Tibiofemoral kinematic analysis of knee flexion for a medial pivot knee

The performance of total knee arthroplasty in deeply flexed postures is of increasing concern as the procedure is performed on younger, more physically active and more culturally diverse populations. Several implant design factors, including tibiofemoral conformity, tibial slope and posterior condylar geometry have been shown directly to affect deep flexion performance. The goal of this study was to evaluate the kinematics of a fixed-bearing, asymmetric, medial rotation arthroplasty design in moderate and deep flexion. Thirteen study participants (15 knees) with a medial rotation knee arthroplasty were observed performing a weight-bearing lunge activity to maximum comfortable flexion and kneeling on a padded bench from 90A degrees to maximum comfortable flexion using lateral fluoroscopy. Subjects averaged 74 years of age and nine were female. At maximum weight-bearing flexion, the knees exhibited 115A degrees of implant flexion (102A degrees-125A degrees) and 7A degrees (-3A degrees to 12A degrees) of tibial internal rotation. The medial and lateral condylar translated posteriorly by 2 and 5 mm, respectively. At maximum kneeling flexion, the knees exhibited 119A degrees of implant flexion (101A degrees aEuro"139A degrees) and 5A degrees (-2A degrees to 14A degrees) of tibial internal rotation. The lateral condyle translated posteriorly by 11 mm. The medial rotation knee exhibited motion patterns similar to those observed in the normal knee, but less tibial rotation. The medially conforming articulation beneficially controls femoral AP position in deep flexion, in patients who require such motion as part of their lifestyle.