Kinematics of the patellofemoral joint in total knee arthroplasty

Sagittal plane patellofemoral kinematics was determined for 81 subjects whi le performing a weight-bearing deep knee bend under fluoroscopic surveillan ce. Fourteen normal knees, 12 anterior cruciate ligment (ACL)-deficient kne es, and 55 total knee arthroplasties (TKAs) were assessed. Of TKAs, 39 had resurfacing with a dome-shaped patella, 8 had resurfacing with an anatomic mobile-bearing patella, and 8 were unresurfaced. TKA patellae experienced m ore Superior patellofemoral contact and higher patellar tilt angles compare d with the normal knees and ACL-deficient knees (P < .05). Patellofemoral s eparation at 5 degrees (+/-3 degrees) extension was seen in 86% cruciate-re taining and 44% cruciate-stabilized TKAs and 8% ACL-deficient knees but not in the normal knees or mobile-bearing TKAs (P < .05). The patellar kinemat ic patterns for subjects having a TKA were more variable than subjects havi ng either a normal knee or an ACL-deficient knee. Kinematic abnormalities o f the prosthetic patellofemoral joint may reduce the effective extensor mom ent after TKA.