Objective: To investigate the incidence and nature of secondary osteonecrosis observed in osteoarthritis (OA) of the femoral head.
Design: This study is based on a retrospective review of the histopathologic and radiologic materials obtained from 906 consecutive cases (1007 femoral heads) diagnosed as OA.
Results: Secondary osteonecrosis was recognized grossly and confirmed microscopically in 38.2% of the femoral heads. The lesions were categorized into two types based on shape, size and depth; 'shallow' flat lesion (median axis 3-10 mm, depth 2-3 mm) with or without cysts (368 cases, 36.5%), and 'deep, wedge-shaped' large lesion (more than 20 mm across and 10 mm in depth) with or without cyst (17 cases, 1.7%). In the 'shallow' flat lesion, the age ranged from 25 to 88 (average 66), the female/male ratio was 0.8, and the location of osteonecrosis correlated best with the direction of migration in OA. In the 'deep, wedge-shaped' lesion, the age ranged from 56 to 92 (average 70), the female/male ratio was 1.8, and the location of osteonecrosis was similar to that found in primary osteonecrosis.
Conclusion: Two different types of osteonecrosis were observed in OA. 'Shallow' osteonecrosis may be pressure necrosis as a result of eburnation, while 'deep, wedge-shaped' osteonecrosis appears to be an independent phenomena presumably caused by similar causal factors to those in primary osteonecrosis.