Rate of Scoliosis Correction After Anterior Spinal Growth Tethering for Idiopathic Scoliosis

Subclassification of Sanders Maturation Stage 3 Demonstrates Differences in Spine and Total Height Velocity Between 3A and 3B in Patients With Idiopathic Scoliosis

STUDY DESIGN

A single-center retrospective case-control study.

OBJECTIVE

To compare the spine and total height velocity between Sanders maturation stage (SMS) 3A and 3B.

SUMMARY OF BACKGROUND DATA

Identifying SMS 3 is critical for treating growing children because it represents the early phase of rapid adolescent growth. However, there is limited literature available that clearly describes the growth differences between 3A and 3B.

MATERIALS AND METHODS

The current study included consecutive patients with idiopathic scoliosis staged SMS 3 from January 2012 to December 2021. T1-S1 spine height, total body height, and curve magnitude were measured at the initial and follow-up visits. In addition to the spine and total height velocity calculated per month, corrected height velocity was estimated for curve magnitude using a validated formula. Mann-Whitney U test was used to compare SMS 3A and 3B outcomes, followed by a multiple linear regression model to evaluate the association of the SMS subclassifications to growth velocity adjusted for confounding factors.

RESULTS

A total of 204 patients (66% girls, mean age: 12.3±1.3 y) met the inclusion criteria. Patients staged SMS 3A had higher spine height velocity (mm/month) in both girls (2.3 vs. 1.5, P <0.001) and boys (2.6 vs. 1.7, P <0.001), as well as total height velocity [mm/month; (5.8 vs. 4.3, P <0.001 for girls; 6.6 vs. 4.5, P <0.001 for boys]. Corrected velocity showed similar results with greater spine and total height velocity in SMS 3A. Multivariate analysis indicated a significant association of the SMS subclassification to the spine and total height velocity. The scoliosis curve progression was comparable between SMS 3A and 3B.

CONCLUSIONS

SMS 3A and 3B had differential growth velocity in the spine and total body height. These results indicate the importance of the SMS 3 subclassification for managing scoliosis treatment, including observation, bracing, and surgical interventions with fusion and growth modulation.

LEVEL OF EVIDENCE

Level III-case-control study.

Learning Curve Associated With Thoracoscopic Anterior Vertebral Body Tether and Double Anterior Vertebral Body Tether for Idiopathic Scoliosis: Analysis of Three Independent Surgeons

BACKGROUND AND OBJECTIVES

Anterior vertebral body tether (VBT) is a fusionless approach to treat idiopathic scoliosis, and surgeons are beginning to implement the technique into current practice. This study aims to evaluate the learning curve for single and double VBT.

METHODS

A retrospective review of 3 surgeons' first 40 single and 20 double VBT was performed. Skeletally immature patients with idiopathic scoliosis who underwent thoracic (single) or thoracolumbar (double) VBT were included. Thoracic VBT was done via video-assisted thoracoscopic surgery and lumbar VBT through a mini-open retroperitoneal approach. Primary outcomes of interest were operative time, radiation exposure, and radiographic correction. Pooled and individual-surgeon analyses were performed.

RESULTS

A total of 180 patients were included: 120 single and 60 double. Mean age was 12.7 years, and 87.8% were female. Mean segments tethered was 7.8 in single and 11.0 in double. Mean preoperative thoracic scoliosis was 51.5: single 50.5° and double 53.3°. Mean lumbar scoliosis was 36.4°: single 30.0° and double 49.0°. Average operating time was 276.2 minutes; double VBT was significantly longer (217.3 vs 394.0 minutes, P < .001). Mean blood loss was 198.5 mL, and mean fluoroscopy dose was 73.0 mGy. For single VBT, there was a decrease in operative time (283.3-174.8 minutes, P < .001) and fluoroscopy dose (70.1-53.5 mGy, P = .047) over time. Every 10 cases resulted in a 31.4 minute decrease in operative time (P < .001). There were no intraoperative complications. Single VBT resulted in 54.9% thoracic curve correction. Double VBT achieved 53.0% thoracic and 56.7% lumbar correction. There were no differences in curve correction across the learning curve.

CONCLUSION

VBT is viable fusionless surgical option for scoliosis. As expected, increased experience resulted in shorter operative time; the threshold for such improvement seems to be 10 cases. Importantly, adequate and consistent curve correction can be achieved at the start of the learning curve while mitigating complications.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Thoracoscopic Anterior Vertebral Body Tethering in Lenke Type-1 Right Adolescent Idiopathic Scoliosis

Background

Vertebral body tethering (VBT) is indicated for skeletally immature patients with progressive adolescent idiopathic scoliosis (AIS) who have failed or are intolerant of bracing and who have a major coronal curve of 40° to 65°. The vertebral body must be structurally and dimensionally adequate to accommodate screw fixation, as determined radiographically. The best indication for VBT is a flexible single major thoracic curve with nonstructural compensating lumbar and proximal thoracic curves (Lenke 1A or 1B). VBT allows for progressive correction of the deformity without spinal fusion by utilizing a minimally invasive fluoroscopic technique.

Description

The procedure for a right thoracic curve is performed with use of a right thoracoscopic approach with the patient in the left lateral decubitus position. The thoracoscope is introduced through a portal at the apex of the curvature in the posterior axillary line. Instrument portals are created lateral to each vertebral body in the mid-axillary line. Screws are inserted into each vertebral body under biplanar fluoroscopic control and with intraoperative neuromonitoring. An electroconductivity probing device, while not mandatory, is routinely utilized at our practice. The tether is attached to the most proximal screw of the construct, and then reduction is obtained sequentially by tensioning the tether from one vertebral screw to the next.

Alternatives

Bracing is the gold-standard treatment for progressive AIS involving the immature spine. The most commonly utilized surgical treatment is posterior spinal fusion (PSF), which should be considered when the major coronal curve exceeds 45°.

Rationale

PSF has proven to be a dependable technique to correct scoliotic deformities. It has a low complication rate and good long-term outcomes. However, concerns exist regarding the stiffness conferred by PSF and the long-term effects of adjacent segment disease. Thus, interest had developed in non-fusion solutions for AIS correction. VBT utilizes the Hueter-Volkmann principle to guide growth and correct deformity. Compressive forces applied to the convexity of the deformity by a polyethylene tether allow the patient's growth to realign the spine. Intraoperative correction triggers growth modulation, and most of the modulation seems to occur during the first 12 months postoperatively. The best results have been seen with a short Lenke type-1A curve in a patient with closed triradiate cartilage, a Risser 3 or lower (ideally Risser 0) iliac apophysis, and a flexible curve characterized by a 50% reduction of the major coronal curve angle on side-bending radiographs.

Expected Outcomes

In 57 immature patients with a Lenke type-1A or 1B curve (i.e., a 30° to 65° preoperative Cobb angle), Samdani et al.3 found a main thoracic Cobb angle reduction from 40° ± 7° preoperatively to 19° ± 13° at 2 years after VBT. In the sagittal plane, the T5-T12 kyphosis measured 15° ± 10° preoperatively, 17° ± 10° postoperatively, and 20° ± 13° at 2 years. No major neurologic or pulmonary complications occurred. A total of 7 (12.3%) of the 57 patients underwent surgical revision, including 5 for overcorrection and 2 to span additional vertebrae. In a study of 21 skeletally mature patients, Pehlivanoglu et al.4 found that the Cobb angle was reduced from 48° preoperatively to 16° on the first-erect postoperative radiograph and finally to 10° at the latest follow-up (mean, 27.4 months). The 2 main complications of VBT reported in the literature are overcorrection and tether breakage. Both may require revision, which explains the higher rate of revision observed for VBT compared with PSF.

Important Tips

Good patient selection is important. VBT is most appropriate in cases of a flexible Lenke type-1A or 1B curve in an immature child before Risser stage 3 and after triradiate cartilage closure.Always monitor and control screw positioning in both anteroposterior and lateral planes fluoroscopically.The screws should be placed parallel to the vertebral end plates or, even better, be angled inferiorly for the upper vertebrae and angled superiorly for the lower vertebrae to decrease the risk of pull-out when tensioning the device and during growth modulation. Less tension on the uppermost and lowermost instrumented vertebrae than at the apex, as controlled by the tensioning device, can also help to limit pull-out.

Acronyms and Abbreviations

VBT = vertebral body tetheringAIS = adolescent idiopathic scoliosisIONM = intraoperative neuromonitoringPSF = posterior spinal fusionUIV = upper instrumented vertebraLIV = lower instrumented vertebraAP = anteroposteriorK-wire = Kirschner wire.

Posterior Vertebral Pedicular Tethering for the Treatment of Idiopathic Adolescent Scoliosis

Over the last decade, there has been a new wave of interest in non-fusion techniques for the treatment of adolescent idiopathic scoliosis. These are not new techniques, as they were first published and presented in the late 1950s, using compression of the convexity or distraction of the concavity of the main curvature. More recently, anterior vertebral body tethering has raised great interest, as although it is a major procedure through the child's chest, it seems appropriate for the thoracic curves. The main objective of this article is to describe Posterior Vertebral Pedicular Tethering (PVPT) as a "new" technique performed as a less invasive spinal procedure for the treatment of certain thoracolumbar and lumbar scoliosis in growing adolescents. It is an alternative growth modulation technique appropriate for thoracolumbar and lumbar curvatures where we observe reduction of the three plane deformity of idiopathic scoliosis in adolescents.

Vertebral Body Tethering in AIS Management-A Preliminary Report

Vertebral Body Tethering (VBT) is a recently developed surgical technique for the treatment of progressive and severe scoliosis in patients with significant growth potential. It has been used since the first exploratory series, which showed encouraging results on the progressive correction of the major curves. This study reports on a retrospective series of 85 patients extracted from a French cohort, with a follow-up at a minimum of two years after a VBT with recent screws-and-tether constructs. The major and compensatory curves were measured pre-operatively, at the 1st standing X-ray, at 1 year, and at the last available follow-up. The complications were also analyzed. A significant improvement was observed in the curve magnitude after surgery. Thanks to growth modulation, both the main and the secondary curves continued to progress over time. Both the thoracic kyphosis and lumbar lordosis remained stable over time. Overcorrection occurred in 11% of the cases. Tether breakage was observed in 2% of the cases and pulmonary complications in 3% of the cases. VBT is an effective technique for the management of adolescent idiopathic scoliosis patients with residual growth potential. VBT opens an era of a more subtle and patient-specific surgical management of AIS that considers parameters such as flexibility and growth.

Vertebral body tethering: An alternative to posterior spinal fusion in idiopathic scoliosis?

Introduction

Skeletally immature patient with adolescent idiopathic scoliosis (AIS) whose curves continue to progress despite bracing should be treated surgically. Vertebral body tethering (VBT) is a non-fusion, compression-based, growth preserving alternative to posterior spinal fusion (PSF) based on the concept of 'growth modulation' to prevent possible functional complications secondary to fusion while correcting scoliotic deformity. This review aims to shed light on the indications of VBT, short- and medium-term outcomes, describe the surgical technique and associated complications, and to compare its efficacy to that of PSF.

Methods

A review of peer-reviewed literature on VBT as a surgical technique, its indications, outcomes, complications, and comparison with other surgical interventions to correct AIS was conducted in December 2022.

Results

Indications remain controversial and mainly include stage of skeletal maturity based on radiographic markers, curve location, magnitude and flexibility, and presence of secondary curve. Assessment of VBT clinical success should not be restricted to improvement in radiographic parameters but should include functional results and patient-centered outcomes, improved body image and pain, and durability of outcomes. In contrast to fusion, VBT seems to be associated with preserved spinal growth, shorter recovery, potentially better functional outcomes, less motion loss but possibly less curve correction.

Discussion

Yet still, with VBT there exists a risk of overcorrection, construct breakage or failure of procedure which require revision and at times conversion to PSF. Patient and family preferences must be accounted for acknowledging gaps in knowledge, attributes and drawbacks of each intervention.

Minimum 3-year experience with vertebral body tethering for treating scoliosis: A systematic review and single-arm meta-analysis

PURPOSE

Over the past 12 years, vertebral body tethering (VBT) has been gradually promoted for treating scoliosis, but there are few published studies, with only short-term follow-up. This study aimed to systematically review VBT efficacy and safety for treating scoliosis.

METHODS

PubMed, Web of Science, Embase, and the Cochrane Library were searched for studies on VBT treatment of scoliosis published up to November 2021. Two researchers independently screened the literature, extracted data, and assessed the risk of bias in included studies. Data on clinical efficacy, unplanned reoperations, and complications were extracted. The meta-analysis was performed with R 4.1.0.

RESULTS

Twenty-six studies involving 1045 patients were included in the meta-analysis. The correction rate of major curve immediately post-operation was 46.6% ± 13.8% (16%-69%) and that at final follow-up was 53.2% ± 17.9% (16%-79%). The single-arm meta-analysis results of all included studies showed that VBT was effective in general. The overall clinical success rate was 73.02% (95% confidence interval [CI]: 68.31%-78.05%). The pooled overall unplanned reoperation rate was 8.66% (95% CI: 5.53%-13.31%). The overall incidence rate of complications was 36.8% (95% CI: 23.9%-49.7%). The subgroup analysis based on follow-up time indicated that patients with follow-up time >36 months had increased clinical success rate, unplanned reoperation rate, and incidence rate of complications compared with those with <36 months' follow-up time. The preliminary results showed that after 36 months of follow-up, only 7.17% (95% CI: 4.81%-10.55%) of patients required posterior spinal fusion (PSF) surgery and nearly 93% of patients avoided spinal fusion surgeries.

CONCLUSIONS

The current evidence from at least 3-year follow-up in different countries indicates that VBT is an effective surgical approach for treating scoliosis, with 73.88% of patients achieving clinical success. Nevertheless, about one in seven patients (15.8%) required unplanned reoperations, but only 7.17% required PSF. About half (52.17%) of the patients experienced complications. Due to the limitation of the study number and quality, our conclusion may be biased and requires verification by further studies with longer follow-up times.

To tether or fuse? Significant equipoise remains in treatment recommendations for idiopathic scoliosis

PURPOSE

Vertebral body tethering (VBT) continues to grow in interest from both a patient and surgeon perspective for the treatment of scoliosis. However, the data are limited when it comes to surgeon selection of both procedure type and instrumented levels. This study sought to assess surgeon variability in treatment recommendation and level selection for VBT versus posterior spinal fusion (PSF) for the management of scoliosis.

METHODS

Surgeon members of the Pediatric Spine Study Group and Harms Study Group were queried for treatment recommendations and proposed upper instrumented vertebra (UIV) and lower instrumented vertebra (LIV) selection for PSF and VBT based on 17 detailed clinical vignettes. Responses were subdivided in each clinical vignette according to surgeon experience and treatment recommendations with assessment of intra-rater reliability. Binomial distribution tests were used to establish equipoise, selecting p < 0.10 to indicate the presence of a treatment choice with consensus set > 70% agreement. For treatment choice, responses were assessed first for consensus on the decision to proceed with PSF or VBT.

RESULTS

Thirty-five surgeons with varied experience completed the survey with 26 surgeons (74%) completing the second follow-up survey. Overall, VBT was the recommended treatment by 47% of surgeons, ranging by clinical vignette. Consensus in treatment recommendation was present for 6 clinical vignettes including 3 for VBT and 3 for PSF, with equipoise present for the remaining 11. Of the 17 vignettes, 12 demonstrated moderate intra-observer reliability including the 3 consensus vignettes for VBT. Sanders stage ≤ 3 and smaller curve magnitude were related with VBT recommendation but neither age nor curve flexibility significantly influenced the decision to recommend VBT. Surgeons with high VBT volume, ≥ 11 VBT cases/year, were more likely to recommend VBT than those with low volumes (0-10 cases per year (p < 0.0001)). High VBT volume surgeons demonstrated consensus in VBT recommendation for Lenke 5/6 curves (75% mean recommendation). High VBT volume surgeons had a significantly higher VBT recommendation rate for Lenke 1A, 2A curves (71.8% vs 48.0%, p = 0.012), and Lenke 3 curves (62% vs 26.9%, p = 0.023). Equipoise was present for all vignettes in low volume surgeons. In addition, high VBT volume surgeons trended toward including more instrumented levels than low VBT volume surgeons (7.17 vs 6.69 levels).

CONCLUSION

Significant equipoise is present among pediatric spine surgeons for treatment recommendations regarding VBT and PSF. Surgeon-, patient-, and curve-specific variables were identified to influence treatment recommendations, including surgeon experience, curve subtype, deformity magnitude, and skeletal maturity. This study highlights the need for continued research in identifying the optimal indications for VBT and PSF in the treatment of pediatric spinal deformity.

Vertebral Body Tethering: Indications, Surgical Technique, and a Systematic Review of Published Results

Vertebral body tethering (VBT) represents a new surgical technique to correct idiopathic scoliosis using an anterior approach, spinal instrumentation with vertebral body screws, and a cable compressing the convexity of the curve. According to the Hueter-Volkmann principle, compression reduces and distraction increases growth on the growth plates. VBT was designed to modulate spinal growth of vertebral bodies and hence, the term ‘growth modulation’ has also been used. This review describes the indications and surgical technique of VBT. Further, a systematic review of published studies was conducted to critically evaluate the results and complications of this technique. In a total of 23 included studies on 843 patients, the preoperative main thoracic curve corrected from 49 to 23 degrees in a minimum 2 year follow-up. The complication rate of VBT was 18%. The results showed that 15% of VBT patients required reoperations for pulmonary or tether-related issues (10%) and less than 5% required conversion to spinal fusion. While the reported median-term results of VBT appear promising, long-term results of this technique are currently lacking.