To determine the degree of acetabular cartilage degeneration and factors that influence acetabular cartilage degeneration in osteonecrosis of the femoral head (ONFH).

We obtained acetabular cartilage from weight bearing and non-weight bearing portions, including subchondral bone, from 34 hips in 32 patients with ONFH who underwent total hip arthroplasty. Histologic grading by Hematoxylin & Eosin staining and Safranin O staining, and immunohistochemical staining with chondroitin sulfate antibody and type II collagen antibody were performed.

Histological grade had no significant correlation with stage, age, weight, or duration or degree of head depression, by the Wilcoxon rank sum test. The weight bearing and the non-weight bearing portions of acetabular cartilage were divided into two groups according to the existence and non-existence of femoral head depression. A significant difference (p=0.01), by Fisher's exact test, was found between the two weight bearing groups in terms of histologic grade. However no significance (p=0.45) was found between the two non-weight bearing groups. The distribution of type II collagen antibody's stainability score show most values in the normal range, while that of chondroitin sulfate antibody's was mainly in the upper.

The degeneration of the weight bearing portion of acetabular cartilage in ONFH is considered to be due to local rather than general changes. When head depression in absent, acetabular cartilage degeneration is less severe than previously reported.