Topographical variation within the articular cartilage and subchondral bone of the normal ovine knee joint: a histological approach

Summary Topographical variation in the articular cartilage and subchondral bone of the normal ovine knee was examined using histological techniques. The articular cartilage was examined grossly, then histological sections were cut and the cartilage thickness and chondrocyte density were measured. Bone mineral density, thickness of the subchondral bone plate (SBP) and volume and surface histomorphometrical parameters and mineral apposition rate were calculated for the subchondral bone. It was found that the articular cartilage on the tibial plateaux was thicker, less cellular, and overlay a thicker SBP than that on the femoral condyles. Similarly, the cartilage in the medial joint compartments was thicker, less cellular and overlying a thicker less dense SBP than that in the lateral joint compartments. There was no variation in bone histomorphometric parameters or mineral apposition rate between regions. Biomechanical testing has shown that loading is not uniform throughout the normal human knee joint. The present results suggest that loading within the ovine knee is also nonuniform, with the central regions of the tibial plateaux bearing greater loads than the femoral condyles, and the medial joint compartment being loaded more than the lateral one. The articular cartilage and subchondral bone have adapted in order to best withstand these variations in loading. These histological findings, plus the topographical variations in cartilage biochemistry reported by Read et al. (Topographical variation in composition, PG-biosynthesis and swelling pressure of cartilages of loaded tibio-femoral joints (Abstract). Proceedings of the Combined Meeting of the Orthopaedic Research Societies of USA, Japan and Canada . Banff, Alberta, October 1991:1.), emphasize the need for focal analysis of tissues in animal models of joint diseases, and the dangers of pooling samples from different joint regions.