Pelvic osteotomies for correction of sagittal imbalance of the spine: An in-silico study comparing four different osteotomies

Three-column spinal osteotomies are common to restore sagittal balance. However, these procedures are challenging. Pelvic osteotomies may be a feasible alternative, although instability and compromised correction are concerning, which dome-shaped osteotomies may mitigate. As a possible and novel alternative for spinal osteotomies, pelvic dome and open wedge osteotomies for correction of sagittal spine balance were compared. Four in-silico pelvic osteotomies were performed on 3D CT-reconstructions: bilateral extending pelvic osteotomy (BEPO) and dome pelvic osteotomies (DPOs) around center of the sacral endplate (SE-DPO), sacroiliac joints (SI-DPO) and centers of the acetabula (A-DPO). We measured pelvic extension and bone contact surface (BCS) after 10°, 15° and 20° extension and the length of the sacropelvic ligaments after 20° extension. In radiographs of five samples of failed back surgery, we measured the effect on sagittal vertical axis (SVA) and Th1 pelvic angle (TPA). Pelvic extension was similar for all types of osteotomy. After 20° extension, BCS was 34.1 % (SE-DPO), 28.2 % (SI-DPO) and 30.6 % (A-DPO). Average shortening of the spinopelvic ligaments was 2.3 % after the BEPO, 22.0 % after SE-SPO, 17.0 % after SI-DPO and 11.8 % after A-DPO. After 15° correction, SVA correction was 12.6 cm and TPA correction 5.8° after BEPO. After SE-DPO, the correction was 14.5 cm and 14.1°, after SI-DPO 13.4 cm and 13.0° and after A-DPO 12.6 cm and 0.0°. A-DPO appeared to the most predictable and reliable pelvic osteotomy. However, this is technically demanding and shortens the pelvic floor ligaments. BEPO is less demanding with minimal effect on the ligaments, however it requires more complex stabilization methods. Feasibility and safety tests are required as a next step.