In vivo movement of femoral flexion axis of a single-radius total knee arthroplasty.

The objective of this study was to investigate in vivo femoro-tibial motion using the movement of femoral flexion axis of a single-radius TKA. We examined 20 clinically successful knees with a single-radius posterior stabilized TKA to evaluate the kinematics of deep knee flexion using 2-3-dimensional registration techniques. The mean knee flexion range of motion was 117.8°. The mean rotation of the femoral component was 7.6° external rotation. The mean knee flexion angle at initial post-cam engagement was 55.2°. No paradoxical movement of femoral component was shown until 70° flexion, afterward the femoral component rolled back with flexion. The data showed that the design of this prosthesis might contribute to reduce the paradoxical anterior femoral movement and provide stability in mid-flexion ranges.

Posterior sliding of the femur during stair ascending and descending in a high-flex posterior stabilized total knee arthroplasty.

This study investigated the anteroposterior stability of the femur during stair motions. We examined 18 knees with a clinically successful high-flexion posterior stabilized total knee arthroplasty to evaluate the in vivo kinematics of stair ascending and descending using two- to three-dimensional registration. Posterior sliding of the femur was observed while shifting weight to the leg during stair ascending and descending in almost all knees. Anterior tibial post impingement was observed in 10 knees when the knee was extended in stair ascending, whereas in stair descending, the impingement was observed in 14 knees when posterior sliding of the femur occurred. The impingement contributed to the stabilization of the knee during stair motion; however, impingement may result in additional polyethylene wear and tibial post failure.

In vivo kinematic analysis of cruciate-retaining total knee arthroplasty during weight-bearing and non-weight-bearing deep knee bending.

The purpose of the present study was to evaluate the in vivo kinematics of the posterior cruciate ligament-retaining total knee arthroplasty during weight-bearing and non-weight-bearing deep knee bending and compare these 2 different conditions. We evaluated the in vivo kinematics of the knee using fluoroscopy and femorotibial translation relative to the tibia tray by 2-dimensional/3-dimensional registration. In the weight-bearing state, the femoral component showed central pivot and bicondylar posterior rollback pattern. During non-weight-bearing, the movement anteriorly occurred on both the medial and lateral side during early flexion, whereas bicondylar femoral component rollback occurred after that. During non-weight-bearing, both the medial and lateral condyle significantly moved anteriorly compared with the weight-bearing state during early flexion. However, bicondylar femoral rollback occurred under both these conditions.

In vivo kinematics of high-flex mobile-bearing total knee arthroplasty, with a new post-cam design, in deep knee bending motion.

PURPOSE: The objective of this study was to evaluate the in vivo knee kinematics to assess the available functional motion of the characteristic mobile-bearing prosthesis design and to examine whether the artificial joint would work in vivo according to its design concept. METHODS: We studied 14 knees (11 patients) implanted with the Vanguard RP Hi-Flex prosthesis. This prosthesis has a highly original form of post-cam called a PS saddle design with high compatibility, and with a rotating plate mobile-bearing mechanism. The cylinder-type post-cam is designed to enable contact in early flexion ranges, and to prevent paradoxical anterior femoral component movement. Each patient performed weight-bearing deep knee bending under fluoroscopic surveillance. Motion between each component including the polyethylene insert was analyzed using the 2D/3D registration technique. RESULTS: The mean range of motion was 122.0°. The mean femoral component rotation for the tibial tray was 5.0°. No paradoxical anterior movement of the nearest point was confirmed between the femoral component and the tibial tray in the early flexion ranges. Initial contact of the post-cam was confirmed at a knee flexion angle of 33.8°. Subsequently, the wide contact of the post-cam was maintained until flexion reached 120° in all knees, but disengagement of the post-cam was observed in two knees when flexion was ≥130°. CONCLUSIONS: The results of this study demonstrated that the prosthesis design generally works in vivo as intended by its design concept. The present kinematic data may provide useful information for improvement of high-flex type prostheses.

The effect of weight-bearing condition on kinematics of a high-flexion, posterior-stabilized knee prosthesis.

The objective of this study was to investigate the effects of weight-bearing (WB) condition on the kinematics of total knee arthroplasty. We investigated 17 patients (20 knees) implanted with a high-flexion posterior-stabilized total knee arthroplasty using 2- to 3-dimensional registration techniques. In vivo kinematics of dynamic deep knee flexion under WB and non-WB (NWB) conditions were compared. Six degree-of-freedom kinematics and articular contacts including post-cam contact were evaluated. At midflexion, femorotibial contact points were located significantly more anteriorly under NWB than WB conditions. As a result, post-cam engagement occurred significantly earlier under NWB than WB conditions. With NWB conditions, early engagement of the femoral cam engages at the top part of tibial post, which puts it at risk of jumping the tibial post particularly if there is instability in midflexion.