ANTERIOR-POSTERIOR STABILITY IN PARTIALLY CONFORMING CONDYLAR KNEE REPLACEMENT

The purpose of the study was to estimate the anterior-posterior displa cements that would occur with total knee prosthetic designs of differe nt sagittal radii under functional conditions. A key question was whet her some designs provided excessive constraint. Patients who had diffe rent total knee prosthetic designs were tested in a special rig where the AP drawer was measured under loaded and unloaded conditions. These same designs of total knee prostheses were then tested in a rig under different conditions of compressive and shear loads. Using these expe riments as verification, a theoretical treatment was developed to pred ict the AP displacement for different activities. It was concluded tha t designs with low to moderate conformity required soft tissue restrai nt under more strenuous activities, or where high shear fortes occurre d under low compressive loads. Designs of moderate to high conformity could be fully self-stabilizing under all realistic conditions. Howeve r, for all designs, the AP displacement was only a few millimeters und er functional loads, indicating that special care must be taken during surgery to avoid conflict between the condylar surfaces and the retai ned cruciate ligaments so that restriction of motion and excessive wea r do not occur.