Towards a Y-Shaped Pelvic Osteotomy To Address Loss of Lumbar Lordosis

Introduction. In severe cases with lumbar lordosis loss > 25°, pedicle subtraction osteotomy is performed surgically to restore the sagittal malalignment. But it has severe limitations. So, we are developing a new Y-shaped pelvic osteotomy that targets the pelvis rather than the spine. This work presents a fixation system tailored to the Y-shaped pelvic osteotomy. Methodology. Criteria for the fixation system were set: Offer compressed fixation on the posterior side (closed wedge), maintain a 15° wedge opening on the anterior side and use conventional fixation components. This resulted in combining a lag-screw posteriorly and a patient-specific osteosynthesis plate anteriorly. To assess feasibility, a basic finite element analysis (FEA) was performed using loads derived from a static free body analysis, and a preliminary test was performed on a Sawbones model to assess surgical usability and osteotomy accuracy. Results. The load input to the FEA was determined to be 397 N in x-direction, 832 N in z-direction, and 18 Nm moment. The FEA showed that the width of the T-shape of the plate crossing the osteotomy should be at least 15 mm to remain below allowable material stress level. The usability gave a score of 3.9 out of 7 for the fixation system. The Sawbone test showed obtained osteotomy angles of 16.6° and 19.5°, respectively compared to the set 15°. The bone contact area was 62% compared to the planned 61%. Conclusion. The preliminary results indicate the feasibility of the Y-shaped pelvic osteotomy in combination with the new fixation system.