Titanium vs cobalt chromium: what is the best rod material to enhance adolescent idiopathic scoliosis correction with sublaminar bands?

Lateral view fulcrum bending radiographs predict postoperative hypokyphosis after selective thoracic fusion in adolescent idiopathic scoliosis

STUDY DESIGN

A retrospective observational study.

PURPOSE

To identify the surgical and preoperative risk factors on fulcrum bending radiographs for postoperative hypokyphosis in patients with Lenke 1 adolescent idiopathic scoliosis (AIS).

OVERVIEW OF LITERATURE

AIS is associated with thoracic hypokyphosis. Persistent hypokyphosis causes reduced pulmonary function and spinopelvic malalignment. Indications for Ponte osteotomies and releases to improve postoperative kyphosis restoration in patients with hypokyphosis are still unclear. Previous studies have demonstrated that kyphosis correction was limited by sagittal flexibility based on lateral view fulcrum bending radiographs.

METHODS

Patients with Lenke 1 AIS undergoing posterior spinal fusion were included. Standing and fulcrum bending radiographs on the coronal and sagittal planes were analyzed at preoperative, immediate, and 2-year postoperative periods. The primary outcome was postoperative hypokyphosis (T5-12 thoracic kyphosis [TK] <20°). Risk factors for postoperative hypokyphosis were identified by multivariate logistic regression, and the optimal cutoff for significant risk factors was determined by receiver operating characteristic analysis.

RESULTS

In total, 156 patients were included in the analysis, of which 68 (43.6%) were hypokyphotic at 2-year follow-up. Low T5-12 TK on lateral view fulcrum bending films (immediate postoperative odds ratio [OR], 0.870; 95% confidence interval [CI], 0.826-0.917; 2-year postoperative OR, 0.916; 95% CI, 0.876-0.959; p<0.001) and high convex side implant density (2-year postoperative OR, 1.749; 95% CI, 1.056-2.897; p=0.03) were significant risk factors for postoperative hypokyphosis. Other baseline demographic and surgical factors did not affect postoperative kyphosis correction. The T5-12 TK cutoff on fulcrum bending for 2-year postoperative hypokyphosis was 12.45° (area under the curve, 0.773; 95% CI, 0.661-0.820).

CONCLUSIONS

Fulcrum bending radiography is useful in assessing coronal and sagittal flexibility for preoperative planning. In patients with T5-12 kyphosis <12.5° on lateral view fulcrum bending radiographs, Ponte osteotomies or releases, or a decrease in convex side implant density should be considered to improve kyphosis restoration and reduce the risk of 2-year postoperative hypokyphosis.

Current issues in the treatment of adolescent idiopathic scoliosis: a comprehensive narrative review

Adolescent idiopathic scoliosis (AIS) is a three-dimensional deformity of unknown etiology that commonly affects adolescents, imposing significant socioeconomic burdens. Effective management necessitates a comprehensive approach that takes into account multiple factors, including growth potential and psychological issues. Despite significant advancements in AIS management, several questions regarding optimal treatment strategies persist. Recent technological advancements are transforming the treatment landscape, encompassing advancements in bracing, robotic-assisted deformity corrections, and other interventions. This review explores current issues debated in the literature concerning the treatment of AIS, focusing on contemporary high-level evidence (e.g., meta-analyses and randomized controlled trials). Furthermore, this review explores cutting-edge developments and future directions in AIS management, including the integration of artificial intelligence and augmented reality.

Advances in implants and bone graft types for lumbar spinal fusion surgery

The increasing prevalence of spinal disorders worldwide necessitates advanced treatments, particularly interbody fusion for severe cases that are unresponsive to non-surgical interventions. This procedure, especially 360° lumbar interbody fusion, employs an interbody cage, pedicle screw-and-rod instrumentation, and autologous bone graft (ABG) to enhance spinal stability and promote fusion. Despite significant advancements, a persistent 10% incidence of non-union continues to result in compromised patient outcomes and escalated healthcare costs. Innovations in lumbar stabilisation seek to mimic the properties of natural bone, with evolving implant materials like titanium (Ti) and polyetheretherketone (PEEK) and their composites offering new prospects. Additionally, biomimetic cages featuring precisely engineered porosities and interconnectivity have gained traction, as they enhance osteogenic differentiation, support osteogenesis, and alleviate stress-shielding. However, the limitations of ABG, such as harvesting morbidities and limited fusion capacity, have spurred the exploration of sophisticated solutions involving advanced bone graft substitutes. Currently, demineralised bone matrix and ceramics are in clinical use, forming the basis for future investigations into novel bone graft substitutes. Bioglass, a promising newcomer, is under investigation despite its observed rapid absorption and the potential for foreign body reactions in preclinical studies. Its clinical applicability remains under scrutiny, with ongoing research addressing challenges related to burst release and appropriate dosing. Conversely, the well-documented favourable osteogenic potential of growth factors remains encouraging, with current efforts focused on modulating their release dynamics to minimise complications. In this evidence-based narrative review, we provide a comprehensive overview of the evolving landscape of non-degradable spinal implants and bone graft substitutes, emphasising their applications in lumbar spinal fusion surgery. We highlight the necessity for continued research to improve clinical outcomes and enhance patient well-being.

Three-dimensional deformity correction in adolescent idiopathic scoliosis patients: what are the benefits of hybrid apical sublaminar bands versus all-pedicle screws?

The amount of three-dimensional (3D) correction with apical sublaminar band (hybrid-SLB) technique has not been compared to all-pedicle screw instrumentation for adolescent idiopathic scoliosis (AIS) using detailed axial correction metrics or comparable rod types. Our purpose is to compare 3D improvement in AIS deformities following posterior spinal instrumentation and fusion (PSIF) with hybrid-SLB and segmental correction to all-pedicle screw correction. Patients ages 10-18 years with AIS who underwent PSIF between 2015 and 2022 and had preoperative and postoperative EOS imaging were included. Electronic medical records were reviewed for demographic, Lenke classification, operative technique, and 3D EOS data. Average changes in major and minor Cobb angle, axial rotation, thoracic kyphosis, and lumbar lordosis were compared. Ninety-five patients met inclusion criteria with 55 in the hybrid-SLB group (mean age 14.9 ± 1.9 years) and 40 in all-pedicle screw (mean age 14.7 ± 2.1 years). While all-pedicle screw demonstrated greater correction of major (45.7 ± 13.4 vs 37.9 ± 14.3 degrees; P = 0.008) and minor (28.7 ± 13.1 vs 17.8 ± 12.5 degrees; P = 0.001) Cobb angles, hybrid-SLB showed greater increase in T4-T12 kyphosis (13.3 ± 15.3 vs 5.6 ± 13.5 degrees; P = 0.01). Correction of T1-T12 kyphosis, axial rotation, and lumbar lordosis was similar between groups. 3D EOS analysis of AIS patients before and after PSIF revealed that all-pedicle screw constructs had greater overall coronal plane correction and hybrid-SLB had greater thoracic sagittal plane correction. Axial corrective abilities were similar. Hybrid-SLB may have advantages for correction of thoracic lordosis or hypokyphosis. Level of evidence: Level III, retrospective cohort study.

Sagittal Balance Parameters and Proximal Junctional Kyphosis in Adolescent Idiopathic Scoliosis

Background: To review and evaluate multiple preoperative and postoperative sagittal parameters and their association with the risk of developing proximal junctional kyphosis (PJK) in patients with adolescent idiopathic scoliosis (AIS) who undergo correction surgery. Methods: A systematic search was performed in December 2022 in PubMed, Embase and the Cochrane Library to retrieve all the studies relevant to our research. After the study selection and data extraction following PRISMA guidelines, RevMan 5.3 was used for statistical analysis. All the analyzed factors were evaluated by using odds ratios and weighted mean differences with 95% confidence intervals. Moreover, the meta-analysis of proportions via MedCalc was used for analyzing quantitative data from the studies. Results: A total of 22 studies were included in our meta-analysis. All the available values of sagittal parameters were evaluated. Among all the potential risk factors, higher preoperative thoracic kyphosis (Test for overall effect Z = 11.79, p < 0.00001), higher preoperative sagittal vertical axis (SVA) (test for overall effect Z = 11.19, p < 0.00001), greater thoracic kyphosis change post-op. compared to pre-op. (test for overall effect Z = 6.02, p < 0.00001), increased postoperative lumbar lordosis (test for overall effect Z = 3.65, p = 0.0003), higher post-op. SVA (test for overall effect Z = 24.93, p < 0.00001) and a larger pelvic incidence/lumbar lordosis (PI/LL) mismatch (test for overall effect Z = 20.50, p < 0.00001) were found to be the risk factors for PJK after AIS surgery. Moreover, a decreased rod contour angle (RCA) (test for overall effect Z = 3.79, p < 0.0002) and higher proximal junctional angle-rod contour angle (PJA-RCA) (test for overall effect Z = 39.18, p < 0.00001) play a significant role in the risk of developing PJK after AIS correction. Conclusions: Sagittal balance is of great importance when considering the surgical correction of AIS. Many factors in our meta-analysis were found to increase the incidence for PJK such as higher preoperative thoracic kyphosis and pre-op. SVA. Furthermore, increased thoracic kyphosis change, increased post-operative lumbar lordosis, SVA and PI/LL mismatch are also factors that influence the possibility of post-op. PJK. Lastly, RCA and PJA-RCA are two important factors that need attention during AIS, as over-contouring of the rod could lead to PJK in AIS patients.

Patient and surgical predictors of 3D correction in posterior spinal fusion: a systematic review

BACKGROUND

Restoration of three-dimensional (3D) alignment is critical in correcting patients with adolescent idiopathic scoliosis using posterior spinal fusion (PSF). However, current studies mostly rely on 2D radiographs, resulting in inaccurate assessment of surgical correction and underlying predictive factors. While 3D reconstruction of biplanar radiographs is a reliable and accurate tool for quantifying spinal deformity, no study has reviewed the current literature on its use in evaluating surgical prognosis.

PURPOSE

To summarize the current evidence on patient and surgical factors affecting sagittal alignment and curve correction after PSF based on 3D parameters derived from reconstruction of biplanar radiographs.

METHODS

A comprehensive search was conducted by three independent investigators on Medline, PubMed, Web of Science, and Cochrane Library to obtain all published information on predictors of postoperative alignment and correction after PSF. Search items included "adolescent idiopathic scoliosis," "stereoradiography," "three-dimensional," "surgical," and "correction." The inclusion and exclusion criteria were carefully defined to include clinical studies. Risk of bias was assessed with the Quality in Prognostic Studies tool, and level of evidence for each predictor was rated with the Grading of Recommendations, Assessment, Development, and Evaluations approach. 989 publications were identified, with 444 unique articles subjected to full-text screening. Ultimately, 41 articles were included.

RESULTS

Strong predictors of better curve correction included preoperative normokyphosis (TK > 15°), a corresponding rod contour, intraoperative vertebral rotation and translation, and upper and lower instrumented vertebrae selected based on sagittal and axial inflection points. For example, for Lenke 1 patients with junctional vertebrae above L1, fusion to NV-1 (1 level above the neutral vertebra) achieved optimal curve correction while preserving motion segments. Pre-op coronal Cobb angle and axial rotation, distal junctional kyphosis, pelvic incidence, sacral slope, and type of instrument were identified as predictors with moderate evidence. For Lenke 1C patients, > 50% LIV rotation was found to increase spontaneous lumbar curve correction. Pre-op thoracolumbar apical translation and lumbar lordosis, Ponte osteotomies, and rod material were found to be predictors with low evidence.

CONCLUSIONS

Rod contouring and UIV/LIV selection should be based on preoperative 3D TK in order to achieve normal postoperative alignment. Specifically, Lenke 1 patients with high-lying rotations should be fused distally at NV-1, while hypokyphotic patients with large lumbar curves and truncal shift should be fused at NV to improve lumbar alignment. Lenke 1C curves should be corrected using > 50% LIV rotation counterclockwise to the lumbar rotation. Further investigation should compare surgical correction between pedicle-screw and hybrid constructs using matched cohorts. DJK and overbending rods are potential predictors of postoperative alignment.

Do hypokyphotic adolescent idiopathic scoliosis patients treated with Ponte osteotomy obtain a better clinical efficacy? A preliminary retrospective study

Study design

A retrospective case–control study.

Objective

To evaluate whether Ponte osteotomy improves thoracic kyphosis and to determine its clinical efficacy in hypokyphotic adolescent idiopathic scoliosis (AIS).

Methods

Eighty consecutive Lenke type 1 AIS patients with hypokyphotic curves who underwent posterior spinal fusion by one spine surgeon at a single institution were recruited. According to whether Ponte osteotomy was performed, the patients were divided into two groups. The preoperative, immediate, one-year postoperative, and two-year postoperative radiographs were analyzed. The demographic characteristics, surgical information, radiographic parameters, Scoliosis Research Societye-22 (SRS-22) questionnaire, and complications were compared.

Results

The sagittal alignment and coronal alignment were both improved in the Ponte group and the control group postoperatively. There was no significant difference in the preoperative parameters between the two groups, except the TL/L, CB, and LL. Significant differences were found in the MT (15.18° ± 2.84° vs. 20.33° ± 3.75°, P < 0.001) and TK (24.23° ± 2.71° vs. 19.93° ± 2.38°, P < 0.001) at the two-year follow-up. The Ponte group had a longer operation time and more intraoperative blood loss. No significant difference was observed between the groups in the SRS-22 scores at the final follow-up.

Conclusions

Ponte osteotomy could obtain better coronal correction and sagittal contour restoration in AIS patients with hypokyphosis. However, Ponte osteotomies might lead to more intraoperative blood loss and longer operation time. Moreover, no discrepancy was found in the postoperative health-related quality of life of the included patients. Therefore, we considered that the Ponte osteotomy may be an alternative method to restore the desired thoracic kyphosis, which needs further study.

Systematic review and meta-analysis for the impact of rod materials and sizes in the surgical treatment of adolescent idiopathic scoliosis

PURPOSE

To assess surgical and safety outcomes associated with different rod materials and diameters in adolescent idiopathic scoliosis (AIS) surgery.

METHODS

A systematic literature review and meta-analysis evaluated the surgical management of AIS patients using pedicle screw fixation systems (i.e., posterior rods and pedicle screws) with rods of different materials and sizes. Postoperative surgical outcomes (e.g., kyphosis and coronal correction) and complications (i.e., hyper/hypo-lumbar lordosis, proximal junctional kyphosis, revisions, reoperations, and infections) were assessed. Random-effects models (REMs) pooled data for outcomes reported in ≥ 2 studies.

RESULTS

Among 75 studies evaluating AIS surgery using pedicle screw fixation systems, 46 described rod materials and/or diameters. Two studies directly comparing titanium (Ti) and cobalt-chromium (CoCr) rods found that CoCr rods provided significantly better postoperative kyphosis angle correction vs. Ti rods during a shorter follow-up (0-3 months, MD = - 2.98°, 95% CI - 5.79 to - 0.17°, p = 0.04), and longer follow-up (≥ 24 months, MD = - 3.99°, 95% CI - 6.98 to - 1.00, p = 0.009). Surgical infection varied from 2% (95% CI 1.0-3.0%) for 5.5 mm rods to 4% (95% CI 2.0-7.0%) for 6 mm rods. Reoperation rates were lower with 5.5 mm rods 1% (95% CI 0.0-3.0%) vs. 6 mm rods [6% (95% CI 2.0-9.0%); p = 0.04]. Differences in coronal angle, lumbar lordosis, proximal junctional kyphosis, revisions, and infections did not differ significantly (p > 0.05) among rods of different materials or diameters.

CONCLUSION

For AIS, CoCr rods provided better correction of thoracic kyphosis compared to Ti rods. Patients with 5.5 mm rods had fewer reoperations vs. 6.0 and 6.35 mm diameter rods.

LEVEL OF EVIDENCE

III.

Proximal junctional kyphosis in pediatric spinal deformity surgery: a systematic review and critical analysis

PURPOSE

Proximal junctional kyphosis (PJK) is a commonly encountered clinical and radiographic phenomenon after pediatric and adolescent spinal deformity surgery that may lead to post-operative deformity, pain, and dissatisfaction. Understanding the risk factors of PJK can be useful for pre-operative informed consent as well as to identify any potential preventative strategies.

METHODS

We performed a systematic review and critical analysis following the PRISMA statement in July 2019 by searching the PubMed, Scopus, and Embase databases, including all prior published studies. We included articles with data on PJK in patients with operative pediatric and adolescent scoliosis and those that detailed risk factors and/or preventative strategies for PJK. Levels of evidence were determined based on consensus. Findings were summarized and grades of recommendation were assigned by consensus. This study was registered in the PROSPERO database; 202,457.

RESULTS

Six hundred and thirty five studies were identified. Thirty-seven studies met criteria for inclusion into the analysis. No studies including neuromuscular scoliosis met inclusion criteria. No findings had Grade A evidence. There were 4 findings found to contribute to PJK with Grade B evidence in EOS: higher number of distractions, disruption of posterior elements, greater sagittal plane correction. There was no difference in incidence noted between etiology of the curvature. Five findings with Grade B evidence were found to contribute to PJK in AIS populations: higher pre-operative thoracic kyphosis, higher pre-operative lumbar lordosis, longer fusion constructs, greater sagittal plane correction, and posterior versus anterior fusion constructs.

CONCLUSION

Greater sagittal plane correction has Grade B evidence as a risk factor for PJK in both EOS and AIS populations. In EOS patients, an increased number of distractions and posterior element disruption are Grade B risk factors. In AIS patients, longer fusion constructs, higher pre-operative thoracic kyphosis and lumbar lordosis, and posterior (as opposed to anterior) constructs also contributed to PJK with Grade B evidence. These findings can guide informed consent and surgical management, and provide the foundation for future studies.

Association between intra-operative hemodynamic changes and corrective procedures during posterior spinal fusion in adolescent patients with scoliosis: A case-control study

Previous reports indicated that a decrease in intra-operative cardiac output and mean arterial pressure occurs due to thoracic cage deformities when patients with scoliosis are placed in the prone position. The aims of this study were to investigate the occurrence of hypotension during posterior spinal fusion in adolescent patients with scoliosis, and the association between hypotension, surgical procedures, changes of thoracic cage morphology.This retrospective, single-center, case-control study included 106 patients who underwent surgeries for spinal deformity at our institute between June 2014 and March 2020. The inclusion criteria were: age ≤19 years at the time of surgery, lowest instrumented vertebra over L5, posterior spinal fusion as the first surgery for scoliosis, and no severe cardiac or pulmonary disease pre-operatively. Finally, 49 patients met the criteria, and were divided to 3 groups as follows: thoracic constructive curve using a 6.0-mm cobalt-chromium alloy circular rod (T-C group; n = 28); thoracolumbar/lumbar constructive curve using a 6.0-mm cobalt-chromium alloy circular rod (L-C group; n = 8); and thoracic constructive curve using a 5.5-mm cobalt-chromium alloy beam-like rod (T-B group; n = 13). The beam-like rod is characteristic as the rod is mounted to screw heads without cantilever force. Intra-operative changes in circulation associated with corrective procedures, perioperative data, and sagittal depth and sternum deviation of thoracic cage were compared between the 3 groups.The T-C group had a higher rate of hypotension alarm than did the other groups (7 vs 0 vs 0; P = .047). Corrective procedures included rodding 4 times, rod rotation maneuver once, and direct vertebral rotation twice. Blood pressure was increased by pausing the correction procedures, increasing infusion, and administering vasopressors. The T-C and T-B groups had greater sternum deviation parameters than the L-C group, both before and after surgery. All parameters associated with sagittal depth and sternum deviation decreased significantly after surgery in the T-C and the T-B groups.In corrective surgery for constructive thoracic scoliosis, the corrective procedures requiring the application of compression force in the forward direction should be closely monitored in view of their possible influence on circulatory conditions.

Expert consensus on surgical treatment for adolescent idiopathic scoliosis in Japan

BACKGROUND

Surgical treatment for adolescent idiopathic scoliosis (AIS) has changed significantly with the advent of new medical devices and surgical procedures. Today, pre- and postoperative management differs widely between institutions. The purpose of this study is to establish consensus regarding the surgical management of AIS in Japan through the use of a questionnaire survey of experienced spine deformity surgeons.

METHODS

From February to March 2020, experienced spine deformity surgeons who perform more than 25 cases of AIS surgery annually were asked to respond to a questionnaire request regarding AIS surgical management formulated by the International Affairs Committee of the Japanese Scoliosis Society. For each of the questions, consensus was achieved upon a 70% agreement among respondents.

RESULTS

Responses were received from 25 of the 32 (78%) experienced spine deformity surgeons. The average age of the responding surgeons was 52 years with an average practice experience of 28 year. Consensus was achieved on 74 (76%) of the 97 aspects of care presented in the questionnaire and is broken down as follows: 12 of 17 items for preoperative management, all 5 items for perioperative management, 11 of 14 items for surgical technique, 9 of 15 items for implant selection, 6 of 8 items for bone grafting, 7 of 10 items for blood conservation, 5 of 7 items for postoperative management, all 17 items for postoperative evaluation, and 2 of 4 items for aftercare.

CONCLUSIONS

Expert consensus was achieved on 74 aspects of the surgical management of AIS in Japan. In implant selection and aftercare, consensus was obtained in less than 70% of the aspects, revealing differences in AIS management between institutions. These findings on AIS surgery in Japan, informed by expert opinion, will conceivably help spine deformity surgeons determine appropriate surgical management of AIS.

Cobalt-chromium versus titanium alloy rods for correction of adolescent idiopathic scoliosis based on 1-year follow-up: a multicenter randomized controlled clinical trial

OBJECTIVE

For instrumented correction surgery for adolescent idiopathic scoliosis (AIS), surgeons are increasingly switching from titanium (Ti) alloy rods to stiffer cobalt-chromium (CoCr) rods. The authors conducted the first multicenter randomized controlled clinical trial to investigate whether these materials affect the outcomes in terms of spine correction and quality of life (QOL). This trial was registered at UMIN Clinical Trials Registry on September 3, 2012, under the identifier UMIN000008838 (level of evidence 1).

METHODS

Female AIS patients (Lenke types 1-3, patient age 10-19 years) were recruited at 5 Japanese institutions and randomized into two cohorts: 6.0-mm-diameter Ti rods were placed in one group, and 6.0-mm-diameter CoCr rods were placed in the other. Patients were followed up at 2 weeks and 3, 6, and 12 months with radiographic examination to quantify the sagittal and coronal correction (Cobb angle, thoracic kyphosis, rib hump, and apical vertebral rotation). Patients completed questionnaires (Scoliosis Research Society-22r, 12-Item Short-Form Health Survey, and Scoliosis Japanese Questionnaire-27) at 6 and 12 months to assess QOL.

RESULTS

A total of 69 AIS patients were randomized to the demographically similar Ti (n = 37) or CoCr (n = 32) cohort. Four adverse events were recorded, two in each cohort, but these were not related to the rod material. At the final follow-up, both Ti and CoCr cohorts showed significant improvement in spinal correction, including the Cobb angle, thoracic kyphosis, and rib hump size. The correction rates were 68.4% and 67.1% for the Ti and CoCr cohorts, respectively. No parameters differed significantly between the cohorts at any time. Survey data showed improved but similar outcomes in both cohorts.

CONCLUSIONS

Both treatments (Ti and CoCr) produced similar results and were efficient in engendering clinically significant spine corrections. Clinical trial registration no.: UMIN000008838 (UMIN Clinical Trials Registry).

Simultaneous translation on two rods improves the correction and apex translocation in adolescent patients with hypokyphotic scoliosis

OBJECTIVE

The objectives of this study were to apply the simultaneous translation on two rods (ST2R) maneuver involving rods contoured with a convexity at the desired thoracic kyphosis (TK) apex level and to assess the effects on the ability to support triplanar deformity corrections, including TK apex improvement, in patients with hypokyphotic adolescent idiopathic scoliosis (AIS).

METHODS

Using retrospective analysis, the authors examined the digital records that included 2- to 4-week, 1-year, and 2-year postoperative radiographic follow-up data of female hypokyphotic (TK < 20°) AIS patients (Lenke type 1-3) treated with ST2R. The authors assessed the corrections of triplanar deformities by examining the main Cobb angle, TK, rib hump, apical vertebral rotation, Scoliosis Research Society 22-item questionnaire scores, and TK apex translocation. In order to better grasp the potential of ST2R, the outcomes were compared with those of a historical matched case-control cohort treated with a standard rod rotation (RR) maneuver.

RESULTS

Data were analyzed for 25 AIS patients treated with ST2R and 27 patients treated with RR. The ST2R group had significant improvements in the main Cobb angle and TK, reduction in the rib hump size at each time point, and a final correction rate of 72%. ST2R treatment significantly increased the kyphosis apex by an average of 2.2 levels. The correction rate was higher at each time point in the ST2R group than in the RR group. ST2R engendered favorable TK corrections, although the differences were nonsignificant, at 2 years compared with the RR group (p = 0.056). The TK apex location was significantly improved in the ST2R cohort (p < 0.001). At the 1-month follow-up, hypokyphosis was resolved in 92% of the ST2R cohort compared with 30% of the RR cohort.

CONCLUSIONS

Resolving hypokyphotic AIS remains challenging. The ST2R technique supported significant triplanar corrections, including TK apex translocation and restoration of hypokyphosis in most patients. Comparisons with the RR cohort require caution because of differences in the implant profile. However, ST2R significantly improved the coronal and sagittal corrections. It also allowed for distribution of correctional forces over two rod implants instead of one, which should decrease the risk of screw pullout and rod flattening. It is hoped that the description here of commercially available reducers used with the authors' surgical technique will encourage other clinicians to consider using the ST2R technique.

Three-dimensional analysis of spinal deformity correction in adolescent idiopathic scoliosis: comparison of two distinct techniques

PURPOSE

To compare 3D postoperative deformity correction using two distinct commonly utilized techniques for the treatment of adolescent idiopathic scoliosis (AIS).

METHODS

AIS patients with major thoracic (Lenke 1-2) curves at two sites who underwent deformity correction via posterior spinal instrumented fusion using one of two distinct techniques were retrospectively reviewed. Patients were matched 1:1 between sites for Lenke type (95% Lenke 1) and follow-up time. The "band site" performed posteromedial translation using thoracic sublaminar bands and 5.5-mm rods. The "screw site" performed spine derotation using differential rod contouring with pedicle screws and 5.5-mm rods. 3D measures of deformity from spinal reconstructions were compared between sites.

RESULTS

Preoperatively, the groups had similar thoracic curve magnitudes (band, 55 ± 12° vs. screw, 52 ± 10°; p > 0.05); the "screw site" had less T5-T12 kyphosis (2 ± 14° vs. 7 ± 12°, p = 0.05) and greater thoracic apical rotation (- 19 ± 7° vs. - 14 ± 8°, p = 0.007). Postoperatively, the "screw site" had greater percent correction (61% vs. 76%, p < 0.001) and kyphosis restoration (p = 0.002). The groups achieved a similar amount of apical derotation (p = 0.9). The "band site" used cobalt chromium rods exclusively; the "screw site" used cobalt chromium (3%) and stainless steel (97%; p < 0.001). The "band site" performed significantly longer fusions.

CONCLUSIONS

Significant variations were found between two commonly utilized techniques in AIS surgery, including rod material, correction mechanisms, and fusion levels. Significantly, a greater 3D deformity correction of the coronal and sagittal planes was observed at the "screw site" compared to the "band site", but with no difference in axial plane correction.

The Effect of Rod Pattern, Outrigger, and Multiple Screw-Rod Constructs for Surgical Stabilization of the 3-Column Destabilized Cervical Spine - A Biomechanical Analysis and Introduction of a Novel Technique

Objective

Anterior-only reconstructions for cervical multilevel corpectomies are prone to fail under continuous mechanical loading. This study sought to define the mechanical characteristics of different constructs in reducing a range of motion (ROM) of the 3-column destabilized cervical spine, including posterior cobalt-chromium (CoCr)-rods, outrigger-rods (OGR), and a novel triple rod construct using lamina screws (6S3R). The clinical implications of biomechanical findings are discussed in depth from the perspective of the challenges surgeons face cervical deformity correction.

Methods

Three-column deficient cervical spinal models were produced based on reconstructed computed tomography scans. The corpectomy defect between C3 and C7 end-level vertebrae was restored with anterior titanium (Ti) mesh-cage. The ROM was evaluated in a customized 6-degree of freedom spine tester. Tests were performed with different rod materials (Ti vs. CoCr), varying diameter rods (3.5 mm vs. 4.0 mm), with and without anterior plating, and using different construct patterns: bilateral rod fixation (standard-group), OGR-group, and 6S3R-Group. Construct stability was expressed in changes and differences of ROM (°).

Results

The largest reduction of ROM was noticed in the 6S3R-group compared to the standard- and the OGR-group. All differences observed were emphasized with an increasing number of corpectomy levels and if anterior plating was not added. For all simulated 1-, 2-, and 3-level corpectomy constructs, the OGR-group revealed decreased ROM for all motion directions compared to the standard-group. An increase of construct stiffness was also recorded for increased rod diameter (4.0 mm) and stiffer rod material (CoCr), though these effects lacked behind the more advanced construct pattern.

Conclusion

A novel reconstructive technique, the 6S3R-construct, was shown to outperform all other constructs and might resemble a new standard of reference for advanced posterior fixation.

Comparison of Effectiveness between Cobalt Chromium Rods versus Titanium Rods for Treatment of Patients with Spinal Deformity: A Systematic Review and Meta-Analysis

Background

Biomechanical properties of rods determine their ability to correct spinal deformity and prevention of postoperative sagittal and coronal changes. The selection of a proper rod material is crucial due to their specific mechanical properties that influence the surgical outcome. The purpose of this study is to compare the effectiveness of cobalt chromium rods versus titanium rods for the treatment of spinal deformity by a systematic review and meta-analysis.

Methods

PubMed, EMBASE, and the Cochrane library were searched for observational and biomechanical studies comparing cobalt chromium and titanium rods in terms of correction rate, thoracic kyphosis, lumbar lordosis, incidence of rod fracture, fatigue life of contoured rod, bending stiffness of rods, and occurrence of proximal junctional kyphosis. The demographic data and mean values of outcomes of interest were extracted from each group and compared by their mean difference as an overall outcome measure. The Review Manager software (RevMan 5.3) was utilized at a 95% significance level.

Results

Eleven eligible studies with 641 participants for 7 observational studies and 35 samples for 4 biomechanical studies were identified. There were no significant differences between cobalt chromium and titanium rods in the correction rate of spinal deformity. Postoperative thoracic kyphosis was well restored in the cobalt chromium group with statistical significance (p value = 0.009). The incidence of rod fracture was high in titanium rods compared to cobalt chromium rods with significant difference (p value = 0.0001). Proximal junctional kyphosis occurs more in the cobalt chromium group with a significant difference (p value = 0.0009). No statistical significance between two materials in terms of lumbar lordosis, fatigue of life, and bending stiffness of rods.

Conclusion

The cobalt chromium rod is better than titanium rod for effective correction of spinal deformity and postoperative stability of the spine. However, the use of cobalt chromium rods is associated with increased risk of proximal junctional kyphosis.

USE OF SUBLAMINAR BANDS FOR ADOLESCENT IDIOPATHIC SCOLIOSIS - A SYSTEMATIC REVIEW

ABSTRACT Objective In 2003, Mazda et al. introduced a new device for surgical correction of Adolescent Idiopathic Scoliosis (AIS) called sublaminar bands (SB). The reduction principle that SBs use is posteromedial spinal translation, similar to Luque’s wiring, but using polyester bands. Methods We performed a systematic review of the literature on this subject, evaluating the technique in terms of coronal correction, sagittal correction, bleeding, mean surgical time, loss of correction, infection, pseudoarthrosis, and neurological and other complications. The total search resulted in 14 articles published over the last 10 years. We found that the use of SBs in hybrid AIS correction instrumentations provides an average correction of 69% in the frontal plane, a 5° increase in thoracic kyphosis (average increase of 55%), overall complications of 4.5%, and no neurological complications were reported in any of the studies analyzed.. The mean blood loss was 682.5 mL and the mean surgical time was 228.6 minutes. Conclusions We conclude that the literature suggests that this instrumentation is safe, allows good correction in the frontal plane and great correction in the sagittal plane. As for complications, mean surgical time, and blood loss, their averages are lower than those of other constructions used for AIS. Level of evidence IIA; Systematic review.

A novel scoliosis instrumentation using special superelastic nickel-titanium shape memory rods: a biomechanical analysis using a calibrated computer model and data from a clinical trial

STUDY DESIGN

Biomechanical analysis of scoliosis instrumentation using superelastic Nickel-titanium shape memory (SNT) rods.

OBJECTIVE

To compare SNT with conventional Titanium (Ti) and Cobalt-chrome (Co-Cr) rods. A clinical trial has documented comparable efficacy between two adolescent idiopathic scoliosis (AIS) cohorts instrumented using SNT versus conventional Ti rods. The shape memory and superelasticity of the SNT rod are thought to allow easy rod insertion, progressive curve correction, and correction from spinal tissue relaxation, but study is yet to be done to assess the effects of the shape memory and superelasticity.

METHODS

Instrumentations of AIS patients from the clinical trial were computationally simulated using SNT, Ti and Co-Cr rods (5.5 or 6 mm; 30°, 50° or 60° sagittal contouring angles; 0°, 25° or 50° coronal over-contouring angles). Curve correction, its improvement from stress relaxation in the spine, and loads in the instrumentation constructs were computed and compared.

RESULTS

The simulated main thoracic Cobb angles (MT) and thoracic kyphosis with the SNT rods were 4°-7° higher and 1°-2° lower than the Ti and Co-Cr rods, respectively. Bone-implant forces with Ti and Co-Cr rods were higher than the SNT rods by 84% and 130% at 18 °C and 35% and 65% at 37 °C, respectively (p < 0.001). Further corrections of the MT from the simulated stress relaxation in the spine were 4°-8° with the SNT rods versus 2°-5° with the Ti and Co-Cr rods (p < 0.001).

CONCLUSION

This study concurs with clinical observation that the SNT rods are easier to insert and can result in similar correction to the conventional rods. The SNT rods allow significantly lower bone-implant forces and have the ability to take advantage of post-instrumentation correction as the tissues relax.

Is Cutibacterium acnes early surgical site infection rate related to the duration of antibiotic prophylaxis in adolescent idiopathic scoliosis surgery?

PURPOSE

Cutibacterium acnes (C. acnes) is a gram-positive anaerobic bacillus located in pilosebaceous glands, usually responsible for late postoperative surgical site infections (SSI). A recent study performed in our institution highlighted an unexpected emergence of C. acnes early SSI. One potential explanation was the change of the perioperative antibioprophylaxis (ATB) protocol, which switched from 48 h postoperative cefamandole to intraoperative only cefazoline. The aim of this study was therefore to investigate the influence of the ATB duration on the occurrence of C. acnes early SSI, by comparing the incidence rates during 3 consecutive ATB protocols.

METHODS

Between January 2007 and September 2017, all patients who underwent posterior fusion for AIS were retrospectively reviewed. Early C. acnes SSI were reported and compared between 3 periods, during which the ATB protocols were modified. January 2007-February 2012: Intraoperative Cefamandole continued 48 h (protocol 1) March 2012-August 2016: Single shot of intraoperative Cefazoline (protocol 2) September 2016-September 2017: Intraoperative Cefazoline continued 48 h (protocol 3).

RESULTS

Fifty-three early SSI (7.2%) were reported among the 732 posterior AIS fusions included. Global incidence of C. acnes infection was 2.9%. The incidence of C. acnes in early SSI increased from 0 to 4.9% between protocol 1 and 2, but was reduced to 1.7% with protocol 3.

CONCLUSIONS

Early C acnes SSI can be explained by the difficulty to eradicate this pathogen with current skin preparation procedures and some Beta-lactam antibiotics tolerance. Longer duration antibioprophylaxis is preferable to prevent from early C. acnes SSI.

Mechanical Analysis of Notch-Free Pre-Bent Rods for Spinal Deformity Surgery

STUDY DESIGN

Experimental study of spinal rod as per the American Society for Testing Materials (ASTM) F2193 methodology for static and dynamic four-point bending.

OBJECTIVE

The hypotheses underlying this study were that the notch-free, curved rod would have a significantly higher ultimate load and fatigue strength compared with conventional notched curved rods. This study aimed to analyze the mechanical properties of notch-free curved rods compared with conventional notched rods.

SUMMARY OF BACKGROUND DATA

The goal of instrumented spinal fusion in the management of spinal deformities is to realign the spine and maintain the correction and stability in order to obtain arthrodesis. Although rod curvature could play an important role, intraoperative contouring of the straight rod induces notches into the rod, leading to decreased fatigue strength.

METHODS

Commercially produced titanium alloy (ϕ6.0 mm) and cobalt chromium alloy (ϕ5.5 mm) spinal rods were assessed by four-point bending tests in accordance with the ASTM F2193.

RESULTS

Static four-point bending tests for the curved spinal rods showed that cobalt chromium alloy rods had significantly higher stiffness compared with titanium alloy rods. Notch-free cobalt chromium alloy rods had a significantly higher ultimate load than the conventional notched cobalt chromium alloy and titanium alloy rods. The dynamic four-point bending test showed that force/displacement at a minimum force at 2,500,000 cycles was larger in the notch-free cobalt chromium alloy rod than in the notched cobalt chromium alloy rod.

CONCLUSION

The notch-free curved cobalt chromium alloy rod is likely to maintain its curvature after spinal deformity surgery with a decreased risk of breakage and could overcome the problems of the conventional notched rod such as breakage and spring-back.

LEVEL OF EVIDENCE

N/A.

Sagittal Balance in Adult Idiopathic Scoliosis

STUDY DESIGN

A narrative review article study.

OBJECTIVE

The objective of this study was to highlight guiding principles and challenges faced with addressing sagittal alignment in patients with adult idiopathic scoliosis (AIS) and to discuss effective surgical strategies based upon our clinical experience.

SUMMARY OF BACKGROUND DATA

Previous research and guidelines for the treatment of AIS have focused on the correction of spinal deformity in the coronal and axial planes. Failure to address sagittal deformity has been associated with numerous adverse clinical outcomes.

METHODS

This is a review of the current body of literature and a description of the rod derotation surgical technique for correction in the sagittal plane.

RESULTS

Several studies have offered general goals for postoperative radiographic measures in the sagittal plane for patients with AIS. However, these guidelines are evolving as diagnostic and therapeutic modalities continue to improve. The rod derotation surgical technique through differential metal rods is one method to potentially address sagittal balance in AIS.

CONCLUSIONS

Alignment in the sagittal plane is a unique challenge facing surgeons for patients with AIS. Further research with an assessment of functional outcomes and longer follow-up is needed to more precisely guide treatment principles.

LEVEL OF EVIDENCE

Level IV.

Patient-specific rods for thoracic kyphosis correction in adolescent idiopathic scoliosis surgery: Preliminary results

INTRODUCTION

Restoring a degree of kyphosis consistent with good sagittal alignment of the spine is a key concern when performing surgery to correct adolescent idiopathic scoliosis (AIS). The objective of this study was to assess the preliminary outcomes of posterior fusion for AIS using patient-specific rods that were pre-contoured based on pelvic incidence. The primary evaluation criterion was thoracic kyphosis at last follow-up.

HYPOTHESIS

The use of pre-bent patient-specific rods has a favourable effect on thoracic kyphosis at last follow-up.

MATERIAL AND METHODS

A total of 37 patients with AIS, including 17 with hypokyphosis, managed with patient-specific rods were included in a prospective study. The rod contouring angles were based on predefined pelvic incidence criteria (25° to 40° for the rod on the convex side and the same value plus 10° for the rod on the concave side). Thoracic kyphosis was assessed before surgery and at last follow-up, after 12-36 months (mean, 19 months). Student's t test was applied to compare means. Multivariate linear regression analysis was performed.

RESULTS

At last follow-up, the mean increase in kyphosis was 14° and was comparable to the planned increase (mean difference=0, p=0.85). Factors associated with kyphosis at last follow-up were the concave rod contouring angle and the pre-operative kyphotic angle of the thoracic segment to be instrumented (p<0.05). Mean differences between kyphosis of the instrumented thoracic segment at last follow-up and target kyphosis were -5° in the subgroup with hypokyphosis (<20°) before surgery and +4° in the subgroup with normal kyphosis before surgery.

CONCLUSION

With patient-specific rods, kyphosis at last follow-up was close to the target value. Predictors of kyphosis at last follow-up were the concave rod contouring angle and pre-operative kyphotic angle of the thoracic segment to be instrumented. Over-contouring of the concave rod seems necessary in patients with preoperative hypokyphosis but not in patients with normal kyphosis.

LEVEL OF EVIDENCE

III, prospective non-comparative study.

Sublaminar polyester bands for the correction of idiopathic and neuromuscular scoliosis

Recent literature suggests that sublaminar bands (SB) can provide good coronal plane correction, comparable to pedicle screw constructs, as well as good correction in the sagittal plane, even in patients with preoperative hypokyphosis; comparable results have been reported in patients with adolescent idiopathic scoliosis (AIS) and in patients with neuromuscular scoliosis (NMS). Two types of SB constructs can be performed: the band-only construct, indicated for non-ambulatory patients with NMS, and the hybrid construct indicted for ambulatory patients with NMS and for patients with AIS. SB are made of polyester or acrylic material and do provide a safe alternative to sublaminar Luque-type wires (stainless steel) as well as an increased contact area between SB and bone allowing higher corrective forces and reduced laminar fracture risk; the use of SB is not associated with increased risk of neurological injury nor with an increased risk of deep postoperative infection. SB used in a hybrid or in a band-only construct in patients with AIS and NMS, appear to be safe in a trained surgeon hands and can achieve well-balanced spine in both coronal and sagittal planes. This article aimed to provide a review of how SB can restore normal frontal and sagittal spine alignment in patients with AIS and NMS.

Biomaterials in Spinal Implants: A Review

The aim to find the perfect biomaterial for spinal implant has been the focus of spinal research since the 1800s. Spinal surgery and the devices used therein have undergone a constant evolution in order to meet the needs of surgeons who have continued to further understand the biomechanical principles of spinal stability and have improved as new technologies and materials are available for production use. The perfect biomaterial would be one that is biologically inert/compatible, has a Young’s modulus similar to that of the bone where it is implanted, high tensile strength, stiffness, fatigue strength, and low artifacts on imaging. Today, the materials that have been most commonly used include stainless steel, titanium, cobalt chrome, nitinol (a nickel titanium alloy), tantalum, and polyetheretherketone in rods, screws, cages, and plates. Current advancements such as 3-dimensional printing, the ProDisc-L and ProDisc-C, the ApiFix, and the Mobi-C which all aim to improve range of motion, reduce pain, and improve patient satisfaction. Spine surgeons should remain vigilant regarding the current literature and technological advancements in spinal materials and procedures. The progression of spinal implant materials for cages, rods, screws, and plates with advantages and disadvantages for each material will be discussed.

Sublaminar polyester bands as a salvage fixation method in the cervical spine: novel application in two patients

Pedicle and lateral mass screws are the most common means of rigid fixation in posterior cervical spine fusions. Various other techniques such as translaminar screw placement, paravertebral foramen screw fixation, sublaminar and spinous process wiring, cement augmentation, and others have been developed for primary fixation or as salvage methods. Use of these techniques can be limited by a prior history of osteotomies, poor bone density, destruction of the bone-screw interface, and unfavorable vascular and osseous anatomy.Here, the authors report on the novel application of cervical sublaminar polyester bands as an adjunct salvage method or additional fixation point used with traditional methods in the revision of prior constructs. While sublaminar polyester bands have been used for decades in pediatric scoliosis surgery in the thoracolumbar spine, they have yet to be utilized as a method of fixation in the cervical spine. In both cases described here, sublaminar banding proved crucial for fixation points where traditional fixation techniques would have been less than ideal. Further study is required to determine the full application of sublaminar polyester bands in the cervical spine as well as its outcomes.

How to Optimize Axial Correction Without Altering Thoracic Sagittal Alignment in Hybrid Constructs With Sublaminar Bands: Description of the "Frame" Technique

STUDY DESIGN

Retrospective monocentric database study.

OBJECTIVES

To describe the "frame" reduction technique and report the 3D quantitative analysis of postoperative corrections in a consecutive series of thoracic adolescent idiopathic scoliosis (AIS) patients.

SUMMARY OF BACKGROUND DATA

Posteromedial translation technique using sublaminar bands have been proved to be efficient and safe for 3D correction of the deformity and overall cosmetic aspect of the trunk. However, the ability to correct the axial plane may tend to rotate the vertebra clockwise instead of counterclockwise, thus increasing apical vertebra axial rotation (AVR) and the rib hump. A technical improvement was developed to emphasize axial correction.

METHODS

60 thoracic AIS patients consecutively operated by posteromedial translation using the "frame" reduction technique were included with a minimum 2-year follow-up. Precontoured rods were connected with fixed transverse connectors according to a personalized preoperative planning. Rods were first inserted distally in the pedicle screws to achieve lumbar correction, and then in the upper anchors, and finally sublaminar bands were connected to their corresponding rods to progressively bring the concave lamina to the concave rod to correct the thoracic deformity. Sagittal and coronal 3D measures were performed preoperatively and at the latest follow-up using SterEOS (EOS Imaging, Paris, France) to assess the efficiency of the technique.

RESULTS

The distance from the center of the apical vertebra to the reference axis in the frontal plane was reduced from 4.7 to 1.1 cm, traducing the efficient medial translation of the spine during correction. T1-T12 kyphosis significantly increased after surgery (28°-35°). 3D location of the upper instrumented vertebra (UIV) was not affected. The apical rotation was significantly reduced after surgery (19°-11°), and the AVR correction rate averaged 42.2%.

CONCLUSION

The "frame" technique is an innovative way of using polyester bands, optimizing axial correction while respecting sagittal alignment.

LEVEL OF EVIDENCE

Level IV.

Cobalt chromium-Titanium rods versus Titanium-Titanium rods for treatment of adolescent idiopathic scoliosis; which type of rod has better postoperative outcomes?

SUMMARY OBJECTIVE; Compare the outcome of spinal deformity correction between Ti-Ti and CrCo-Ti rods for the treatment of spinal Adolescent Idiopathic Scoliosis (AIS) using rods mentioned with all pedicle screws and translation technique. METHOD; 59 patients operated for spinal deformity (Lenke 1 or 2) AIS. The patients were divided into two groups by random allocation using Ti-Ti rods (n = 29) and CrCo-Ti rods (n = 30) and the alone difference among them in the surgical procedure was rod material (Ti-Ti or CrCo-Ti rods) and finally, radiological outcomes were compared preoperatively, postoperatively and at last follow-up for 12 months. RESULTS; Patients’ main curve correction after surgical procedure regardless type of rod was 48.95±11.04 (13-75) degree. Success rate of spinal deformity correction following surgical procedure regardless of type of administered rod was 86.76 ± 11.30 percent (62.5-100%). Mean of deformity correction rate was 91.49±10.67% using CrCo-Ti rods versus 81.86±9.88% using Ti-Ti rods (P-value=0.01). Angle change was 3.29±6.60 for kyphosis angle and 0.59±7.76 for lordosis angle. Rate of main curve correction was not significantly different considering patients’ gender (P-value0.657). Main curve correction success rate was in association with patients’ age and type of rod (P-value=0.054, r=-1.863 and P-value=0.001, r=8.865 respectively). CONCLUSION; CrCo-Ti rods have the ability to produce higher correction rates in AIS compared to Ti-Ti rod of the same diameter. CrCo-Ti rods provide significant and stable spinal correction, especially in correction of main curve. This rate was associated with patients’ age and type of rod administered but not gender.

Cobalt-chrome and titanium alloy rods provide similar coronal and sagittal correction in adolescent idiopathic scoliosis

BACKGROUND

Cobalt-chrome (CoCr) and the titanium alloy TA6V (Ti) are the materials most widely used for spinal instrumentations in patients with adolescent idiopathic scoliosis (AIS). The objective of this work was to compare the effectiveness of CoCr and Ti rods in terms of coronal and sagittal correction by pedicle screw constructs in patients with AIS.

HYPOTHESIS

Correction is similar with CoCr and Ti rods in patients with AIS.

MATERIAL AND METHOD

A retrospective single surgeon study was conducted in patients with AIS managed using pedicle screw posterior spinal fusion with high implant density and reduction by postero-medial translation. Follow-up was more than 2 years in all patients. Patients were divided into two groups based on whether the rods used were made of CoCr (n=30) or Ti (n=33). The groups were identical for age, Risser classification, follow-up duration, type of curve, and implant density. Coronal and sagittal parameters on standing full-spine radiographs were analysed using graphics software before surgery then 1 month after surgery and at last follow-up. Quantitative data were compared by applying Student's t test.

RESULTS

The percentage of main curve correction at last follow-up was the same in the two groups (76%/75%) (p=0.7). Gains in thoracic kyphosis (12°/13°) and lumbar lordosis (8°/10°) were not significantly different between groups. At last follow-up, 3 patients had proximal junctional kyphosis, 1 in the CoCr group and 2 in the Ti group (p=0.6).

CONCLUSION

For posterior spinal fusion to treat AIS, with a high density of pedicle screws, correction by translation, and 6 mm rods, CoCr rods and Ti rods produce the same amount of coronal and sagittal correction.

LEVEL OF EVIDENCE

IV, comparative retrospective study with no control group.

Choice of Rods in Surgical Treatment of Adolescent Idiopathic Scoliosis: What Are the Clinical Implications of Biomechanical Properties? - A Review of the Literature

The surgical treatment of adolescent idiopathic scoliosis (AIS) involves 3-dimensional curve correction with multisegmental pedicle screws attached to contoured bilateral rods. The substantial corrective forces exert a high level of stress on the rods, and the ability of the rod to withstand these forces without undergoing permanent deformation relies on its biomechanical properties. These properties, in turn, are dependent on the material, diameter, and shape of the rod. The surgical treatment of AIS is characterized by the requirement for a special biomechanical profile that may differ substantially from what is needed for adult deformity surgery. This overview summarizes the current knowledge of rod biomechanics in frequently used rod constructs, with a particular focus on translational research between biomechanical studies and clinical applicability in AIS patients.

Improved restoration of thoracic kyphosis using a rod construct with differentiated rigidity in the surgical treatment of adolescent idiopathic scoliosis

OBJECTIVE The objective of this study was to compare postoperative sagittal alignment among 3 rod constructs with different rigidity profiles. METHODS This was a dual-center retrospective cohort study involving 2 consecutive cohorts in which patients were surgically treated for adolescent idiopathic scoliosis. Lenke Type 5 curves were excluded. Patients were operated on with all-pedicle screw instrumentation using 3 different rod constructs. The first group was operated on using a hybrid construct (HC) consisting of a normal circular rod on the convex side and a beam-like rod (BR) on the concave side. The second group was operated on with a standard construct (SC) using bilateral BRs in the full length of the fusion. The third group was operated on with a modified construct (MC). The modified rods have a beam-like shape in the caudal portion, but in the cranial 2 or 3 fusion levels the rod transitions to a circular shape with a smaller anteroposterior diameter. Radiographs were analyzed preoperatively and at the first postoperative follow-up (range 1-8 weeks). The primary outcome was pre- to postoperative change in thoracic kyphosis (TK), and the secondary outcome was the ability to achieve postoperative TK within the normal range. RESULTS The HC, SC, and MC groups included 23, 70, and 46 patients, respectively. The 3 groups did not differ significantly in preoperative demographic or radiographic parameters. The mean ± standard deviation of the preoperative main curve was 60.7° ± 12.6°, and the mean of curve correction was 62.9% ± 10.4% with no significant difference among groups (p ≥ 0.680). The groups did not differ significantly in coronal balance or proximal or thoracolumbar curve correction (p ≥ 0.189). Mean postoperative TK was 23.1° ± 6.3°, 19.6° ± 7.6°, and 23.4° ± 6.9° in the HC, SC and MC groups, respectively (p = 0.013), and the mean change in TK was -3.5° ± 11.3°, -7.1° ± 11.6°, and 0.1° ± 10.9°, respectively (p = 0.005). The MC group had significantly higher postoperative TK and less loss of TK compared with the SC group (p ≤ 0.018). Postoperative TK ≤ 10° was found in 12 patients (17%) in the SC group, 1 patient (5%) in the HC group, and 1 patient (2%) in the MC group (p = 0.021). There were no differences in proximal alignment, thoracolumbar alignment, or sagittal vertical axis (p ≥ 0.249). Lumbar lordosis was 58.9° ± 11.2° in the HC group versus 52.0° ± 1.3° and 55.0° ± 11.0° and the SC and MC groups, respectively (p = 0.040). CONCLUSIONS In the 3 rod constructs with different rigidity profiles, significantly better restoration of kyphosis was achieved with the use of bilateral modified rods compared with bilateral standard rods. In the MC and HC groups, the rate of severe postoperative hypokyphosis was significantly lower than in the SC group. This is the first study to describe the clinical use of a rod with a reduced proximal diameter and show marked radiographic improvement in sagittal alignment.

Prospective assessment of the safety and early outcomes of sublaminar band placement for the prevention of proximal junctional kyphosis

OBJECTIVE

Proximal junctional kyphosis (PJK) can progress to proximal junctional failure (PJF), a widely recognized early and serious complication of multisegment spinal instrumentation for the treatment of adult spinal deformity (ASD). Sublaminar band placement has been suggested as a possible technique to prevent PJK and PJF but carries the theoretical possibility of a paradoxical increase in these complications as a result of the required muscle dissection and posterior ligamentous disruption. In this study, the authors prospectively assess the safety as well as the early clinical and radiological outcomes of sublaminar band insertion at the upper instrumented vertebra (UIV) plus 1 level (UIV+1).

METHODS

Between August 2015 and February 2017, 40 consecutive patients underwent either upper (T2–4) or lower (T8–10) thoracic sublaminar band placement at the UIV+1 during long-segment thoracolumbar arthrodesis surgery. Outcome measures were prospectively collected and uploaded to a web-based REDCap database specifically designed to include demographic, clinical, and radiological data. All patients underwent clinical assessment, as well as radiological assessment with anteroposterior and lateral 36-inch whole-spine standing radiographs both pre- and postoperatively.

RESULTS

Forty patients (24 women and 16 men) were included in this study. Median age at surgery was 64.0 years with an IQR of 57.7–70.0 years. Median follow-up was 12 months (IQR 6–15 months). Three procedure-related complications were noted, including 2 intraoperative cerebrospinal spinal fluid leaks and 1 transient neurological deficit. Median visual analog scale (VAS) scores for back pain significantly improved after surgery (preoperatively: 8.0, IQR 6.0–10.0; 1-year follow-up: 2.0, IQR 0.0–6.0; p = 0.001). Median Oswestry Disability Index (version 2.1a) scores also significantly improved after surgery (preoperatively: 56.0, IQR 45.0–64.0; 1-year follow-up: 46.0, IQR 22.2–54.0; p < 0.001). Sagittal vertical axis (preoperatively: 9.0 cm, IQR 5.3–11.6 cm; final follow-up: 4.7 cm, IQR 2.0–6.6 cm; p < 0.001), pelvic incidence-lumbar lordosis mismatch (24.7°, IQR 11.2°–31.2°; 7.7°, IQR −1.2° to 19.5°; p < 0.001), and pelvic tilt (28.7°, IQR 20.4°–32.6°; 17.1°, IQR 10.8°–25.2°; p < 0.001) were all improved at the final follow-up. While proximal junctional (PJ) Cobb angles increased overall at the final follow-up (preoperatively: 4.2°, IQR 1.9°–7.4°; final follow-up: 8.0°, IQR 5.8°–10.3°; p = 0.002), the significant increase was primarily noted starting at the immediate postoperative time point (7.2°, IQR 4.4°–11.8°; p = 0.001) and not beyond. Three patients (7.5%) developed radiological PJK (mean ΔPJ Cobb 15.5°), while there were no instances of PJF in this cohort.

CONCLUSIONS

Sublaminar band placement at the UIV+1 during long-segment thoracolumbar instrumented arthrodesis is relatively safe and is not associated with an increased rate of PJK. Moreover, no subjects developed PJF. Prospective large-scale and long-term analysis is needed to define the potential benefit of sublaminar bands in reducing the incidence of PJK and PJF following surgery for ASD.

Clinical trial registration no.: NCT02411799 (clinicaltrials.gov)

Biomechanical comparison between titanium and cobalt chromium rods used in a pedicle subtraction osteotomy model

Instrumentation failure is a common complication following complex spinal reconstruction and deformity correction. Rod fracture is the most frequent mode of hardware failure and often occurs at or near a 3-column osteotomy site. Titanium (Ti) rods are commonly utilized for spinal fixations, however, theoretically stiffer materials, such as cobalt-chrome (CoCr) rods are also available. Despite ongoing use in clinical practice, there is little biomechanical evidence that compares the construct ability to withstand fatigue stress for Ti and Co-Cr rods. Six models using 2 polyethylene blocks each were used to simulate a pedicle subtraction osteotomy. Within each block 6.0×45 mm polyaxial screws were placed and connected to another block using either two 6.0×100 mm Ti (3 models) or CoCr rods (3 models). The rods were bent to 40° using a French bender and were secured to the screws to give a vertical height of 1.5 cm between the blocks. The blocks were fatigue tested with 700N at 4 Hz until failure. The average number of cycles to failure for the Ti rod models was 12840 while the CoCr rod models failed at a significantly higher, 58351 cycles (P=0.003). All Ti models experienced rod fracture as the mode of failure. Two out of the three CoCr models had rod fractures while the last sample failed via screw fracture at the screw-tulip junction. The risk of rod failure is substantial in the setting of long segment spinal arthrodesis and corrective osteotomy. Efforts to increase the mechanical strength of posterior constructs may reduce the occurrence of this complication. Utilizing CoCr rods in patients with pedicle subtraction osteotomy may reduce the rate of device failure during maturation of the posterior fusion mass and limit the need for supplemental anterior column support.

Influence of screw density on thoracic kyphosis restoration in hypokyphotic adolescent idiopathic scoliosis

Background

Previous studies have reported that rod composition and diameter, as well as the correction technique are key factors associated with thoracic kyphosis (TK) restoration. However, few study has analyzed the correlation between screw density and TK restoration in hypokyphotic adolescent idiopathic scoliosis (AIS).

Methods

Fifty-seven thoracic AIS patients with preoperative TK < 10° treated with all pedicle screw fixation with a minimum 2-year follow-up were recruited. Preoperative and postoperative radiographic measurements, and information of posterior instrumentation were reviewed. Pearson and Spearman correlation coefficient analysis were used to assess relationships between change in TK and number of variables. Then, the included patients were classified into two groups (Group 1: postoperative TK ≥ 20°; Group 2: postoperative TK < 20°) to evaluate the influence factors of TK restoration.

Results

The average preoperative TK was 4.75°, which was significantly restored to 17.30° (P < 0.001). Significant correlations were found between change in TK and flexibility of major thoracic curve (r = 0.357, P = 0.006), preoperative TK (r = −0.408, P = 0.002), and screw density of concave side (r = 0.306, P = 0.021), respectively. In the subgroup comparison, 17 patients (29.8%) maintain the postoperative TK ≥ 20°, increased flexibility of major thoracic curve (P < 0.001), screw number of concave side (P = 0. 029), and cobalt chromium rods (P = 0.041) were found in the group of postoperative TK ≥ 20°.

Conclusions

TK restoration remains a challenge for AIS patients with hypokyphosis, especially for the poor flexibility ones. Except for thicker and cobalt chromium rods, screw density of concave side might be another positive predictor of restoring normal kyphosis, which provides a stronger corrective force on the sagittal plane with more pedicle screws.