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

ABSTRACT

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