The gluteus medius is affected by changes in joint mechanics due to osteoarthritis with acetabular dysplasia and corresponding total hip arthroplasty.

Abstract

To examine the effects of superior lateralisation of the centre of rotation and femoral offset shortening on the gluteus medius in developmental dysplasia of the hip (DDH), and the impact of biomechanical restoration by total hip arthroplasty (THA). Horizontal (femoral, acetabular, and combined offset) and vertical (centre height, leg length) radiographic parameters, as well as gluteus medius radiodensity measured by computed tomography, were evaluated preoperatively and 1 year postoperatively in 100 hips (87 patients). Patients were grouped by whether radiodensity improved postoperatively. Correlations between parameter changes and radiodensity were analysed. In advanced osteoarthritis, radiodensity deterioration correlated with femoral offset shortening (<i>p</i> = 0.0011) and increased centre height (<i>p</i> < 0.0001). Postoperative radiodensity improvement correlated with increased combined offset (<i>p</i> = 0.0380) and leg lengthening (<i>p</i> = 0.0002). Multivariate analysis showed that the non-improvement group had a significantly smaller combined offset (<i>p</i> = 0.0399). Gluteus medius fatty infiltration improved mainly with leg lengthening, but insufficient combined offset limited this recovery.