Periacetabular Osteotomy Improves Hip Microinstability Between Supine and Standing Radiographs in Symptomatic Hip Dysplasia.

Background: Whether periacetabular osteotomy (PAO) improves hip microinstability in patients with symptomatic hip dysplasia remains poorly understood.

Purpose: To assess the femoral head translation with static postural change, considered a potential indicator of hip microinstability, comparing dysplastic hips before and after PAO with normal hips.

Study Design: Descriptive laboratory study.

Methods: A total of 26 patients (30 hips) with hip dysplasia underwent PAO, and 18 healthy individuals (18 hips) were eligible. Using a 3-dimensional-to-2-dimensional registration technique, femoral head translation before and after PAO was quantified as the displacement of the center of the femoral head relative to the center of the acetabulum between supine and standing positions. Morphological factors on supine anteroposterior pelvic radiographs before and after PAO correlated with the femoral head translation, particularly lateral translation, were examined.

Results: Femoral head translation decreased after PAO (1.5 ± 0.4 mm vs 1.0 ± 0.4 mm; < .001) but remained larger than in controls (1.0 ± 0.4 mm vs 0.7 ± 0.3 mm; = .01). The more severe the hip dysplasia before PAO was, the greater the femoral head translation. However, the femoral head translation improved after PAO with sufficient acetabular correction. The acetabular roof obliquity (ARO) showed the strongest correlation with lateral translation of the femoral head from the supine to standing position before PAO. In contrast, no correlation was found after PAO.

Conclusion: This study demonstrates that the severity of hip dysplasia influences hip microinstability, that PAO mitigates hip microinstability with adequate acetabular correction, and that PAO does not normalize hip stability because of residual joint incongruity. In patients with a larger ARO, the femoral head has more lateral translation in the standing position. Therefore, weightbearing postural radiographs are crucial for understanding hip biomechanics in hip dysplasia and refining surgical corrections during PAO.

Clinical Relevance: PAO can make the hip more stable in hip dysplasia, but not as stable as the normal hip. In hip dysplasia, pre-PAO standing radiographs should be evaluated due to their accurately representing the femoral head position relative to the acetabulum.