Significance of size and location of the lesion for prognosis of collapse of osteonecrosis of the femoral head for patients treated with tantalum rod

Abstract

The purpose of this study is to predict osteonecrosis of the femoral head by examining location and size of the lesion of the femoral head. A triangulation approximation algorithm is used for the computation of the geometric center of the lesion based on MRI scans for patients treated with a tantalum rod. Twenty nine patients (thirty four hips) with osteonecrosis of the femoral head were treated with the tantalum rod procedure. The mean age was 39,21 years (14 - 59). All necrotic lesions were confirmed by magnetic resonance imaging. A customized triangulation approximation algorithm was developed in order to compute the geometric center of the lesion of the reconstructed model. Lesion volume, the distance from the origin (ρ or R), latitude and longitude (θ) of the geometric center of the lesion within the femoral head were calculated. The mean follow-up was 3 (1-7) years. Ten hips (29.4%) showed radiographic progression. Statistical method Cox regression analysis showed that lesion volume and longitude angle (θ) were important factors to predict radiographic progression. Lesions having an angle (θ) of [15° - 35°] and [50° - 60°] and size c in Steinberg scale with lesion size greater than 27% of the femoral head were more likely to develop radiographic progression. For hips that developed radiographic progression out of this range, lesion size was the only significant factor. The results suggest that lesion volume is an important factor strongly correlated with the risk of collapse of the femoral head. The location of the lesion of the necrotic area is an important supplemental parameter in order to predict with accuracy the progression of the disease. However further studies with the current algorithm that computes the geometric center of the lesion, larger study groups and long-term follow-up are needed in order to predict accurately the progression of the disease and the collapse of the femoral head. © 2010 World Scientific Publishing Co. Pte. Ltd.