Contact studies of the canine femoropatellar joint.

During development of a closed impact-trauma model, using the canine femoropatellar articulation, animal weight or other readily measured physical characters were correlated with surface area, location, and shape of femoropatellar contact at various femorotibial angulations. The information allows making reasonable predictions regarding femoropatellar contact just before delivery of calibrated closed impact-trauma to the patella. Femoropatellar contact area location, shape, and size were determined in the left pelvic limbs of 10 dogs, ranging in weight from 20.0 to 40.9 kg (mean 27.2 kg). Determinations were made at 90, 110, and 130 degrees femorotibial angulations, using a new casting technique and at 70, 90, 110, 130, and 150 degrees, using a previously described dye technique. Location and shape of the contact areas were relatively constant for a given femorotibial angulation. Bipartite areas of contact were seen on 3 specimens. Using data from the dye technique, a definitive correlation was established between antemortem animal weight and contact area size. Patellar dimensions also correlated well with contact surface area. An inverse relationship between contact area per unit body weight and total body weight was observed. Contact area size did not vary significantly with increasing compressive force resulting from changes in femorotibial angulation. These determinations allow making reasonable predictions of both location and size of articular contact area immediately preceding delivery of closed impact to the joint.