Summary

Large reduction in postoperative posterior tibial slope in UKA should be avoided because it is associated with anterior collapse of the tibial component.

Abstract

Background

Although the posterior tibial slope (PTS) of tibial component in unicompartmental knee arthroplasty (UKA) is recommended to be between 3 º and 7º, variations in preoperative PTS are wide. The purpose of this study was to evaluate the influence of the changes in preoperative and postoperative PTS on clinical outcomes.

Methods

One-hundred and eighty-two knees that underwent medial fixed-bearing UKA were evaluated retrospectively. The mean follow-up period was 36.4 ± 13.2 months (range, 24 to 63 months). Pre- and postoperative PTS were measured on lateral radiographs. Knees were classified in the large reduction group if the postoperative PTS was reduced by more than 5º compared with the preoperative value and in the small reduction group if not. Knee flexion angle and 2011 Knee Society Knee Scoring System (KSS 2011) were evaluated at last follow-up of at least 2 years.

Results

Thirty-three knees were classified in the large reduction group and 149 knees were classified in the small reduction group. The pre and postoperative PTS of large and small reduction groups were 10.9 ± 2.2, 3.6 ± 2.4 degrees and 7.7 ± 2.7, 7.1 ± 2.4 degrees, respectively. Flexion angle and KSS 2011 were not significantly different between the groups. However, the incidence of anterior collapse of the tibial component in the large group was significantly higher than the other group (P<0.001).

Conclusion

Although the knee flexion angle and PROMs at the last follow-up were not significantly different between the groups, large reduction in postoperative posterior tibial slope may be associated with anterior collapse of the tibial component in UKA. This study shows one potential benefit for matching native slope.