Does lesion size affect the outcome in avascular necrosis?

The size of the necrotic lesion may be a significant factor in predicting o utcome 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 ne crosis were evaluated, 11 in Stage I and 62 in Stage II. All were treated w ith core decompression and bone grafting. Patients were followed up 2 to 6 years (mean, 39 months). The results were determined by change in Harris hi p score, degree of radiographic progression, and the need for total hip rep lacement. Outcome was correlated with the lesion size, stage, etiology, and other factors. In Stage I, the true three-dimensional size of the lesion w as 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 grou ps 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 signifi cant differences in outcome between Stages I and II and no relationship to Etiology or other demographic factors. When correlated with lesion size, ra diographs on a 21-point scale showed progression by 1.1, 4.2, and 4.3 point s; 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 aas required in 7%, 31%, and 33% of Group A, B, and C lesions, respectively. The difference in outcome b etween small lesions and large or medium lesions was statistically signific ant, but no significant, differences were seen between medium and large les ions. These observations emphasize the importance of lesion size in predict ing 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 inclu de a determination of lesion size and stage.