Rib cage surgery for the treatment of scoliosis: a biomechanical study of correction mechanisms

Abstract

Rib shortening or lengthening are surgical options that are used to address the cosmetic rib cage deformity in scoliosis, but can also alter the equilibrium of forces acting on the spine, thus possibly counteracting in a mechanical way the scoliotic process and correcting the spinal deformities. Although rib surgeries have been successful in animal models, they have not gained wide clinical acceptance for mechanical correction of scoliosis due to the lack of understanding of the complex mechanisms of action involved during and after the operation. The objective of this study was to assess the biomechanical action of different surgical approaches on the rib cage for the treatment of scoliosis using a patient-specific finite element model of the spine and rib cage. Several unilateral and bilateral rib shortening/lengthening procedures were tested at different locations on the ribs (convex/concave side of the thoracic curvature; at the costo-transverse/costo-chondral joint; 20 and 40 mm adjustments). A biomechanical analysis was performed to assess the resulting geometry and load patterns in ribs, costo-vertebral articulations and vertebrae. Only slight immediate geometric variations were obtained. However, concave side rib shortening and convex side rib lengthening induced important loads on vertebral endplates that may lead to possible scoliotic spine correction depending on the remaining growth potential. Convex side rib shortening and concave side rib lengthening produced mostly cosmetic rib cage correction, but generated inappropriate loads on the vertebral endplates that could aggravate vertebral wedging. This study supports the concept of using concave side rib shortening or convex side rib lengthening as useful means to induce correction of the spinal scoliotic deformity during growth, though the effects of growth modulation from induced loads must be addressed in more detail to prove the usefulness of rib shortening/lengthening techniques.