Measurable Lumbar Motion Remains 1 Year After Vertebral Body Tethering

Radiological Outcomes of Re-tethering for Adolescent Idiopathic Scoliosis: A 2-to-5-year Follow-Up Case Series After Index Vertebral Body Tethering Failure

PURPOSE

Vertebral Body Tethering (VBT) has been shown to have a less predictable outcome compared to spinal fusion in patients with adolescent idiopathic scoliosis (AIS). Tether breakage is a common mechanical event that sometimes leads to loss of correction. No data has been published that evaluates the outcome of re-tethering in patients who underwent revision surgery for failed VBT, which was the purpose of this study.

METHODS

This is an analysis of a prospectively collected single center database of 290 patients who have had VBT. Patients for this study were included if they have had re-tethering after failed VBT and a minimum follow up of 24 months after index surgery as well as a minimum follow up of 12 months after revision surgery. Revision surgeries included tether exchange, tether reinforcement and/or mono- and bisegmental lateral fusion. Main outcome of interest was curve magnitude at latest follow up.

RESULTS

11 patients were identified who received VBT for 16 curves of which 13 curves have had failed index surgery. Mean follow up from index surgery was 40 months, time between index and revision surgery was 22 months and latest follow up after revision surgery 19 months. Re-tethering resulted in an additional correction of 42% for thoracic and 63% for thoracolumbar curves. These results remained clinically stable with only minor loss of correction at final follow up. No patient underwent or was indicated for spinal fusion.

CONCLUSION

Re-tethering is feasible and able to achieve additional correction and a sustainable result.

Early-term outcome of apical fusion with vertebral body tethering for thoracolumbar curves in adolescent idiopathic scoliosis: a preliminary study

INTRODUCTION

Vertebral body tethering (VBT) has become an alternative option for select patients with idiopathic scoliosis. However, studies have shown a high number of tether breakages, specifically after thoracolumbar (TL) VBT, that can have a negative impact on the outcome, when the breakage occurs within the first year after surgery. In order to overcome this problem, we have started to apply an apical fusion (AF) in combination with TL VBT for select patients. This study aims to analyze the outcome after AF plus VBT.

METHODS

This is a retrospective single surgeon's data analysis. All patients were included who have had TL VBT after January 2022 and a follow-up of 12 months. Patients were grouped based on whether they only had VBT or VBT + AF.

RESULTS

Twenty-five patients were analyzed (15 VBT, 10 VBT + AF). Both groups showed a significant curve correction for thoracic and TL curves. Minor loss of correction was observed in both groups. A significant difference was seen regarding early tether breakages, which were found in 60% of VBT patients and 10% of VBT + AF patients.

CONCLUSION

The preliminary data shows a significant reduction of early tether breakages when TL VBT is applied in combination with AF.

How Long Can You Delay? Curve Progression While Awaiting Vertebral Body Tethering Surgery

Background: The implications of delaying surgical intervention for patients with adolescent idiopathic scoliosis (AIS) wishing to undergo vertebral body tethering (VBT) have not yet been explored. It is important to understand how these delays can impact surgical planning and patient outcomes. Methods: This was a retrospective review that analyzed all AIS patients treated between 2015 and 2021 at a single tertiary center. Time to surgery from initial surgical consultation and ultimate surgical plan were assessed. Patient characteristics, potential risk factors associated with increased curve progression, and reasons for delay were also analyzed. Results: 174 patients were evaluated and 95 were scheduled for VBT. Four patients later required a change to posterior spinal fusion (PSF) due to excessive curve progression. Patients requiring PSF were shown to have significantly longer delays than those who received VBT. Additionally, longer delays, younger age, greater curve progression, and lower skeletal maturity were correlated with significant curve progression (≥5 degrees). Conclusions: Surgical delays for AIS patients awaiting VBT may lead to significant curve progression and necessitate more invasive procedures. Patients with longer delays experienced an increased risk of needing PSF instead of VBT. Of those requiring PSF, the majority were due to insurance denials. Optimizing surgical timing and shared decision-making among patients, families, and healthcare providers are essential for achieving the best outcomes.

Evidence-based Indications for Vertebral Body Tethering in Spine Deformity

Posterior spinal fusion has long been established as an effective treatment for the surgical management of spine deformity. However, interest in nonfusion options continues to grow. Vertebral body tethering is a nonfusion alternative that allows for the preservation of growth and flexibility of the spine. The purpose of this investigation is to provide a practical and relevant review of the literature on the current evidence-based indications for vertebral body tethering. Early results and short-term outcomes show promise for the first generation of this technology. At this time, patients should expect less predictable deformity correction and higher revision rates. Long-term studies are necessary to establish the durability of early results. In addition, further studies should aim to refine preoperative evaluation and patient selection as well as defining the benefits of motion preservation and its long-term effects on spine health to ensure optimal patient outcomes.

Anterior Vertebral Body Tethering: A Review of the Available Evidence

Idiopathic scoliosis is a complex three-dimensional deformity of the spine with anterior overgrowth (hypokyphosis), coronal curvature, and axial rotation. Scoliosis treatment in the skeletally immature spine is therapeutically challenging because of growth and was commonly limited to observation, bracing treatment, or fusion. Fusion accomplishes powerful deformity correction at the expense of future growth and mobility of the involved segments, increasing the risk of adjacent segment degeneration and intervertebral disk disease later in life. Anterior vertebral body tethering is a motion-preserving technique that exploits the Hueter-Volkmann principle by applying compression at the anterior and convex aspects of the curve to stimulate differential vertebral growth for gradual deformity reduction without fusion. The appropriate timing, curve magnitude, tensioning, growth prediction, indications, and limitations of tethering are being refined as this technique becomes more prevalent. Early outcome studies show that growth modulation with vertebral body tethering is safe, can achieve good results, and preserve motion in select patients.

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

BACKGROUND CONTEXT

Vertebral body tethering is the most popular nonfusion treatment for adolescent idiopathic scoliosis. The effect of the tether cord on the spine can be segmentally assessed by comparing the angle between two adjacent screws (interscrew angle) over time. Tether breakage has historically been assessed radiographically by a change in adjacent interscrew angle by greater than 5° between two sets of imaging. A threshold for growth modulation has not yet been established in the literature. These angle measurements are time consuming and prone to interobserver variability.

PURPOSE

The purpose of this study was to develop an automated deep learning algorithm for measuring the interscrew angle following VBT surgery.

STUDY DESIGN/SETTING

Single institution analysis of medical images.

PATIENT SAMPLE

We analyzed 229 standing or bending AP or PA radiographs from 100 patients who had undergone VBT at our institution.

OUTCOME MEASURES

Physiologic Measures: An image processing algorithm was used to measure interscrew angles.

METHODS

A total of 229 standing or bending AP or PA radiographs from 100 VBT patients with vertebral body tethers were identified. Vertebral body screws were segmented by hand for all images and interscrew angles measured manually for 60 of the included images. A U-Net deep learning model was developed to automatically segment the vertebral body screws. Screw label maps were used to develop and tune an image processing algorithm which measures interscrew angles. Finally, the completed model and algorithm pipeline was tested on a 30-image test set. Dice score and absolute error were used to measure performance.

RESULTS

Inter- and Intra-rater reliability for manual angle measurements were assessed with ICC and were both 0.99. The segmentation model Dice score against manually segmented ground truth across the 30-image test set was 0.96. The average interscrew angle absolute error between the algorithm and manually measured ground truth was 0.66° and ranged from 0° to 2.67° in non-overlapping screws (N=206). The primary modes of failure for the model were overlapping screws on a right thoracic/left lumbar construct with two screws in one vertebra and overexposed images. An algorithm step which determines whether an overlapping screw was present correctly identified all overlapping screws, with no false positives.

CONCLUSION

We developed and validated an algorithm which measures interscrew angles for radiographs of vertebral body tether patients with an accuracy of within 1° for the majority of interscrew angles. The algorithm can process five images per second on a standard computer, leading to substantial time savings. This algorithm may be used for rapid processing of large radiographic databases of tether patients and could enable more rigorous definitions of growth modulation and cord breakage to be established.

Radiographic and perioperative outcomes following anterior thoracic vertebral body tethering and posterior lumbar spine tethering: a pilot series

BACKGROUND AND CONTEXT

 In patients with adolescent idiopathic scoliosis (AIS) of main thoracic and lumbar spine regions, combined anterior thoracic vertebral body tethering and posterior lumbar spine tethering (ATVBT/PLST) is a novel non-fusion treatment option for growth modulation and conservation of motion.

METHODS

 Fourteen patients with AIS who underwent ATVBT/PLST with at least 2-year follow-up were included. Primary outcomes included quality of life as assessed by SRS-22 instruments, radiographic analysis, and revision operations. We secondarily reported perioperative metrics and post-operative opiate morphine equivalents (OME). Clinical success was defined as patients who achieved skeletal maturity with ≤ 30° curve magnitude of both their main thoracic and thoracolumbar/lumbar curves and who did not undergo posterior spine instrumentation and fusion (PSIF).

RESULTS

Patients had a mean age of 11.6 years (range 10-14 years), majority were girls (92%), and mean follow-up was 3.0 years (range 2-4.8 years). All patients were skeletally immature with a Risser ≤ 2. Included curves were Lenke 1C, 3C, or 6C. Mean preoperative curve magnitudes were 53° ± 8° (range 45°-65°) main thoracic and 49° ± 9° (range 40°-62°) thoracolumbar/lumbar curves. At most recent follow-up, patients had a mean main thoracic curve of 29° ± 8° (range 15°-40°) and a mean thoracolumbar/lumbar curve of 20° ± 15° (range 4°-35°). 50% required a revision operation. Cable breakage occurred in 43%, which did not always require revision. One patient progressed to thoracic fusion, but no patient underwent lumbar fusion. Patients had a mean SRS-22 outcome score of 4.2 ± 0.4.

CONCLUSIONS

ATVBT/PLST is a potential alternative to spine fusion for select immature patients with AIS at a minimum 2-year follow-up. ATVBT/PLST potentially offers motion conservation at the cost of a higher revision rate. Further study and reporting of results are necessary to refine indications and techniques, which in turn will improve outcomes of this procedure.

LEVEL OF EVIDENCE

Level IV-Case series without comparative group.

Central Airway Obstruction with Persistent Pulmonary Decline After Vertebral Body Tethering: A Case Report

CASE

An 11-year-old girl with pectus excavatum presented with an acute airway obstruction and persistent pulmonary compromise after vertebral body tethering (VBT). The anterior instrumentation was occluding her right basilar bronchus, resulting in hyperinflation. Removal of the instrumentation reversed the hyperinflation.

CONCLUSION

This case illustrates the difficulty of performing VBT in a small patient with severe scoliosis and significant asymmetric pectus excavatum. We recommend using low-profile instrumentation and ensuring the trajectory of the instrumentation is anterior to the rib head and parallel to the articular facets.

Biomechanical modeling and assessment of lumbar vertebral body tethering configurations

PURPOSE

Vertebral body tethering (VBT) is a fusionless spinal growth modulation technique, which shows promise for pediatric idiopathic scoliosis (IS) curve correction. This technique, mainly used for thoracic curves, is increasingly being used to treat lumbar curves in order to preserve spine flexibility. It remains necessary to adequately define the cord tension to be applied during the operation and the instrumented levels to biomechanically predict correction over time for the lumbar spine.

METHODS

Twelve pediatric patients with lumbar IS, treated with lumbar-only or lumbar and thoracic VBT, were selected for this study. Three independent variables were tested alternately using a patient-specific finite element model (FEM), which includes an algorithm modeling vertebra growth and spine curve changes due to growth modulation for 24 months post-operatively according to the Hueter-Volkmann principle. Parameters included cable tensioning (150N/250N), upper instrumented level (actual UIV, UIV-1) and lower instrumented level (actual LIV, LIV + 1). Each FEM was personalized using 3D radiographic reconstruction and flexibility supine radiographs.

RESULT

An increase in cord tension (from 150 to 250N) had significant effects on main thoracic and thoraco-lumbar/lumbar Cobb angles, as well as on lumbar lordosis, after surgery (supplementary average correction of 3° and 8°, and increase of 1.4°, respectively) and after 24 months (4°, 10° and 1.1°) (p < 0.05). Adding a level to the actual UIV or LIV did not improve correction.

CONCLUSION

This parametric study showed that cord tension is the most important biomechanical parameter on the simulated immediate and 2-year increase in lumbar curve correction. Our preliminary model suggests that it is not advantageous to add additional instrumented levels.

LEVEL OF EVIDENCE

This computational study uses a retrospective validation cohort (level of evidence 3).

Outcomes of vertebral body tethering in the lumbar spine

PURPOSE

The use of vertebral body tethering (VBT) for the treatment of main thoracic deformities in adolescent idiopathic scoliosis patients is becoming increasingly more common, but limited data exist on its safety and efficacy in thoracolumbar deformities. We aimed to evaluate the postoperative outcomes of patients with thoracolumbar (TL) deformities that were treated with VBT.

METHODS

We assessed clinical and radiographic data from twenty-eight consecutive patients that were surgically managed with VBT, all of whom exhibited a TL deformity with at least two years (mean: 44.7 ± 14.5 months) of postoperative follow-up. Standard radiographic parameters were extracted from left hand wrist and standing posterior-anterior and lateral spine radiographs at various timepoints. Outcome variables were assessed based on preoperative Lenke Classification and included: deformity measures, complications, surgical revisions, and postoperative success.

RESULTS

The mean age at the time of instrumentation was 13.4 ± 1.3 years, with an average preoperative Sanders Stage of 4.6 ± 1.4. A significant reduction in preoperative deformities was observed at most postoperative timepoints. A perioperative complication was observed in three patients and surgical revision was required in another four patients. A suspected broken tether was observed in sixteen patients, most of which occurred at the apex of the lumbar deformity. Only one patient required surgical revision due to a suspected broken tether. We observed an overall success rate of 57%, regardless of Lenke Classification.

CONCLUSIONS

These data indicate that VBT can successfully correct TL deformity patterns in 57% of patients without an increase in the rate of perioperative complications, suspected broken tethers, or surgical revisions.

Radiographic outcome after vertebral body tethering of the lumbar spine

INTRODUCTION

Multiple studies have analyzed the outcome after thoracic Vertebral Body Tethering (VBT). The results seem reproducible with most studies reporting coronal correction rates around 50% and a tether breakage rate near 20% at two years follow-up. There is a paucity of data on lumbar VBT, and no study has yet analyzed the radiographic outcome after lumbar VBT in a double tether technique at two years follow-up, which was the aim of this study.

METHODS

This is a retrospective, single surgeons' data analysis of all consecutive immature patients who have had VBT of the lumbar spine (to L3 or L4) between January 2019 and September 2020. Primary interest focused on coronal curve correction at two years post-operatively. Suspected tether breakages were analyzed separately and defined as an angular change of more than 5° between two adjacent screws.

RESULTS

Forty-one patients were eligible for this study and 35 (85%) had complete two-year follow-up data. Average age at surgery was 14.3 years. All patients had a Sanders stage of 7 or below. Average curve correction for thoracolumbar/lumbar curves at two years follow-up was 50%. 90% of patients had at least one level with a suspected tether breakage. No patient required a revision surgery within two years from surgery but two patients were surgically revised after two years.

CONCLUSION

VBT in the lumbar spine resulted in 50% coronal curve correction two years post-operatively despite a tether breakage in 90% of patients.

The different applications of Vertebral Body Tethering - Narrative review and clinical experience

Background

Vertebral body tethering (VBT) has been originally developed as a growth modulation technique for the surgical management of skeletally immature patients with adolescent idiopathic scoliosis (AIS). Given the positive results obtained in this setting, the use of VBT is gradually expanding to other patient categories, such as those with no or limited remaining growth or with non-idiopathic scoliosis. Aim of this manuscript is to offer an overview over the current applications of VBT, along with imaging and comments derived from the clinical experience. The work was based on a literature search conducted in January 2023 on Pubmed, Scopus and Web of Science databases. Following keywords were used for the search: vertebral body tethering, adolescent idiopathic scoliosis, early onset scoliosis, neuromuscular scoliosis, syndromic scoliosis.

Results

Three patient categories in which VBT has been applied have been highlighted: VBT for growth modulation in AIS, VBT as anterior scoliosis correction in AIS and VBT for non-idiopathic curves or early-onset scoliosis.

Conclusion

While growth modulation in AIS still represents the most widespread use of VBT, the use of this technique has yielded positive results in different settings as well, such as scoliosis correction in AIS or temporary or definitive curve management in non-AIS curves. While long-term results are lacking, patient selection seems to play a central role to reduce the complication rate and ensure predictable and stable results.