Minor varus alignment provides better results than neutral alignment in medial UKA

Few data exist regarding the outcome and survivorship of medial UKA in patients with minor varus alignment. The purpose of this study was therefore to analyse the clinical results of medial UKA implanted with no more than 7° of varus, and to verify whether there was a relationship between limb alignment and overall outcomes.

One hundred and twenty five medial fixed-bearing UKAs with no more than 7° of varus were retrospectively analysed. The varus/valgus inclination and thickness of the bone cuts were performed relating to the proximal tibial epiphyseal axis. Patients were assessed with the IKS scores and range of knee motion. The subjects were classified into three groups according to the postoperative femoro-tibial mechanical alignment angle (group A: − 2° to 1°; group B: 2° to 4°; group C: 5° to 7°).

The mean follow-up was 7.6 years (range, 3.5–9.3). IKS knee scores increased proportionally with increasing varus according to a linear relationship ( p ≪ 0.01). Additionally, IKS knee scores were significantly higher in group B and still higher in group C if compared to those in group A ( p = 0.003). Finally, a significantly higher frequency of IKS function scores > 90 points in subjects with femoro-tibial mechanical alignment angle ≥ 4° was found ( p = 0.009).

Minor varus alignment does not compromise the mid- to long-term outcome of a medial UKA, and gives better results compared to neutral or close-to-neutral alignment.

IV — Retrospective case series study.