Three-Dimensional Evaluation of Hip Center Shift After Periacetabular Osteotomy for Hip Dysplasia

To quantify the three-dimensional shift of the femoral head after periacetabular osteotomy and to identify the relevant morphological factors. This retrospective study included 26 patients (30 hips) who underwent periacetabular osteotomy at a single institution. Pre- and postoperative supine and standing anteroposterior two-dimensional images and pelvic computed tomography scans were obtained. Using three-dimensional-to-two-dimensional model-image registration techniques, we quantified acetabular and femoral head center shifts in both the supine and standing positions along three axes based on the anterior pelvic plane. Correlations between femoral head shift and pre- and postoperative hip morphological parameters on standardized supine radiographs were examined. In the supine position, the femoral head center shifted significantly (5.0 ± 2.3 mm), with medial (-1.5 ± 3.8 mm) and posterior (-1.8 ± 3.5 mm) displacement. Similarly, in standing, the femoral head center shifted significantly (4.8 ± 2.4 mm), with medial (-1.5 ± 3.8 mm) and posterior (-1.4 ± 3.6 mm) displacement. Lower preoperative anterior wall index was correlated with greater medial shift (r = 0.37, p = 0.04) and less posterior shift (r = -0.40, p = 0.03). Periacetabular osteotomy was associated with measurable three-dimensional reorientation of the hip center in both supine and standing positions. Lower preoperative anterior wall index was correlated with greater medial shift and less posterior shift, although the effect sizes were modest. These findings suggest that hip center shift after periacetabular osteotomy is a secondary effect of multiplanar acetabular reorientation and that three-dimensional assessment may provide information beyond conventional two-dimensional evaluation, particularly for anteroposterior changes.