Osteonecrosis of the knee. A clinicopathological study in twenty-eight patients.

Specimens from thirty-four knees in twenty-eight patients with histologically proved osteonecrosis were reviewed. Twelve knees had the clinical diagnosis of so-called idiopathic osteonecrosis; eight, osteoarthrosis; and fourteen, rheumatoid arthritis. Pathologically, the necrosis was localized in the subchondral region of the medial femoral condyle in 67 per cent of the knees. There were pathological fracture and collapse and fragmentation of the necrotic segment leading to marked deformities in most cases. The response to necrosis consisted of histiocytic resorption of necrotic material and formation of granulation tissue and reactive new bone surrounding it. The response was relatively less prominent in the knees with degenerative joint disease and rheumatoid arthritis.