An articulated spine and ribcage kinematic model for simulation of scoliosis deformities

Musculoskeletal multibody modeling can offer valuable insight into aetiopathogenesis behind adolescent idiopathic scoliosis, which has remained unclear. However, the underlying model should represent anatomical joints with compatible kinematic constraints while allowing the model to attain scoliotic postures. This work presents an improved and kinematically determinate model including the whole spine and ribcage, which can attain typical scoliosis deformations of the thorax with compatible constraint strategy and simulate the interaction between all the bony segments of the ribcage and the spine. In the model, costovertebral/costotransverse joints were defined as universal joints based on reported anatomical studies. Articulations between ribs and the sternum were defined as spherical joints except in the ninth and tenth levels, which have one additional anteroposterior degree-of-freedom. The model is controlled by fifteen kinematic parameters including spinal rhythms and parameters relating to clinical metrics of scoliosis. These input values were measured from the bi-planar radiographs of a 17-year-old scoliosis patient with a right main thoracic curve of 33° Cobb angle. Dependent kinematic variables with clinical relevance were selected for validation purposes and compared with measurements from radiographs. The average errors of rib-vertebra angles, rib-vertebra angle differences, and rib humps were 6.3° and 10.5°, and 8.7mm. The model appeared to reproduce the spine and rib deformation pattern conforming to radiographs, results in simulating the rib prominence, rib spread, rib-vertebra angles, and sternum orientation, therefore supporting the constraint definitions. The model can subsequently be used to investigate the kinetics of scoliosis and contribute to uncovering the aetiology.