What would be the annual cost savings if fewer screws were used in adolescent idiopathic scoliosis treatment in the US?

Implant density in adolescent idiopathic scoliosis: a meta-analysis of clinical and radiological outcomes

BACKGROUND

Adolescent idiopathic scoliosis (AIS) affects 1-3% of adolescents, and treatment approaches, including the density of constructs in surgical fusion, vary among orthopedic surgeons. Studies have sought to establish whether high-density or low-density constructs offer superior clinical and radiological outcomes, yet conclusive results are lacking. This meta-analysis aims to provide a definitive answer to the controversial and ambiguous question surrounding the efficacy of different pedicle screw densities in treating AIS.

METHODS

PubMed, Cochrane, and Google Scholar (page 1-20) were searched till December 2023. The studied outcomes were Major Cobb angle, major curve correction, lumbar curve, kyphosis (T5-T12), lumbar lordosis, coronal balance, LIV Tilt angle, TAV translation, LAV translation, apical trunk rotation, trunk shift, SRS-22, operative time, blood loss, complications and cost.

RESULTS

Twenty-four studies (total of 1985 patients, 1045 in LD group and 940 in HD group) were included in this meta-analysis. A statistically significant better improvement in ATR (p = 0.02) and LIV tilt angle (p = 0.02) was seen in the high-density group. On the other hand, longer operative time (p = 0.002), blood loss (p = 0.0004) and costs (p = 0.02) were seen in the high-density group. No difference was seen in the remaining radiographic and clinical outcomes between both surgeries.

CONCLUSION

Both low-density (LD) and high-density (HD) screw constructs show comparable and satisfactory radiographic and QOL for AIS patients. Furthermore, HD constructs had increased costs, operative time, and blood loss associated. However, a definitive conclusion cannot be made and more studies taking into account multiple additional variables are necessary to do so.

A bending model for assessing relative stiffness and strength of orthopaedic fixation constructs

BACKGROUND

The purpose of this study is to develop a simple and reproducible bending model that is compatible with a wide range of orthopaedic fixation devices and 3D printed spacers.

METHODS

A robust 4-point bending model was constructed by securing sawbones blocks with different orthopaedic fixation device constructs. Stress strain curves derived from a fundamental mechanics model were used to assess the effect of bone density, type of hardware (staple vs intramedullary beam), the use of dynamic compression, orientation of staples (dorsal vs plantar), and the use of 3D printed titanium spacers.

FINDINGS

The high throughput 4-point bending model is simple enough that the methods can be easily repeated to assess a wide range of fixation methods, while complex enough to provide clinically relevant information.

INTERPRETATIONS

It is recommended that this model is used to assess a large initial set of fixation methods in direct and straightforward comparisons.

Biomechanical Computational Study of Pedicle Screw Position and Density in Adolescent Idiopathic Scoliosis Instrumentation

STUDY DESIGN

Computer simulation of adolescent idiopathic scoliosis instrumentation.

OBJECTIVE

To test the hypothesis that different screw densities would result in different apical vertebral rotation (AVR) corrections and bone-screw forces in adolescent idiopathic scoliosis instrumentation.

SUMMARY OF BACKGROUND DATA

The "Minimize Implants Maximize Outcomes" Clinical Trial revealed that the use of more versus fewer screws resulted in similar coronal plane correction for Lenke 1A curves. However, the biomechanical impact of screw density on transverse plane correction is still unclear. Further investigation is needed to determine if and how transverse plane correction is correlated with screw density.

PATIENTS AND METHODS

We simulated apical vertebral derotation after segmental translation using patient-specific computer models of 30 patients from the "Minimize Implants Maximize Outcomes" Trial. For each case, 10 alternative screw patterns were tested with overall densities ranging between 1.2 and 2 screws per level fused, and local density at the 3 apical levels ranging between 0.7 and 2 (total: 600 simulations). Main thoracic (MT) Cobb angle, thoracic kyphosis (TK), AVR, and bone-screw forces were computed and compared.

RESULTS

The presenting MT (62 ± 11°; range: 45° to 86°), TK (27 ± 20°; -5° to 81°), and AVR (14±7°; -2° to 25°) were corrected through segmental translation to 22 ± 7° (10° to 41°), 26 ± 5° (18° to 45°), and 14 ± 7° (-4° to 26°). After apical vertebral derotation, they became 16 ± 8° (1° to 41°), 24 ± 4° (13° to 40°), and 4 ± 5° (-12° to 18°). There was no significant difference in MT among screw patterns; higher screw density had lower bone-screw forces ( P < 0.05). The apical vertebral derotation maneuver reduced AVR by an average of 70%, positively correlated with apical screw density ( r = 0.825, P < 0.05). There was no significant difference in TK.

CONCLUSION

Screw density had no significant effect on 3-dimensional correction through the primary segmental translation maneuver. Transverse plane correction through subsequent apical vertebral derotation was positively correlated with screw density at the apical levels ( r = 0.825, P < 0.05). Bone-screw forces were negatively correlated with overall screw density ( P < 0.05).

Intermittent pedicle screw application provides better kyphosis restoration in adolescent idiopathic scoliosis for Lenke type 1 and type 2 curves

PURPOSE

There is still no consensus on the optimum pedicle screw density required for the desired thoracic kyphosis restoration in adolescent idiopathic surgery (AIS). The aim of this study to evaluate the effect of pedicle screw density on thoracic kyphosis restoration in AIS surgery.

METHODS

The data of 106 patients from two centers that operated for Lenke type 1 and 2 AIS were retrospectively reviewed. Two groups were constituted according to the pedicle screw density: intermittent pedicle screw constructs (IPSC) (n = 52 patients) and consecutive pedicle screw construct (CPSC) (n = 54 patients) groups. The preoperative and at least 24-month follow-up radiographs and SRS-22 scores were evaluated. The Cobb angle of the main and concomitant curves in the coronal plane and the sagittal plane were measured and compared.

RESULTS

The mean follow-up period for the IPSC and CPSC groups was 72.3 ± 37.2 and 62.9 ± 28.8 months, respectively. In the SRS-22 questionnaire, there was no significant difference between the two groups in terms of self-image/appearance domain scores (p = 0.466), but better results were obtained in the IPSC group in terms of treatment satisfaction domain scores (p = 0.010) and better thoracic kyphosis restoration was achieved in IPSC group radiologically for Lenke type 1 curves with - 81.4 ± 81.4% in the IPSC group and 6.8 ± 83.8% in the CPSC group (p < 0.001).

CONCLUSION

It was considered that better thoracic kyphosis restoration could be achieved with the less lordotic effect of IPSC in Lenke type 1 curves. Although the current situation had a significant impact on radiological outcomes, its effect on SRS-22 scores was limited.

All Pedicle Screw versus Hybrid Hook-Screw Instrumentation in the Treatment of Thoracic Adolescent Idiopathic Scoliosis (AIS): A Prospective Comparative Cohort Study

Background: Posterior spinal correction and fusion remains the most common surgical treatment in AIS. Surgeons currently favour all pedicle screw (AS) correction techniques with alternative implants being less utilised. The purpose of this study was to assess whether a hybrid hook−screw (HS) construct could achieve similar outcomes. Methods: A single centre, prospective cohort study was conducted. Patients with moderate and severe thoracic AIS (Lenke 1) were included. Clinical and radiological results of a standardised hybrid HS technique were compared with those obtained with an AS construct. All patients had a minimum 2-year follow-up. Results: 160 patients were included in this series (80 patients/group). The HS group had significantly reduced surgical time, blood loss and implant density. Both techniques achieved ≥75% scoliosis correction. The HS group was superior in restoring thoracic kyphosis and global sagittal balance with an average 31% increase in kyphosis compared to 10% with the AS group (p < 0.001). There was significant improvement in SRS-22 scores at 2 years postoperative (p < 0.001) in both groups. There were no neurological or visceral complications related to instrumentation, no detected non-union and no reoperations. The HS implant cost was significantly lower than that of AS, with a mean instrumentation saving of almost £2000/patient. Conclusion: A standardised hybrid HS technique achieved excellent correction of thoracic scoliosis, high patient satisfaction and low complication rates in patients with thoracic AIS. These results were comparable to the AS group. The HS technique achieved better correction of thoracic kyphosis and sagittal balance than the AS technique, together with reduced surgical time, blood loss and implant cost.

Ninety-day complication, revision, and readmission rates for current-generation robot-assisted thoracolumbar spinal fusion surgery: results of a multicenter case series

OBJECTIVE

Robotics is a major area for research and development in spine surgery. The high accuracy of robot-assisted placement of thoracolumbar pedicle screws is documented in the literature. The authors present the largest case series to date evaluating 90-day complication, revision, and readmission rates for robot-assisted spine surgery using the current generation of robotic guidance systems.

METHODS

An analysis of a retrospective, multicenter database of open and minimally invasive thoracolumbar instrumented fusion surgeries using the Mazor X or Mazor X Stealth Edition robotic guidance systems was performed. Patients 18 years of age or older and undergoing primary or revision surgery for degenerative spinal conditions were included. Descriptive statistics were used to calculate rates of malpositioned screws requiring revision, as well as overall complication, revision, and readmission rates within 90 days.

RESULTS

In total, 799 surgical cases (Mazor X: 48.81%; Mazor X Stealth Edition: 51.19%) were evaluated, involving robot-assisted placement of 4838 pedicle screws. The overall intraoperative complication rate was 3.13%. No intraoperative implant-related complications were encountered. Postoperatively, 129 patients suffered a total of 146 complications by 90 days, representing an incidence of 16.1%. The rate of an unrecognized malpositioned screw resulting in a new postoperative radiculopathy requiring revision surgery was 0.63% (5 cases). Medical and pain-related complications unrelated to hardware placement accounted for the bulk of postoperative complications within 90 days. The overall surgical revision rate at 90 days was 6.63% with 7 implant-related revisions, representing an implant-related revision rate of 0.88%. The 90-day readmission rate was 7.13% with 2 implant-related readmissions, representing an implant-related readmission rate of 0.25% of cases.

CONCLUSIONS

The results of this multicenter case series and literature review suggest current-generation robotic guidance systems are associated with low rates of intraoperative and postoperative implant-related complications, revisions, and readmissions at 90 days. Future outcomes-based studies are necessary to evaluate complication, revision, and readmission rates compared to conventional surgery.

Surgical outcomes of severe spinal deformities exceeding 100° or treated by vertebral column resection (VCR). Does implant density matter?: an observational study of deformity groupings

STUDY DESIGN

Prospective multicenter international observational study.

OBJECTIVE

To investigate the effect of implant density on clinical outcomes in complex pediatric spine reconstruction. Implant density in spine deformity surgery has been a subject of much debate with some authors advocating higher density for better correction. Few studies have looked at the effect of implant density on severe curves > 100 deg or treated with vertebral column resection (VCR).

METHODS

250/311 pts with 2-year f/u enrolled in the FOX pediatric database from 17 international sites were queried for the impact of implant density and surgical outcomes. Patients were grouped into three implant density categories for comparative analysis Group 1 (density ≤ 1), Group 2 (1 < density < 1.5) and Group 3 (density; 1.5-2).

RESULTS

250 pts: 47 (Grp1)/99 (Grp2) /104 (Grp3); Pre-op age and etiology and curve types were similar in all groups, but body mass index (BMI) was higher in Grp3. Grps 1 and 2 had significantly higher sagittal deformity angular ratio (S-DAR) compared to Grp 3 (p < 0.001). Pre-op Halo Gravity Traction (HGT) was used in 55.3%/44.4%/31.7%, p = 0.017; Grp1/Grp2/Grp3, respectively. Average duration of surgery (min) was higher in Grp3 relative to Grp1 only: 352.5/456.5/515.0, p = 0.0029. Blood loss was similar in all Grps. Rate of VCR, PSO and SPO was similar in all Grps. Pre-op Coronal Cobb avg 96.1/83.6/88.6, p = 0.2342, attained similar correction after HGT (24.6%/27.2%/23.2%, p = 0.4864. Coronal Cobb corrections at 2-year follow-up (FU) were (37.1%/40.3%/53.5%, p = 0.0004). Pre-op sagittal Cobb was (105.4/101.9/75.9, p < 0.01.), achieved similar %correction in HGT (19.1%/22.3%/22.5%, p = 0.6851) and at 2-year FU (39.6%/41.4%/29.8%, p = 0.1916). After adjusting for C-DAR, S-DAR, pre-op coronal and sagittal Cobb, etiology, curve types, age, BMI and number of rods in multivariate analysis, the odds of developing post-operative implant complication was 11 times greater in group 1 compared to group 3 (OR = 11.17,95% CI 2.34-53.32). There was significant improvement in SRS scores in all Grps at 2-year FU.

CONCLUSION

Although higher implant density was observed to be associated with greater curve correction and lower rates of post-operative implant-related complication and revision in heterogeneous case groups, the results may not imply causality of implant density on the outcomes in severe pediatric spine reconstruction.

Implant Distribution Versus Implant Density in Lenke Type 1 Adolescent Idiopathic Scoliosis: Does the Position of the Screw Matter?

STUDY DESIGN

Retrospective study.

OBJECTIVE

Previous studies have demonstrated that increased implant density (ID) results in improved coronal deformity correction. However, low-density constructs with strategically placed fixation points may achieve similar coronal correction. The purpose of this study was to identify key zones along the spinal fusion where high ID statistically correlated to improved coronal deformity correction. Our hypothesis was that high ID within the periapical zone would not be associated with increased percent Cobb correction.

METHODS

We identified patients with Lenke type 1 curves with a minimum 2-year follow up. The instrumented vertebral levels were divided into 4 zones: (1) cephalad zone, (2) caudal zone, (3) apical zone, and (4) periapical zone. High and low percent Cobb correction groups were compared, high percent Cobb group was defined as percent correction >67%. Total ID, total concave ID, total convex ID, and ID within each zone of the curve were compared between the groups. A multivariable analysis was performed to identify independent predictors for coronal correction. Subsequently increased and decreased thoracic kyphosis (TK) groups were compared, increased TK was defined as post-operative TK being larger than preoperative TK and decreased TK was defined as post-operative TK being less than preoperative TK.

RESULTS

The cohort included 68 patients. The high percent Cobb group compared with the low percent Cobb group had significantly greater ID for the entire construct, the total concave side, the total convex side, the apical convex zone, the periapical zone, and the cephalad concave zone. The high percent Cobb group had greater pedicle screw density for the total construct, total convex side, and total concave side. In the multivariate model ID and pedicle screw density remained significant for percent Cobb correction. Ability to achieve coronal balance was not statistically correlated to ID (P = .78).

CONCLUSIONS

Increased ID for the entire construct, the entire convex side, the entire concave side, and within each spinal zone was associated with improved percent Cobb correction. The ability to achieve coronal balance was not statistically influence by ID. The results of this study support that increasing ID along the entire length of the construct improves percent Cobb correction.

Biomechanical analysis of the number of implants for the immediate sacroiliac joint fixation

PURPOSE

The fusion of the sacroiliac joint (SIJ) is the last treatment option for chronic pain resulting from sacroiliitis. With the various implant systems available, there are different possible surgical strategies in terms of the type and number of implants and trajectories. The aim was to quantify the effect of the number of cylindrical threaded implants on SIJ stabilization.

METHODS

Six cadaveric pelvises were embedded in resin simulating a double-leg stance. Compression loads were applied to the sacral plate. The pelvises were tested non-instrumented and instrumented progressively with up to three cylindrical threaded implants (12-mm diameter, 60-mm length) with a posterior oblique trajectory. Vertical (VD) and angular (AD) displacements of the SIJ were measured locally using high-precision cameras and digital image correlation.

RESULTS

Compared to the non-instrumented initial state, instrumentation with one implant significantly decreased the VD (- 24% ± 15%, p = 0.028), while the AD decreased on average by - 9% (± 15%; p = 0.345). When compared to the one-implant configuration, adding a second implant further statistically decreased VD (- 10% ± 7%, p = 0.046) and AD (- 19% ± 15, p = 0.046). Adding a third implant did not lead to additional stabilization for VD nor AD (p > 0.5).

CONCLUSION

Compared to the non-instrumented initial state, the two-implant configuration reduces both vertical and angular displacements the most, while minimizing the number of implants.

How low can you go? Implant density in posterior spinal fusion converted from growing constructs for early onset scoliosis

STUDY DESIGN

Retrospective, multicenter comparative.

OBJECTIVES

Our purpose was to compare early onset scoliosis (EOS) patients treated with ultra-low, low, and high implant density constructs when undergoing conversion to definitive fusion. Larson et al. demonstrated that implant density (ID) at fusion does not correlate with outcomes in the treatment of adolescent idiopathic scoliosis, but did not address growth-friendly graduates.

METHODS

EOS patients treated with growth-friendly constructs converted to fusion between 2000 and 2017 were reviewed from a multicenter database. ID was defined as number of pedicle screws, hooks, and sublaminar/bands per level fused. Patients were divided into ultra-low ID (< 1.3), low (≥ 1.3 and < 1.6), and high ID (≥ 1.6).

EXCLUSION CRITERIA

< 2 years follow-up from fusion or inadequate radiographs.

RESULTS

A total of 152 patients met inclusion criteria with 39 (26%) patients in the high ID group, 33 (22%) patients in the low ID group, and 80 (52%) in the ultra-low ID group. Groups were similar in operative time (p = 0.61), pre-fusion major curve (p = 0.71), mean number of levels fused (p = 0.58), clinical follow-up (p = 0.30), and radiographic follow-up (p = 0.90). Patients in the low ID group (11.6 ± 1.5 years) were slightly younger at the time of definitive fusion than patients in the ultra-low ID group (12.9 ± 2.2 years) and high ID group (12.5 ± 1.7 years) (p = 0.009). There was significantly more blood loss in the high ID group than the other two groups (high ID: 946.8 ± 606.0 mL vs. low ID: 733.9 ± 434.5 mL and ultra-low ID: 617.4 ± 517.2 mL; p = 0.01), but there was no significant difference with regard to percent of total blood volume lost (high ID: 59.3 ± 48.7% vs. low ID: 54.5 ± 37.5% vs. ultra-low ID: 51.7 ± 54.9%; p = 0.78). There was a difference in initial improvement in major curve between the groups (high ID: 21.6° vs. low ID: 18.0° vs. ultra-low ID: 12.6°; p = 0.01). However, during post-fusion follow-up, correction decreased 7.1° in the high ID group, 2.6 in the low ID group, and 2.8 in the ultra-low ID group (p = 0.19). At final follow-up, major curve correction from pre-fusion was similar between groups (high ID: 14.5° vs. low ID: 15.5° vs. ultra-low ID: 9.7°, p = 0.14). At final follow-up, there was no difference in T1-T12 length gain (p = 0.85), T1-S1 length gain (p = 0.68), coronal balance (p = 0.56), or sagittal balance (p = 0.71). The revision rate was significantly higher in the ultra-low ID group (13.8%; 11/80) versus the high ID group (2/39; 5.1%) and low ID group (0/33; 0%) (p = 0.04).

CONCLUSIONS

Although an ID < 1.3 in growth-friendly graduates produces similar outcomes with regard to curve correction and spinal length gain as low and high ID, this study suggests that an ID < 1.3 is associated with an increased revision rate.

LEVEL OF EVIDENCE

III.

Can Postoperative CT Imaging in Spine Surgery Be Replaced by Intraoperative 3D Rotation With the C-Arm?: Results of a Prospective Single Center Cohort Study

Objective: Dorsal instrumentation of the spine is an established treatment option for a range of spinal pathologies. Intraoperative fluoroscopy connected with navigation minimize the risk of incorrect screws placement. In several cases, post-operative CT scans are needed to verify possible mismatches. In this study, we evaluated the efficacy of 3D intraoperative fluoroscopy as compared to post-operative CT and the need of post-operative CT.

Methods: We conducted a prospective single-center cohort study, 94 patients were included. The screws were implanted using 3D rotation with C-arm and navigation system. The definitive position of the screws was verified by a post-operative CT scan. Finally, we compared the discrepance between intraoperative imaging and post-operative CT scan using Rampersaud-grade (A-D).

Results: 607 screws in 94 patients were included. Some 3% of the screws had to be replaced immediately intraoperative due to inadequate position with lateral or medial trajectory. An A-score was achieved for 85.5% of the 3D controlled screws and 87% of the post-operative CT. A B-score was found in 11.5% of either groups. In the 3D group a C-score was achieved for 2.5% and in the CT group for 0.8%. A D-score was found in 0.5% of the screws in both groups, p = 0.45. Only a mismatch of 3% could be detected for the intraoperative and post-operative imaging results.

Conclusion: Our study data shows that the placement of screws using the 3D rotation and navigation tool is safe and accurate. There were no relevant mismatches between intraoperative images and the post-operative CT.

Perioperative outcome and complications following single-staged Posterior Spinal Fusion (PSF) using pedicle screw instrumentation in Adolescent Idiopathic Scoliosis (AIS): a review of 1057 cases from a single centre

Background

There has been a growing interest in using all pedicle screw construct in posterior spinal fusion (PSF) for adolescent idiopathic scoliosis (AIS) surgery in recent years. However, studies focusing on perioperative outcome and complications utilizing only pedicle screw system in AIS population are lacking. This study aims to evaluate perioperative outcomes and to determine the prevalence of major and minor complications following single-staged PSF for AIS.

Methods

In this retrospective study of prospectively collected data, 1057 AIS patients operated between 2012 and 2019 were included. Main outcome measures were operative time, intraoperative blood loss, allogeneic blood transfusion rate, length of hospital stay after surgery, complication rate, and mean drop of haemoglobin (Hb) level. We documented the number of fusion levels, screw density, and postoperative radiographic parameters.

Results

There were 917 females and 140 males. Majority were Lenke 1 curve type (46.9%). Mean age was 15.6 ± 3.7 years, with mean BMI of 18.6 ± 3.2 kg/m². Mean operative time was 146.8 ± 49.4 min. Average intraoperative blood loss was 952.9 ± 530.4 ml with allogeneic blood transfusion rate of 5%. Mean screw density was 1.27 ± 0.21 screws per fusion level. Average hospital stay after surgery was 3.5 ± 0.9 days. Twenty-four complications were documented: twelve superficial infections (1.14%), five transient neurological deficits (0.47%), two deep infections (0.19%), two superior mesenteric artery syndrome, and one case each (0.09%) for massive intraoperative blood loss, intraoperative seizure, and lung atelectasis.

Conclusion

AIS patients treated with single-staged PSF using pedicle screw construct had a 0.95% rate of major complications and 1.32% rate of minor complications. Rate of neurologic complication was 0.47% while non-neurologic postoperative complications was 1.80% with infection being the leading complication at 1.32%.

Higher pedicle screw density does not improve curve correction in Lenke 2 adolescent idiopathic scoliosis

Purpose

Higher pedicle screw density posterior spinal fusion (PSF) constructs have not been shown to result in improved curve correction in Lenke 1 and 5 adolescent idiopathic scoliosis (AIS) but do increase cost. The purpose of this study questioned whether higher screw density constructs improved curve correction and maintenance of correction in Lenke 2 AIS. Secondary goals were to identify predictive factors for correction and postoperative magnitude of curves in Lenke 2 AIS.

Methods

We identified patients 11 to 17 years old who underwent primary PSF for Lenke 2 AIS between 2007 and 2017 who had minimum follow-up of 2 years. Demographic and radiographic data were collected to perform regression and elimination analysis.

Results

Thirty patients (21 females, 9 males) were analyzed. Average age and SD at time of surgery was 14.0 ± 1.8 years (range, 11–17 years), and median follow-up was 2.8 years (IQR 2.1–4.0 years). Implant density did not predict final postoperative curve magnitude. Predictors of final postoperative curve magnitude were sex and preoperative curve magnitude. Predictors of percentage of correction of major curve were sex and age at the time of surgery. Predictors of final postoperative thoracic kyphosis were sex and percent flexibility preop. Females had lower final postoperative major curve magnitude, a higher percent curve correction, and lower postoperative thoracic kyphosis.

Conclusions

Increased implant density is not predictive of postoperative curve magnitude in Lenke 2 AIS. Predictors of postoperative curve magnitude are sex and preoperative curve magnitude.

Level of evidence

Level III, retrospective observational

Different fixation pattern for thoracolumbar fracture of ankylosing spondylitis: A finite element analysis

The objective of this study is to establish an ankylosing spondylitis (AS) thoracolumbar fracture finite element (FE) model and provide a proper posterior fixation choice from the biomechanical perspective. The ankylosing spondylitis T9-L5 FE model was built and the range of motion (ROM) was compared to previous studies. The L1 transverse fracture was simulated and was separately fixed by five different patterns. The pull force and yielding force of the screws, the von Mises stress of the internal fixation, and the displacement of fracture site were analyzed to evaluate the proper fixation pattern for thoracolumbar fracture of AS. ROM of AS model was obviously restricted comparing to the normal vertebral experimental data. All the fixation patterns can stabilize the fracture. At least four levels of fixation can reduce the von Mises stress of the internal fixation. Four levels fixation has a higher pull force than the six levels fixation. Skipped level fixation did not reduce the stress, pull force and yielding force. The kyphosis correction did not change the biomechanical load. At least 4 levels fixation was needed for AS thoracolumbar fracture. The cemented screws should be chosen in 4 levels fixation to increase the holding of the screws. The skipped fixation has no advantage. The kyphosis correction can be chosen after weighing the pros and cons.

How do spine instrumentation parameters influence the 3D correction of thoracic adolescent idiopathic scoliosis? A patient-specific biomechanical study

BACKGROUND

Patient-specific models promises to support the surgical decision-making process, particularly in adolescent idiopathic scoliosis. The present computational biomechanical study investigates how specific instrumentation parameters impact 3D deformity correction in thoracic scoliosis.

METHODS

1080 instrumentation simulations of a representative patient were run. The independent instrumentation parameters were: screw pattern, upper and lower instrumented vertebrae, rod curvature and rod stiffness. ANOVA and correlation analyses analyzed how the instrumentation parameters influenced the 3D correction.

FINDINGS

Coronal plane correction was affected by the lower instrumented vertebra and rod stiffness (explaining 84% and 11%, respectively, of its overall variance). The sagittal profile was controlled by rod curvature and the upper vertebra (56% and 36%). The transverse plane vertebral rotation was influenced by lower, upper instrumented vertebra and screw pattern (35%, 32% and 19%). The Cobb angle correction was strongly correlated with the number of fused vertebrae, particularly when grouped by the upper instrumented vertebra (r = -0.91) and rod stiffness (r = -0.73). Thoracic kyphosis was strongly correlated with the number of fused vertebrae grouped by rod curvature (r = 0.84). Apical vertebral rotation was moderately correlated with the number of fused vertebrae grouped by upper/lower instrumented vertebra (r = 0.55/0.58), although variations were minimal.

INTERPRETATION

Instrumenting the last vertebra touching the central sacral vertical line improves 3D correction. A trade-off between a more cranial vs. caudal upper instrumented vertebra, respectively beneficial for coronal/sagittal vs. transverse plane correction, is required. High rod stiffness, differential rod contouring, and screw pattern were effective for coronal correction, thoracic kyphosis, and axial vertebral derotation, respectively.

The Transverse Process Trajectory Technique: An Alternative for Thoracic Pedicle Screw Implantation-Radiographic and Biomechanical Analysis

BACKGROUND

This study evaluates the accuracy, biomechanical profile, and learning curve of the transverse process trajectory technique (TPT) compared to the straightforward (SF) and in-out-in (IOI) techniques. SF and IOI have been used for fixation in the thoracic spine. Although widely used, there are associated learning curves and symptomatic pedicular breaches. We have found the transverse process to be a reproducible pathway into the pedicle.

METHODS

Three surgeons with varying experience (experienced [E] with 20 years in practice, surgeon [S] with less than 10 years in practice, and senior resident trainee [T] with no experience with TPT) operated on 8 cadavers. In phase 1, each surgeon instrumented 2 cadavers, alternating between TPT and SF from T1 to T12 (n = 48 total levels). In phase 2, the E and T surgeons instrumented 1 cadaver each, alternating between TPT and IOI. Computed tomography scans were analyzed for accuracy of screw placement, defined as the percentage of placements without critical breaches. Axial pullout and derotational force testing were performed. Statistical analyses include paired t test and analysis of variance with Tukey correction.

RESULTS

Overall accuracy of screw placement was comparable between techniques (TPT: 92.7%; SF: 97.2%; IOI: 95.8%; P = .4151). Accuracy by technique did not differ for each individual surgeon (E: P = .7733; S: P = .3475; T: P = .4191) or by experience level by technique (TPT: P = .1127; FH: P = .5979; IOI: P = .5935). Pullout strength was comparable between TPT and SF (571 vs 442 N, P = .3164) but was greater for TPT versus IOI (454 vs 215 N, P = .0156). There was a trend toward improved derotational force for TPT versus SF (1.06 vs 0.93 Nm/degrees, P = .0728) but not for TPT versus IOI (1.36 vs 1.16 Nm/degrees, P = .74). Screw placement time was shortest for E and longest for T for TPT and SF and not different for IOI (TPT: P = .0349; SF: P < .0001; IOI: P = .1787) but did not vary by technique.

CONCLUSIONS

We describe the TPT, which uses the transverse process as a corridor through the pedicle. TPT is an accurate method of thoracic pedicle screw placement with potential biomechanical advantages and with acceptable learning curve characteristics.

CLINICAL RELEVANCE

This study provides the surgeon with a new trajectory for pedicle screw placement that can be used in clinical practice.

Biomechanical influence of the surgical approaches, implant length and density in stabilizing ankylosing spondylitis cervical spine fracture

Ankylosing spondylitis cervical spine fractures (ASCFs) are particularly unstable and need special consideration when selecting appropriate internal fixation technology. However, there is a lack of related biomechanical studies. This study aimed to investigate the biomechanical influence of the pattern, length, and density of instrumentation for the treatment of ASCF. Posterior, anterior, and various combined fixation approaches were constructed using the finite element model (FEM) to mimic the surgical treatment of ASCFs at C5/6. The rate of motion change (RMC) at the fractured level and the internal stress distribution (ISD) were observed. The results showed that longer segments of fixation and combined fixation approaches provided better stability and lowered the maximal stress. The RMC decreased more significantly when the length increased from 1 to 3 levels (302% decrease under flexion, 134% decrease under extension) than from 3 to 5 levels (22% decrease under flexion, 23% decrease under extension). Longer fixation seems to be more stable with the anterior/posterior approach alone, but 3-level posterior fixation may be the most cost-effective option. It is recommended to perform surgery with combined approaches, which provide the best stability. Long skipped-screwing posterior fixation is an alternative technique for use in ASCF patients.

In silico patient-specific optimization of correction strategies for thoracic adolescent idiopathic scoliosis

BACKGROUND

With modelling and simulation (or in silico) techniques, patient-specific optimization algorithms represent promising tools to support the surgical decision-making process, particularly in 3D correction of adolescent idiopathic scoliosis, where the best intraoperative instrumentation strategy and the correction goals are debated.

METHODS

1080 biomechanical intraoperative simulations of a representative pediatric thoracic curve were run according to a full-factorial design approach. Widely accepted instrumentation configurations (5 screw patterns, 4 upper and 3 lower instrumented vertebrae, 6 rod curvatures and 3 rod stiffnesses) were analyzed, assuming concave rod rotation and en bloc derotation as main correction maneuvers. Results in terms of 3D correction and mobility were rated using an objective function for thoracic scoliosis also including surgeon-dependent correction objectives. An extensive sensitivity analysis on correction objectives was performed.

FINDINGS

Multiple optimal strategies were identified, depending on the selected correction objective. They provided significantly better coronal (67% vs. 55%) correction, using comparable instrumented levels (9.9 ± 1.6 vs. 10.7 ± 2.1), screw patterns and significantly higher implant density (1.6 ± 0.3 vs. 1.4 ± 0.2 screws/vertebra) compared to worst ones. Optimal strategies typically included the neutral and the last touching vertebrae in the construct and high stiffness (CoCr, 6 mm) differentially/highly contoured rods.

INTERPRETATION

The computerized algorithm determined the best instrumentation parameters to achieve optimal correction for the considered thoracic case. Multiple clinically equivalent strategies may be used, as supported by the variety of considered correction objectives. The current approach could be translated to any scoliotic curves, including surgeon preferences in terms of instrumentation parameters, intraoperative correction maneuvers and correction objectives.

Correction objectives have higher impact than screw pattern and density on the optimal 3D correction of thoracic AIS: a biomechanical study

STUDY DESIGN

Assessment of screw pattern, implant density (ID), and optimization of 3D correction through computer-based biomechanical models.

OBJECTIVE

To investigate how screw pattern and ID affect intraoperative 3D correction of thoracic curves in adolescent idiopathic scoliosis, and how different correction objectives impact the optimal screw pattern. Screw pattern, ID, correction objectives and surgical strategies for posterior fusion of AIS are highly variable among experienced surgeons. The "optimal" instrumentation remains not well defined.

METHODS

10 patient-specific multibody models of representative adolescent idiopathic scoliosis Lenke 1A cases were built and used to compare alternative virtual correction surgeries. Five screw patterns and IDs (average: 1.6 screws/instrumented level, range: 1.2-2) were simulated, considering concave rod rotation, en bloc derotation, and compression/distraction as primary correction maneuvers. 3D correction descriptors were quantified in the coronal, sagittal and transverse planes. An objective function weighting the contribution of intraoperative 3D correction and mobility allowed rating of the outcomes of the virtual surgeries. Based on surgeon-dependent correction objectives, the optimal result among the simulated constructs was identified.

RESULTS

Low-density (ID ≤ 1.4) constructs provided equivalent 3D correction compared to higher (ID ≥ 1.8) densities (average differences ranging between 2° and 3°). The optimal screw pattern varied from case to case, falling within the low-density screw category in 14% of considered scenarios, 73% in the mid-density (1.4 < ID < 1.8) and 13% in the high-density. The optimal screw pattern was unique in five cases; multiple optima were found in other cases depending on the considered correction objectives.

CONCLUSIONS

Low-density screw patterns provided equivalent intraoperative 3D correction to higher-density patterns. Simulated surgeon's choice of correction objectives had the greatest impact on the selection of the optimal construct for 3D correction, while screw density and ID had a limited impact.

LEVEL OF EVIDENCE

N/A.

Trends in Medical Costs for Adolescent Idiopathic Scoliosis Surgery in Japan

STUDY DESIGN

A retrospective review of clinical data and costs was performed for surgeries for adolescent idiopathic scoliosis (AIS) conducted from 2008 to 2017.

OBJECTIVE

Cost containment and healthcare value have become focal points in Japanese health care policy. The purpose of the study was to investigate trends over time in medical costs for surgery for AIS.

METHODS

A total of 83 patients underwent surgery for AIS from 2008 to 2017 at our hospital. Clinical data and length of stay were collected, and medical costs for surgery, local bone grafting, fees per day, and surgical instruments were evaluated.

RESULTS

There were slight year-by-year decreases in fees per day and decreases in costs of surgical instruments. The average length of stay was 16.4 days and gradually decreased over time. In contrast, scoliosis surgery costs increased about 1.6 times in 10 years from $9515 to $15 130.

CONCLUSION

The trends for decreases in fees per day and prices for surgical instruments reflect recent government medical cost control policies. The cost for scoliosis surgery is also defined by the government, and the increase over 10 years may reflect the perspective of valuing effective and advanced surgeries. This study of cost trends of operative spinal intervention provides an assessment of surgical benefit and is likely to influence health care costs.

The Role of Intraoperative Image Guidance Systems (Three-Dimensional C-arm versus O-arm) in Spinal Surgery: Results of a Single-Center Study

OBJECTIVE

Spinal dorsal instrumentation is an established treatment option for a range of spinal disorders. In combination with navigation, intraoperative fluoroscopy reduces the risk of incorrectly placing screws. This study aimed to evaluate the efficacy and validity of fluoroscopy (intraoperative navigation with three-dimensional rotation of C-arm vs. O-arm).

METHODS

In this retrospective single-center study, 240 patients were included between July 2017 and April 2020. Intraoperative images were acquired using a Siemens-Arcadis Orbic 3D C-arm with a navigation system (Brainlab, AG, Munich, Germany) or using O-arm (Medtronic, Minneapolis, Minnesota, USA) with a navigation system (S7 StealthStation). Finally, we compared mismatches between intraoperative and postoperative computed tomography imaging results using Rampersaud-grade (A-D).

RESULTS

A total of 1614 screws were included: 94 patients in the C-arm group (cAG) and 146 in the O-arm group (oAG). In cAG, 3% (n = 20) of the screws had to be replaced directly due to inadequate positioning with median or lateral breaches, and 3.5 % of screws in oAG (n = 35). An A-score was achieved for 85.7% in the cAG and 87.4% in the oAG. A B-score was found in 11.5% in the cAG and 11.9% in the oAG. In the cAG, a C-score was achieved for 2.5% and in oAG for 0.7%. For 0.3% of the screws, a D-score was found in cAG and for none in oAG.

CONCLUSIONS

Our study shows that placement of screws using intraoperative imaging in combination with a navigation tool is accurate. Furthermore, navigation coupled with the O-arm had significant advantages in accuracy over navigation with 3D C-arm fluoroscopy. However, both systems offer a high level of accuracy.

Willingness to enroll in a surgical randomized controlled trial: patient and parent preferences regarding implant density for adolescent idiopathic scoliosis fusion

STUDY DESIGN

Prospective survey of adolescent idiopathic scoliosis (AIS) patients/parents with surgical magnitude curves.

OBJECTIVE

We hypothesized that patients and families considering fusion surgery would be willing to enroll in a randomized controlled trial (RCT) evaluating the effect of number of implants on curve correction. Surgical RCTs are infrequently performed, particularly in a pediatric population. Parental willingness to enroll affects both study design and trial feasibility. The Minimize Implants Maximize Outcomes (MIMO) Clinical Trial proposes to randomize patients to more versus fewer screws (high or low density) for Lenke 1A curve patterns, but it is unclear whether families and patients are willing to enroll in such a trial.

METHODS

This study was undertaken at 4 of the 14 sites participating in the MIMO Clinical Trial. AIS patients with Cobb > 45° were included. Implant density is defined as screws per level fused. Patients and families reviewed the MIMO education module describing proposed advantages and disadvantages of high (> 1.8) vs. low (< 1.4) density screw constructs and completed a custom survey regarding their preferences about the trial.

RESULTS

159 individuals were surveyed (78 families), including 82 parents/guardians, and 77 patients. Of those surveyed, 95% mostly or completely understood the trial (range 47-78%), and 63% agreed to enroll. Parents and patients who completely understood the trial were significantly more likely to enroll.

CONCLUSION

Randomization in the MIMO Trial was acceptable to the majority (63%) of patients and parents. Clear patient and parent education materials and access to the surgeon may facilitate enrollment in the trial. Parents afforded the child much autonomy when considering enrollment, although most families agree both child and parent should be in agreement before entering the trial.

LEVEL OF EVIDENCE

II.

History of Spinal Fusion: Where We Came from and Where We Are Going

Spinal fusion surgery is performed all over the world to help patients with cervical and thoracolumbar pathology. As outcomes continue to improve in patients with spine-related pathology, it is important to understand how we got to modern day spinal fusion surgery. Scientific innovations have ranged from the first spinal fusions performed with basic instrumentation in the late nineteenth century to contemporary tools such as pedicle screws, bone grafts, and interbody devices. This article tracks this technological growth so that surgeons may better serve their patients in treating spine-related pain and disability.

Predictors of cost for posterior spinal fusion in adolescent idiopathic scoliosis

STUDY DESIGN

Single-center retrospective review of pediatric patients who underwent posterior spinal fusion for adolescent idiopathic scoliosis (AIS).

OBJECTIVE

To determine what clinical and operative factors influence inflation-adjusted hospital costs of posterior spine fusion surgery for AIS. With rising healthcare costs and the advent of bundled payments, it is essential understand the predictors of costs for surgical procedures. We sought to determine the components of hospital costs for AIS posterior spine fusion surgery using standardized, inflation-adjusted, line-item costs for services and procedures.

METHODS

The study population comprised 148 AIS patients who underwent spinal fusion surgery at a large tertiary care center between 2009 and 2016. Data on medical characteristics, curve type, curve magnitude, number of screws and the number of levels was collected through manual chart review of X-rays and medical records. Hospital costs from admission until discharge were retrieved from an institutional database that contained line-item details of all procedures and services billed during the hospital episode. Bottom-up microcosting valuation techniques were used to generate standardized inflation-adjusted estimates of costs and standard deviations in 2016 dollars.

RESULTS

Mean cost of AIS surgery was $48,058 ± 9379. Physician fees averaged 15% of the total cost ($7045 ± 1732). Implant costs and surgical/anesthesia/surgeon's fees accounted for over 70% of the hospital costs. Mean number of screws was 16 ± 4.5, mean number of levels fused was 11.2 ± 2.2, and the mean implant density (screws per level fused) was 1.45 ± 0.35. On multivariate analysis, the number of screws per level fused, number of levels fused, curve magnitude and length of stay were all significantly associated with hospital costs (p < 0.01).

CONCLUSIONS

Bundled payments for AIS surgery should include adjustments for number of levels fused and curve size. Areas for cost savings include further reduction in implant costs, shortening length of stay, and reducing intraoperative costs.

LEVEL OF EVIDENCE

III.

The implant density does not change the correction rate of the main and the accompanying curves: A comparison between consecutive and intermittent pedicle screw constructs

OBJECTIVE

The aim of this study was to evaluate the clinical outcomes and the coronal correction rate of the main and accompanying curves of adolescent idiopathic scoliosis (AIS) corrected with pedicle screws inserted consecutively or intermittently.

METHODS

The prospectively collected data of 60 patients (8 men and 52 women; mean age: 14.6±2.5 years) who underwent corrective surgery for AIS between January 2010 and December 2015 were reviewed retrospectively. Two groups were constituted according to the pedicle screw construct type: consecutive pedicle screw construct (CPSC) and intermittent pedicle screw construct (IPSC) groups. The preoperative, early postoperative, and 24-month follow-up radiographs and the Scoliosis Research Society-22 (SRS-22) scores were reevaluated. The Cobb angle of the main and accompanying curves, the correction rate, and the flexibility of the curves were calculated.

RESULTS

The mean preoperative Cobb angles were 57.03° and 57.46°, the mean postoperative Cobb angles were 14.93° and 14.4°, and the mean correction rates were 76.22% and 75.31% in IPSC and CPSC groups, respectively (p>0.05). The preoperative and postoperative accompanying curve magnitudes and correction rates were similar (p>0.05). These radiographic outcomes were also consistent with the SRS-22 scores.

CONCLUSION

Both the pedicle screw constructs had satisfactory outcomes following the surgery, which were confirmed by both the SRS-22 scores and radiographs taken perioperatively and at follow-ups. The IPSC and CPSC groups did not demonstrate a significant change in the correction rate of the main and minor or major accompanying structural and nonstructural curves, and also in the SRS-22 scores.

LEVEL OF EVIDENCE

Level III, Retrospective comparative study.

Selection of the lowest instrumented vertebra in main thoracic adolescent idiopathic scoliosis: Is it safe to fuse shorter than the last touched vertebra?

HYPOTHESIS

Fusing shorter than the last touched vertebra (LTV) is a safe approach in flexible main thoracic (MT) adolescent idiopathic scoliosis (AIS) curves.

METHODS

This was a prospective study on consecutive AIS patients surgically treated with selective fusion of the MT curve. Fusion-level selection was based on the fulcrum-bending radiograph method. Patients were grouped based on the position of the lowest instrumented vertebra as proximal to the LTV (proxLTV, n = 43), at the LTV (atLTV, n = 45), and distal to the LTV (distLTV, n = 21).

RESULTS

A total of 109 patients were included in the study. Preoperatively, the distLTV group had greater lumbar Cobb angle, lumbar apical translation, and less flexibility in the MT curve. At 2-year follow-up, the groups did not differ in MT curve correction, but the distLTV had larger lumbar Cobb angle, more apical translation, and worse coronal balance. Distal adding-on was observed in 11 patients (26%) in the proxLTV group, four patients (9%) in the atLTV group, and one patient (5%) in the distLTV group (p = 0.031). Adding-on was associated with younger patients and lower Risser grade at the time of surgery but not with any other radiographic parameter. No differences in SRS-22r scores were observed between the groups.

CONCLUSIONS

Proximal fusion carries the risk of adding-on, but leaving unfused segments in the lower spine increases the potential for compensatory mechanisms to improve spinal and truncal balance. In mature patients with a flexible MT curve, surgeons may consider fusion at or cranial to the LTV.

The correlations between the anchor density and the curve correction of adolescent idiopathic scoliosis surgery

Background

The optimal anchor density in adolescent idiopathic scoliosis (AIS) surgery to achieve good curve correction remains unclear. The purpose of the study is to analyze the correlations between three-dimensional curve correction and anchor density in the pedicle screw-based posterior fusion of AIS.

Methods

One hundred and twenty-seven AIS patients receiving primary posterior fusion with pedicle screw instrumentation were retrospectively reviewed. Anchor density (AD) was defined as the screws number per fused spinal segment. The correlations between three-dimensional curve correction radiographic parameters and anchor density were analyzed with subgroup analysis based on different curve types, curve magnitudes, and curve flexibilities. The differences of curve correction parameters between the low-density (AD ≤1.4), middle-density (1.4 < AD ≤1.7) and high-density (AD > 1.7) groups were also calculated. Independent t-test, analysis of variance (ANOVA), and Pearson’s correlation coefficient were used for statistical analysis.

Results

There were no correlations between the anchor density and the coronal curve correction or apical vertebral rotation (AVR) correction. In the sagittal plane, mild positive correlations existed between anchor density and thoracic kyphosis correction in all patients (r = 0.27, p = 0.002). Subgroup analysis revealed similar mild positive correlations in Lenke 1 (r = 0.31, p = 0.02), Lenke 1–3 (r = 0.27, p = 0.01), small curves (40°-60°, r = 0.38, p <  0.001), and flexible curves (flexibility > 40%, r = 0.34, p = 0.01).

There were no differences between low-density (mean 1.31), middle-density (mean 1.55), and high-density (mean 1.83) in terms of coronal or axial curve correction parameters. Low-density group has longer fused level (mean difference 2.14, p = 0.001) and smaller thoracic kyphosis correction (mean difference 9.25°, p = 0.004) than high-density group.

Conclusion

In our study, the anchor density was not related to coronal or axial curve corrections. Mild positive correlations with anchor density were found in thoracic kyphosis correction, especially in patients with smaller and flexible curves. Low anchor density with longer fusion level achieves similar curve corrections with middle or high anchor density in adolescent idiopathic scoliosis surgery.

Periapical-dropout Screws Strategy For 3-Dimensional Correction of Lenke 1 Adolescent Idiopathic Scoliosis in Patients Treated by Posterior Spinal Fusion

STUDY DESIGN

This was a single-center, retrospective study.

OBJECTIVE

The objective of this study was to compare periapical-dropout screws strategy (PDSS) with traditional-multilevel pedicle screws strategy (TMSS) for 3-plane correction of Lenke 1 adolescent idiopathic scoliosis deformity.

SUMMARY OF BACKGROUND DATA

There are limited data in 3-plane correction and the optimal pedicle screw (PS) configuration for Lenke 1 adolescent idiopathic scoliosis surgery.

MATERIALS AND METHODS

Sixty-one consecutive patients with Lenke 1 curves (range: 50-80 degrees), undergoing single-stage posterior spinal fusion with PS fixation, were included. Patients with a minimum follow-up of 1 year were divided into 2 groups according to PS strategy. The PDSS group included 33 patients with PS placement bilaterally at both ends and apex of the construct. The TMSS group included 28 patients with conventional PS placement. Baseline, immediate, and last follow-up demographic, radiographic, and clinical outcomes were analyzed. Radiographic outcomes were assessed in axial (using rib index and apical vertebral rotation using Raimondi ruler and Upasani methods), coronal, and sagittal planes. The implant costs were also evaluated.

RESULTS

There were no differences in demographic, preoperative radiographic parameters and levels fused. The number of PSs per level fused was significantly lower in the PDSS group (1.3 vs. 1.4; P=0.0002). At last follow-up, major Cobb correction averaged 79% for the PDSS group and 69.5% for the TMSS group (P=0.001). T2-T12 kyphosis angle changes were 1 degree in the PDSS group and -2.5 degrees in the TMSS group (P=0.35). Rib index correction was 28.2% for the PDSS group and 17.7% for the TMSS group (P=0.02). Upasani grade apical vertebral rotation was significantly better in the PDSS group (0.7 vs. 1.4; P=0.0001). Clinical outcomes evaluated by Scoliosis Research Society-30 scores were similar in both groups. Total implant costs were significantly lower in the PDSS group ($16,852 vs. $18,926; P<0.001).

CONCLUSION

The PDSS construct provides better deformity correction in all 3 planes and helps decrease implant costs compared with the TMSS construct. Thus, the PDSS construct can be considered as a rational strategy and cost-effective technique when treating moderate Lenke 1 curves with posterior spinal fusion.

The Utility of Preoperative Neuromonitoring for Adolescent Idiopathic Scoliosis

Background

Intraoperative neuromonitoring is well established and widely used to assist in completing corrective surgery for adolescent idiopathic scoliosis (AIS) safely. The role of preoperative measurement of somatosensory evoked potentials (SSEPs) and/or transcranial magnetic stimulation (TMS) to determine if there is transpinal pathology, however, is not clear. We sought to determine if preoperative SSEP and/or TMS measurement provided clinical benefit to patients with AIS.

Methods

A review of medical charts between 2010 and 2012 was conducted for patients undergoing surgery for scoliosis. Patients with diagnoses other than AIS were excluded. Patients with incomplete preoperative or intraoperative data were also excluded. Relevant clinical information such as age, sex, number of levels fused, and major Cobb angle were recorded. Preoperative neuromonitoring measurements and intraoperative neuromonitoring results were reviewed by an attending neurologist. Any instance in which an intraoperative surgical plan or neuromonitoring result interpretation was influenced by preoperative results was recorded. Further imaging obtained based on preoperative results was noted. Any acute neurologic complication such as paralysis was noted.

Results

Eighty-one patients met inclusion criteria (64 female, 17 male). Average age was 15 years (± 1.92). Major Cobb angle at preoperative evaluation averaged 57.5 degrees (± 10.81 degrees). Ten patients had abnormal preoperative SSEP/TMS results. There were no changes in protocol during intraoperative neuromonitoring based upon preoperative neuromonitoring findings. No additional imaging was required for patients with abnormal preoperative neuromonitoring results. There was no statistically significant difference in preoperative Cobb angle between the group of patients with abnormal preoperative neuromonitoring and those with normal baseline testing.

Conclusion

Preoperative SSEP/TMS measurement prior to corrective surgery for AIS has limited utility. There were no instances in which a patient's clinical course was improved by testing. We recommend against routine use of preoperative SSEP/TMS testing for AIS patients requiring corrective surgery.

Anterior and Posterior Fusion for Large, Rigid Idiopathic Scoliosis: Does Implant Density Matter?

BACKGROUND

Despite advancements in surgical techniques, controversy remains regarding the optimal implant density for the correction of idiopathic scoliosis. Recent evidence has suggested that equivalent radiographic and clinical outcomes can be achieved with lower implant densities for those with moderate curves and good flexibility. Among the experts, the consensus has continued that higher implant densities should be used for larger, stiffer curves. The purpose of the present study was to compare the radiographic results between high-implant density (HID) and low-implant density (LID) constructs in patients with large (>65°), rigid (<50% flexibility) curves who had undergone anterior release and posterior spinal fusion.

METHODS

We reviewed the idiopathic scoliosis cases performed at a single institution from 2006 to 2014. Only those meeting the inclusion criteria were selected. The patients were divided into HID and LID groups. The postoperative radiographs were compared for coronal correction, thoracic kyphosis, pelvic tilt, lumbar lordosis, and sagittal vertical axis.

RESULTS

A statistically significant improvement in coronal correction was detected in the HID group at all follow-up points (final follow-up: HID, 81.1% vs. LID, 70.4%; P = 0.01). When preoperative thoracic kyphosis was considered, no differences were found between the 2 groups. No differences were found in the other sagittal parameters.

CONCLUSION

In patients with large, rigid idiopathic scoliosis undergoing anterior release and posterior spinal fusion, a small, but statistically, significant improvement in the coronal Cobb angle was seen. It remains to be determined whether this small difference in radiographic correction will have any influence on the clinical outcome.

Use of a novel corrective device for correction of deformities in adolescent idiopathic scoliosis

BACKGROUND

Adolescent idiopathic scoliosis (AIS), with an incidence of 3%, is a common deformity. Correction of severe curvature of the deformity has attracted much investigation to achieve safe, reproducible results. We present our experience with a novel device for the correction of deformities across a spectrum of curve types, the rod link reducer. This system allows direct visualization of a mass derotation to achieve deformity correction.

METHODS

Prospective cohort study of patients with severe AIS treated in our institution during 2017 with major TL/L curves. Pre- and postoperative Cobb angles and coronal balance; operative time; and estimated blood loss, fusion levels, and screw density were recorded. Our results were split between those with a Lenke A/B classification and Lenke C, with a goal of correction of curve in the former and achieving good coronal balance with a preservation of distal motion segments in the latter.

RESULTS

There were 31 patients enrolled in our series. Within the Lenke A/B group, there were 18 patients, achieving a mean correction of 56% (SD 10%) and a correction of a mean coronal balance of 14.5 mm (SD 12.5 mm) of C7 from the CSVL to 10.9 mm (SD 10.6 mm). Our screw density was 1.3 screws (SD 0.1) per vertebrae fused. Our operative time was 185 min (SD 38 min). Average recorded blood loss was 721 ml (SD 289). In our Lenke C cohort, preoperative and postoperative mean Cobb angles (SD) were 73.3 (13.4) and 33.8 (11.9), respectively, with an average correction of 54% (SD 11%). The mean (SD) operative time was 03:35 (SD 00:35). Fusion levels were over a mean of 12.1 (SD 1.7) vertebrae, with a screw density of 1.3 (SD 0.1) per level. Mean intraoperative blood loss was 829 ml (SD 355). No patient received an allogenic blood transfusion. There were no adverse neurological events in this patient cohort.

CONCLUSIONS

The link rod system allows for excellent correction of spinal deformity and a short operative time.

Two Surgeon Approach for Complex Spine Surgery: Rationale, Outcome, Expectations, and the Case for Payment Reform

There is an increased trend in complex spine deformity cases toward a two attending surgeon approach, but the practice has not become widely accepted by payers. Multiple studies have shown that spine surgery complications increase with the duration of case, estimated blood loss, and use of transfusions, as well as in certain high-risk populations or those requiring three-column osteotomies. Dual-surgeon cases have been shown to decrease estimated blood loss, transfusion rate, surgical times, and therefore complication rates. Although this practice comes at an uncertain price to medical training and short-term costs, the patient's quality of care should be prioritized by institutions and payers to include dual-surgeon coverage for these high-risk cases. Because we enter an era where the value of spine care and demonstrating cost-effectiveness is essential, dual surgeon attending approaches can enhance these tenets.

Big Data Research in Pediatric Neurosurgery: Content, Statistical Output, and Bibliometric Analysis

BACKGROUND/AIMS

We sought to describe pediatric "big data" publications since 2000, their statistical output, and clinical implications.

METHODS

We searched 4 major North American neurosurgical journals for articles utilizing non-neurosurgery-specific databases for clinical pediatric neurosurgery research. Articles were analyzed for descriptive and statistical information. We analyzed effect sizes (ESs), confidence intervals (CIs), and p values for clinical relevance. A bibliometric analysis was performed using several key citation metrics.

RESULTS

We identified 74 articles, which constituted 1.7% of all pediatric articles (n = 4,436) published, with an exponential increase after 2013 (53/74, 72%). The Healthcare Cost and Utilization Project (HCUP) databases were most frequently utilized (n = 33); hydrocephalus (n = 19) was the most common study topic. The statistical output (n = 49 studies with 464 ESs, 456 CIs, and 389 p values) demonstrated that the majority of the ESs (253/464, 55%) were categorized as small; half or more of the CI spread (CIS) values and p values were high (274/456, 60%) and very strong (195/389, 50%), respectively. Associations with a combination of medium-to-large ESs (i.e., magnitude of difference), medium-to-high CISs (i.e., precision), and strong-to-very strong p values comprised only 20% (75/381) of the reported ESs. The total number of citations for the 74 articles was 1,115 (range per article, 0-129), with the median number of citations per article being 8.5. Four studies had > 50 citations, and 2 of them had > 100 citations. The calculated h-index was 16, h-core citations were 718, the e-index was 21.5, and the Google i10-index was 34.

CONCLUSIONS

There has been a dramatic increase in the use of "big data" in the pediatric neurosurgical literature. Reported associations that may, as a group, be of greatest interest to practitioners represented only 20% of the total output from these publications. Citations were weighted towards a few highly cited publications.

Quality, Safety, and Value in Pediatric Spine Surgery

The article addresses patient safety topics in spine surgery, including infection, length of stay, instrumentation strategies, pedicle screw malposition, radiation exposure, and neurologic events. Quality, safety, and value are concepts that are practical, easy to understand, and can be implemented on any scale and may be matched to individual practices. Further, with quality improvement, there is a culture shift to openly share information, protocols, and strategies so that more patients can rapidly benefit.

Finite Element Analysis of Long Posterior Transpedicular Instrumentation for Cervicothoracic Fractures Related to Ankylosing Spondylitis

STUDY DESIGN

Biomechanical finite element model analysis.

OBJECTIVES

Spinal fractures related to ankylosing spondylitis (AS) are often treated by long posterior stabilization. The objective of this study is to develop a finite element model (FEM) for spinal fractures related to AS and to establish a biomechanical foundation for long posterior stabilization of cervicothoracic fractures related to AS.

METHODS

An existing FEM (consisting of 2 separately developed models) including the cervical and thoracic spine were adapted to the conditions of AS (all discs fused, C0-C1 and C1-C2 mobile). A fracture at the level C6-C7 was simulated. Besides a normal spine (no AS, no fracture) and the uninstrumented fractured spine 4 different posterior transpedicular instrumentations were tested. Three loads (1.5g, 3.0g, 4.5g) were applied according to a specific load curve.

RESULTS

All posterior stabilization methods could normalize the axial stability at the fracture site as measured with gap distance. The maximum stress at the cranial instrumentation end (C3-C4) was slightly greater if every level was instrumented, than in the skipped level model. The skipped level instrumentation achieved similar rotatory stability as the long multilevel instrumentation.

CONCLUSIONS

Skipping instrumentation levels without giving up instrumentation length reduced stresses in the ossified tissue within the range of the instrumentation and did not decrease the stability in a FEM of a cervicothoracic fracture related to AS. Considering the risks associated with every additional screw placed, the skipped level instrumentation has advantages regarding patient safety.

Implant density is not related to patient-reported outcome in the surgical treatment of patients with idiopathic scoliosis

Aims

There is little information about the optimum number of implants to be used in the surgical treatment of idiopathic scoliosis. Retrospective analysis of prospectively collected data from the Swedish spine register was undertaken to discover whether more implants per operated vertebra (implant density) leads to a better outcome in the treatment of idiopathic scoliosis. The hypothesis was that implant density is not associated with patient-reported outcomes, the correction of the curve or the rate of reoperation.

Patients and Methods

A total of 328 patients with idiopathic scoliosis, aged between ten and 20 years at the time of surgery, were identified in the Swedish spine register (Swespine) and had patient reported outcomes including the Scoliosis Research Society 22r instrument (SRS-22r) score, EuroQol 5 dimensions quality of life, 3 level (EQ-5D-3L) score and a Viual Analogue Score (VAS) for back pain, at a mean follow-up of 3.1 years and reoperation data at a mean follow-up of 5.5 years. Implant data and the correction of the curve were assessed from radiographs, preoperatively and a mean of 1.9 years postoperatively. The patients were divided into tertiles based on implant density. Data were analyzed with analysis of variance, logistic regression or log-rank test. Some analyses were adjusted for gender, age at the time of surgery, the flexibility of the major curve and follow-up.

Results

The mean number of implants per operated vertebra in the low, medium and high-density groups were 1.36 (1.00 to 1.54), 1.65 (1.55 to 1.75) and 1.91 (1.77 to 2.00), respectively. There were no statistically significant differences in the correction of the curve, the SRS-22r total score, EQ-5D-3L index or number of reoperations between the groups (all p > 0.34). In the SRS-22r domains, self-image was marginally higher in the medium implant density group (p = 0.029) and satisfaction marginally higher in the high implant density group (p = 0.034).

Conclusion

These findings suggest that there is no clear advantage in using a high number of implants per operated vertebra in the surgical treatment of patients with idiopathic scoliosis. Cite this article: Bone Joint J 2018;100-B:1080–6.

Fulcrum flexibility of the main curve predicts postoperative shoulder imbalance in selective thoracic fusion of adolescent idiopathic scoliosis

PURPOSE

To identify preoperative predictors for postoperative shoulder imbalance (PSI) after corrective surgery of adolescent idiopathic scoliosis (AIS) and using the fulcrum-bending radiograph to assess flexibility.

METHODS

A consecutive surgical cohort of AIS patients undergoing selective thoracic fusion with alternate-level pedicle screw fixation was prospectively studied. Preoperative anteroposterior, lateral and fulcrum-bending radiographs were analysed. Postoperatively, a minimum of 2 years clinical and imaging follow-up was performed of all patients. PSI was defined as a radiographic shoulder height difference of more than 20 mm.

RESULTS

A total of 80 patients were included, and 14 patients (18%) were confirmed with PSI at final follow-up. The flexibility of MT curve was an independent risk factor for PSI (odds ratio (OR) = 3.3 per 10% decrease, 95% confidence interval (CI) 1.6-8.2). Twenty-seven patients had a preoperative MT flexibility of < 55% (OR = 11.5, 95% CI 2.8-46.2). Postoperative T1 tilt was significantly higher in the PSI group (p < 0.001), and a T1 tilt of more than 9° resulted in 7.2 times higher odds of developing PSI (95% CI 2.0-26.0). Fulcrum-bending correction index (FBCI) was significantly higher in the PSI group at final follow-up, and 25 patients had a final postoperative MT FBCI above 120% (OR = 8.5 (95% CI 2.3-31.0).

CONCLUSIONS

A low preoperative curve flexibility is a significant predictor for PSI. The surgical strategy should consider proximal fusion in presence of low-flexibility MT curves and consider less aggressive MT curve correction. Achieving a level T1 should be a main priority during intraoperative correction and may require fusion of the PT curve.

LEVEL OF EVIDENCE

III. These slides can be retrieved under Electronic Supplementary Material.

Implant Density at the Apex Is More Important Than Overall Implant Density for 3D Correction in Thoracic Adolescent Idiopathic Scoliosis Using Rod Derotation and En Bloc Vertebral Derotation Technique

STUDY DESIGN

Biomechanical analysis of 3D correction and bone-screw forces through numerical simulations of scoliosis instrumentation with different pedicle screw patterns.

OBJECTIVE

To analyze the effect of different screw densities and distributions on 3D correction and bone-screw forces in adolescent idiopathic scoliosis (AIS) instrumentation.

SUMMARY OF BACKGROUND DATA

Instrumentation constructs with various numbers of pedicle screws and patterns have been proposed for thoracic AIS instrumentation. However, systematic biomechanical studies have not yet been completed on the appropriate screw patterns for optimal 3D correction.

METHODS

Patient-specific biomechanical models of the spine were created for 10 AIS cases (Lenke 1). For each case, surgical instrumentation patterns were computationally simulated using respectively a reference screw pattern (two screws per level fused) and six alternative screw patterns with fewer screws. Simulated surgical maneuvers and model definition were unchanged between simulations except the number and distribution of screws. 3D correction and bone-screw forces were compared.

RESULTS

A total of 140 posterior instrumentations were computationally simulated. Mean corrections in the coronal and sagittal planes with alternative screw patterns were within 4° to the reference pattern. Increasing screw density in the apical region from one to two screws per level improved percent apical vertebral rotation (AVR) correction (r = 0.887, P < 0.05). Average bone-screw force associated with the reference screw pattern was 243N ± 54N and those with the alternative screw patterns were 11% to 48% lower.

CONCLUSION

Compared with the reference maximal screw density pattern, alternative screw patterns allowed similar corrections in the coronal and sagittal planes. AVR correction was strongly correlated with screw density in the apical region; AVR correction varied significantly with screw patterns of the same overall screw density when an en bloc vertebral derotation technique was simulated. High screw density tended to overconstrain the instrumented spine and resulted in higher forces at the bone-screw interface.

LEVEL OF EVIDENCE

N/A.

The Adult Deformity Surgery Complexity Index (ADSCI): a valid tool to quantify the complexity of posterior adult spinal deformity surgery and predict postoperative complications

BACKGROUND CONTEXT

In 2008, Mirza et al. designed and validated the first and only index capable of quantifying the complexity of spine surgery. However, this index is not fully applicable to adult spinal deformity (ASD) surgery as it does not include the surgical techniques most commonly used and most strongly associated with perioperative complications in patients with ASD.

PURPOSE

The objective of this study is to develop an "Adult Deformity Surgery Complexity Index" (ADSCI) to quantify objectively the complexity of the ASD posterior surgery.

STUDY DESIGN/SETTING

This is an expert consensus (Delphi process) and retrospective analysis of prospectively collected data using multiple regression models.

PATIENT SAMPLE

Patients were prospectively enrolled in two comparable multicenter ASD databases sharing the same inclusion criteria.

OUTCOME MEASURES

The ADSCI was internally and externally validated using R² for intraoperative bleeding and length of surgery. Receiver operating characteristics (ROC) and area under the curve (AUC) analysis was used to assess the sensitivity and specificity of ADSCI.

METHODS

The development and validation of ADSCI was based on the construction and comparison of three different tools: ADSCI score was constructed by three rounds of expert consensus (ADSCI-Delphi) and two multiple regression models (ADSCI-RM-Simple and ADSCI-RM-Mixed). Their predictive capability was compared by means of R² values in the same subrogated of surgical complexity as in the Mirza index validation: intraoperative bleeding and duration of surgery. Sensitivity and specificity were evaluated using ROC curves and AUC analysis. The external validity was also examined by evaluating its predictive capability in another multicenter ASD database of comparable patients in the United States.

RESULTS

At the time of the study, the database included 1,325 patients. Four hundred seventy-five patients were eligible for the study, having been treated surgically using a posterior approach only (52.2 years standard deviation 20; 77.7% women; 85.4% American Society of Anesthesiologists I/II). Fifty-one international experts participated in the Delphi consensus process. The surgical variables selected by consensus and included in the equation were divided into actions and factors. Actions selected were number of fused segments, decompressions, interbody fusions, and cemented levels; number and type of posterior osteotomies; and use of pelvic fixation. The factors included were implant density, revision surgery, and team experience. ADSCI-RM-Mixed (regression model with Delphi formula interactions) provided the best estimates and predictive value, well above Mirza's invasiveness index. The ADSCI-RM-Mixed, with greater AUCs (>0.70), was also the most sensitive and specific for both of the dependent variables studied and for complication prediction. ADSCI-RM-Mixed obtained also the highest R² value in the validation cohort in predicting blood loss (R²=0.34) and surgical time (R²=0.26) with effect sizes similar to those for the derivation cohort.

CONCLUSIONS

The ADSCI is the first tool to be specifically developed for the preoperative assessment of the complexity of ASD surgery. This study confirms its validity, specificity, and sensitivity, and shows that it has greater predictive capability than the more generic Mirza invasiveness index. The ADSCI should be useful for quantitatively estimating the increased risk associated with more invasive surgery and adjusting for surgical case-mix when making safety comparisons in ASDS.

Characterization and Predictive Value of Segmental Curve Flexibility in Adolescent Idiopathic Scoliosis Patients

STUDY DESIGN

A prospective radiographic analysis of adolescent idiopathic scoliosis (AIS) patients managed with alternate-level pedicle screw fixation was performed.

OBJECTIVE

The objective of this study was to characterize segmental curve flexibility and to determine its predictive value in curve correction in AIS patients.

SUMMARY OF BACKGROUND DATA

Little is known regarding the distinct segmental curve characteristics and their ability to predict curve correction in patients with AIS.

METHODS

The segmental Cobb angle was measured on posteroanterior standing radiographs and on fulcrum bending radiographs. Radiographs were analyzed preoperatively and at 2 years postoperatively and the curve was divided into upper, mid, and lower segments based on predefined criteria. The segmental flexibility and the segmental fulcrum bending correction index (FBCI) were calculated.

RESULTS

Eighty patients were included with mean age of 15 years. Preoperative mean segmental Cobb angles were 18, 31, and 17 degrees in the upper, mid, and lower segments, respectively. Segmental bending Cobb angles were 6, 13, and 4 degrees, respectively, corresponding to segmental flexibilities of 50%, 47%, and 83% in the upper, mid, and lower segments, respectively (P < 0.001). At 2-year follow up, the mean segmental FBCI were 155%, 131%, and 100% in the upper, mid, and lower segments, respectively (P < 0.001), which suggested that the lower segment of the curve was more flexible than the other segments and that higher correction was noted in the upper segments. A significant, positive correlation was noted between the segmental bending Cobb angle and the segmental FBCI (P < 0.05), whereby the strength of the correlation varied based on the curve segment.

CONCLUSION

This is the first study to demonstrate the segmental variations in curve flexibility using the fulcrum bending radiograph in AIS patients. Curve flexibility is not uniform throughout the curve and different segments exhibit greater flexibility/correctibility than others. Segmental flexibility should be considered in assessing AIS patients and in the clinical decision-making strategy to optimize curve correction outcomes.

LEVEL OF EVIDENCE

03.

Comparison of low density and high density pedicle screw instrumentation in Lenke 1 adolescent idiopathic scoliosis

BACKGROUND

The correlation between implant density and deformity correction has not yet led to a precise conclusion in adolescent idiopathic scoliosis (AIS). The aim of this study was to evaluate the effects of low density (LD) and high density (HD) pedicle screw instrumentation in terms of the clinical, radiological and Scoliosis Research Society (SRS)-22 outcomes in Lenke 1 AIS.

METHODS

We retrospectively reviewed 62 consecutive Lenke 1 AIS patients who underwent posterior spinal arthrodesis using all-pedicle screw instrumentation with a minimum follow-up of 24 months. The implant density was defined as the number of screws per spinal level fused. Patients were then divided into two groups according to the average implant density for the entire study. The LD group (n = 28) had fewer than 1.61 screws per level, while the HD group (n = 34) had more than 1.61 screws per level. The radiographs were analysed preoperatively, postoperatively and at final follow-up. The perioperative and SRS-22 outcomes were also assessed. Independent sample t tests were used between the two groups.

RESULTS

Comparisons between the two groups showed no significant differences in the correction of the main thoracic curve and thoracic kyphosis, blood transfusion, hospital stay, and SRS-22 scores. Compared with the HD group, there was a decreased operating time (278.4 vs. 331.0 min, p = 0.004) and decreased blood loss (823.6 vs. 1010.9 ml, p = 0.048), pedicle screws needed (15.1 vs. 19.6, p < 0.001), and implant costs ($10,191.0 vs. $13,577.3, p = 0.003) in the LD group.

CONCLUSIONS

Both low density and high density pedicle screw instrumentation achieved satisfactory deformity correction in Lenke 1 AIS patients. However, the operating time and blood loss were reduced, and the implant costs were decreased with the use of low screw density constructs.

Treatment patterns of children with spine and spinal cord tumors: national outcomes and review of the literature

BACKGROUND

Tumors of the spine in children are rare, and further clinical description is necessary.

OBJECTIVE

This study investigated epidemiology, interventions, and outcomes of pediatric patients with spine and spinal cord tumors.

METHODS

The National Inpatient Sample and Kids' Inpatient Database were used for the study. Outcomes were studied, and bivariate significant trends were analyzed in a multivariate setting.

RESULTS

Analysis of 2870 patients between 2000 and 2009 found a median age of diagnosis of 11 years (Tables 1 and 2). Most were white (65.2%) and had private insurance (62.3%), and 46.8% of procedures were emergent operations. Treatment occurred at teaching (93.6%) and non-children's hospitals (81.1%). Overall mortality rate was 1.7%, non-routine discharges occurred at a rate 19.9%, complications at 21.1%, and average total charges were $66,087. A majority of patients (87.5%) had no intervention, and of those patients receiving treatment, 78.2% underwent surgery and 23.1% had radiotherapy. Treatment with surgery alone increased significantly over time (p < 0.0001). Odds ratio (OR) of mortality was significantly higher in 2006 (OR 3.5) and 2009 (OR 2.6) when compared to 2000. Complications (OR 7.9) and disease comorbidities (OR 1.5) were associated with significantly increased odds of mortality.

CONCLUSIONS

Hospital characteristics, length of stay, and charges remained relatively unchanged. In recent years, there has been a decreasing incidence of spine and spinal cord tumors in children. Notably, a higher mortality rate is evident over time in addition to an increase in the proportion of patients undergoing surgery. The high percentage of emergent operations suggests a weak recognition of spine tumors in children and should prompt a call for increased awareness of this cancer. In spite of these findings, lack of tumor type identification was a limitation to this study.

Defining the number and type of fixation anchors for optimal main curve correction in posterior surgery for adolescent idiopathic scoliosis

BACKGROUND CONTEXT

The number and type of fixation anchors to use during posterior surgery for adolescent idiopathic scoliosis (AIS) is still debated, and the relationship with curve correction remains unclear.

PURPOSE

This study aimed to determine the number and type of fixation anchors associated with optimal curve correction following posterior surgery for AIS.

STUDY DESIGN

A retrospective study of the relationship between fixation anchors and main curve correction in AIS surgery was carried out.

PATIENT SAMPLE

A cohort of 137 AIS patients operated from a posterior-only approach using hooks and pedicle screws comprised the study sample.

OUTCOME MEASURES

Correction of the main scoliotic curve was the outcome measure.

METHODS

Implant density (ID) was defined as the number of fixation anchors divided by the number of available anchor sites within the main curve. Pedicle screw ratio (PSR) was defined as the number of pedicle screws divided by the total number of fixation anchors within the main curve. Multiple linear regressions were performed to analyze the influence of ID and PSR on main curve correction, while taking into account age, gender, curve type, preoperative main Cobb angle, main curve reducibility, number of fused levels, and number of levels within the main curve.

RESULTS

Main coronal curve correction was significantly related only to ID for all patients and for the subgroup of patients with a main thoracic curve. Constructs with an ID ≥70% and <90% provided a correction similar to that obtained with an ID ≥90%. However, main coronal curve correction was inferior for constructs with an ID <70%, when compared with constructs with ID ≥90%. Implant density and PSR were not related to the change in thoracic kyphosis in the multiple linear regressions.

CONCLUSIONS

Implant density is an important predictor of main coronal curve correction in posterior surgery for AIS. Increasing the number of fixation anchors within the main curve-rather than favoring screws over hooks-can lead to better correction in the coronal plane. However, after reaching an ID of ≥70% in the main curve, adding fixation anchors is not likely to result in significantly greater correction of the main curve in the coronal plane.

Resource Utilization in Adolescent Idiopathic Scoliosis Surgery: Is There Opportunity for Standardization?

INTRODUCTION

Recent healthcare reforms have raised the importance of cost and value in the management of disease. Value is a function of benefit and cost. Understanding variability in resources utilized by individual surgeons to achieve similar outcomes may provide an opportunity for cutting costs though greater standardization. The purpose of this study is to evaluate differences in use of implants and hospital resources among surgeons performing adolescent idiopathic scoliosis (AIS) surgery.

METHODS

A multicenter prospective AIS operative database was queried. Patients were matched for Lenke curve type and curve magnitude, resulting in 5 surgeons and 35 matched groups (N = 175). Mean patient age was 14.9 years and curve magnitude 50°. Parameters of interest were compared between surgeons via ANOVA and Bonferroni pairwise comparison.

RESULTS

There was no significant difference in percentage curve correction or levels fused between surgeons. Significant differences between surgeons were found for percentage posterior approach, operative time, length of stay (LOS), estimated blood loss (EBL), cell saver transfused, rod material, screw density, number of screws, use of antifibrinolytics, and cessation of intravenous analgesics. Despite differences in EBL and cell saver transfused, there were no differences in allogenic blood (blood bank) use.

CONCLUSION

Significant variability in resource utilization was noted between surgeons performing AIS operations, although radiographic results were uniform. Standardization of resource utilization and cost containment opportunities include implant usage, rod material, LOS, and transition to oral analgesics, as these factors are the largest contributors to cost in AIS surgery.

Does higher screw density improve radiographic and clinical outcomes in adolescent idiopathic scoliosis? A systematic review and pooled analysis

OBJECTIVE The radiographic and clinical outcomes of low-density (LD) versus high-density (HD) screw constructs in patients with adolescent idiopathic scoliosis (AIS) treated with all-pedicle screw constructs are still controversial. A systematic review and pooled analysis were performed to compare radiographic, perioperative, and quality-of-life (QOL) outcomes and complications in patients with moderate AIS treated with LD or HD screw constructs. METHODS The MEDLINE, Embase, and Web of Science databases were searched for English-language articles addressing LD versus HD screw constructs in AIS patients treated with all-pedicle screw constructs. The division of LD and HD groups was based on relative screw density and screw techniques. This systematic analysis strictly followed the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines, and all articles included in the analysis met the criteria specified in the guidelines. Two reviewers independently assessed the quality of the studies using the Newcastle-Ottawa Scale. Date on radiographic, perioperative, and QOL outcomes and complications were extracted from the included studies. RESULTS Twelve studies, involving a total of 827 patients (480 treated with LD constructs, 347 with HD), were analyzed-1 randomized controlled trial, 1 quasi-randomized controlled trial, and 10 retrospective studies. The patients' age at surgery, preoperative Cobb angle of the major curve, amount of thoracic kyphosis, and major curve flexibility were reasonably distributed, and no statistically significant differences were found. Regarding the outcomes at most recent follow-up, there were no significant differences in the Cobb angle of the major curve (mean difference 0.96°, 95% CI -0.06° to 1.98°, p = 0.06, I² = 1%), major curve correction (mean difference -0.72%, 95% CI -2.96% to 1.52%, p = 0.53, I² = 0%), thoracic kyphosis (mean difference -1.67°, 95% CI -4.59° to 1.25°, p = 0.26, I² = 79%), complications (odds ratio [OR] 0.66, 95% CI 0.31-1.42, p = 0.29, I² = 0%), and QOL outcomes. Reduced operative time (mean difference -48.56 minutes, 95% CI -82.69 to -14.43 minutes, p = 0.005, I² = 87%), blood loss (mean difference -77.85 ml, 95% CI -153.10 to -2.60 ml, p = 0.04, I² = 0%), and hospital charges (mean difference -$5.92K, 95% CI -$6.59K to -$5.26K, p < 0.00001, I² = 0%) were found in the LD group, compared with the HD group. CONCLUSIONS LD and HD screw constructs are both associated with satisfactory radiographic and QOL outcomes with few complications. This study supports the use of LD screw constructs for the treatment of moderate AIS, because they resulted in reduced operative time, blood loss, and hospital charges while maintaining radiographic and QOL outcomes and complication rates similar to those achieved with HD screw constructs.