Abstract
Introduction
Despite improvements in the survivorship of total knee replacements (TKR) over the years, patient satisfaction following TKR has not improved, with approximately 20% of patients recording dissatisfaction with their new knee joint. It is unclear why many patients feel this way, but it may relate in part to implant designs that do not provide a “natural” feeling knee. Implant manufacturers continue to introduce new concepts for implant design, which are essential for reaching the goal of a “normal” knee after TKR surgery. The Journey II TKR (Smith & Nephew) was developed with this goal in mind. Its anatomical design attempts to mimic the normal knee joint structure to return more natural kinematics to the joint, with emphasis on eliminating both paradoxical anterior motion and reduced posterior femoral rollback. Our objective is to examine patients receiving the Journey II TKR to measure the knee joint contact kinematics of the Journey II TKR compared to a non-anatomically designed implant by the same manufacturer. We hypothesize that the Journey II TKR will have more natural contact kinematics that differ from the non-anatomically designed implant.
Methods
A total of 28 individuals were recruited to receive a Journey II TKR, matching an existing prior cohort with a non-anatomical design from the same manufacturer (Legion TKR, Smith & Nephew). For both groups, a series of radiostereometric analysis (RSA) images were acquired at different knee flexion angles, ranging in 20° increments from 0° to 120°. Model-based RSA software (RSACore, Leiden, Netherlands) was used to obtain the 3D positions and orientations of the femoral and tibial implant components, which were in turn used to obtain kinematic measures (contact locations and magnitude of excursion) for each condyle. Results from the Journey II TKR group at 3 months post-operation were compared to the 2-year post-operative measurements from the Legion TKR group.
Results
Preliminary results for the anterior-posterior (AP) contact locations from 38 patients (15 Journey II TKR, 23 Legion TKR) are displayed in Figure 1. The Journey II TKR group showed more anterior contact medially and laterally relative to the Legion TKR group at many angles, however the overall pattern from 0°–120° was similar. There was no significant difference between groups with respect to magnitude of excursion on both medial (mean difference=1.29 mm, p=0.19) and lateral (mean difference=0.69 mm, p=0.60) condyles.
Conclusions
Early results suggest that paradoxical anterior motion and reduced posterior femoral rollback are present in the anatomically designed Journey II TKR, suggesting that it does not provide substantially different knee kinematics compared to the non-anatomically designed Legion TKR.
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