Abstract
Introduction
Surgeons performing a total knee replacement (TKR) have two available techniques available to help them achieve the proper bone resections and ligament tension – gap balancing (GB) and measured resection (MR). GB relies on balancing ligaments prior to bony resections whereas bony resections are made based on anatomical landmarks in MR. Many studies have been done to compare the joint kinematics between the two techniques, however the results have been varied. These studies were not done with anatomically designed prostheses. The Journey II (Smith & Nephew, Memphis, TN) is one such design which 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. Given the design differences between anatomical and non-anatomical prostheses, it is important to investigate whether one technique provides superior kinematics when an anatomical design is used. We hypothesize that there will be no difference between the two techniques.
Methods
A total of 56 individuals were recruited to receive a Journey II prosthesis and randomized evenly to groups where the GB technique or MR technique is used. For all patients in the study, a series of radiostereometric analysis (RSA) images were acquired at 3-months post-operatively 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
Preliminary results for the anterior-posterior (AP) contact locations from 33 patients (18 GB, 15 MR) are displayed in Figure 1. There were no significant differences in medial and lateral contact locations between the GB and MR groups for all angles of flexion. However, the pattern of medial contact for the MR technique displays more paradoxical anterior motion at mid-flexion (40°–60°) than the GB group. There were no significant differences in magnitude of excursion between groups on both medial (mean difference=1.96 mm, p=0.16) and lateral (mean difference=0.21 mm, p=0.79) condyles, indicating that posterior femoral rollback is similar between groups.
Conclusions
Early results suggest that the MR technique is associated with slightly more abnormal kinematics than the GB technique when an anatomical prosthesis design is used for TKR. The GB technique may be more appropriate than MR technique for implanting anatomically designed knee replacements.
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