Finite Element Comparison of Different Growth Sparring Instrumentation Systems for the Early Treatment of Idiopathic Scoliosis

Fusionless growth sparring implants seek to restore spinal alignment through the early intervention of pediatric scoliosis. Amongst a growing number of concepts, the stainless steel (SS) staple, flexible tether and shape memory alloy (SMA) staple have demonstrated their validity by retarding convex vertebral growth while modifying spinal alignment. The purpose of this study was to explore the biomechanics of these devices in a human scoliotic finite element model (FEM) constructed from patient data. A FEM of a scoliotic anterior spine (28° thoracic curve) was developed to include growth dynamics and shown to represent typical scoliotic progression. The explored implant concepts were alternatively introduced around the apical vertebra of the FEM (T5–T9). Immediate impact (asymmetrical loading of the vertebral growth plates and correction of scoliotic curve) and long term impact (correction of scoliotic curve after 2 years of growth) were simulated and compared to the behavior of the non-instrumented model and patient data. Results of the difference in asymmetrical growth plate stress between instrumented and non-instrumented models reveal: insignificant initial impact by the SS staple, a 52% reduction with the flexible tether, and a 31% reduction with the SMA staple. Initial and long term modifications of coronal spinal alignment following simulated growth was respectfully 28° to 62°in non-instrumented model and patient data, 28° to 31° with SS staple, 23° to 31° with flexible tether, and 27° to 34° with SMA staple. The interpretation of such methods suggests that the long term correction, achieved via growth modulation, would benefit from improved control of asymmetrical stresses within the growth plates. From a biomechanical perspective, fusionless growth sparring techniques for the early treatment of idiopathic scoliosis show promising preliminary results.