In vivo quantification of the cat patellofemoral joint contact stresses and areas.

A new method for in vivo measurement of patellofemoral joint contact areas, stresses, and patellar displacements, with joint loading approximating physiologic conditions was developed. Joint contact measurements were obtained using pressure sensitive film inserted directly between articular joint surfaces. Two-dimensional joint kinematics were measured using a high-speed video based motion analysis system. Joint loading, provided by quadriceps muscle stimulation, was measured with an implantable force transducer (IFT). Variations in joint mechanics as a function of joint flexion angle, joint loading and joint stability (anterior cruciate ligament intact or transected) were determined for four adult male cats. The contact measurements obtained with the pressure sensitive film displayed high repeatability with a standard error of +/- 6.8% of the mean value of the median pressure and +/- 4.4% of the mean contact area value. Substantial differences in joint mechanics were reliably detected with the new technique. The influence of experimental procedures, such as incisions in the joint capsule and insertion of pressure sensitive film between the articular surfaces, produced minimal changes in the joint kinematics during muscular contraction.