Objective: The objective of this study was to define, in unilateral hip osteoarthritis (OA), factors predicting the outcome of the other hip.
Materials and methods: We examined the anteroposterior radiographs of the pelvis of 95 white patients with unilateral idiopathic (56 patients) or secondary to congenital hip diseases (39 patients) OA. The other hip was free from symptoms (pain or limping) at the initial examination and without radiographic evidence of OA; it was what we call a "normal" hip. Two parameters were evaluated: (1) the type of osteoarthritis of the involved hip and (2) the range of four radiographic indices of the contralateral hip: the sourcil inclination (weight-bearing surface), the acetabular angle, the Wiberg's center-edge angle, and the neck-shaft angle. Follow-up radiographs for the hips that remained OA-free were available for 10 to 35 years and for those that developed OA, at the time of initial symptoms, range 2 to 31 years.
Results: Logistic regression analysis showed that the presence of idiopathic OA in one hip had a statistically significant effect on the development of OA on the other hip (p < 0.001). Minor deviations of radiographic indices of the contralateral hip is not a predictive factor for its outcome. When the radiographic indices are examined together with the pathology of the involved hip, only WBS was shown to have a significant effect to the development of OA and its type (p < 0.001).
Conclusions: The following conclusions can be drawn from this study: 1. Patient with idiopathic OA of one hip is at increased risk of developing OA in the other hip. 2. The outcome of the other hip cannot be predicted only on the basis of the evaluation of its radiographic indices. 3. Among the different indices, WBS seems to have a strong influence toward the development of OA.