Hybrid Fusion–Tether Strategy vs Bilateral Vertebral Body Tethering for Double Curves in AIS: A Matched Cohort Analysis with Follow-up Equalization

Hybrid Fusion–Tether Strategy vs Bilateral Vertebral Body Tethering for Double Curves in AIS: A Matched Cohort Analysis with Follow-up Equalization | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Hybrid Fusion–Tether Strategy vs Bilateral Vertebral Body Tethering for Double Curves in AIS: A Matched Cohort Analysis with Follow-up Equalization Matteo Traversari, Altug Yucekul, Feyzi Kilic, Fedde Weenink, and 7 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9355992/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 7 You are reading this latest preprint version Abstract Purpose Vertebral body tethering (VBT) has emerged as a fusionless alternative for the treatment of adolescent idiopathic scoliosis (AIS) in skeletally immature patients. In patients presenting with double (false or major) curve patterns, bilateral VBT has been proposed as a fully motion-preserving strategy, although concerns remain regarding its corrective power and mechanical reliability. Hybrid constructs combining selective thoracic fusion (STF) with lumbar VBT have recently been introduced. The aim of this study is to compare bilateral VBT and hybrid surgery in terms of radiographic, patient-reported, pulmonary, complication, and implant-survival outcomes. Methods A retrospective matched cohort study was conducted using a prospectively collected dataset of AIS patients treated with either bilateral VBT or hybrid surgery. A 1:1 matched cohort (15 pairs) was created using greedy nearest-neighbor matching based on preoperative thoracolumbar/lumbar (TL/L) Cobb angle, Sanders maturity stage, and cervical vertebral maturation. Follow-up was pairwise equalized by capping the analysis at the shorter follow-up time of each pair. Radiographic outcomes, pulmonary function tests, SRS-22 scores, complications, and tether breakage–free survival were analyzed. Results Thirty patients (15 bilateral VBT, 15 hybrid) were included with a mean capped follow-up of 31.3 months. Hybrid surgery demonstrated significantly greater correction of both thoracic and TL/L curves at first-erect and latest follow-up ≤ cap (p < 0.05). A higher proportion of patients in the hybrid cohort achieved residual thoracic curves ≤ 30° (p < 0.05). Bilateral VBT showed greater improvement in the SRS-22 function domain (p = 0.026). Tether breakage occurred more frequently in the bilateral VBT cohort, although the difference did not reach statistical significance. Conclusion Hybrid surgery combining STF with lumbar VBT provided superior radiographic results compared with bilateral VBT in patients with double-curve AIS. While bilateral VBT demonstrated greater improvement in functional patient-reported outcomes, hybrid constructs may offer greater deformity correction and result predictability while preserving lumbar motion segments. Vertebral body tethering VBT Double-sided VBT Bilateral VBT Tether breakage Adolescent idiopathic scoliosis Adolescent spinal deformities Growth modulation Posterior spinal fusion Hybrid Figures Figure 1 Figure 2 Figure 3 Introduction Posterior spinal fusion (PSF) is the current gold standard for treating progressive or severe adolescent idiopathic scoliosis (AIS).[ 1 ] Vertebral body tethering (VBT) is an alternative fusionless technique indicated for skeletally immature AIS patients.[ 2 – 4 ] VBT allows correction of the spine curvature while maintaining a certain degree of spinal flexibility and enabling continued deformity correction through growth modulation, according to the Hueter–Volkmann principle [ 2 , 5 , 6 ]. Motion preservation becomes more important when there is a need to extend fusion into the lumbar spine [ 7 , 8 ]. In cases of double major curves or thoracic curves with a significant compensatory lumbar curve (e.g. Lenke 1C), several authors have recently extended VBT to the thoracolumbar/lumbar (TL/L) spine in addition to thoracic VBT [ 9 – 19 ]. While some have reported favorable outcomes with bilateral VBT, others have raised concerns regarding the safety of the technique, reporting high rates of tether breakage, revision surgeries and suboptimal correction [ 10 , 13 , 17 , 18 ]. Trunk motion analysis studies have demonstrated negligible preservation of spinal mobility following thoracic VBT [ 19 ] compared to the lumbar spine [ 20 – 22 ]. This has led to a progressive abandonment of thoracic VBT in cases that do not strictly meet the criteria for ideal candidates [ 17 ]. However, the importance of preserving lumbar spinal mobility remains undeniable. Therefore, some authors have introduced a hybrid strategy combining selective thoracic fusion (STF) with lumbar VBT [ 23 ]. To date, there is no comparative data regarding these two techniques. The aim of the present study is to compare bilateral VBT and hybrid surgery in terms of efficacy and safety through a matched, follow-up–equalized evaluation of radiographic, patient-reported, pulmonary, complication, and implant-survival outcomes. Material and Methods Study design A retrospective matched cohort study was conducted in an ethics board approved single-center prospectively recorded dataset of consecutive patients treated with VBT. A 1:1 matched cohort was created to compare bilateral VBT and hybrid surgery (STF combined with TL/L VBT). Matching was performed using a greedy 1:1 nearest-neighbor matching without replacement applied using predefined clinical criteria: preoperative TL/L Cobb angle within ± 5°, Simplified Skeletal Maturity Staging (SSMS) within ± 1, Cervical vertebral maturation (CVM) within ± 2. In case of multiple potential matches, pairs were selected according to the smallest absolute difference in preoperative TL/L Cobb angle, followed by SSMS, and then CVM stage. The matching process yielded 15 matched pairs. Standardized mean differences (SMD) were used to assess covariate balance between groups. Preoperative balance was considered acceptable when SMD < 0.25. To ensure comparable follow-up duration between matched pairs, all longitudinal analyses were capped at the shorter follow-up time of each pair (latest follow-up ≤ cap). Patients’ characteristics and inclusion criteria Patients who were diagnosed with AIS that had undergone either bilateral VBT or hybrid surgery with at least 24 months of follow-up were included. Patients who did not have a preoperative whole-body biplanar EOS scanning image with a concomitant left-hand radiograph, patients who reached skeletal maturity pre-operatively and patients who had undergone previous spine surgeries were excluded. Surgical technique Thoracoscopic and retroperitoneal approaches were performed by thoracic and vascular access surgeons, respectively. Details regarding surgical technique of VBT and postoperative care are given in previous papers [ 2 , 24 ], and in supplementary material file 1. Regarding STF, the fusion levels were defined as follows: the upper instrumented vertebra (UIV) was selected between T2 and T4 based on preoperative shoulder balance and the structural or compensatory nature of the proximal thoracic (PT) curve [ 1 ]. The lower instrumented vertebra (LIV) was chosen as the neutral vertebra (NV) or NV + 1 depending on the degree of NV translation from the central sacral vertical line (CSVL), in accordance with the last substantially touched vertebra (LSTV) concept [ 25 ]. All pedicle screws were placed under intra-operative CT-guided navigation [ 26 ]. Two 6mm cobalt-chrome rods were asymmetrically contoured to the desired postoperative sagittal alignment and to achieve indirect vertebral derotation. In situ correction with segmental compression/distraction was performed to optimize local alignment. Bilateral VBT surgeries were applied as same-day two-stage surgeries. When hybrid surgery required proximal extension of VBT instrumentation to L1 or above, ipsilateral thoracoscopic approach was used and the tether was passed from the thoracic cage to the retroperitoneal space. Staging of the hybrid procedure was based on intraoperative degree of spontaneous lumbar curve correction (SLCC) and STF operative time. In cases of relevant SLCC, lumbar VBT was staged and postoperative full-body standing EOS imaging was obtained to assess the need for additional lumbar VBT. In staged patients, the average interval between the two operation was 7 days. Demographic, radiographic, pulmonary and clinical data Demographic data included age at surgery, gender and ethnicity. Preoperative body weight, height and body mass index (BMI) were collected. Skeletal maturity data included Modified Risser score, SSMS and CVM. Perioperative data included surgical technique, operative time, estimated blood loss (EBL), length of hospital stay (LOS), Intensive care unit (ICU) requirement and the number of levels tethered/fused both in the thoracic and TL/L spine. Radiographic data included PT, main thoracic (MT) and TL/L coronal measurements and flexibility percentages, thoracic kyphosis (TK) and lumbar lordosis (LL) Cobb angles, preoperatively, postoperatively and at the latest follow-up ≤ cap. Surgical (pre- to postoperative) and total (preoperative to latest follow-up ≤ cap) correction percentages were calculated. Measurements were done using a validated software (Sectra IDS7, Sectra AB, Sweden). Percent predicted FVC (FVC%) and percent predicted FEV1 (FEV1%) were recorded, along with SRS-22 questionnaires, preoperatively and yearly at each postoperative follow-up time point. Outcome Measures Outcome Measures A negative sign was assigned to an overcorrected curve. Pulmonary, mechanical and curve behavior complications, readmissions and reoperations were noted. Broken tethers were indicated by ≥ 6° increase of angulation between adjacent screws between any two postoperative radiographs. Statistical Analysis Continuous variables are presented as mean±standard deviation (SD) or median (range) and categorical variables as counts and percentages. All parameters were evaluated for normal distribution with the Shapiro–Wilk test. Between-group comparisons for continuous variables were performed using Student’s t-test, Welch’s t-test, or the Mann–Whitney U test. Categorical variables were compared using the chi-square or Fisher’s exact test. Survival analysis was performed using the Kaplan–Meier method and compared between groups with the log-rank test. Cox proportional hazards analysis was used to estimate the relative risk of tether breakage between groups. p < 0.05 was considered significant. Statistical analyses were performed using Jamovi statistical analysis software (The jamovi project (2025), jamovi Version 2.6) and Microsoft Excel (Microsoft Corporation, Redmond, WA, USA). Results A total of 205 VBT procedures were performed in 180 patients at our institution. Of these, 25 patients underwent bilateral VBT and 33 underwent hybrid surgery. After matching, 30 patients were included in the present study. The mean follow-up for the whole cohort was 39.2 ± 14.3 (24.2–85.4) months. Mean follow-up for the bilateral VBT cohort was 46.8 ± 16.3 (25.9–85.4) months, while the mean follow-up for the hybrid cohort was 32.5 ± 5.7 (24.2–41.7) months. After follow-up equalization, the pairwise capped mean follow-up was 31.3 ± 5.5 (24.2–41.7) months. Demographics and skeletal maturity Twenty-nine (96.7%) patients were female. There were 15 patients in each cohort. The mean age of patients in bilateral VBT and hybrid cohorts was 13.0 ± 1.5 years and 13.3 ± 1.3 years, respectively (p = 0.541). No statistical differences were observed regarding skeletal maturity preoperatively (p > 0.05 for all indexes). At the latest follow-up ≤ cap, 14 patients (93.3%) in the bilateral VBT cohort and 10 patients (66.7%) in the hybrid cohort had limited growth potential (Sanders ≥ 7). Perioperative data Preoperatively the two cohorts were similar in terms of body weight, height and BMI (p = 0.838, p = 0.907 and p = 0.689, respectively). Surgical time, EBL and LOS were similar between the 2 cohorts (p = 0.404, p = 0.142 and p = 0.141, respectively). Regarding instrumented levels, the median number of lumbar tethered levels was similar, with a median of 5 tethered levels for both the bilateral VBT and hybrid cohorts (p = 0.362). On the contrary, hybrid cohort had a significantly higher number of thoracic instrumented levels with a median of 11 fused levels compared to 7 tethered levels for the bilateral VBT cohort (p < 0.001). Patients baseline characteristics and perioperative data along with mean paired differences are summarized in table 1. Radiographic Outcomes Preoperative PT, MT and TL/L curve magnitudes were similar between the 2 cohorts (p = 0.056, p = 0.686 and p = 0.736, respectively), as well as TK and LL (p = 0.989 and p = 0.405, respectively). There were no significant differences in preoperative flexibility both for MT and TL/L curves (p = 0.444 and p = 0.639, respectively). Postoperatively, the hybrid cohort demonstrated significantly lower PT and MT curve magnitudes than bilateral VBT cohort, with a paired difference (hybrid−bilateral) of -13.0° and − 20.0°, respectively (p < 0.001 and p < 0.001, respectively). This was accompanied by a significantly greater surgical correction rate for both the MT and TL/L curves in the hybrid cohort (+ 33.8% and + 11.4%, respectively; p < 0.001 and p = 0.045). Although the TL/L coronal Cobb angle at first erect X-ray was lower in the hybrid group (− 5.5°), this did not reach statistical significance. No significant differences were observed between the two cohorts in terms of sagittal alignment at first-erect X-ray. At the latest follow-up ≤ cap, the hybrid cohort continued to show significantly lower PT, MT, and TL/L curve magnitudes (− 8.9°, − 16.1°, and − 9.6°, respectively; p = 0.020, p < 0.001, and p = 0.010), along with higher total correction rates for MT and TL/L curves (+ 26.9% and + 19.7%, respectively; p < 0.001 and p = 0.019). At latest follow-up ≤ cap, a greater proportion of patients in the hybrid cohort achieved residual curve magnitudes ≤ 30° for both MT and TL/L curves compared to the bilateral VBT cohort (93.3% vs 66.7% and, 86.7% vs 46.7% respectively), with statistical significance observed only for the MT curve (p = 0.041 and p = 0.168, respectively). No patient in the hybrid cohort had an MT curve ≥ 40°, whereas 5 patients (33.3%) in the bilateral VBT cohort did, representing potential candidates for revision with PSF (p = 0.042). For the TL/L curve, no patient in the hybrid cohort had a curve ≥ 40°, compared with two patients in the bilateral VBT cohort. Detailed coronal and sagittal radiographic outcomes, correction rates, and mean paired differences are presented in Table 2. Pulmonary function test analysis Pre-operative FVC% predicted and FEV1% predicted were comparable between the two cohorts (p = 0.197 and p = 0.326, respectively). At latest follow-up ≤ cap, no significant differences were observed regarding both FVC% and FEV1% predicted (p = 0.342 and p = 0.411, respectively). Within-group analysis showed an increase in FVC% predicted in the bilateral VBT cohort (81.3 ± 12.9 to 96.3 ± 31.7), which did not reach statistical significance (p = 0.061). When comparing the total changes between groups, no differences were observed in both ΔFVC% and ΔFEV1% predicted (p = 0.089 and p = 0.245, respectively). PFTs data are summarize in Table 3. Patient reported outcomes analysis Both cohorts demonstrated improvement across all SRS domains. A smaller improvement in the Function domain was observed in the hybrid cohort compared to the bilateral VBT cohort (0.08 ± 0.55 vs 0.63 ± 0.65), with a mean paired difference (hybrid−bilateral) of − 0.55 ± 0.62 (p = 0.026). No significant differences were observed between cohorts in the Pain, Self-image, Mental Health, and Sub-total domains (all p > 0.05). Improvement in Self-image was higher in the hybrid cohort (1.05 ± 0.76 vs 0.76 ± 0.96) without statistical significance (p = 0.391). At MCID analysis, a lower proportion of patients in the hybrid cohort achieved MCID in the Function domain compared to the bilateral VBT cohort (23% vs 57%, p = 0.072). No significant differences were observed in MCID achievement for the remaining domains. PROMs data are summarized in Table 4. Complication analysis No pulmonary complications were observed in either cohort. Overcorrection occurred in four patients (26.7%) in the hybrid cohort and in two patients (13.3%) in the bilateral VBT cohort (p = 0.651). No cases of curve worsening were observed in the hybrid cohort, compared with 3 patients (20.0%) in the bilateral VBT cohort (p = 0.224). Similarly, no new Cobb formation was observed in the hybrid cohort, whereas one patient (6.7%) in the bilateral VBT cohort during follow-up. Tether breakage occurred in 6 patients (40.0%) in the hybrid cohort and in 12 patients (80.0%) in the bilateral VBT cohort (p = 0.060). No implant failures or other mechanical complications were documented. One patient (6.7%) in the bilateral VBT cohort developed postural orthostatic tachycardia. No readmissions or reoperations were recorded within the matched cohort during the capped follow-up period. Tether-breakage-free survival analysis Kaplan–Meier analysis showed a trend toward higher tether breakage–free survival in the hybrid cohort ( Fig. 1 ). At 12 months, tether breakage-free survival was 100% in the hybrid cohort versus 86.7% (95%CI 56.4–96.5) in the bilateral VBT cohort. At 24 months, tether breakage-free survivals were 73.3% (95%CI 43.6–89.1) and 60.0% (95%CI 31.8–79.7) in the hybrid and bilateral VBT cohort, respectively. However, the difference between cohort did not reach statistical significance (p = 0.246). Cox proportional hazards analysis showed a non-significant trend toward a higher risk of tether breakage in the bilateral VBT cohort (p = 0.249). Discussion In this matched cohort study with pairwise follow-up equalization, hybrid surgery combining STF with TL/L VBT was associated with lower coronal curve magnitudes and higher correction rates compared to bilateral VBT, both postoperatively and at latest follow-up ≤ cap. A higher proportion of patients in the hybrid cohort achieved residual curves ≤ 30°, while larger residual curves (≥ 40°) were observed only in the bilateral VBT cohort. Pulmonary function and most patient-reported outcomes were comparable between groups, although greater improvement in the Function domain was noted in the bilateral cohort. Complication rates were similar overall; however, tether breakage was more frequent in the bilateral VBT cohort, with a corresponding trend toward higher tether breakage–free survival in the hybrid group. The strong superiority of hybrid surgery regarding both the PT and MT curve correction should be interpreted also in light of the absence of anatomical limitations on proximal thoracic spine instrumentation in STF. Thoracic VBT instrumentation typically extends up to T5, and only rarely to T4. ( Fig. 2 . ) In contrast, STF routinely allows instrumentation up to the proximal end vertebra and, when required, direct control of the PT curve by extending the construct proximally to T2. ( Fig. 3 . ) These findings are consistent with those reported by Newton et al [ 27 ]. Regarding the lumbar curve, only moderate differences emerged between the two cohorts on first-erect X-rays, whereas at latest follow-up, hybrid surgery showed a significant superiority for both TL/L curve magnitude and total correction rate. This finding may be interpreted by considering lumbar VBT as an enhancer of SLCC. Several studies investigated SLCC after STF[ 28 – 31 ] and thoracic VBT[ 17 , 32 – 34 ]. The available evidence on STF suggests a strong correlation between the intraoperative MT correction rate and subsequent SLCC (p < 0.001 for all the reports) [ 28 – 31 ]. Catanzano et al.[ 34 ] reported a similar correlation in a cohort of 218 patients undergoing thoracic VBT. Despite a similar proportional relationship, the absolute SLCC has been reported to be lower after thoracic VBT [ 27 , 32 – 34 ] than after STF [ 28 , 29 , 31 ] at a minimum 2-year follow-up. Accordingly, greater MT correction results in greater SLCC [ 28 ], thereby reducing the amount of correction required at the lumbar level and, in the present setting, the tension required on the lumbar tether. This interpretation may partially explain the tendency toward lower absolute tether breakage rate and increased tether breakage–free survival observed in the hybrid cohort. Likewise, the significant superiority of the hybrid cohort at latest follow-up, both in terms of TL/L total correction rate and residual TL/L curve magnitude, may reflect a relative loss of correction in the bilateral VBT cohort secondary to early tether breakages. Despite inferior radiographic outcomes, bilateral VBT showed a greater improvement in the function domain of the SRS-22, highlighting that, although thoracic motion preservation after VBT appears limited[ 19 ], it may still play a role in the patient’s postoperative functional perception. PFT outcomes did not differ significantly between groups, both at baseline and at latest follow-up. The bilateral VBT cohort showed a nonsignificant trend toward greater FVC improvement, possibly reflecting more physiological thoracic cage biomechanics and development during adolescence. The paradigm of hybrid surgery is based on a trade-off between deformity correction and motion preservation, combining the benefits of PSF in the relatively less mobile thoracic spine [ 19 ] with TL/L VBT [ 23 ]. By contrast, the completely fusionless strategy of bilateral VBT appears to come at the cost of reduced corrective power and lower predictability of results [ 10 , 17 ], to the point that Pahys et al.[ 17 ] questioned the additive value of lumbar VBT in Lenke 1C curves, showing that bilateral VBT neither provided greater TL/L correction nor improved TL/L curve magnitude compared with thoracic-only VBT. A possible explanation for these suboptimal results of bilateral VBT across heterogeneous curve patterns is the large number of difficult-to-control variables inherent to this approach, including differential thoracic and lumbar flexibility, disc maturity and soft tissue behavior, tether mechanics, intraoperative amount of correction, relationship between thoracic and lumbar modulation over time, and loss of correction after tether breakage. The final outcome of bilateral VBT depends not only on the intraoperative result, but also on balanced postoperative modulation of both curves and, most importantly, on preventing overcorrection of the transitional segment between the two curves. This event, which is relatively frequent in the proximal lumbar spine, may lead to thoracic curve adding-on and postoperative coronal imbalance[ 10 ]. The main advantage of hybrid surgery may lie in its greater predictability, as STF is a well standardized and reproducible procedure [ 1 , 35 – 37 ], therefore hybrid surgery may be viewed as a conceptual extension of STF for patients with double curves who fall outside the traditional indications for isolated STF, thoracic VBT, or lumbar VBT, as part of a selective motion-preserving strategy. To the best of our knowledge, this is the first study directly comparing hybrid surgery and bilateral VBT using individual patient matching based on skeletal maturity and TL/L curve magnitude, follow-up equalization, and outcome assessment after a mean capped follow-up exceeding 2 years. The limitations of the present study should be acknowledged. First, despite individual matching and pairwise follow-up capping, the retrospective design may have introduced selection bias. In addition, the matching process itself may have generated further selection bias by selectively excluding curve patterns more frequently treated with one of the two techniques. Furthermore, the study lacks established criteria for bilateral VBT or hybrid surgery, given the substantial overlap in indications. The decision was at the discretion of the surgeon and may therefore not have been consistent throughout the study period, particularly given the progressive shift from bilateral VBT to hybrid surgery for double-curve patterns. This temporal trend may also have been associated with technical improvements related to increasing surgical experience. Second, the sample size remained limited, which likely reduced the statistical power to detect differences in implant survival and tether breakage despite consistent trends favoring the hybrid cohort. Third, the present analysis did not include objective clinical measures of thoracic asymmetry or rib hump, thereby limiting the ability to directly support the proposed aesthetic advantage of hybrid surgery. Finally, longer-term follow-up investigations with larger cohorts will be necessary to determine whether the observed radiographic differences are maintained into adulthood along with the quality-of-life outcomes. Conclusion In this matched cohort analysis with follow-up equalization, hybrid surgery combining selective thoracic fusion with lumbar VBT demonstrated superior radiographic outcomes compared with bilateral VBT in patients with double-curve AIS. Hybrid cohort showed greater correction of both thoracic and TL/L curves and resulted in a higher proportion of patients reaching acceptable residual curve magnitudes at latest follow-up ≤ cap. Despite inferior radiographic outcomes, bilateral VBT demonstrated greater improvement in the SRS-22 function domain. Overall, hybrid surgery may represent a balanced treatment strategy that combines reliable deformity correction with selective motion preservation. Declarations Ethical statement The study received approval from the appropriate ethical review board before being conducted, which ensures that the research adhered to ethical standards and regulations. The requirement of obtaining informed consent from all patients was waived due to the retrospective nature of the study. Competing Interests AA has received grants from DePuy Synthes and Medtronic, consultancy fees from Globus and HighRidge Medical, and royalties from Highridge. CY serves as a consultant for Medtronic. The remaining authors (AY, FW, MT, FK, CF, TZ, EGC, SS, GE) declare that they have no conflict of interest. Author Contribution AA and AY did the conception and designed the manuscript. CY, FK, FW and CF analyzed and interpreted details. MT drafted the manuscript. EGC and TZ collected the data. 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Eur Spine J 16:1335–1342 Kluck D, Sullivan TB, Bastrom TP, Bartley CE, Yaszay B, Newton PO (2021) Predictors of spontaneous lumbar curve correction in thoracic-only fusions: 3D analysis in AIS. Spine Deformity 9:461–469 Givens RR, Malka MS, Rymond CC, Lu K, Miyanji F, Rodriguez JC, Smit K, El-Hawary R, Parent S, Truong WH (2025) Behavior of the un-instrumented lumbar curve following exclusive tethering of the thoracic region. Spine Deformity :1–12 Miyanji F, Pawelek J, Nasto LA, Simmonds A, Parent S (2020) Safety and efficacy of anterior vertebral body tethering in the treatment of idiopathic scoliosis: a multicentre review of 57 consecutive patients. bone joint J 102:1703–1708 Catanzano AA Jr, Newton PO, Bastrom TP, Bartley CE, Parent S, Miyanji F, Hoernschemeyer DG, Alanay A, Blakemore L, Neal K (2022) Spontaneous lumbar curve correction following vertebral body tethering of main thoracic curves. JBJS 104:1629–1638 Edwards CC, Lenke LG, Peelle M, Sides B, Rinella A, Bridwell KH (2004) Selective thoracic fusion for adolescent idiopathic scoliosis with C modifier lumbar curves: 2-to 16-year radiographic and clinical results. Spine 29:536–546 Larson AN, Fletcher ND, Daniel C, Richards BS (2012) Lumbar curve is stable after selective thoracic fusion for adolescent idiopathic scoliosis: a 20-year follow-up. Spine 37:833–839 Lonstein JE (2018) Selective thoracic fusion for adolescent idiopathic scoliosis: long-term radiographic and functional outcomes. Spine deformity 6:669–675 Tables Tables 1 to 4 are available in the Supplementary Files section. Additional Declarations Competing interest reported. AA has received grants from DePuy Synthes and Medtronic, consultancy fees from Globus and HighRidge Medical, and royalties from Highridge. CY serves as a consultant for Medtronic. The remaining authors (AY, FW, MT, FK, CF, TZ, EGC, SS, GE) declare that they have no conflict of interest. Supplementary Files Table1.Patientsbaselinecharacteristicsandperioperativedata.jpeg Table2.Radiographicoutcomesdata.jpeg Table3.Pulmonaryfunctiontestanalysis.jpeg Table4.Patientsreportedoutcomesdata.jpeg Supplementarymaterialfile1SurgicalTechnique.docx Cite Share Download PDF Status: Under Review Version 1 posted Reviews received at journal 07 May, 2026 Reviewers agreed at journal 28 Apr, 2026 Reviewers agreed at journal 28 Apr, 2026 Reviewers invited by journal 28 Apr, 2026 Editor assigned by journal 13 Apr, 2026 Submission checks completed at journal 13 Apr, 2026 First submitted to journal 08 Apr, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9355992","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":631321701,"identity":"f3a4a673-686a-45d4-830a-1a6722bdb1f8","order_by":0,"name":"Matteo Traversari","email":"","orcid":"","institution":"Orthopaedic and Traumatologic Clinic, IRCCS Istituto Ortopedico Rizzoli","correspondingAuthor":false,"prefix":"","firstName":"Matteo","middleName":"","lastName":"Traversari","suffix":""},{"id":631321702,"identity":"36462aca-f35c-4f30-a0aa-8691e0cb19a5","order_by":1,"name":"Altug Yucekul","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAyklEQVRIiWNgGAWjYNCCAwwy/CA6oYAELTySDSAtBqRoMTgAYhCjhX9GjuGHD2cO8xifX5344YEBgzy/2AH8WiRu5BhLzrhxmMfsxtvNEkCHGc6cnUDAmhs5Zsw8H0Bazm4AaUkwuE1AizxIyx+gFuMZZzf/IEqLAUgLA9BhBvy924izxfDMs2LJnjPpPBI3eLdZJBhIEPaL3PHkjR9+HLOW4+8/u/nmjwobeX5pAloYBGAKJMAMCQLKQYD/ADpjFIyCUTAKRgEaAABWj0dwZi90JgAAAABJRU5ErkJggg==","orcid":"","institution":"Acibadem Mehmet Ali Aydinlar University School of Medicine, Department of Orthopedics and Traumatology","correspondingAuthor":true,"prefix":"","firstName":"Altug","middleName":"","lastName":"Yucekul","suffix":""},{"id":631321703,"identity":"a73cf2a6-afd8-4843-8e88-e54576fbeca0","order_by":2,"name":"Feyzi Kilic","email":"","orcid":"","institution":"Comprehensive Spine Center, Acibadem University Maslak Hospital","correspondingAuthor":false,"prefix":"","firstName":"Feyzi","middleName":"","lastName":"Kilic","suffix":""},{"id":631321704,"identity":"c773e692-4afa-4672-b596-ce28abef44f0","order_by":3,"name":"Fedde Weenink","email":"","orcid":"","institution":"Vrije Universiteit Amsterdam Faculty of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Fedde","middleName":"","lastName":"Weenink","suffix":""},{"id":631321705,"identity":"49b8d795-2b02-43db-9c86-bc114866fdba","order_by":4,"name":"Gokhan Ergene","email":"","orcid":"","institution":"Department of Operating Room Services, Acibadem Mehmet Ali Aydinlar University Vocational School of Health Sciences","correspondingAuthor":false,"prefix":"","firstName":"Gokhan","middleName":"","lastName":"Ergene","suffix":""},{"id":631321706,"identity":"81a6c6ee-2263-412a-bbc7-7fdc18ae4bc7","order_by":5,"name":"Sahin Senay","email":"","orcid":"","institution":"Department of Cardiovascular Surgery, Acibadem Mehmet Ali Aydinlar University School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Sahin","middleName":"","lastName":"Senay","suffix":""},{"id":631321707,"identity":"798ee9f9-d432-4fce-b7cb-d7017ca84cd9","order_by":6,"name":"Cesare Faldini","email":"","orcid":"","institution":"Orthopaedic and Traumatologic Clinic, IRCCS Istituto Ortopedico Rizzoli","correspondingAuthor":false,"prefix":"","firstName":"Cesare","middleName":"","lastName":"Faldini","suffix":""},{"id":631321708,"identity":"7ab5f060-0638-426d-987b-85ec75ea4c26","order_by":7,"name":"Elif Gizem Carus","email":"","orcid":"","institution":"Comprehensive Spine Center, Acibadem University Maslak Hospital","correspondingAuthor":false,"prefix":"","firstName":"Elif","middleName":"Gizem","lastName":"Carus","suffix":""},{"id":631321709,"identity":"dd58a05e-b7f7-432f-b06a-5f9085d83b7a","order_by":8,"name":"Tais Zulemyan","email":"","orcid":"","institution":"Comprehensive Spine Center, Acibadem University Maslak Hospital","correspondingAuthor":false,"prefix":"","firstName":"Tais","middleName":"","lastName":"Zulemyan","suffix":""},{"id":631321710,"identity":"d55e67d9-43bc-4621-ab21-85df3fc42448","order_by":9,"name":"Caglar Yilgor","email":"","orcid":"","institution":"Koc University, Koc University Hospital Spine Center","correspondingAuthor":false,"prefix":"","firstName":"Caglar","middleName":"","lastName":"Yilgor","suffix":""},{"id":631321711,"identity":"9f9bfd95-670b-4d9f-8f90-9d13186daa67","order_by":10,"name":"Ahmet Alanay","email":"","orcid":"","institution":"Acibadem Mehmet Ali Aydinlar University School of Medicine, Department of Orthopedics and Traumatology","correspondingAuthor":false,"prefix":"","firstName":"Ahmet","middleName":"","lastName":"Alanay","suffix":""}],"badges":[],"createdAt":"2026-04-08 11:00:53","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9355992/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9355992/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":108950503,"identity":"35426b7c-6146-4fb6-b519-183066f9a9eb","added_by":"auto","created_at":"2026-05-11 07:05:55","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":60792,"visible":true,"origin":"","legend":"\u003cp\u003eTether breakage-free survival analysis. Kaplan-Meier analysis showed a tendency to higher tether breakage-free survival in hybrid cohort without reaching statistical significance. At 12 months, survival was 100% and 86.7% in the hybrid and bilateral VBT cohort, respectively. At 24 months, survival was 73.3% and 60% in the hybrid and bilateral VBT cohort, respectively (p=0.246).\u003c/p\u003e","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9355992/v1/50c18c80c37d6a772d79cee0.jpeg"},{"id":108977818,"identity":"85ff60c8-c7b4-4cfe-ae94-fd7d42491e08","added_by":"auto","created_at":"2026-05-11 11:33:03","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":276089,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eExemplificative patient from the bilateral VBT cohort. \u003c/strong\u003e11 years old patient with Lenke 1CN curve pattern, skeletal maturity indexes were TRC closed, Risser 0, SSMS 3B and CVM 4. Preoperatively, coronal Cobb angles of MT and TL/L curves were 66° and 50°, respectively. At first erect X-ray, coronal Cobb angles of MT and TL/L curves reduced to 33° and 20°, respectively. A L2-L3 tether breakage was observed at 36 months of follow-up. At latest follow-up≤cap (36 months), the patient showed Risser 4, SSMS 8 and CVM 5. Coronal Cobb angles of MT and TL/L curves were 21° and 25°, respectively.\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9355992/v1/cbd8f3e442090181b1616357.jpeg"},{"id":108950507,"identity":"1ef3752c-f072-40c4-b2d0-e16e12762fa2","added_by":"auto","created_at":"2026-05-11 07:05:55","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":311891,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eExemplificative patient from the hybrid cohort.\u003c/strong\u003e12 years old patient with Lenke 4CN curve pattern, skeletal maturity indexes were TRC closed, Risser 1, SSMS 4 and CVM 4. Preoperatively, coronal Cobb angles of MT and TL/L curves were 80° and 56°, respectively. At first erect X-ray, coronal Cobb angles of MT and TL/L curves reduced to 10° and 7°, respectively. A minor overcorrection occurred in the proximal lumbar spine. At latest follow-up≤cap (39 months), the patient showed Risser 5, SSMS 8 and CVM 5. Coronal Cobb angles of MT and TL/L curves were 11° and -4°, respectively.\u003c/p\u003e","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9355992/v1/8a80bcf764b548d1a394e3ca.jpeg"},{"id":109082844,"identity":"0afbf690-0354-4a6d-b63e-005a6c919fe8","added_by":"auto","created_at":"2026-05-12 12:44:24","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":873779,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9355992/v1/d1c688d0-fa3d-4e4e-9c1c-e34fd3c240ba.pdf"},{"id":108978014,"identity":"6eb94c8e-ca5e-4a83-a998-6fe9b03f05d5","added_by":"auto","created_at":"2026-05-11 11:33:42","extension":"jpeg","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":306833,"visible":true,"origin":"","legend":"","description":"","filename":"Table1.Patientsbaselinecharacteristicsandperioperativedata.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9355992/v1/024b6237488e081ff3bfbf3e.jpeg"},{"id":109081478,"identity":"7ec44007-5499-431a-aede-2b171aea5811","added_by":"auto","created_at":"2026-05-12 12:18:43","extension":"jpeg","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":508074,"visible":true,"origin":"","legend":"","description":"","filename":"Table2.Radiographicoutcomesdata.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9355992/v1/7e0f2d948943735d277061dd.jpeg"},{"id":108950505,"identity":"3dadd382-0cb5-49e5-bdb6-adfd555ba0f6","added_by":"auto","created_at":"2026-05-11 07:05:55","extension":"jpeg","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":128841,"visible":true,"origin":"","legend":"","description":"","filename":"Table3.Pulmonaryfunctiontestanalysis.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9355992/v1/924bff2491061eed0ca2b337.jpeg"},{"id":108950508,"identity":"bebec29e-73ad-42c6-b8f6-50ec778b9fd4","added_by":"auto","created_at":"2026-05-11 07:05:55","extension":"jpeg","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":194559,"visible":true,"origin":"","legend":"","description":"","filename":"Table4.Patientsreportedoutcomesdata.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9355992/v1/d45dc01d4b1af11dbb1c7f9e.jpeg"},{"id":108950509,"identity":"8623f501-ee52-4e77-8325-799362a2d4bc","added_by":"auto","created_at":"2026-05-11 07:05:55","extension":"docx","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":15393,"visible":true,"origin":"","legend":"","description":"","filename":"Supplementarymaterialfile1SurgicalTechnique.docx","url":"https://assets-eu.researchsquare.com/files/rs-9355992/v1/e0c60ccfd55dd90ef494bab6.docx"}],"financialInterests":"Competing interest reported. AA has received grants from DePuy Synthes and Medtronic, consultancy fees from Globus and HighRidge Medical, and royalties from Highridge. CY serves as a consultant for Medtronic. The remaining authors (AY, FW, MT, FK, CF, TZ, EGC, SS, GE) declare that they have no conflict of interest.","formattedTitle":"Hybrid Fusion–Tether Strategy vs Bilateral Vertebral Body Tethering for Double Curves in AIS: A Matched Cohort Analysis with Follow-up Equalization","fulltext":[{"header":"Introduction","content":"\u003cp\u003ePosterior spinal fusion (PSF) is the current gold standard for treating progressive or severe adolescent idiopathic scoliosis (AIS).[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e] Vertebral body tethering (VBT) is an alternative fusionless technique indicated for skeletally immature AIS patients.[\u003cspan additionalcitationids=\"CR3\" citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/p\u003e \u003cp\u003eVBT allows correction of the spine curvature while maintaining a certain degree of spinal flexibility and enabling continued deformity correction through growth modulation, according to the Hueter\u0026ndash;Volkmann principle [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Motion preservation becomes more important when there is a need to extend fusion into the lumbar spine [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. In cases of double major curves or thoracic curves with a significant compensatory lumbar curve (e.g. Lenke 1C), several authors have recently extended VBT to the thoracolumbar/lumbar (TL/L) spine in addition to thoracic VBT [\u003cspan additionalcitationids=\"CR10 CR11 CR12 CR13 CR14 CR15 CR16 CR17 CR18\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. While some have reported favorable outcomes with bilateral VBT, others have raised concerns regarding the safety of the technique, reporting high rates of tether breakage, revision surgeries and suboptimal correction [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTrunk motion analysis studies have demonstrated negligible preservation of spinal mobility following thoracic VBT [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e] compared to the lumbar spine [\u003cspan additionalcitationids=\"CR21\" citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThis has led to a progressive abandonment of thoracic VBT in cases that do not strictly meet the criteria for ideal candidates [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. However, the importance of preserving lumbar spinal mobility remains undeniable. Therefore, some authors have introduced a hybrid strategy combining selective thoracic fusion (STF) with lumbar VBT [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTo date, there is no comparative data regarding these two techniques. The aim of the present study is to compare bilateral VBT and hybrid surgery in terms of efficacy and safety through a matched, follow-up\u0026ndash;equalized evaluation of radiographic, patient-reported, pulmonary, complication, and implant-survival outcomes.\u003c/p\u003e"},{"header":"Material and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStudy design\u003c/h2\u003e \u003cp\u003e A retrospective matched cohort study was conducted in an ethics board approved single-center prospectively recorded dataset of consecutive patients treated with VBT. A 1:1 matched cohort was created to compare bilateral VBT and hybrid surgery (STF combined with TL/L VBT). Matching was performed using a greedy 1:1 nearest-neighbor matching without replacement applied using predefined clinical criteria: preoperative TL/L Cobb angle within \u0026plusmn;\u0026thinsp;5\u0026deg;, Simplified Skeletal Maturity Staging (SSMS) within \u0026plusmn;\u0026thinsp;1, Cervical vertebral maturation (CVM) within \u0026plusmn;\u0026thinsp;2. In case of multiple potential matches, pairs were selected according to the smallest absolute difference in preoperative TL/L Cobb angle, followed by SSMS, and then CVM stage. The matching process yielded 15 matched pairs. Standardized mean differences (SMD) were used to assess covariate balance between groups. Preoperative balance was considered acceptable when SMD\u0026thinsp;\u0026lt;\u0026thinsp;0.25. To ensure comparable follow-up duration between matched pairs, all longitudinal analyses were capped at the shorter follow-up time of each pair (latest follow-up \u0026le;\u0026thinsp;cap).\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003ePatients’ characteristics and inclusion criteria\u003c/h3\u003e\n\u003cp\u003ePatients who were diagnosed with AIS that had undergone either bilateral VBT or hybrid surgery with at least 24 months of follow-up were included. Patients who did not have a preoperative whole-body biplanar EOS scanning image with a concomitant left-hand radiograph, patients who reached skeletal maturity pre-operatively and patients who had undergone previous spine surgeries were excluded.\u003c/p\u003e\n\u003ch3\u003eSurgical technique\u003c/h3\u003e\n\u003cp\u003eThoracoscopic and retroperitoneal approaches were performed by thoracic and vascular access surgeons, respectively. Details regarding surgical technique of VBT and postoperative care are given in previous papers [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], and in supplementary material file 1.\u003c/p\u003e \u003cp\u003eRegarding STF, the fusion levels were defined as follows: the upper instrumented vertebra (UIV) was selected between T2 and T4 based on preoperative shoulder balance and the structural or compensatory nature of the proximal thoracic (PT) curve [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. The lower instrumented vertebra (LIV) was chosen as the neutral vertebra (NV) or NV\u0026thinsp;+\u0026thinsp;1 depending on the degree of NV translation from the central sacral vertical line (CSVL), in accordance with the last substantially touched vertebra (LSTV) concept [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. All pedicle screws were placed under intra-operative CT-guided navigation [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Two 6mm cobalt-chrome rods were asymmetrically contoured to the desired postoperative sagittal alignment and to achieve indirect vertebral derotation. In situ correction with segmental compression/distraction was performed to optimize local alignment.\u003c/p\u003e \u003cp\u003eBilateral VBT surgeries were applied as same-day two-stage surgeries. When hybrid surgery required proximal extension of VBT instrumentation to L1 or above, ipsilateral thoracoscopic approach was used and the tether was passed from the thoracic cage to the retroperitoneal space. Staging of the hybrid procedure was based on intraoperative degree of spontaneous lumbar curve correction (SLCC) and STF operative time. In cases of relevant SLCC, lumbar VBT was staged and postoperative full-body standing EOS imaging was obtained to assess the need for additional lumbar VBT. In staged patients, the average interval between the two operation was 7 days.\u003c/p\u003e\n\u003ch3\u003eDemographic, radiographic, pulmonary and clinical data\u003c/h3\u003e\n\u003cp\u003eDemographic data included age at surgery, gender and ethnicity. Preoperative body weight, height and body mass index (BMI) were collected. Skeletal maturity data included Modified Risser score, SSMS and CVM. Perioperative data included surgical technique, operative time, estimated blood loss (EBL), length of hospital stay (LOS), Intensive care unit (ICU) requirement and the number of levels tethered/fused both in the thoracic and TL/L spine.\u003c/p\u003e \u003cp\u003eRadiographic data included PT, main thoracic (MT) and TL/L coronal measurements and flexibility percentages, thoracic kyphosis (TK) and lumbar lordosis (LL) Cobb angles, preoperatively, postoperatively and at the latest follow-up \u0026le;\u0026thinsp;cap. Surgical (pre- to postoperative) and total (preoperative to latest follow-up \u0026le;\u0026thinsp;cap) correction percentages were calculated. Measurements were done using a validated software (Sectra IDS7, Sectra AB, Sweden). Percent predicted FVC (FVC%) and percent predicted FEV1 (FEV1%) were recorded, along with SRS-22 questionnaires, preoperatively and yearly at each postoperative follow-up time point.\u003c/p\u003e\n\u003ch3\u003eOutcome Measures\u003c/h3\u003e\n\u003cdiv class=\"Heading\"\u003eOutcome Measures\u003c/div\u003e \u003cp\u003eA negative sign was assigned to an overcorrected curve. Pulmonary, mechanical and curve behavior complications, readmissions and reoperations were noted. Broken tethers were indicated by \u0026ge;\u0026thinsp;6\u0026deg; increase of angulation between adjacent screws between any two postoperative radiographs.\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eStatistical Analysis\u003c/h2\u003e \u003cp\u003eContinuous variables are presented as mean\u0026plusmn;standard deviation (SD) or median (range) and categorical variables as counts and percentages. All parameters were evaluated for normal distribution with the Shapiro\u0026ndash;Wilk test. Between-group comparisons for continuous variables were performed using Student\u0026rsquo;s t-test, Welch\u0026rsquo;s t-test, or the Mann\u0026ndash;Whitney U test. Categorical variables were compared using the chi-square or Fisher\u0026rsquo;s exact test. Survival analysis was performed using the Kaplan\u0026ndash;Meier method and compared between groups with the log-rank test. Cox proportional hazards analysis was used to estimate the relative risk of tether breakage between groups. p\u0026thinsp;\u0026lt;\u0026thinsp;0.05 was considered significant. Statistical analyses were performed using Jamovi statistical analysis software (The jamovi project (2025), jamovi Version 2.6) and Microsoft Excel (Microsoft Corporation, Redmond, WA, USA).\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eA total of 205 VBT procedures were performed in 180 patients at our institution. Of these, 25 patients underwent bilateral VBT and 33 underwent hybrid surgery. After matching, 30 patients were included in the present study.\u003c/p\u003e \u003cp\u003eThe mean follow-up for the whole cohort was 39.2\u0026thinsp;\u0026plusmn;\u0026thinsp;14.3 (24.2\u0026ndash;85.4) months. Mean follow-up for the bilateral VBT cohort was 46.8\u0026thinsp;\u0026plusmn;\u0026thinsp;16.3 (25.9\u0026ndash;85.4) months, while the mean follow-up for the hybrid cohort was 32.5\u0026thinsp;\u0026plusmn;\u0026thinsp;5.7 (24.2\u0026ndash;41.7) months.\u003c/p\u003e \u003cp\u003eAfter follow-up equalization, the pairwise capped mean follow-up was 31.3\u0026thinsp;\u0026plusmn;\u0026thinsp;5.5 (24.2\u0026ndash;41.7) months.\u003c/p\u003e\n\u003ch3\u003eDemographics and skeletal maturity\u003c/h3\u003e\n\u003cp\u003eTwenty-nine (96.7%) patients were female. There were 15 patients in each cohort. The mean age of patients in bilateral VBT and hybrid cohorts was 13.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.5 years and 13.3\u0026thinsp;\u0026plusmn;\u0026thinsp;1.3 years, respectively (p\u0026thinsp;=\u0026thinsp;0.541). No statistical differences were observed regarding skeletal maturity preoperatively (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05 for all indexes). At the latest follow-up \u0026le;\u0026thinsp;cap, 14 patients (93.3%) in the bilateral VBT cohort and 10 patients (66.7%) in the hybrid cohort had limited growth potential (Sanders\u0026thinsp;\u0026ge;\u0026thinsp;7).\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003ePerioperative data\u003c/h2\u003e \u003cp\u003ePreoperatively the two cohorts were similar in terms of body weight, height and BMI (p\u0026thinsp;=\u0026thinsp;0.838, p\u0026thinsp;=\u0026thinsp;0.907 and p\u0026thinsp;=\u0026thinsp;0.689, respectively). Surgical time, EBL and LOS were similar between the 2 cohorts (p\u0026thinsp;=\u0026thinsp;0.404, p\u0026thinsp;=\u0026thinsp;0.142 and p\u0026thinsp;=\u0026thinsp;0.141, respectively).\u003c/p\u003e \u003cp\u003eRegarding instrumented levels, the median number of lumbar tethered levels was similar, with a median of 5 tethered levels for both the bilateral VBT and hybrid cohorts (p\u0026thinsp;=\u0026thinsp;0.362). On the contrary, hybrid cohort had a significantly higher number of thoracic instrumented levels with a median of 11 fused levels compared to 7 tethered levels for the bilateral VBT cohort (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001).\u003c/p\u003e \u003cp\u003ePatients baseline characteristics and perioperative data along with mean paired differences are summarized in table 1.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eRadiographic Outcomes\u003c/h2\u003e \u003cp\u003ePreoperative PT, MT and TL/L curve magnitudes were similar between the 2 cohorts (p\u0026thinsp;=\u0026thinsp;0.056, p\u0026thinsp;=\u0026thinsp;0.686 and p\u0026thinsp;=\u0026thinsp;0.736, respectively), as well as TK and LL (p\u0026thinsp;=\u0026thinsp;0.989 and p\u0026thinsp;=\u0026thinsp;0.405, respectively). There were no significant differences in preoperative flexibility both for MT and TL/L curves (p\u0026thinsp;=\u0026thinsp;0.444 and p\u0026thinsp;=\u0026thinsp;0.639, respectively).\u003c/p\u003e \u003cp\u003ePostoperatively, the hybrid cohort demonstrated significantly lower PT and MT curve magnitudes than bilateral VBT cohort, with a paired difference\u003csub\u003e(hybrid\u0026minus;bilateral)\u003c/sub\u003e of -13.0\u0026deg; and \u0026minus;\u0026thinsp;20.0\u0026deg;, respectively (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001 and p\u0026thinsp;\u0026lt;\u0026thinsp;0.001, respectively). This was accompanied by a significantly greater surgical correction rate for both the MT and TL/L curves in the hybrid cohort (+\u0026thinsp;33.8% and +\u0026thinsp;11.4%, respectively; p\u0026thinsp;\u0026lt;\u0026thinsp;0.001 and p\u0026thinsp;=\u0026thinsp;0.045). Although the TL/L coronal Cobb angle at first erect X-ray was lower in the hybrid group (\u0026minus;\u0026thinsp;5.5\u0026deg;), this did not reach statistical significance. No significant differences were observed between the two cohorts in terms of sagittal alignment at first-erect X-ray. At the latest follow-up \u0026le;\u0026thinsp;cap, the hybrid cohort continued to show significantly lower PT, MT, and TL/L curve magnitudes (\u0026minus;\u0026thinsp;8.9\u0026deg;, \u0026minus;\u0026thinsp;16.1\u0026deg;, and \u0026minus;\u0026thinsp;9.6\u0026deg;, respectively; p\u0026thinsp;=\u0026thinsp;0.020, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001, and p\u0026thinsp;=\u0026thinsp;0.010), along with higher total correction rates for MT and TL/L curves (+\u0026thinsp;26.9% and +\u0026thinsp;19.7%, respectively; p\u0026thinsp;\u0026lt;\u0026thinsp;0.001 and p\u0026thinsp;=\u0026thinsp;0.019).\u003c/p\u003e \u003cp\u003eAt latest follow-up \u0026le;\u0026thinsp;cap, a greater proportion of patients in the hybrid cohort achieved residual curve magnitudes\u0026thinsp;\u0026le;\u0026thinsp;30\u0026deg; for both MT and TL/L curves compared to the bilateral VBT cohort (93.3% vs 66.7% and, 86.7% vs 46.7% respectively), with statistical significance observed only for the MT curve (p\u0026thinsp;=\u0026thinsp;0.041 and p\u0026thinsp;=\u0026thinsp;0.168, respectively). No patient in the hybrid cohort had an MT curve\u0026thinsp;\u0026ge;\u0026thinsp;40\u0026deg;, whereas 5 patients (33.3%) in the bilateral VBT cohort did, representing potential candidates for revision with PSF (p\u0026thinsp;=\u0026thinsp;0.042). For the TL/L curve, no patient in the hybrid cohort had a curve\u0026thinsp;\u0026ge;\u0026thinsp;40\u0026deg;, compared with two patients in the bilateral VBT cohort. Detailed coronal and sagittal radiographic outcomes, correction rates, and mean paired differences are presented in Table\u0026nbsp;2.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003ePulmonary function test analysis\u003c/h2\u003e \u003cp\u003ePre-operative FVC% predicted and FEV1% predicted were comparable between the two cohorts (p\u0026thinsp;=\u0026thinsp;0.197 and p\u0026thinsp;=\u0026thinsp;0.326, respectively). At latest follow-up \u0026le;\u0026thinsp;cap, no significant differences were observed regarding both FVC% and FEV1% predicted (p\u0026thinsp;=\u0026thinsp;0.342 and p\u0026thinsp;=\u0026thinsp;0.411, respectively). Within-group analysis showed an increase in FVC% predicted in the bilateral VBT cohort (81.3\u0026thinsp;\u0026plusmn;\u0026thinsp;12.9 to 96.3\u0026thinsp;\u0026plusmn;\u0026thinsp;31.7), which did not reach statistical significance (p\u0026thinsp;=\u0026thinsp;0.061).\u003c/p\u003e \u003cp\u003eWhen comparing the total changes between groups, no differences were observed in both ΔFVC% and ΔFEV1% predicted (p\u0026thinsp;=\u0026thinsp;0.089 and p\u0026thinsp;=\u0026thinsp;0.245, respectively). PFTs data are summarize in Table\u0026nbsp;3.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003ePatient reported outcomes analysis\u003c/h2\u003e \u003cp\u003eBoth cohorts demonstrated improvement across all SRS domains. A smaller improvement in the Function domain was observed in the hybrid cohort compared to the bilateral VBT cohort (0.08\u0026thinsp;\u0026plusmn;\u0026thinsp;0.55 vs 0.63\u0026thinsp;\u0026plusmn;\u0026thinsp;0.65), with a mean paired difference \u003csub\u003e(hybrid\u0026minus;bilateral)\u003c/sub\u003e of \u0026minus;\u0026thinsp;0.55\u0026thinsp;\u0026plusmn;\u0026thinsp;0.62 (p\u0026thinsp;=\u0026thinsp;0.026). No significant differences were observed between cohorts in the Pain, Self-image, Mental Health, and Sub-total domains (all p\u0026thinsp;\u0026gt;\u0026thinsp;0.05). Improvement in Self-image was higher in the hybrid cohort (1.05\u0026thinsp;\u0026plusmn;\u0026thinsp;0.76 vs 0.76\u0026thinsp;\u0026plusmn;\u0026thinsp;0.96) without statistical significance (p\u0026thinsp;=\u0026thinsp;0.391).\u003c/p\u003e \u003cp\u003eAt MCID analysis, a lower proportion of patients in the hybrid cohort achieved MCID in the Function domain compared to the bilateral VBT cohort (23% vs 57%, p\u0026thinsp;=\u0026thinsp;0.072). No significant differences were observed in MCID achievement for the remaining domains. PROMs data are summarized in Table\u0026nbsp;4.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eComplication analysis\u003c/h2\u003e \u003cp\u003eNo pulmonary complications were observed in either cohort. Overcorrection occurred in four patients (26.7%) in the hybrid cohort and in two patients (13.3%) in the bilateral VBT cohort (p\u0026thinsp;=\u0026thinsp;0.651). No cases of curve worsening were observed in the hybrid cohort, compared with 3 patients (20.0%) in the bilateral VBT cohort (p\u0026thinsp;=\u0026thinsp;0.224). Similarly, no new Cobb formation was observed in the hybrid cohort, whereas one patient (6.7%) in the bilateral VBT cohort during follow-up.\u003c/p\u003e \u003cp\u003eTether breakage occurred in 6 patients (40.0%) in the hybrid cohort and in 12 patients (80.0%) in the bilateral VBT cohort (p\u0026thinsp;=\u0026thinsp;0.060). No implant failures or other mechanical complications were documented. One patient (6.7%) in the bilateral VBT cohort developed postural orthostatic tachycardia. No readmissions or reoperations were recorded within the matched cohort during the capped follow-up period.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eTether-breakage-free survival analysis\u003c/h2\u003e \u003cp\u003eKaplan\u0026ndash;Meier analysis showed a trend toward higher tether breakage\u0026ndash;free survival in the hybrid cohort \u003cb\u003e(\u003c/b\u003eFig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e\u003cb\u003e).\u003c/b\u003e At 12 months, tether breakage-free survival was 100% in the hybrid cohort versus 86.7% (95%CI 56.4\u0026ndash;96.5) in the bilateral VBT cohort. At 24 months, tether breakage-free survivals were 73.3% (95%CI 43.6\u0026ndash;89.1) and 60.0% (95%CI 31.8\u0026ndash;79.7) in the hybrid and bilateral VBT cohort, respectively. However, the difference between cohort did not reach statistical significance (p\u0026thinsp;=\u0026thinsp;0.246). Cox proportional hazards analysis showed a non-significant trend toward a higher risk of tether breakage in the bilateral VBT cohort (p\u0026thinsp;=\u0026thinsp;0.249).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn this matched cohort study with pairwise follow-up equalization, hybrid surgery combining STF with TL/L VBT was associated with lower coronal curve magnitudes and higher correction rates compared to bilateral VBT, both postoperatively and at latest follow-up \u0026le;\u0026thinsp;cap. A higher proportion of patients in the hybrid cohort achieved residual curves\u0026thinsp;\u0026le;\u0026thinsp;30\u0026deg;, while larger residual curves (\u0026ge;\u0026thinsp;40\u0026deg;) were observed only in the bilateral VBT cohort. Pulmonary function and most patient-reported outcomes were comparable between groups, although greater improvement in the Function domain was noted in the bilateral cohort. Complication rates were similar overall; however, tether breakage was more frequent in the bilateral VBT cohort, with a corresponding trend toward higher tether breakage\u0026ndash;free survival in the hybrid group.\u003c/p\u003e \u003cp\u003eThe strong superiority of hybrid surgery regarding both the PT and MT curve correction should be interpreted also in light of the absence of anatomical limitations on proximal thoracic spine instrumentation in STF. Thoracic VBT instrumentation typically extends up to T5, and only rarely to T4. \u003cb\u003e(\u003c/b\u003eFig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003cb\u003e)\u003c/b\u003e In contrast, STF routinely allows instrumentation up to the proximal end vertebra and, when required, direct control of the PT curve by extending the construct proximally to T2. \u003cb\u003e(\u003c/b\u003eFig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003cb\u003e)\u003c/b\u003e These findings are consistent with those reported by Newton et al [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eRegarding the lumbar curve, only moderate differences emerged between the two cohorts on first-erect X-rays, whereas at latest follow-up, hybrid surgery showed a significant superiority for both TL/L curve magnitude and total correction rate. This finding may be interpreted by considering lumbar VBT as an enhancer of SLCC. Several studies investigated SLCC after STF[\u003cspan additionalcitationids=\"CR29 CR30\" citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e] and thoracic VBT[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan additionalcitationids=\"CR33\" citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. The available evidence on STF suggests a strong correlation between the intraoperative MT correction rate and subsequent SLCC (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001 for all the reports) [\u003cspan additionalcitationids=\"CR29 CR30\" citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. Catanzano et al.[\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e] reported a similar correlation in a cohort of 218 patients undergoing thoracic VBT. Despite a similar proportional relationship, the absolute SLCC has been reported to be lower after thoracic VBT [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan additionalcitationids=\"CR33\" citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e] than after STF [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e] at a minimum 2-year follow-up. Accordingly, greater MT correction results in greater SLCC [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e], thereby reducing the amount of correction required at the lumbar level and, in the present setting, the tension required on the lumbar tether. This interpretation may partially explain the tendency toward lower absolute tether breakage rate and increased tether breakage\u0026ndash;free survival observed in the hybrid cohort. Likewise, the significant superiority of the hybrid cohort at latest follow-up, both in terms of TL/L total correction rate and residual TL/L curve magnitude, may reflect a relative loss of correction in the bilateral VBT cohort secondary to early tether breakages.\u003c/p\u003e \u003cp\u003eDespite inferior radiographic outcomes, bilateral VBT showed a greater improvement in the function domain of the SRS-22, highlighting that, although thoracic motion preservation after VBT appears limited[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e], it may still play a role in the patient\u0026rsquo;s postoperative functional perception. PFT outcomes did not differ significantly between groups, both at baseline and at latest follow-up. The bilateral VBT cohort showed a nonsignificant trend toward greater FVC improvement, possibly reflecting more physiological thoracic cage biomechanics and development during adolescence.\u003c/p\u003e \u003cp\u003eThe paradigm of hybrid surgery is based on a trade-off between deformity correction and motion preservation, combining the benefits of PSF in the relatively less mobile thoracic spine [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e] with TL/L VBT [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. By contrast, the completely fusionless strategy of bilateral VBT appears to come at the cost of reduced corrective power and lower predictability of results [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e], to the point that Pahys et al.[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] questioned the additive value of lumbar VBT in Lenke 1C curves, showing that bilateral VBT neither provided greater TL/L correction nor improved TL/L curve magnitude compared with thoracic-only VBT.\u003c/p\u003e \u003cp\u003eA possible explanation for these suboptimal results of bilateral VBT across heterogeneous curve patterns is the large number of difficult-to-control variables inherent to this approach, including differential thoracic and lumbar flexibility, disc maturity and soft tissue behavior, tether mechanics, intraoperative amount of correction, relationship between thoracic and lumbar modulation over time, and loss of correction after tether breakage.\u003c/p\u003e \u003cp\u003eThe final outcome of bilateral VBT depends not only on the intraoperative result, but also on balanced postoperative modulation of both curves and, most importantly, on preventing overcorrection of the transitional segment between the two curves. This event, which is relatively frequent in the proximal lumbar spine, may lead to thoracic curve adding-on and postoperative coronal imbalance[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. The main advantage of hybrid surgery may lie in its greater predictability, as STF is a well standardized and reproducible procedure [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan additionalcitationids=\"CR36\" citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e], therefore hybrid surgery may be viewed as a conceptual extension of STF for patients with double curves who fall outside the traditional indications for isolated STF, thoracic VBT, or lumbar VBT, as part of a selective motion-preserving strategy.\u003c/p\u003e \u003cp\u003eTo the best of our knowledge, this is the first study directly comparing hybrid surgery and bilateral VBT using individual patient matching based on skeletal maturity and TL/L curve magnitude, follow-up equalization, and outcome assessment after a mean capped follow-up exceeding 2 years.\u003c/p\u003e \u003cp\u003eThe limitations of the present study should be acknowledged. First, despite individual matching and pairwise follow-up capping, the retrospective design may have introduced selection bias. In addition, the matching process itself may have generated further selection bias by selectively excluding curve patterns more frequently treated with one of the two techniques.\u003c/p\u003e \u003cp\u003eFurthermore, the study lacks established criteria for bilateral VBT or hybrid surgery, given the substantial overlap in indications. The decision was at the discretion of the surgeon and may therefore not have been consistent throughout the study period, particularly given the progressive shift from bilateral VBT to hybrid surgery for double-curve patterns. This temporal trend may also have been associated with technical improvements related to increasing surgical experience.\u003c/p\u003e \u003cp\u003eSecond, the sample size remained limited, which likely reduced the statistical power to detect differences in implant survival and tether breakage despite consistent trends favoring the hybrid cohort. Third, the present analysis did not include objective clinical measures of thoracic asymmetry or rib hump, thereby limiting the ability to directly support the proposed aesthetic advantage of hybrid surgery. Finally, longer-term follow-up investigations with larger cohorts will be necessary to determine whether the observed radiographic differences are maintained into adulthood along with the quality-of-life outcomes.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn this matched cohort analysis with follow-up equalization, hybrid surgery combining selective thoracic fusion with lumbar VBT demonstrated superior radiographic outcomes compared with bilateral VBT in patients with double-curve AIS. Hybrid cohort showed greater correction of both thoracic and TL/L curves and resulted in a higher proportion of patients reaching acceptable residual curve magnitudes at latest follow-up \u0026le;\u0026thinsp;cap. Despite inferior radiographic outcomes, bilateral VBT demonstrated greater improvement in the SRS-22 function domain. Overall, hybrid surgery may represent a balanced treatment strategy that combines reliable deformity correction with selective motion preservation.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003cem\u003eEthical statement\u003c/em\u003e \u003c/p\u003e \u003cp\u003e The study received approval from the appropriate ethical review board before being conducted, which ensures that the research adhered to ethical standards and regulations. The requirement of obtaining informed consent from all patients was waived due to the retrospective nature of the study.\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eCompeting Interests\u003c/strong\u003e\u003cp\u003eAA has received grants from DePuy Synthes and Medtronic, consultancy fees from Globus and HighRidge Medical, and royalties from Highridge. CY serves as a consultant for Medtronic. The remaining authors (AY, FW, MT, FK, CF, TZ, EGC, SS, GE) declare that they have no conflict of interest.\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eAA and AY did the conception and designed the manuscript. CY, FK, FW and CF analyzed and interpreted details. MT drafted the manuscript. EGC and TZ collected the data. AA and AY critically revised the manuscript. AA supervised the manuscript. All authors read and approved the submitted version of the manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eLenke LG, Betz RR, Harms J, Bridwell KH, Clements DH, Lowe TG, Blanke K (2001) Adolescent idiopathic scoliosis: a new classification to determine extent of spinal arthrodesis. JBJS 83:1169\u0026ndash;1181\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAlanay A, Yucekul A, Abul K, Ergene G, Senay S, Ay B, Cebeci BO, Dikmen PY, Zulemyan T, Yavuz Y (2020) Thoracoscopic vertebral body tethering for adolescent idiopathic scoliosis: follow-up curve behavior according to sanders skeletal maturity staging. Spine 45:E1483\u0026ndash;E1492\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHoernschemeyer DG, Boeyer ME, Robertson ME, Loftis CM, Worley JR, Tweedy NM, Gupta SU, Duren DL, Holzhauser CM, Ramachandran VM (2020) Anterior vertebral body tethering for adolescent scoliosis with growth remaining: a retrospective review of 2 to 5-year postoperative results. JBJS 102:1169\u0026ndash;1176\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNugraha HK, Haber LL, Hoernschemeyer DG, Cahill PJ, Samdani AF, Miyanji F, Newton PO, Larson AN, Group HS (2026) Outcomes of Vertebral Body Tethering in Adolescent Idiopathic Scoliosis: A Prospective, Multicenter Study. JBJS Open Access 11:e25\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNewton PO, Bartley CE, Bastrom TP, Kluck DG, Saito W, Yaszay B (2020) Anterior spinal growth modulation in skeletally immature patients with idiopathic scoliosis: a comparison with posterior spinal fusion at 2 to 5 years postoperatively. JBJS 102:769\u0026ndash;777\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNewton PO, Farnsworth CL, Faro FD, Mahar AT, Odell TR, Mohamad F, Breisch E, Fricka K, Upasani VV, Amiel D (2008) Spinal growth modulation with an anterolateral flexible tether in an immature bovine model: disc health and motion preservation. Spine 33:724\u0026ndash;733\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNohara A, Kawakami N, Seki K, Tsuji T, Ohara T, Saito T, Kawakami K (2015) The effects of spinal fusion on lumbar disc degeneration in patients with adolescent idiopathic scoliosis: a minimum 10-year follow-up. Spine deformity 3:462\u0026ndash;468\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eOhashi M, Bastrom TP, Marks MC, Bartley CE, Newton PO (2020) The benefits of sparing lumbar motion segments in spinal fusion for adolescent idiopathic scoliosis are evident at 10 years postoperatively. Spine 45:755\u0026ndash;763\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eStein AA, Samdani AF, Sch\u0026uuml;pper AJ, Zeller S, Naseer ZA, Pahys JM, Quinonez A, Nice E, Kirk K, Hwang SW (2025) Bilateral anterior lumbar vertebral body tethering: a feasibility cohort study. Spine Deformity :1\u0026ndash;6\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHoernschemeyer DG, Elliott P, Lonner BS, Eaker L, Boeyer ME (2024) Bilateral vertebral body tethering: identifying key factors associated with successful outcomes. Eur Spine J 33:723\u0026ndash;731\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDe Varona-Cocero A, Ani F, Kim N, Robertson D, Myers C, Ashayeri K, Maglaras C, Protopsaltis T, Rodriguez-Olaverri JC (2025) Correction of L5 Tilt in 2-row vertebral body tethering versus posterior spinal fusion for adolescent idiopathic scoliosis. Clin Spine Surg 38:E186\u0026ndash;E192\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLonner B, Eaker L, Hoernschemeyer D, Zhang J, Wilczek A, Elliot P, Boeyer ME, Fletcher ND, Alanay A, Yilgor C (2024) Double major curvature treated with vertebral body tethering of both curves: how do outcomes compare to posterior spinal fusion? Spine Deformity 12:651\u0026ndash;662\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePehlivanoglu T, Oltulu I, Erdag Y, Korkmaz E, Sarioglu E, Ofluoglu E, Aydogan M (2021) Double-sided vertebral body tethering of double adolescent idiopathic scoliosis curves: radiographic outcomes of the first 13 patients with 2 years of follow-up. Eur Spine J 30:1896\u0026ndash;1904\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTrobisch PD, Kim HJ, Da Paz S, Chang D-G (2024) The efficacy of anterior vertebral body tethering in lenke type 6 curves for adolescent idiopathic scoliosis. Eur Spine J 33:2696\u0026ndash;2703\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBaroncini A, Rodriguez L, Verma K, Trobisch PD (2021) Feasibility of single-staged bilateral anterior scoliosis correction in growing patients. Global spine J 11:76\u0026ndash;80\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLau D, Kurland DB, Neifert S, Pahys J, Samdani A, Hwang S (2025) Learning curve associated with thoracoscopic anterior vertebral body tether and double anterior vertebral body tether for idiopathic scoliosis: analysis of three independent surgeons. Operative Neurosurg 28:43\u0026ndash;51\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePahys JM, Samdani AF, Quinonez A, Hwang SW (2025) Outcomes of Single-sided Thoracic Versus Bilateral Thoracic and Lumbar Anterior Vertebral Body Tethering in Lenke 1 Curves With Lumbar C Modifier. Spine 50:1516\u0026ndash;1522\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTrobisch PD, Baroncini A (2021) Preliminary outcomes after vertebral body tethering (VBT) for lumbar curves and subanalysis of a 1-versus 2-tether construct. Eur Spine J 30:3570\u0026ndash;3576\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePahys JM, Samdani AF, Hwang SW, Warshauer S, Gaughan JP, Chafetz RS (2022) Trunk range of motion and patient outcomes after anterior vertebral body tethering versus posterior spinal fusion: comparison using computerized 3D motion capture technology. JBJS 104:1563\u0026ndash;1572\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMathew SE, Milbrandt TA, Larson AN (2022) Measurable lumbar motion remains 1 year after vertebral body tethering. J Pediatr Orthop 42:e861\u0026ndash;e867\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNicolini LF, Kobbe P, Seggewi\u0026szlig; J, Greven J, Ribeiro M, Beckmann A, Da Paz S, Eschweiler J, Prescher A, Markert B (2022) Motion preservation surgery for scoliosis with a vertebral body tethering system: a biomechanical study. Eur Spine J 31:1013\u0026ndash;1021\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRibeiro M, Fancello EA, Seggewi\u0026szlig; J, Greven J, Prescher A, Markert B, Stoffel M, Beckmann A, Da Paz S, Trobisch PD (2025) Segmental range of motion of vertebral body tethering: an in-vitro analysis of single-tether, double-tether, and hybrid constructs. J Orthop Surg Res 20:1015\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCherian D, Samdani AF, Sch\u0026uuml;pper AJ, Stein AA, Naseer Z, Pahys JM, Nice E, Hwang SW (2023) Early outcomes in hybrid fixation for idiopathic scoliosis: posterior fusion combined with anterior vertebral body tethering. Patient series. Journal of Neurosurgery: Case Lessons 6\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYucekul A, Demirci N, Akpunarli B, Kindan P, Kilic F, Carus EG, Zulemyan T, Ergene G, Senay S, Turgut S (2025) Two to five years pulmonary functions after thoracic, thoracolumbar and bilateral vertebral body tethering surgery. Eur Spine J 34:2750\u0026ndash;2761\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eQin X, Sun W, Xu L, Liu Z, Qiu Y, Zhu Z (2016) Selecting the last substantially touching vertebra as lowest instrumented vertebra in Lenke type 1A curve: radiographic outcomes with a minimum of 2-year follow-up. Spine 41:E742\u0026ndash;E750\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eOba H, Ebata S, Takahashi J, Koyama K, Uehara M, Kato H, Haro H, Ohba T (2018) Pedicle perforation while inserting screws using O-arm navigation during surgery for adolescent idiopathic scoliosis: risk factors and effect of insertion order. Spine 43:E1463\u0026ndash;E1468\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNewton PO, Parent S, Miyanji F, Alanay A, Lonner BS, Neal KM, Hoernschemeyer DG, Yaszay B, Blakemore LC, Shah SA (2022) Anterior vertebral body tethering compared with posterior spinal fusion for major thoracic curves: a retrospective comparison by the Harms Study Group. JBJS 104:2170\u0026ndash;2177\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKoller H, Hitzl W, Marks M, Newton P (2019) Accurate prediction of spontaneous lumbar curve correction following posterior selective thoracic fusion in adolescent idiopathic scoliosis using logistic regression models and clinical rationale. Eur Spine J 28:1987\u0026ndash;1997\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChang K-W, Chang K-I, Wu C-M (2007) Enhanced Capacity for spontaneous correction of lumbar curve in the treatment of major thoracic\u0026ndash;compensatory C modifier lumbar curve pattern in idiopathic scoliosis. Spine 32:3020\u0026ndash;3029\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJansen RC, van Rhijn LW, Duinkerke E, van Ooij A (2007) Predictability of the spontaneous lumbar curve correction after selective thoracic fusion in idiopathic scoliosis. Eur Spine J 16:1335\u0026ndash;1342\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKluck D, Sullivan TB, Bastrom TP, Bartley CE, Yaszay B, Newton PO (2021) Predictors of spontaneous lumbar curve correction in thoracic-only fusions: 3D analysis in AIS. Spine Deformity 9:461\u0026ndash;469\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGivens RR, Malka MS, Rymond CC, Lu K, Miyanji F, Rodriguez JC, Smit K, El-Hawary R, Parent S, Truong WH (2025) Behavior of the un-instrumented lumbar curve following exclusive tethering of the thoracic region. Spine Deformity :1\u0026ndash;12\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMiyanji F, Pawelek J, Nasto LA, Simmonds A, Parent S (2020) Safety and efficacy of anterior vertebral body tethering in the treatment of idiopathic scoliosis: a multicentre review of 57 consecutive patients. bone joint J 102:1703\u0026ndash;1708\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCatanzano AA Jr, Newton PO, Bastrom TP, Bartley CE, Parent S, Miyanji F, Hoernschemeyer DG, Alanay A, Blakemore L, Neal K (2022) Spontaneous lumbar curve correction following vertebral body tethering of main thoracic curves. JBJS 104:1629\u0026ndash;1638\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEdwards CC, Lenke LG, Peelle M, Sides B, Rinella A, Bridwell KH (2004) Selective thoracic fusion for adolescent idiopathic scoliosis with C modifier lumbar curves: 2-to 16-year radiographic and clinical results. Spine 29:536\u0026ndash;546\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLarson AN, Fletcher ND, Daniel C, Richards BS (2012) Lumbar curve is stable after selective thoracic fusion for adolescent idiopathic scoliosis: a 20-year follow-up. Spine 37:833\u0026ndash;839\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLonstein JE (2018) Selective thoracic fusion for adolescent idiopathic scoliosis: long-term radiographic and functional outcomes. Spine deformity 6:669\u0026ndash;675\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTables 1 to 4 are available in the Supplementary Files section.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"european-spine-journal","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"esjo","sideBox":"Learn more about [European Spine Journal](http://link.springer.com/journal/586)","snPcode":"586","submissionUrl":"https://submission.springernature.com/new-submission/586/3","title":"European Spine Journal","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Vertebral body tethering, VBT, Double-sided VBT, Bilateral VBT, Tether breakage, Adolescent idiopathic scoliosis, Adolescent spinal deformities, Growth modulation, Posterior spinal fusion, Hybrid","lastPublishedDoi":"10.21203/rs.3.rs-9355992/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9355992/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cb\u003ePurpose\u003c/b\u003e\u003c/p\u003e \u003cp\u003eVertebral body tethering (VBT) has emerged as a fusionless alternative for the treatment of adolescent idiopathic scoliosis (AIS) in skeletally immature patients. In patients presenting with double (false or major) curve patterns, bilateral VBT has been proposed as a fully motion-preserving strategy, although concerns remain regarding its corrective power and mechanical reliability. Hybrid constructs combining selective thoracic fusion (STF) with lumbar VBT have recently been introduced. The aim of this study is to compare bilateral VBT and hybrid surgery in terms of radiographic, patient-reported, pulmonary, complication, and implant-survival outcomes.\u003c/p\u003e\u003cp\u003e\u003cb\u003eMethods\u003c/b\u003e\u003c/p\u003e \u003cp\u003eA retrospective matched cohort study was conducted using a prospectively collected dataset of AIS patients treated with either bilateral VBT or hybrid surgery. A 1:1 matched cohort (15 pairs) was created using greedy nearest-neighbor matching based on preoperative thoracolumbar/lumbar (TL/L) Cobb angle, Sanders maturity stage, and cervical vertebral maturation. Follow-up was pairwise equalized by capping the analysis at the shorter follow-up time of each pair. Radiographic outcomes, pulmonary function tests, SRS-22 scores, complications, and tether breakage\u0026ndash;free survival were analyzed.\u003c/p\u003e\u003cp\u003e\u003cb\u003eResults\u003c/b\u003e\u003c/p\u003e \u003cp\u003eThirty patients (15 bilateral VBT, 15 hybrid) were included with a mean capped follow-up of 31.3 months. Hybrid surgery demonstrated significantly greater correction of both thoracic and TL/L curves at first-erect and latest follow-up \u0026le;\u0026thinsp;cap (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). A higher proportion of patients in the hybrid cohort achieved residual thoracic curves\u0026thinsp;\u0026le;\u0026thinsp;30\u0026deg; (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Bilateral VBT showed greater improvement in the SRS-22 function domain (p\u0026thinsp;=\u0026thinsp;0.026). Tether breakage occurred more frequently in the bilateral VBT cohort, although the difference did not reach statistical significance.\u003c/p\u003e\u003cp\u003e\u003cb\u003eConclusion\u003c/b\u003e\u003c/p\u003e \u003cp\u003eHybrid surgery combining STF with lumbar VBT provided superior radiographic results compared with bilateral VBT in patients with double-curve AIS. While bilateral VBT demonstrated greater improvement in functional patient-reported outcomes, hybrid constructs may offer greater deformity correction and result predictability while preserving lumbar motion segments.\u003c/p\u003e","manuscriptTitle":"Hybrid Fusion–Tether Strategy vs Bilateral Vertebral Body Tethering for Double Curves in AIS: A Matched Cohort Analysis with Follow-up Equalization","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-05-11 07:05:35","doi":"10.21203/rs.3.rs-9355992/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"editorInvitedReview","content":"","date":"2026-05-07T07:19:49+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"145221622443288648955700485558901822296","date":"2026-04-28T20:44:00+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"54267676532714561802738609856013135903","date":"2026-04-28T15:11:46+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-04-28T14:05:34+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-04-13T11:19:40+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-04-13T11:19:26+00:00","index":"","fulltext":""},{"type":"submitted","content":"European Spine Journal","date":"2026-04-08T10:43:15+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"european-spine-journal","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"esjo","sideBox":"Learn more about [European Spine Journal](http://link.springer.com/journal/586)","snPcode":"586","submissionUrl":"https://submission.springernature.com/new-submission/586/3","title":"European Spine Journal","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"8476f28f-932f-4a34-9078-a070d993f7a5","owner":[],"postedDate":"May 11th, 2026","published":true,"recentEditorialEvents":[{"type":"editorInvitedReview","content":"","date":"2026-05-07T07:19:49+00:00","index":12,"fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-11T07:05:36+00:00","versionOfRecord":[],"versionCreatedAt":"2026-05-11 07:05:35","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9355992","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9355992","identity":"rs-9355992","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}