OP2.2 Accounting for Femoral Head Translation Affects Three-Dimensional Surgical Planning Indices for Periacetabular Osteotomy

Introduction: Periacetabular osteotomy (PAO) is a surgical treatment for developmental dysplasia of the hip to prevent osteoarthritis by reorientation of the acetabulum. Dysplastic hips exhibit increased femoral head translation compared with healthy hips. Despite this known behavior, preoperative surgical planning methods for PAO frequently do not take into account the effects of translation of the femoral head. Therefore, the aim of this study was to quantify the influence of femoral head translation on standard indices during three-dimensional PAO planning.

Methods: Patient-specific pelvis and femur bone models were reconstructed from computed tomography images for 17 retrospective PAO patients (22 hips) with hip dysplasia. The femoral head position was initially adjusted to be coincident with the center of the best-fit sphere to the acetabulum. Preoperative surgical planning was then performed without femoral head translation by an experienced PAO surgeon for each patient. A fully-automated, optimization algorithm to reposition the femoral head within the reoriented acetabular fragment was applied to the initial plan. The algorithm maximized the uniformity of separation between the femoral head and the lunate surfaces and constrained the minimal and maximum separation to within 2 mm and 4 mm, respectively. Changes in lateral center-edge angle, anterior center-edge angle, femoral head coverage, anterior and posterior wall coverage, and range of motion were measured.

Results: The mean femoral translation across all patients was 1.2±0.5 mm (anterior, inferior, and lateral) during fragment reorientation and 1.7±0.6 mm (posterior, superior, and medial) during range-of-motion simulation. The differences in lateral and anterior center-edge angles were 1.7±1.5 and 1.7±1.0 degrees, respectively. Total femoral head coverage changed by 4.6±3.9% with femoral translation. Both anterior and posterior wall coverage changed by 2±2%. Range-of-motion varied by 2.4±1.8 degrees of internal rotation at 90 degrees of hip flexion.

Conclusion: Integrating femoral head translation during preoperative planning for periacetabular osteotomy results in appreciable changes in common indices. Further study is necessary to determine if these differences are clinically significant.