Changes in coronal tibiofemoral subluxation before and after medial unicompartmental knee arthroplasty: an observation for ten years.

INTRODUCTION

Residual coronal tibiofemoral subluxation (CTFS) can cause peripheral contact between the implant components after medial unicompartmental knee arthroplasty (UKA), resulting in premature failure. The aim of this study was to investigate the changes in CTFS before and after surgery.

METHODS

Fifty-nine knees of 51 patients who underwent fixed-bearing medial UKA were retrospectively analyzed. CTFS was measured using anteroposterior knee radiographs in the standing position and under valgus stress before surgery and at two weeks and one, five, and 10 years after surgery. The preoperative and postoperative alignment of the knee and tibial component inclination angle (TCIA) were also evaluated.

RESULTS

Mean preoperative CTFS decreased significantly from 4.6 ± 1.5 mm in the standing position to 3.3 ± 1.1 mm under valgus stress and to 3.5 ± 1.4 mm in the standing position immediately after surgery. No changes in mean CTFS were observed during the 10-year follow-up period. The CTFS at 2 weeks after surgery was strongly correlated positively with the CTFS at the 10-year follow-up and the preoperative CTFS under valgus stress. The postoperative medial proximal tibial angle (MPTA) was strongly correlated negatively with the two-week postoperative CTFS, while TCIA was significantly correlated positively with that.

CONCLUSIONS

Residual CTFS after medial UKA did not change during the mid-term follow-up period, which was predictable to some extent based on the observations noted using the preoperative valgus stress radiographs. Close attention should be paid to patients with severe uncorrectable preoperative CTFS and small MPTA values when considering the indications for medial UKA.

LEVEL OF EVIDENCE

IV.