Injury to articular cartilage joint surfaces: II. Displaced fractures of underlying bone. A histopathologic study of human tissue specimens.

Thirty-two pathologic specimens from patients who previously had sustained intraarticular fractures, usually of either the radial head or the patella, and subsequently had excision of the affected bone, were analyzed with respect to the healing mechanisms of articular fractures in humans. The cases were divided into five groups based on the duration of the time interval between fracture and joint-surface resection. The fracture clefts were sometimes perpendicular to the joint surface but often were more complex, and microscopically showed far more comminution than was appreciated from the gross examination. In all cases the articular chondrocytes demonstrated minimal reactive or reparative response to the injuries, even those cells that were situated directly adjacent to a fracture cleft. All significant repair was derived from the fracture-exposed bone marrow. At early stages, this consisted of granulation tissue. Later specimens showed fibrous tissue bridging the cartilage fracture gaps. Chondrous metaplasia within the surface layers of this fibrous callus could be observed occasionally, particularly in specimens with older fractures. However, it was often absent. In the cancellous bone, the healing of the fractures was by osseous, not chondroosseous, callus. In comminuted fractures areas of osteonecrosis were demonstrated in a number of cases.