TOPOGRAPHICAL VARIATION WITHIN THE ARTICULAR-CARTILAGE AND SUBCHONDRAL BONE OF THE NORMAL OVINE KNEE-JOINT - A HISTOLOGICAL APPROACH

Topographical variation in the articular cartilage and subchondral bon e of the normal ovine knee was examined using histological techniques. The articular cartilage was examined grossly, then histological secti ons were cut and the cartilage thickness and chondrocyte density were measured. Bone mineral density, thickness of the subchondral bone plat e (SEP) and volume and surface histomorphometrical parameters and mine ral apposition rate were calculated for the subchondral bone. It was f ound that the articular cartilage on the tibial plateaux was thicker, less cellular, and overlay a thicker SEP than that on the femoral cond yles. Similarly, the cartilage in the medial joint compartments was th icker, less cellular and overlying a thicker less dense SEP than that in the lateral joint compartments. There was no variation in bone hist omorphometric parameters or mineral apposition rate between regions. B iomechanical 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, a nd the medial joint compartment being loaded more than the lateral one . The articular cartilage and subchondral bone have adapted in order t o best withstand these variations in loading. These histological findi ngs, plus the topographical variations in cartilage biochemistry repor ted by Read ct al. (Topographical variation in composition, PG-biosynt hesis and swelling pressure of cartilages of loaded tibio-femoral join ts (Abstract). Proceedings of the Combined Meeting of the Orthopaedic Research Societies of USA, Japan and Canada. Banff, Alberta, October 1 991:1.), emphasize the need for focal analysis of tissues in animal mo dels of joint diseases, and the dangers of pooling samples from differ ent joint regions.