Delayed hemothorax after anterior vertebral body tethering in adolescent idiopathic scoliosis: a case report.

PURPOSE: The aim of this case report is to report that delayed hemothorax is possible after anterior vertebral body tethering (aVBT) and to illustrate the course of treatment. METHODS: We present a 15-year-old boy with adolescent idiopathic scoliosis who underwent an anterior thoracoscopic assisted vertebral body tethering who developed a massive right-sided hemothorax 12 days post-operatively. A chest tube was placed to drain the hemothorax and later required embolectomy with tissue plasminogen activator (TPA) to drain the retained hemothorax. RESULTS: At 1 month follow up post discharge the patient was asymptomatic, and radiograph did not demonstrate evidence of residual hemothorax and scoliosis. We have followed this patient for 5 years postoperative and he continues to do well clinically and radiographically. CONCLUSIONS: Pulmonary complications are a known drawback of anterior thoracoscopic spinal instrumentation. Delayed hemothorax is possible after aVBT. In the case of a retained hemothorax, chest tube treatment with TPA is a safe and effective method of embolectomy.

Meta-analysis on the efficacy and safety of anterior vertebral body tethering in adolescent idiopathic scoliosis.

PURPOSE: In this meta-analysis, we analyzed the efficacy and safety of anterior vertebral body tethering in patients with adolescent idiopathic scoliosis. METHODS: We performed a literature search and analyzed the following data: baseline characteristics, efficacy measures (corrections of the main thoracic curve, proximal thoracic curve, and thoracolumbar curve, thoracic kyphosis, lumbosacral lordosis, rib hump, lumbar prominence and SRS-22 scores, and complications. Analyses were performed with Cochrane's Review Manager version 5.4. RESULTS: Twelve studies met the inclusion criteria. Significant corrections of the main thoracic (MD 22.51, 95% CI 12.93 to 32.09) proximal thoracic (MD 10.14°, 95% CI 7.25° to 13.02°), and thoracolumbar curve (MD 12.16, 95% CI 9.14 to 15.18) were found. No statistically significant corrections were observed on the sagittal plane assessed by thoracic kyphosis (MD - 0.60°, 95% CI - 2.45 to 1.26; participants = 622; studies = 4; I2 = 36%) and lumbosacral lordosis (MD 0.19°, 95% CI - 2.16° to 2.54°). Significant corrections were identified for rib hump (MD 5.26°, 95% CI 4.19° to 6.32°) and lumbar prominence (MD 1.20°, 95% CI 0.27° to 2.13°) at final follow-up. Significant improvements of total SRS-22 score (MD - 0.96, 95% CI - 1.10 to - 0.83) were achieved at final follow-up. The most common complication was overcorrection (8.0%) and tether breakage (5.9%), with a reoperation rate of 10.1%. CONCLUSIONS: Anterior vertebral body tethering is effective to reduce the curve in the coronal plane and clinical deformity. Maximum correction is achieved at one year. The method should, however, be optimized to reduce the rate of complications.

Can anterior vertebral body tethering provide superior range of motion outcomes compared to posterior spinal fusion in adolescent idiopathic scoliosis? A systematic review.

PURPOSE: Anterior vertebral body tethering (AVBT) was introduced as a fusionless alternative to treating adolescent idiopathic scoliosis (AIS) while preserving range of motion (ROM). This is the first systematic review to compare the ROM outcomes between AVBT and PSF in treating AIS. METHODS: We conducted a comprehensive search on PubMed, EMBASE, MEDLINE, and Cochrane Library. Inclusion criteria were patients with AIS treated with AVBT or PSF or both, and clearly defined ROM outcomes; exclusion criteria were scoliosis other than AIS, biomechanical or cadaveric studies, non-English publications, case reports, conference summaries, unpublished literature, commentaries, and reviews. Primary outcome was ROM. Secondary outcomes included Cobb angle correction, quality of life (QOL), complications, and muscle strength and endurance. RESULTS: Twelve studies were included in this review. We found moderate evidence to support that AVBT results in superior ROM outcomes than PSF while achieving comparable Cobb angle correction with low evidence. The comparison of QOL outcomes between AVBT and PSF remained inconclusive. In addition to the complications noted conventionally in PSF, AVBT could result in over-correction and distal adding-on. We also found very low evidence to support that AIS patients treated with AVBT have superior muscle strength and endurance when compared to those treated with PSF. CONCLUSIONS: AVBT provides better preservation of ROM and muscle strength postoperatively when compared with PSF, while achieving comparable curve correction. Future studies should explore the spinal growth trajectory to determine the window of opportunity for AVBT in AIS.

Chest tube management following two row vertebral body tethering for adolescent idiopathic scoliosis.

BACKGROUND: The current gold standard of scoliosis correction procedures is still posterior spinal fusion, an extensively studied procedure. anterior vertebral body tethering is a newer surgical technique for the correction of scoliotic curves. Consequently, best practices have yet to be determined. METHODS: A single-institution, retrospective, review of all patients diagnosed with adolescent idiopathic scoliosis who underwent two row anterior vertebral body tethering between June 2020 and April 2022 was performed. RESULTS: Over the study period, 95 patients met inclusion: 79 females (83.2%) and 16 males (16.8%), age 14.4 ± 2.5 years, with a body mass index of 20.0 ± 2.9, and an average of 8.4 ± 2.1 levels treated. 28 (29.5%) procedures were for double curves and 67 (70.5%) for single curves. After tethering, a chest tube was positioned in each corrected side. A total of 123 chest tubes were analyzed, including 67 single curves and 28 double curves. The average chest tube duration was 2.5 ± 1.1 days and the average length of stay was 5.0 ± 2.0 days. The average chest tube output eight hours prior to removal was 61.1 ± 45.6 mL. There was no significant difference in average length of stay for patients who underwent correction of a single curve versus a double curve nor was there a difference in average length of stay or chest tube duration for revisions compared to primary procedures. For the entire cohort, the 30-day emergency department visit rate was 7.4% (n = 7) and the readmission rate was 4.2% (n = 4). CONCLUSIONS: This early review of a 2-year two row vertebral body tethering postoperative experience provides a report of a safe and effective approach to chest tube management at a single academic center.

Results of posterior spinal fusion after failed anterior vertebral body tethering.

PURPOSE: In patients with adolescent idiopathic scoliosis (AIS) undergoing anterior vertebral tethering (AVBT), some will subsequently require posterior spinal fusion (PSF). Limited data exist on clinical and radiographic outcomes of fusion after tether failure. METHODS: 490 patients who underwent AVBT were retrospectively analyzed. Twenty patients (4.1%) subsequently underwent conversion to PSF. A control group of patients with primary PSF (no previous AVBT) was matched for comparison. Data were compared using paired t-tests and Fisher Exact Tests. RESULTS: There was a significant increase in estimated blood loss (EBL) (p = 0.002), percent estimated blood volume (%EBV) (p = 0.013), operative time (p = 0.002), and increased amount of fluoroscopy (mGy) (p = 0.04) as well as number of levels fused (p = 0.02) in the AVBT conversion group compared to primary fusion. However, no difference was found in implant density (p = 0.37), blood transfusions (p = 0.11), or intraoperative neuromonitoring events (p > 0.99). Both groups attained similar thoracic and lumbar percent correction (major coronal curve angle) from pre-op to the latest follow-up (thoracic p = 0.507, lumbar p = 0.952). CONCLUSION: A subset of patients with AVBT will require conversion to PSF. Although technically more challenging, revision surgery can be safely performed with similar clinical and radiographic outcomes to primary PSF.

Coronal decompensation following thoracic vertebral body tethering in idiopathic scoliosis.

PURPOSE: Post-operative coronal decompensation (CD) continues to be a challenge in the treatment of adolescent idiopathic scoliosis (AIS). CD following selective spinal fusion has been studied. However, there is currently little information regarding CD following Vertebral Body Tethering (VBT). Thus, the goal of this study is to better understand the incidence and risk factors for CD after VBT. METHODS: Retrospective review of a prospective multicenter database was used for analysis. Inclusion criteria were patients undergoing thoracic VBT, a minimum 2-year follow-up, LIV was L1 or above, skeletally immature (Risser ≤ 1), and available preoperative and final follow-up AP and lateral upright radiographs. Radiographic parameters including major and minor Cobb angles, curve type, LIV tilt/translation, L4 tilt, and coronal balance were measured. CD was defined as the distance between C7PL and CSVL > 2 cm. Multiple logistic regression model was used to identify significant predictors of CD. RESULTS: Out of 136 patients undergoing VBT, 94 patients (86 female and 6 male) met the inclusion criteria. The mean age at surgery was 12.1 (9-16) and mean follow-up period was 3.4 years (2-5 years). Major and minor curves, AVR, coronal balance, LIV translation, LIV tilt, L4 tilt were significantly improved after surgery. CD occurred in 11% at final follow-up. Lenke 1A-R (24%) and 1C (26%) had greater incidence of CD compared to 1A-L (4%), 2 (0%), and 3 (0%). LIV selection was not associated with CD. Multivariate logistic regression analysis yielded 1A-R and 1C curves as a predictor of CD with the odds ratio being 17.0. CONCLUSION: CD occurred in 11% of our thoracic VBT patients. Lenke 1A-R and 1C curve types were predictors for CD in patients treated with VBT. There were no other preoperative predictors associated with CD.

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

BACKGROUND CONTEXT: Vertebral body tethering is the most popular nonfusion treatment for adolescent idiopathic scoliosis. The effect of the tether cord on the spine can be segmentally assessed by comparing the angle between two adjacent screws (interscrew angle) over time. Tether breakage has historically been assessed radiographically by a change in adjacent interscrew angle by greater than 5° between two sets of imaging. A threshold for growth modulation has not yet been established in the literature. These angle measurements are time consuming and prone to interobserver variability. PURPOSE: The purpose of this study was to develop an automated deep learning algorithm for measuring the interscrew angle following VBT surgery. STUDY DESIGN/SETTING: Single institution analysis of medical images. PATIENT SAMPLE: We analyzed 229 standing or bending AP or PA radiographs from 100 patients who had undergone VBT at our institution. OUTCOME MEASURES: Physiologic Measures: An image processing algorithm was used to measure interscrew angles. METHODS: A total of 229 standing or bending AP or PA radiographs from 100 VBT patients with vertebral body tethers were identified. Vertebral body screws were segmented by hand for all images and interscrew angles measured manually for 60 of the included images. A U-Net deep learning model was developed to automatically segment the vertebral body screws. Screw label maps were used to develop and tune an image processing algorithm which measures interscrew angles. Finally, the completed model and algorithm pipeline was tested on a 30-image test set. Dice score and absolute error were used to measure performance. RESULTS: Inter- and Intra-rater reliability for manual angle measurements were assessed with ICC and were both 0.99. The segmentation model Dice score against manually segmented ground truth across the 30-image test set was 0.96. The average interscrew angle absolute error between the algorithm and manually measured ground truth was 0.66° and ranged from 0° to 2.67° in non-overlapping screws (N=206). The primary modes of failure for the model were overlapping screws on a right thoracic/left lumbar construct with two screws in one vertebra and overexposed images. An algorithm step which determines whether an overlapping screw was present correctly identified all overlapping screws, with no false positives. CONCLUSION: We developed and validated an algorithm which measures interscrew angles for radiographs of vertebral body tether patients with an accuracy of within 1° for the majority of interscrew angles. The algorithm can process five images per second on a standard computer, leading to substantial time savings. This algorithm may be used for rapid processing of large radiographic databases of tether patients and could enable more rigorous definitions of growth modulation and cord breakage to be established.

Anterior Vertebral Body Tethering for Skeletally Immature Patients with AIS: Indication for Spinal Fusion at Skeletal Maturity Is Not Obviated in 60% of Cases.

The role of anterior vertebral body tethering (aVBT) in obviating the need for spinal fusion in patients with AIS remains unclear, and a large amount of variation exists in the data among different studies. The present study aims to investigate and analyze what factors have a potential influence on aVBT outcome. Skeletally immature patients with AIS who underwent aVBT for scoliosis correction were followed up until skeletal maturity. The mean age at the time of surgery was 13.4 ± 1.1, and the mean follow-up time was 2.5 ± 0.5 years. The Cobb angle of the main curve was 46.6 ± 9° at the time of surgery and was significantly corrected to 17.7 ± 10.4° (p < 0.001) immediately postoperatively. A significant loss of correction was observed during the latest follow-up (Cobb angle 33.8 ± 18.7°; p < 0.001). An indication for spinal fusion at skeletal maturity was not obviated in 60% of the patients. The factors identified as having an influence on the outcome were preoperative bone age and the magnitude of the major curve. Patients with advanced bone age and larger curves were more likely to reach an indication for spinal fusion at skeletal maturity. In conclusion, no general recommendation for aVBT can be made for AIS patients. The method can be discussed as a treatment option in skeletally very immature preadolescent patients (Sanders Stadium ≤ 2) with a moderate Cobb angle (≤50°) who failed previous brace therapy.

Anterior vertebral body tethering for adolescent idiopathic scoliosis associated with less early post-operative pain and shorter recovery compared with fusion.

PURPOSE: While posterior spinal instrumentation and fusion (PSIF) for severe adolescent idiopathic scoliosis (AIS) is the gold standard, anterior vertebral body tethering (AVBT) is becoming an alternative for select cases. Several studies have compared technical outcomes for these two procedures, but no studies have compared post-operative pain and recovery. METHODS: In this prospective cohort, we evaluated patients who underwent AVBT or PSIF for AIS for a period of 6 weeks after operation. Pre-operative curve data were obtained from the medical record. Post-operative pain and recovery were evaluated with pain scores, pain confidence scores, PROMIS scores for pain behavior, interference, and mobility, and functional milestones of opiate use, independence in activities of daily living (ADLs), and sleeping. RESULTS: The cohort included 9 patients who underwent AVBT and 22 who underwent PSIF, with a mean age of 13.7 years, 90% girls, and 77.4% white. The AVBT patients were younger (p = 0.03) and had fewer instrumented levels (p = 0.03). Results were significant for decreased pain scores at 2 and 6 weeks after operation (p = 0.004, and 0.030), decreased PROMIS pain behavior at all time points (p = 0.024, 0.049, and 0.001), decreased pain interference at 2 and 6 weeks post-operative (p = 0.012 and 0.009), increased PROMIS mobility scores at all time points (p = 0.036, 0.038, and 0.018), and faster time to functional milestones of weaning opiates, independence in ADLs, and sleep (p = 0.024, 0.049, and 0.001). CONCLUSION: In this prospective cohort study, the early recovery period following AVBT for AIS is characterized by less pain, increased mobility, and faster recovery of functional milestones, compared with PSIF. LEVEL OF EVIDENCE: IV.

Prediction of post-operative adding-on or compensatory lumbar curve correction after anterior vertebral body tethering.

PURPOSE: Anterior Vertebral Body Tethering (AVBT), a fusionless surgical technique based on growth modulation, aims to correct pediatric scoliosis over time. However, medium-term curvature changes of the non-instrumented distal lumbar curve remains difficult to predict. The objective was to biomechanically analyze the level below the LIV to evaluate whether adding-on or compensatory lumbar curve after AVBT can be predicted by intervertebral disc (ID) wedging and force asymmetry. METHODS: 33 retrospective scoliotic cases instrumented with AVBT were used to computationally simulate their surgery and 2-year post-operative growth modulation using a finite element model. The cohort was divided into two subgroups according to the lumbar curvature evolution over 2 years: (1) correction > 10° (C); (2) maintaining ± 10° (M). The lumbar Cobb angle and residual ID wedging angle under LIV were measured. Simulated pressures and moments at the superior endplate of LIV + 1 were post-processed. These parameters were correlated at 2 years postoperatively. FINDINGS: On average, the LIV + 1 simulated moment was 538 Nmm for subgroup C, 155 Nmm for subgroup M with lumbar Cobb angle > 20° and 34 Nmm for angle < 20° whereas the ID angle was 1° for C and 0° for M. INTERPRETATION: On average, a positive moment on the LIV + 1 superior growth plate led to correction of the lumbar curvature, whereas a null moment kept it stable, and a parallel immediate postoperative ID under LIV contributed to its correction or preservation. Nevertheless, the significant interindividual variability suggested that other parameters are involved in the distal non-instrumented curvature evolution. LEVEL OF EVIDENCE: IV.

Early outcomes in hybrid fixation for idiopathic scoliosis: posterior fusion combined with anterior vertebral body tethering. Patient series.

BACKGROUND: Anterior vertebral body tethering (AVBT) and posterior spinal fusion (PSF) are options for patients with idiopathic scoliosis. Combining both procedures in patients with double curves, a procedure in which PSF is performed for the thoracic curve and AVBT for the lumbar curve, provides maximal correction of the thoracic curve with a theoretical maintenance of motion in the lumbar spine. OBSERVATIONS: The authors retrospectively reviewed 20 skeletally immature patients diagnosed with idiopathic scoliosis at a single institution with an average age of 12.7 ± 1.6 years and who had undergone hybrid treatment with an average follow-up of 8 months. The PSF procedures averaged 276 ± 63 minutes with 442.8 ± 295 mL of blood loss, and the AVBT averaged 275 ± 54 minutes with 118.3 ± 80 mL of blood loss. Following the hybrid correction, the thoracic and lumbar coronal curve angles improved from 67.6° to 21.6° and from 65.2° to 24°, respectively. The three-dimensional kyphosis improved from 3.3° to 24°. LESSONS: A combined approach of PSF and AVBT is safe and effective for idiopathic scoliosis. This approach combines the gold standard of thoracic fusion with the motion preservation benefits of AVBT in the lumbar spine. This study will continue to refine indications for AVBT.

Thoracic posterior spinal instrumented fusion vs. thoracic anterior spinal tethering for adolescent idiopathic scoliosis with a minimum of 2-year follow-up: a cost comparison of index and revision operations.

PURPOSE: To compare direct costs of index and revision operations of thoracic posterior spinal instrumented fusion (TPSIF) and thoracic anterior spinal tethering (TAST) for adolescent idiopathic thoracic scoliosis in children. METHODS: Children (ages 11-18 years) who underwent TPSIF and TAST (2/2013-9/2019) were reviewed. Follow-up < 2 years and cervical instrumentation and/or instrumentation of a lumbar level at L3 or below were exclusion criteria. Patient demographics, radiographic curve magnitude, index operations and postoperative data, as well as indications for revisions/readmissions were collected. Direct costs were identified and compared for index and revision operations during follow-up. RESULTS: One hundred and four patients were included (TPSIF: 78; TAST: 25). TAST procedures were performed in children significantly younger and for smaller curve magnitudes. They had significantly fewer levels instrumented, shorter operating room (OR) times, and less estimated blood loss (EBL). After operation, a significantly higher percentage of TAST were admitted to ICU. Hospital length of stay (LOS) was similar between groups. Index operations' average direct costs were significantly higher for TAST than TPSIF ($52,947 v. $46,641; p = 0.02). Major cost drivers for both groups were implants, OR services, post-anesthesia care unit (PACU), and room/board. Revisions following TAST were more frequent than for TPSIF (36 v. 11.5%). Majority of TPSIF revisions were for junctional deformity. Curve progression and overcorrection were most common reason for TAST revisions. Average direct costs for revisions/readmissions were similar between groups (TPSIF: $28,485 v. TAST: $27,590; p = 0.46). CONCLUSIONS: Index operations' average direct costs were statistically similar between TPSIF and TAST for adolescent idiopathic scoliosis. Major cost drivers were implants, OR services, PACU, and room/board. TAST index operations' direct costs and associated direct costs for implants and room/board were significantly higher, while their anesthesia and OR services were significantly lower than TPSIF. TAST revisions were for overcorrection and curve progression, while TPSIF revisions were most commonly for junctional deformity. Overall average direct costs for revisions were similar despite revision rates being higher for TAST. LEVEL OF EVIDENCE: III.

Video-Assisted Thoracoscopy for Vertebral Body Tethering of Juvenile and Adolescent Idiopathic Scoliosis: Tips and Tricks of Surgical Multidisciplinary Management.

VATS (video assisted thoracoscopic surgery) is routinely and successfully performed in minor and major complex thoracic procedures. This technique has been recently introduced for the treatment of severe forms of idiopathic scoliosis (IS) with the aim to repair the deformity, reduce morbidity and to prevent its progression in patients with skeletal immaturity. This study aims to present VATS in anterior vertebral body tethering (AVBT) approach to support the pediatric orthopedic surgeons during vertebral body fixation. Surgical and anesthesiologic tips and tricks are reported to assure a safe procedure. The study includes preadolescents with IS and a grade of scoliosis >40° that had a high probability of deterioration due to remaining growth (December 2018 to April 2021). Skeletal immaturity of enrolled patients was assessed by Sanders classification and Risser sign. Patients had a Risser score between 0 and 1 and a Sanders score >2 and <5. AVBT technique using VATS was performed by a senior pediatric surgeon assisting the pediatric orthopedic surgeon. Twenty-three patients have been submitted to VATS AVBT in the period of study (age range 9-14 years). The patients had a classified deformity Lenke 1A or B convex right and all types of curves were treated. In all patients, the vertebrae submitted to tethering surgery ranged from D5 to D12; mean curve correction was 43%. Three postoperative complications occurred: one late postoperative bleeding requiring a chest tube positioning on 12th postoperative day; one screw dislodged and needed to be removed; one child showed worsening of the scoliosis and needed a posterior arthrodesis. Initial results of VATS AVBT in growing patients with spinal deformities are encouraging. An appropriate selection of patients and a pediatric dedicated multidisciplinary surgical approach decrease intraoperative complications, time of operation and postoperative sequelae and guarantee an optimal outcome.

When successful, anterior vertebral body tethering (VBT) induces differential segmental growth of vertebrae: an in vivo study of 51 patients and 764 vertebrae.

PURPOSE: This study aimed to determine (1) does vertebral body tethering (VBT) produce differential growth modulation in individual vertebrae in patients with idiopathic scoliosis, (2) does VBT change disc shape, and (3) does VBT affect total spine length? METHODS: Patients with idiopathic scoliosis treated with VBT of the main thoracic curve and minimum 2-year follow-up were included. Vertebrae and discs were categorized as uninstrumented proximal thoracic, instrumented main thoracic, or uninstrumented thoracolumbar-lumbar. The left- and right-sided heights of each vertebra and disc were measured on subsequent radiographs to assess for differential growth. T1-T12 thoracic and T1-S1 thoracolumbar growth velocities were compared with standardized reference data. RESULTS: Fifty-one patients (764 vertebrae and 807 discs) were analyzed. The average major curve magnitude improved from 46° ± 11° to 17° ± 11° at 2-year follow-up. Differential growth was observed in MT vertebrae, in which the left/concave side grew 2.0 ± 2.2 mm compared with 1.5 ± 2.3 mm on the right/convex (tethered) side (p < 0.001). Differential height changes were observed for all discs, but were most pronounced in instrumented MT discs, in which the right/convex sides decreased by an average of 1.2 mm each, compared with no significant height change on the left/concave side. Total spinal growth velocities were not significantly different from standard reference data. CONCLUSION: Vertebral body tethering limits convex spinal growth as designed while permitting concave growth. Curve correction results from differential vertebral growth and decreased convex disc height. Overall spinal growth continues at the expected rate. LEVEL OF EVIDENCE: Level IV case series.

Anterior vertebral body tethering for idiopathic scoliosis in growing children: A systematic review.

BACKGROUND: The management of idiopathic scoliosis (IS) in skeletally immature patients should aim at three-dimensional deformity correction, without compromising spinal and chest growth. In 2019, the US Food and Drug Administration approved the first instrumentation system for anterior vertebral body tethering (AVBT), under a Humanitarian Device Exception, for skeletally immature patients with curves having a Cobb angle between 35° and 65°. AIM: To summarize current evidence about the efficacy and safety of AVBT in the management of IS in skeletally immature patients. METHODS: From January 2014 to January 2021, Ovid Medline, Embase, Cochrane Library, Scopus, Web of Science, Google Scholar and PubMed were searched to identify relevant studies. The methodological quality of the studies was evaluated and relevant data were extracted. RESULTS: Seven clinical trials recruiting 163 patients were included in the present review. Five studies out of seven were classified as high quality, whereas the remaining two studies were classified as moderate quality. A total of 151 of 163 AVBT procedures were performed in the thoracic spine, and the remaining 12 tethering in the lumbar spine. Only 117 of 163 (71.8%) patients had a nonprogressive curve at skeletal maturity. Twenty-three of 163 (14.11%) patients required unplanned revision surgery within the follow-up period. Conversion to posterior spinal fusion (PSF) was performed in 18 of 163 (11%) patients. CONCLUSION: AVBT is a promising growth-friendly technique for treatment of IS in growing patients. However, it has moderate success and perioperative complications, revision and conversion to PSF.

Shoulder balance in patients with Lenke type 1 and 2 idiopathic scoliosis appears satisfactory at 2 years following anterior vertebral body tethering of the spine.

BACKGROUND: Shoulder balance is an important factor for patient satisfaction following surgery for idiopathic scoliosis (IS). There is no literature reporting the effect of anterior vertebral body tethering (AVBT) on shoulder balance. The purpose of this study was to report the prevalence of postoperative shoulder imbalance in patients undergoing AVBT for IS. METHODS: In this retrospective case series, patients enrolled in a multicenter scoliosis registry who underwent AVBT from 2013 to 2017 in two Canadian centers were identified. The primary outcome was shoulder imbalance, defined as an absolute radiographic shoulder height of > 2 cm, at 2 years postoperatively (follow-up range: 22-30 months). Clavicular angle and T1 tilt angle were also investigated. RESULTS: Of the 50 patients identified (92% female; preoperative age: 11.9 ± 1.4 years), there were 43 (86%) patients with Lenke 1 and 7 (14%) patients with Lenke 2 curves. The mean Cobb angles of the proximal thoracic and main thoracic curves were 22.8° ± 8.8° and 49.4° ± 8.5° preoperatively and 13.1° ± 7.5° and 24.9° ± 9.5° at a mean follow-up time of 2.1 years. Absolute clavicular angle and T1 tilt angle were 2.8° ± 2.2° and 4.8° ± 3.5° preoperatively and 2.2° ± 1.7° and 4.7° ± 4.2° at 2-year follow-up. Preoperatively, absolute shoulder height averaged 15.6 ± 10.4 mm, and 15 (30%) patients had shoulder imbalance. At 2-year follow-up, absolute shoulder height averaged 11.2 ± 8.3 mm, and 8 (16%) patients had shoulder imbalance. Of the patients who had acceptable shoulder balance preoperatively, 4 (11.4%) became imbalanced at 2 years postoperatively. CONCLUSION: Postoperative shoulder imbalance in this early group of patients with IS undergoing AVBT was seen in 16% of patients, a reduction from 30% preoperatively. These results likely reflect the potential of the proximal thoracic curve to correct spontaneously following AVBT. LEVEL OF EVIDENCE: Level III.

Efficacy of Anterior Vertebral Body Tethering in Skeletally Mature Children with Adolescent Idiopathic Scoliosis: A Preliminary Report.

BACKGROUND: Anterior vertebral body tethering (AVBT) offers a dynamic fusionless correction option for children with adolescent idiopathic scoliosis (AIS). Few existing clinical studies evaluating novel AVBT in skeletally immature children have questioned the midterm efficacy with concerns of overcorrection and curve progression with remaining growth. The current study investigates the effect of this technique in skeletally mature children (Risser ≥ 4 and Sanders ≥ 7) with AIS with limited remaining growth potential. METHODS: We evaluated skeletally mature children with AIS who underwent the AVBT technique for a single structural major curve between 40° and 80° with ≥50% flexibility on dynamic radiographs and a minimum of 1 year of follow-up. Pertinent clinical and radiographic data collected include skeletal maturity, curve type, Cobb angle, sagittal parameters, and a patient-reported outcome measure Scoliosis Research Society-22 (SRS-22) questionnaire. RESULTS: All 10 children were female with a mean age of 14.9 ± 2.7 years at the time of surgery. The mean follow-up was 24.1 ± 3.6 months. The mean Risser and Sanders scores were 4.2 ± 0.6 and 7.2 ± 0.6, respectively. Three patients had major thoracic curves, and 7 patients had thoracolumbar/lumbar curves. Cranial and caudal instrumented levels were T5 and L4. Mean preoperative Cobb's angle was 52.0° ± 11.6° and was corrected to 15.9° ± 6.8° on the first erect postoperative radiograph, with stabilization of corrected curve at the 1-year follow-up (mean Cobb's angle of 15.3° ± 8.7°). Mean preoperative and postoperative SRS-22 scores were 78.0 ± 3.2 and 92.5 ± 3.1, respectively (P < .01). No complications were noted until the last follow-up. CONCLUSION: Our preliminary experience with this novel AVBT as an alternative technique to fusion to stabilize progressive idiopathic scoliosis in skeletally mature children is promising. LEVEL OF EVIDENCE: 4.

Could have tethered: predicting the proportion of scoliosis patients most appropriate for thoracic anterior spinal tethering.

BACKGROUND: Posterior spinal fusion (PSF) has proven to be a safe, reliable technique to treat spinal deformities in adolescents. In recent early reports, vertebral body tethering (VBT) is showing promise as a method to modulate growth, driving scoliosis correction, while offering the potential added benefit of maintaining some flexibility in the instrumented segment. With recent FDA humanitarian device exemption (HDE) approval, VBT is poised to become more widely available as a treatment for a subset of current PSF candidates. Our aim was to use approved criteria from a recent FDA IDE to determine who could have been tethered in the years preceding approval. METHODS: A retrospective analysis was performed of patients with idiopathic scoliosis treated with PSF or VBT at a large pediatric spine center from 1/1/2016 to 6/25/2019. Tethering indications followed the criteria outlined by an ongoing FDA IDE: age 8-16, Sanders bone age ≤ 4, primary thoracic curve between 35° and 60°, and lumbar curve < 35°. Risser sign and triradiate cartilage status were also employed to ascertain skeletal maturity in the absence of Sanders score. RESULTS: Of the 359 patients (78.6% female) who underwent PSF or VBT for idiopathic scoliosis, 75 (20.9%) met IDE criteria for VBT (57 had PSF and 18 had VBT). 284 were not appropriate for thoracic VBT: 77 (21.4%) had a non-thoracic primary curve, 80 (22.3%) were too mature at presentation, 36 (10.0%) had a lumbar curve > 34°, 9 (2.5%) had a main thoracic curve out of range, and 1 had a proximal thoracic curve > 40°. 81 patients (22.6%) had multiple exclusionary criteria. CONCLUSIONS: After decades with a successful treatment for AIS (PSF), we are at an inflection point: VBT is conditionally approved by the FDA as an HDE device, unleashing more widespread use. Many pediatric spine surgeons will want to know what proportion of PSFs will someday be VBTs. If FDA IDE criteria are used to ensure that a VBT candidate has an appropriate maturity stage and scoliosis deformity pattern, 20.9% of our 359 surgical range patients would have qualified for thoracic VBT. LEVEL OF EVIDENCE: Level III.

3D correction over 2years with anterior vertebral body growth modulation: A finite element analysis of screw positioning, cable tensioning and postoperative functional activities.

BACKGROUND: Anterior vertebral body growth modulation is a fusionless instrumentation to correct scoliosis using growth modulation. The objective was to biomechanically assess effects of cable tensioning, screw positioning and post-operative position on tridimensional correction. METHODS: The design of experiments included two variables: cable tensioning (150/200N) and screw positioning (lateral/anterior/triangulated), computationally tested on 10 scoliotic cases using a personalized finite element model to simulate spinal instrumentation, and 2years growth modulation with the device. Dependent variables were: computed Cobb angles, kyphosis, lordosis, axial rotation and stresses exerted on growth plates. Supine functional post-operative position was simulated in addition to the reference standing position to evaluate corresponding growth plate's stresses. FINDINGS: Simulated cable tensioning and screw positioning had a significant impact on immediate and after 2years Cobb angle (between 5°-11°, p<0.01). Anterior screw positioning significantly increased kyphosis after 2years (6°-8°, p=0.02). Triangulated screw positioning did not significantly impact axial rotation but significantly reduced kyphosis (8°-10°, p=0.001). Growth plates' stresses were increased by 23% on the curve's convex side with cable tensioning, while screw positioning rather affected anterior/posterior distributions. Supine position significantly affected stress distributions on the apical vertebra compared to standing position (respectively 72% of compressive stresses on convex side vs 55%). INTERPRETATION: This comparative numerical study showed the biomechanical possibility to adjust the fusionless instrumentation parameters to improve correction in frontal and sagittal planes, but not in the transverse plane. The convex side stresses increase in the supine position may suggest that growth modulation could be accentuated during nighttime.