Prediction of collapse of the osteonecrosis of the hip by determining location and size of the lesion: A 2 to 17 years study

Osteonecrosis of the femoral head is a disease responsible for a large number of arthroplasties in young and active patients in the western world. Prediction of outcome of the disease remains a difficult task. The purpose of this study is to predict the outcome of the osteonecrosis of the femoral head by calculating the geometric center (GC) of the lesion in a spherical coordinate system and relating size and location of the lesion with the outcome of the disease. Thirty four patients (thirty eight hips) with osteonecrosis of the femoral head were collected from the Larissa district in Greece and were treated with the free vascularized fibular graft procedure. The mean age was 41 years (18-64). All necrotic lesions were confirmed by magnetic resonance imaging. A customized method of triangles algorithm was developed for the computation of the geometric center of the lesion in 3D reconstructed models. Lesion volume, the distance from the origin R, latitude (φ) and longitude (θ) of the geometric center of the lesion within the femoral head were calculated. The mean follow up was 9.5 (2-17) years. Fifteen hips (39.5%) showed radiographic progression. Logistic regression analysis showed that lesion volume and angle (θ) were important factors to predict the progression of the disease. Lesions having small values of angle (θ) were more likely to develop radiographic progression. The results suggest that lesion volume is an important factor strongly correlated with the risk of collapse of the femoral head. The location of longitude (θ) of the necrotic lesion is an important parameter in order to predict with accuracy the progression of the disease.