Biomechanical Simulation and Analysis of Scoliosis Correction Using a Fusionless Intravertebral Epiphyseal Device

Study Design. Computer simulations to analyze the biomechanics of a novel compression-based fusionless device (hemistaple) that does not cross the disc for the treatment of adolescent idiopathic scoliosis. Objective. To biomechanically model, simulate, and analyze the hemistaple action using a human finite element model (FEM). Summary of Background Data. A new fusionless growth sparing instrumentation device (hemistaple), which locally compresses the growth plate without spanning the disc, was previously developed and successively tested on different animal models. Methods. Patient-specific FEMs of the spine, rib cage, and pelvis were built using radiographs of 10 scoliotic adolescents (11.7 +/- 0.9 yr; Cobb thoracic: 35 degrees +/- 7 degrees, lumbar: 24 degrees +/- 6 degrees). A validated algorithm allowed simulating the growth (0.8-1.1 mm/yr/vertebra) and growth modulation process (Hueter-Volkmann principle) during a period of 2 years. Four instrumentation configurations on the convex curves were individually simulated (Config 1: 5 thoracic vertebrae with hemistaples on superior endplates; Config 2: same as Config 1 with hemistaples on both endplates; Config 3: same as Config 1 + 4 lumbar vertebrae; Config 4: same as Config 2 + 4 lumbar vertebrae). Results. Without hemistaples, on average the thoracic and lumbar Cobb angles, respectively, progressed from 35 degrees to 56 degrees and 24 degrees to 30 degrees, whereas the vertebral wedging at curve apices progressed from 5 degrees to 12 degrees. With the hemistaple Config 1, the Cobb angles progressed but were limited to 42 degrees and 26 degrees, whereas the wedging ended at 8 degrees. With Config 3, Cobb and wedging were kept nearly constant (38 degrees, 21 degrees, 7 degrees). With hemistaples on both endplates (Confi g 2, Config 4), the Cobb and wedging were all reduced (thoracic Cobb for Confi g 2 and 4: 24 degrees and 15 degrees; lumbar Cobb: 21 degrees and 11 degrees; wedging: 2 degrees and 1 degrees). Conclusion. This study suggests that the hemistaple has the biomechanical potential to control the scoliosis progression and highlights the importance of the instrumentation configuration to correct the spinal deformities. It biomechanically supports the new fusionless device concept as an alternative for the early treatment of idiopathic scoliosis.