Toward biomechanically optimized intraoperative correction in lumbar vertebral body tethering

Abstract

Purpose To identify the appropriate intraoperative correction in lumbar vertebral body tethering (VBT) to optimize outcomes and to avoid under- or over-correction at skeletal maturity by accounting for preoperative deformity size and stiffness, body weight, and skeletal maturity. Methods Fifteen cases of pediatric idiopathic scoliosis (average lumbar Cobb angle: 48 degrees (40-59 degrees) were used to build validated 3D patient-specific finite element models, which were calibrated to various preoperative characteristics. Physics-based numerical simulations of VBT were performed in the intraoperative lateral decubitus position, with actual instrumented vertebrae (T10-T12 to L2-L4). Intraoperative correction levels (from 50 to 90%) were simulated under four growth remaining scenarios corresponding to Sanders Stage (SS) 3A, 3B, 4, and 5. Postoperative growth and growth modulation were simulated over a 2-year period. The targeted result was a curve at 10 degrees +/- 5 degrees at 2-year follow-up. Results Simulations indicated that achieving the targeted two-year coronal correction required significantly lower intraoperative correction in SS 3A compared with the more mature stages (3B, 4, 5) (p < 0.01). No significant differences were observed among SS 3B, 4, and 5. The corresponding target intraoperative corrections were 65% (53-75%), 72% (60-80%), 73% (60-80%), and 73% (68-80%) for SS 3A, 3B, 4, and 5, respectively. Separately, body weight and spinal flexibility did not statistically impact the intraoperative target. However, their interaction significantly influenced the intraoperative correction targets in SS 3A and 3B cases (p < 0.05). Conclusion Optimal intraoperative correction in lumbar VBT appears to depend primarily on preoperative skeletal maturity status. In patients who are more immature, body weight and spinal flexibility should also be considered when selecting correction targets. This simulating tool could be used as a planning tool to provides a pathway toward precise, individualized intraoperative correction strategies aimed at improving the reliability of VBT outcomes.