In vivo determination of knee kinematics for subjects implanted with a unicompartmental arthroplasty

Femorotibial contact positions for 20 subjects implanted with a unicompartmental knee arthroplasty (UKA) were analyzed using videofluoroscopy. Femorotibial contact paths were determined using a computer-automated model-fitting technique. Subjects having a medial UKA experienced on average -0.8 mm of posterior femoral rollback, whereas subjects having a lateral UKA experienced -2.5 mm of posterior femoral rollback. Twelve of 17 subjects having a medial UKA and 2 of 3 subjects having a lateral UKA experienced normal axial rotation (average, 3.3degrees and 11.2degrees). The results for some subjects suggest that the anterior cruciate ligament was unable to thrust the femur anteriorly at full extension. These results support the findings that the anterior cruciate ligament plays a significant role in knee kinematics, which may contribute to UKA longevity.