Articular cartilage degeneration in post-collapse osteonecrosis of the femoral head - Radiographic staging, macroscopic grading, and histologic changes

Background: Osteonecrosis of the femoral head is a debilitating condition characterized by progressive degeneration of bone that eventually leads to collapse of the femoral head in the majority of patients. Femoral head-sparing procedures have been more successful in pre-collapse stages of osteonecrosis than in post-collapse stages, although some patients with early post-collapse disease have had no additional progression of the disorder. Nevertheless, the effects of collapse on the articular cartilage are not well understood, and radiographic staging of femoral head collapse does not address the condition of the articular cartilage. Methods: In the current study, we investigated the relationship between the mechanical properties of post-collapse articular cartilage and the histologic findings and macroscopic grades of the articular cartilage from hips with stage-IV osteonecrosis, those with stage-V osteonecrosis, and those without osteonecrosis. Results: The cartilage from both stage-IV and stage-V hips showed significant degeneration compared with the normal control cartilage, but there was no significant difference between the two stages. There was significant variability in the histologic and mechanical properties of these samples that correlated strongly with the gross appearance of the cartilage surface but not with the lesion size. Conclusions: These results suggest that articular cartilage that appears macroscopically normal may remain mechanically functional even in patients with large osteonecrotic lesions or a late radiographic stage of the disease. Clinical Relevance: These findings lend support to the position that femoral head-sparing surgical strategies designed to restore the contour of the femoral head may have utility in some patients with advanced osteonecrotic disease. The gross appearance of the articular cartilage may be a useful tool for identifying those patients.