Abstract
Background
In a mobile-bearing unicondylar knee arthroplasty (UKA) stability is very important for the knee function and to prevent dislocation of the insert. A tension-guided technique to determine the position of the optimal posterior bone cut should theoretically lead to a better varus-valgus stability. The goal of this study was to measure the difference in valgus laxity in flexion and extension between a tension-guided and spacer-guided system for mobile-bearing UKA. Also clinical function was evaluated between the groups.
Patients and Methods
A tension-guided UKA system (BalanSysTM, Mathys, Bettlach, Switzerland) was compared with a retrospective group of a spacer-guided system (Oxford, Biomet Ltd, Bridgend, UK). A total of 30 tension-guided UKAs were placed and compared to 35 spacer-guided prostheses. Valgus laxity was measured at least 6 months postoperatively in both groups using stress radiographs. The flexion stress radiographs were made fluoroscopically aided in 70 degrees of knee flexion. Laxity measurements in extension were performed on stress radiographs obtained with the Telos device. Knee Society Scores (KSS) were obtained at follow-up.
Results
Valgus laxity in flexion was significantly higher in the tension-guided group compared to the spacer-guided group: 3.9° and 2.4°, respectively, p<0.001) In extension, valgus laxity was 1.8° in the tension-guided group compared to 2.7° in the spacer-guided group, which was significantly different (p<0.001). There was no significant difference between the two groups in the KSS at 6 months follow-up. (p=0.31)
Discussion and conclusion
The tensor-guided system resulted in significantly more valgus laxity in flexion compared to the spacer-guided system. However, in extension the situation was reversed: the tension-guided system resulted in less valgus laxity than the spacer-guided system. Clinically, there were no differences between the groups. The valgus laxity found with the spacer-guided system better approximates the valgus laxity values of healthy elderly.
