Remodeling of articular defects in an animal model.

When treating displaced intraarticular fractures, the goal has been to restore normal articular cartilage contour to decrease local contact stresses that may lead to the development of posttraumatic osteoarthritis. To confirm observations that articular cartilage step-offs can remodel with time and to determine how the articular surface and subchondral bone remodels after an intraarticular fracture, joint surface changes were examined in a weightbearing sheep model with an intraarticular fracture. Articular surface pressure changes were observed across a 1-mm osteotomy. Twelve weeks after an intraarticular osteotomy, there was a decrease in differential pressure distribution between the normal articular cartilage and the depressed articular surface. Histologic analysis showed thinning of the articular cartilage on the high side of the osteotomy with collagen compression and bending of the collagen fibrils. On the low side of the osteotomy, increased chondrocyte cellularity and hypertrophy were observed. In addition, bending of collagen fibrils was observed in an unloaded state in an attempt to form a smooth overlapping shelf at the osteotomy site. Because intraarticular incongruency, with resultant joint contact pressure differences, seems to be involved in the development of posttraumatic arthritis, methods to improve cartilage remodeling may improve outcome after intraarticular fractures.