The size of the necrotic lesion may be a significant factor in predicting outcome and determining treatment in hips with avascular necrosis. However, to date most reports on the treatment of this condition have not attempted to correlate outcome with lesion size. Seventy-three hips with avascular necrosis were evaluated, 11 in Stage I and 62 in Stage II. All were treated with core decompression and bone grafting. Patients were followed up 2 to 6 years (mean, 39 months). The results were determined by change in Harris hip score, degree of radi-ographic progression, and the need for total hip replacement. Outcome was correlated with the lesion size, stage, etiology, and other factors. In Stage I, the true three-dimensional size of the lesion was measured with a new technique of quantitative magnetic resonance imaging. In Stage II, measurements were obtained from radiographs using a modular system for quantitative digital analysis. Hips were divided into three groups based on lesion size: Group A, less than 15% of femoral head involvement; Group B, 15% to 30%; and Group C, greater than 30%. There were no significant differences in outcome between Stages I and II and no relationship to etiology or other demographic factors. When correlated with lesion size, radiographs on a 21-point scale showed progression by 1.1,4.2, and 4.3 points; the Harris hip score showed an improvement of 10.6 and 3.3 points and a loss of 3.6 points; and total hip replacement was required in 7%, 31%, and 33% of Group A, B, and C lesions, respectively. The difference in outcome between small lesions and large or medium lesions was statistically significant, but no significant differences were seen between medium and large lesions. These observations emphasize the importance of lesion size in predicting outcome after core decompression and grafting and possibly after other surgical and nonsurgical methods of managing hips with avascular necrosis. They also encourage the use of methods of evaluation and staging that include a determination of lesion size and stage.
*Departments of Orthopaedic Surgery
**Departments of Radiology, University of Pennsylvania School of Medicine, Philadelphia. PA.