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 rabbit as a model for the development of post-traumatic arthritis. A system to impact the cartilage was designed that consisted of an apparatus to deliver a blow of quantifiable force, a method to apply the stress uniformly over the impact area, and a way to accurately measure the impact area. The knee joints of cadaveric New Zealand White rabbits were surgically exposed with the knee flexed so that the distal femoral articular surface was perpendicular to an impactor. With the knee fixed in position, a cup containing polymethylmethacrylate bone cement was applied to create an exact contour of the femoral surface, and the cement 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 compressive force) that was attached to the cup. The area of the impacted surface was determined and, with the measured force, was used to calculate an accurate estimate of the impact stress. This method can be performed under sterile conditions, and therefore it is well suited for survival experiments in which the long-term effects of impact to cartilage will be studied.