Damage to the articular cartilages of the patellofemoral joint is frequently observed in humans and is one sign associated with osteoarthritis. Loading of articular cartilage influences the biological responses and thus the health of this tissue in both an amplitude and frequency sensitive manner. Furthermore, chondrocyte and nuclear deformation that occurs with cartilage deformation has been proposed as a transduction mechanism which enables the cells to detect and biologically respond to changes in their local environment. The majority of these data have been derived from experiments using expiants of articular cartilage removed from healthy joints. Therefore the chondrocyte response in-situ and in-vivo and the effects of anterior cruciate ligament transection on this response still require investigation.

In this research we firstly quantified the contact areas and pressures in the feline patellofemoral joint in-situ. Secondly, we developed methods to apply a static load to articular cartilage still fully intact and attached to its native bone and systematically evaluated cartilage and chondrocyte deformation throughout tissue depth. Thirdly, we used this technique to apply a physiological magnitude of load to healthy, short- and long-term anterior cruciate ligament transected feline patellofemoral articular cartilage. Finally, we developed methods to apply a repeatable, measurable and muscle induced cyclical load to an intact patellofemoral joint and measure the biological responses of the articular cartilages at the mRNA level.

We found that significant chondrocyte deformation did occur when a physiological magnitude of compression was applied to the fully intact articular cartilages of the patellofemoral joint. This observation was consistent in healthy, short- and long-term anterior cruciate ligament deficient feline knees. This result supports the notion that significant chondrocyte deformation occurs in cartilage during in-vivo loading and could therefore be one way in which chondrocytes can detect and respond to changes in their environment. Secondly, we found that the articular cartilages of the patellofemoral joint were heterogeneous mechanically, histologically, biologically and in their response to anterior cruciate ligament deficiency and an applied load. This heterogeneity was evident when comparing different surfaces of the joint as well as different areas and/or depths of the same surface.