Method for Delivering a Controlled Impact to Articular Cartilage in the Rabbit Knee

OBJECTIVE The authors aimed to develop a mechanical model for delivering controlled impact injuries to an articular cartilage surface, with the ability to control peak contact pressure while maintaining a constant rate of loading across all impact levels. METHODS A pendulum-style impactor with a direct contact interface was fabricated, based on previously published successful models. This impactor was tested in 2 separate experiments: first with a single analog specimen and next with 15 cadaveric rabbit knee specimens. In both experiments, impacts were performed at 3 pressure levels with multiple repetitions. Peak pressure, rate of pressure application, impulse, and time to peak were evaluated. RESULTS There was a significant difference between each of the pressure level groups for both the analog and cadaveric experiments. There was no significant difference between the rates of pressure application for the analog specimen and a statistically significant difference only between the highest and lowest pressure level groups for the cadaveric specimen. CONCLUSIONS Previous studies have shown that peak pressure and rate of pressure application are both significant contributors to cartilage injury. Previous models have controlled only peak contact pressure, allowing rate of loading to change as a function of peak contact pressure. This model is the first to control both variables, with a rate of pressure application that is typical of an athletic or traumatic injury in humans. Use of this model will enable researchers to investigate the isolated effects of peak pressure on progressive cartilage injuries.