The patient-specific spine geometry was reconstructed using calibrated coronal and sagittal radiographs. The spine biomechanical properties were adapted from experimental data and further adjusted using the patient's side-bending radiographs. Instrumentation constructs were modeled as rigid bodies connected by kinematic joints. The instrumentation maneuvers of 6 cases were simulated for which the simulation parameters were extracted from the surgery documentation and video. The correction maneuvers and resulting effects were analyzed.
The simulations agreed well with the real surgery (differences on Cobb angles < 5°). The vertebral position relative to the rod was determined by 5 independent variables (position and orientation) vs. 2 for a monoaxial screw, thus increasing the possible correction of the connected vertebrae. The DIST system allows the spine deformity to be reduced by either gradually pulling the spine towards the rod through helical connections or translating it by pivoting the posts. Load at the vertebra-implant connection did not exceed 338 N, and was well distributed (standard deviation < 110 N).
The study shows that the DIST system allows good control of the scoliotic vertebrae with good load sharing among implants.