Background: To achieve sufficient socket coverage by the native bone, high placement of cementless acetabular cup is often required. We previously reported, using computer simulation, that higher hip centre improved the bone coverage but decreased the range of motion in total hip arthroplasty (THA) for patients with hip dysplasia. However, in a clinical setting, the correlation between the hip centre height and dislocation after primary THA is still unclear. We examined whether a high hip centre affects dislocation after THA.
Methods: A total of 910 patients, with 1079 dysplastic hips, who underwent primary THA were retrospectively reviewed. The age at THA averaged 63.0 years and mean follow-up was 74.3 months. Vertical centre of rotation (V-COR) was defined as the distance from the head centre to the interteardrop line. Uni- and multivariate logistic regression models were applied to identify significant factors affecting dislocation.
Results: Ten hips in nine patients (0.9%) had dislocation after THA. In univariate analysis, age at surgery and V-COR were significant risk factors for dislocation. Multivariate analysis identified advanced age at operation (odds ratio [OR] 1.8/5 years), Crowe classification (OR 15.6), V-COR (OR 3.1/5 mm), and femoral head size (OR 11.6) as independent risk factors for dislocation. Receiver operating characteristic curve analysis revealed the cutoff value of the V-COR for dislocation as 23.9 mm.
Conclusions: A higher hip centre with the V-COR > 23.9 mm affected dislocation after THA for DDH. Our results would be useful for reconstruction of the hip centre, particularly with cementless acetabular cups.
Keywords: Centre of rotation (COR); Developmental dysplasia of the hip (DDH); Dislocation; High hip centre; Total hip arthroplasty.