METHOD TO IMPACT IN-VIVO RABBIT FEMORAL CARTILAGE WITH BLOWS OF QUANTIFIABLE STRESS

The purpose of this study was to develop a technique by which a known stress could be applied uniformly across the femoral cartilage of a ra bbit as a model for the development of post-traumatic arthritis. A sys tem to impact the cartilage was designed that consisted of an apparatu s to deliver a blow of quantifiable force, a method to apply the stres s uniformly over the impact area, and a way to accurately measure the impact area. The knee joints of cadaveric New Zealand White rabbits we re surgically exposed with the knee flexed so that the distal femoral articular surface was perpendicular to an impactor, With the knee fixe d in position, a cup containing polymethylmethacrylate bone cement was applied to create an exact contour of the femoral surface, and the ce ment was allowed to cure. The form was then rested on the rabbit knee, and a drop tower released a weight of known mass from a known height onto an impactor (instrumented with strain gauges to measure the compr essive force) that was attached to the cup. The area of the impacted s urface was determined and, with the measured force, was used to calcul ate an accurate estimate of the impact stress. This method can be perf ormed under sterile conditions, and therefore it is well suited for su rvival experiments in which the long-term effects of impact to cartila ge will be studied.