Joint injuries in humans are frequent and similar to those seen in all mammalian species. The most commonly used method to study the correlation between trauma and cartilage survival (post-traumatic arthritis) has been conducted using in-vivo animal models. In a majority of these animal models a single or multiple impact was delivered to the patello-femoral joint (PFJ) using a drop tower type apparatus [1–6]. A main limitation of these models is with the drop tower itself and the impaction of a “whole joint”. A free-falling mass impacting the specimen abruptly decelerates, generating a nonlinear inertial force upon the tissue due to cartilage’s structural non-homogeneity. Haut et al. [2] specifically commented that it was difficult to control the impact stress using a drop tower apparatus. In addition, the rate of loading is difficult to control because changes in potential energy will generate different stress magnitudes and rates of loading. Thus, it is hard to correlate these high-loading rate experiments to slow loading rate experiments [6,7]. Only one study reported exposing and directly traumatizing the articular surface of the joint, but again utilized a drop tower device [4,5]. All these studies correlated “impact energy” or “impact force” to the amount of cartilage damage but did not evaluate the influence of stress magnitude or the rate of loading.

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