Morphologic alterations of the subchondral bone in advanced degenerative arthritis.

A series of 535 femoral heads surgically excised at the time of total hip arthroplasty for degenerative arthritis were analyzed by gross photography, specimen roentgenograms, and whole-mount histologic sections. Limited regenerative capacity was apparent in the chondrous tufts in the exposed bone of the osteoarthritic joint surface. The mechanism for the formation of subchondral cysts was interpreted to be the proliferation of viable myxomatous cells within the bone marrow. Osseous remodeling adjacent to the cysts was secondary to expansion of the soft tissue contents of the early cysts and later vascularization with fibrosis in the older cysts. Stress fracturing was a focal feature secondary to the remodeling of live bone. Advanced degenerative arthritis demonstrated focal osteocytic necrosis in the exposed osseous surface. Bone necrosis was also observed when small segments of the surface were undermined by cysts. Finally, bone necrosis was occasionally observed as focal infarcts of the joint surface (2-6 mm). In all three instances, bone necrosis in degenerative arthritis appeared to be a secondary reaction, presumably related to local disruption of blood supply.