Interdependency between corrections in the three anatomic planes in AIS instrumentation

Methods A validated patient-specific biomechanical modeling and simulation technique was used to assess the 3D correction of a Lenke-1 AIS case through posterior spinal instrumentation. Uniplanar pedicle screws were bilaterally placed at the 2 proximal, 2 distal, and 3 apical levels. The simulation steps included only the concave side 5.5 mm CobaltChrome rod attachment and its derotation followed by apical vertebral derotation. Eighteen instrumentation simulations were performed with different rod contours (curvatures of 10, 20 and 30 degrees), rod derotation (70, 90 and 110 degrees), and vertebral derotation torques (3 and 5 Nm per screw at the 3 apical levels). Indices in the 3 planes (Cobb angle, thoracic kyphosis, apical vertebral rotation (AVR)) were computed for each simulation.