescent idiopathic scoliosis. The effect of the tether cord on the spine can be segmentally assessed by comparing the angle between two adjacent screws (interscrew angle) over time. Tether breakage has historically been assessed radiographically by a change in adjacent interscrew angle by greater than 5° between two sets of imaging. A threshold for growth modulation has not yet been established in the literature. These angle measurements are time consuming and prone to interobserver variability.

PURPOSE

The purpose of this study was to develop an automated deep learning algorithm for measuring the interscrew angle following VBT surgery.

STUDY DESIGN/SETTING

Single institution analysis of medical images.

PATIENT SAMPLE

We analyzed 229 standing or bending AP or PA radiographs from 100 patients who had undergone VBT at our institution.

OUTCOME MEASURES

Physiologic Measures: An image processing algorithm was used to measure interscrew angles.

METHODS

A total of 229 standing or bending AP or PA radiographs from 100 VBT patients with vertebral body tethers were identified. Vertebral body screws were segmented by hand for all images and interscrew angles measured manually for 60 of the included images. A U-Net deep learning model was developed to automatically segment the vertebral body screws. Screw label maps were used to develop and tune an image processing algorithm which measures interscrew angles. Finally, the completed model and algorithm pipeline was tested on a 30-image test set. Dice score and absolute error were used to measure performance.

RESULTS

Inter- and Intra-rater reliability for manual angle measurements were assessed with ICC and were both 0.99. The segmentation model Dice score against manually segmented ground truth across the 30-image test set was 0.96. The average interscrew angle absolute error between the algorithm and manually measured ground truth was 0.66° and ranged from 0° to 2.67° in non-overlapping screws (N=206). The primary modes of failure for the model were overlapping screws on a right thoracic/left lumbar construct with two screws in one vertebra and overexposed images. An algorithm step which determines whether an overlapping screw was present correctly identified all overlapping screws, with no false positives.

CONCLUSION

We developed and validated an algorithm which measures interscrew angles for radiographs of vertebral body tether patients with an accuracy of within 1° for the majority of interscrew angles. The algorithm can process five images per second on a standard computer, leading to substantial time savings. This algorithm may be used for rapid processing of large radiographic databases of tether patients and could enable more rigorous definitions of growth modulation and cord breakage to be established.

Bilateral vertebral body tethering: identifying key factors associated with successful outcomes

PURPOSE

The treatment of operative double major pediatric spinal deformities (e.g., Lenke 3 or 6) with bilateral vertebral body tethering (VBT) can be significantly more challenging when compared to other deformity patterns (e.g., Lenke 1) or treatment with a posterior spinal fusion. We aimed to identify preoperative and perioperative characteristics that were associated with successful postoperative outcomes in patients treated with both a thoracic and thoracolumbar (e.g., bilateral) tether.

METHODS

We retrospectively assessed radiographic and clinical data from patients enrolled in a large multi-center study who had a minimum postoperative follow-up of two years. Standard radiographic parameters were extracted from standing spine and left hand-wrist radiographs at various timepoints. We classified patients based on their preoperative deformity pattern (Primary Thoracic [TP] vs. Primary Thoracolumbar [TLP]) and assessed: (1) deformity balance, (2) tilt of the transitional vertebra, and (3) postoperative success.

RESULTS

We analyzed data from thirty-six patients (TP: 19 and TLP: 17). We observed no relationship between deformity balance at first erect and postoperative success (p = 0.354). Patients with a horizontal transitional vertebra at first erect were significantly (p = 0.001) more likely to exhibit a successful outcome when compared to those who exhibited a tilted transitional vertebra (83% vs. 62%). Patients who had TLP were also more likely to exhibit a successful outcome when compared to patients who exhibited TP (76% vs. 50%).

CONCLUSION

These data indicate that double major deformities can be successfully treated with VBT, particularly for those who exhibit TLP.

Predicting radiographic outcomes of vertebral body tethering in adolescent idiopathic scoliosis patients using machine learning

Anterior Vertebral Body Tethering (AVBT) is a growing alternative treatment for adolescent idiopathic scoliosis (AIS), offering an option besides spinal fusion. While AVBT aims to correct spinal deformity through growth correction, its outcomes have been mixed. To improve surgical outcomes, this study aimed to develop a machine learning-based tool to predict short- and midterm spinal curve correction in AIS patients who underwent AVBT surgery, using the most predictive clinical, radiographic, and surgical parameters. After institutional review board approval and based on inclusion criteria, 91 AIS patients who underwent AVBT surgery were selected from the Shriners Hospitals for Children, Philadelphia. For all patients, longitudinal standing (PA or AP, and lateral) and side bending spinal Radiographs were retrospectively obtained at six visits: preop and first standing, one year, two years, five years postop, and at the most recent follow-up. Demographic, radiographic, and surgical features associated with curve correction were collected. The sequential backward feature selection method was used to eliminate correlated features and to provide a rank-ordered list of the most predictive features of the AVBT correction. A Gradient Boosting Regressor (GBR) model was trained and tested using the selected features to predict the final correction of the curve in AIS patients. Eleven most predictive features were identified. The GBR model predicted the final Cobb angle with an average error of 6.3 ± 5.6 degrees. The model also provided a prediction interval, where 84% of the actual values were within the 90% prediction interval. A list of the most predictive features for AVBT curve correction was provided. The GBR model, trained on these features, predicted the final curve magnitude with a clinically acceptable margin of error. This model can be used as a clinical tool to plan AVBT surgical parameters and improve outcomes.

Reducing Uncertainty in Anterior Vertebral Body Tethering: Predicting Postoperative Curvature With Fulcrum Bending Radiographs

STUDY DESIGN

Retrospective Cohort Study.

OBJECTIVES

Mid-term Anterior Vertebral Body Tethering (AVBT) results demonstrate an acceptable degree of clinical success, yet the revision rate remains notably higher than fusion. Fulcrum-bending radiographs have previously been shown to more reliably predict radiological outcomes in Adolescent Idiopathic Scoliosis (AIS) as compared to supine-lateral bending radiographs. This study aims to discern how Fulcrum Flexibility Rate (FFR) correlates with Correction Rate (CR) and establish whether this can reliably predict residual deformity following AVBT surgery.

METHODS

A review of 38 consecutive AIS patients undergoing thoracic AVBT between 2015 - 2020 was performed. Preoperative (standing and fulcrum-bending) and postoperative (first-erect) radiographs were evaluated for curve magnitude using the Cobb-method. The FFR, CR and Fulcrum Bending Correction Index (FBCI) were calculated. Patients were also percentile-ranked according to their FFR and dichotomized into flexible and rigid cohorts for comparison. Student t-test, Pearson correlation and linear stepwise regression was applied.

RESULTS

AVBT resulted in a significant improvement in the major Cobb angle (Preoperative: 50.9±7.5° vs Postoperative: 19.9±9.4°; P < .0001) with a mean FBCI of 98.0%. Bivariate correlation revealed a moderate relationship between fulcrum-bending and first-erect Cobb angle (r = .5306, P = .0006). Linear regression demonstrated a predictive relationship between fulcrum-bending and first-erect Cobb using the equation 'Postoperative Cobb = 7.5 + .65(Fulcrum-bending Cobb).'

CONCLUSION

This is the first study to demonstrate the ability of fulcrum-bending radiographs to predict early radiographic outcomes following AVBT, 'timepoint-zero' for the growth modulation process.

Thoracoscopic Surgery in the Management of Idiopathic Scoliosis: Systematic Literature Review according to the Prisma Protocol

Idiopathic scoliosis is characterized by a three-dimensional deformity of the spine with axial rotation and lateral inclination with an angle greater than 10° according to the Cobb method. Its approach can be conservative or surgical, depending on the degree of angulation, musculoskeletal development and age of the affected child or adolescent, or even depending on the functional impairment resulting from the condition. The aim of this study was to analyze the impact of videoassisted thoracoscopic surgery in the management of idiopathic scoliosis. This is a systematic literature review, built according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) protocol and registered with PROSPERO under number CRD42022351466. The search for studies was performed between August 2022 and September of the same year, in bibliographic databases including MEDLINE, The Cochrane Library and Web of Science. The technique is a minimally invasive alternative to thoracotomy that has shown great evolution in recent years. The main advantages include less blood loss during the procedure, shorter hospital stay and improved post-surgical esthetics. One of the disadvantages mentioned by the authors is the greater complexity and technological requirement, longer surgical time and the need for careful selection of patients, according to degrees of vertebral deviation. The use of analgesics and anti-inflammatory drugs had no significant difference between traditional procedures (thoracotomy) or thoracoscopic surgery.

A twitter analysis of patient and family experience in pediatric spine surgery

BACKGROUND

There is little data on patient and caregiver perceptions of spine surgery in children and youth. This study aims to characterize the personal experiences of patients, caregivers, and family members surrounding pediatric spine surgery through a qualitative and quantitative social media analysis.

METHODS

The Twitter application programming interface was searched for keywords related to pediatric spine surgery from inception to March 2022. Relevant tweets and accounts were extracted and subsequently classified using thematic labels. Tweet metadata was collected to measure user engagement via multivariable regression. Sentiment analysis using Natural Language Processing was performed on all tweets with a focus on tweets discussing the personal experiences of patients and caregivers.

RESULTS

2424 tweets from 1847 individual accounts were retrieved for analysis. Patients and caregivers represented 1459 (79.0%) of all accounts. Posts discussed the personal experiences of patients and caregivers in 83.5% of tweets. Pediatric spine surgery research was discussed in few posts (n=90, 3.7%). Within the personal experience category, 975 (48.17%) tweets were positive, 516 (25.49%) were negative, and 533 (26.34%) were neutral. Presence of a tag (beta: -6.1, 95% CI -9.7 to -2.5) and baseline follower count (beta<0.001, 95% CI <0.001 to <0.001) significantly affected tweet engagement negatively and positively, respectively.

CONCLUSIONS

Patients and caregivers actively discuss topics related to pediatric spine surgery on Twitter. Posts discussing personal experience are most prevalent, while posts on research are scarce, unlike previous social media studies. Pediatric spine surgeons can leverage this dialogue to better understand the worries and needs of patients and their families.

Vertebral body tethering for idiopathic scoliosis: a systematic review and meta-analysis

PURPOSE

Vertebral body tethering (VBT) is a recent procedure to correct and reduce spinal curves in skeletally immature patients with adolescent idiopathic scoliosis (AIS). The purpose of this systematic review and meta-analysis is to determine the expected curve reduction and potential complications for adolescent patients after VBT.

METHODS

PubMed, Embase, Google Scholar and Cochrane databases were searched until February 2022. Records were screened against pre-defined inclusion and exclusion criteria. Data sources were prospective and retrospective studies. Demographics, mean differences in Cobb angle, surgical details and complication rates were recorded. Meta-analysis was conducted using a random-effects model.

RESULTS

This systematic review includes 19 studies, and the meta-analysis includes 16 of these. VBT displayed a statistically significant reduction in Cobb angle from pre-operative to final (minimum 2 years) measurements. The initial mean Cobb angle was 47.8° (CI 95% 42.9-52.7°) and decreased to 22.2° (CI 95% 19.9-24.5°). The mean difference is - 25.8° (CI 95% - 28.9-22.7) (p < 0.01). The overall complication rate was 23% (CI 95% 14.4-31.6%), the most common complication was tether breakage 21.9% (CI 95% 10.6-33.1%). The spinal fusion rate was 7.2% (CI 95% 2.3-12.1%).

CONCLUSION

VBT results in a significant reduction of AIS at 2 years of follow-up. Overall complication rate was relatively high although the consequences of the complications are unknown. Further research is required to explore the reasons behind the complication rate and determine the optimal timing for the procedure. VBT remains a promising new procedure that is effective at reducing scoliotic curves and preventing spinal fusion in the majority of patients.

LEVEL OF EVIDENCE

Systematic review of Therapeutic Studies with evidence level II-IV.

Radiographic and perioperative outcomes following anterior thoracic vertebral body tethering and posterior lumbar spine tethering: a pilot series

BACKGROUND AND CONTEXT

 In patients with adolescent idiopathic scoliosis (AIS) of main thoracic and lumbar spine regions, combined anterior thoracic vertebral body tethering and posterior lumbar spine tethering (ATVBT/PLST) is a novel non-fusion treatment option for growth modulation and conservation of motion.

METHODS

 Fourteen patients with AIS who underwent ATVBT/PLST with at least 2-year follow-up were included. Primary outcomes included quality of life as assessed by SRS-22 instruments, radiographic analysis, and revision operations. We secondarily reported perioperative metrics and post-operative opiate morphine equivalents (OME). Clinical success was defined as patients who achieved skeletal maturity with ≤ 30° curve magnitude of both their main thoracic and thoracolumbar/lumbar curves and who did not undergo posterior spine instrumentation and fusion (PSIF).

RESULTS

Patients had a mean age of 11.6 years (range 10-14 years), majority were girls (92%), and mean follow-up was 3.0 years (range 2-4.8 years). All patients were skeletally immature with a Risser ≤ 2. Included curves were Lenke 1C, 3C, or 6C. Mean preoperative curve magnitudes were 53° ± 8° (range 45°-65°) main thoracic and 49° ± 9° (range 40°-62°) thoracolumbar/lumbar curves. At most recent follow-up, patients had a mean main thoracic curve of 29° ± 8° (range 15°-40°) and a mean thoracolumbar/lumbar curve of 20° ± 15° (range 4°-35°). 50% required a revision operation. Cable breakage occurred in 43%, which did not always require revision. One patient progressed to thoracic fusion, but no patient underwent lumbar fusion. Patients had a mean SRS-22 outcome score of 4.2 ± 0.4.

CONCLUSIONS

ATVBT/PLST is a potential alternative to spine fusion for select immature patients with AIS at a minimum 2-year follow-up. ATVBT/PLST potentially offers motion conservation at the cost of a higher revision rate. Further study and reporting of results are necessary to refine indications and techniques, which in turn will improve outcomes of this procedure.

LEVEL OF EVIDENCE

Level IV-Case series without comparative group.

Pre-operative parameters influencing vertebral body tethering outcomes: patient's characteristics play an important role in determining the outcomes at a minimum of 2 years post-op

PURPOSE

The aim of this study is to determine preoperative predictors of good radiographic outcomes in VBT patients at a minimum 2-year follow-up.

METHODS

From a single-center dataset, we reviewed patients who underwent VBT from January 2014 to November 2018. Data analysis included age, gender, Risser grade and biometric data. Radiographically, maximum Cobb angle, C-DAR and apical vertebral and disc wedging were measured preop and at a minimum 2-year follow-up. Patients were divided into two cohorts following two different outcome measures: (1) vertebral growth modulation, those patients that growth modulated or corrected ≥ 5° and those who did not; and (2) Maximum Cobb angle at 2 years, < and ≥ 40°. Student T and Chi2 tests were used for comparison and a multiple linear correlation test was implemented between statistically significant variables.

RESULTS

79 patients were recruited. 26 patients (33%) did growth modulate their spine at 2-year follow-up. These patients were significantly younger, and more skeletally immature with less height (147 cm vs 155 cm; p < 0.0001), weight (38 kg vs. 45 kg; p = 0.0009) and BMI (17 vs 18.8; p = 0.0229) as those who did not. Multiple linear regression model with these variables resulted in a moderate correlation (r2 = 0.234). 67 patients (85%) finished at a 2-year follow-up with a maximum Cobb angle < 40°. These patients were also younger and skeletally immature. We found significant differences in outcome 2 regarding the average preoperative maximum Cobb angle (48.5° ± 9.5 vs. 59.1° ± 10), average C-DAR (7 ± 1.5 vs. 8.5 ± 2.1), average apical vertebral wedging (6.5° vs. 8.3°), average vertebral/disc wedging ratio (1.5 vs. 2.4) and the average immediate postoperative Cobb angle (25° vs. 38°). These variables predicted a 36% of the variation in final Cobb angle measurement at a 2-year follow-up (r2 = 0.362).

CONCLUSION

Curve severity determined by a preoperative C-DAR, preoperative Cobb angles and immediate postoperative Cobb angle are significantly related to curves < 40° at a minimum 2-year follow-up, while the potential to growth modulate the spine is more dependent on skeletal maturity, lower body weight and lower BMI. These patients' characteristics should be considered preoperatively.