Lower limb alignment control: Is it more challenging in lateral compared to medial unicondylar knee arthroplasty?

•Limb alignment is important factor in unicondylar knee arthroplasty (UKA).•We compared limb alignment following medial and lateral UKA.•Alignment overcorrection was significantly higher in the lateral UKA.•There is increased risk of “overcorrection” and greater difficulty in predicting alignment when performing lateral UKAs compared to medial UKAs.

IntroductionLimb alignment after unicondylar knee arthroplasty (UKA) has a significant impact on outcomes. The literature lacks lateral UKA alignment studies, making our understanding of this issue based on medial UKA.MethodsWe evaluated limb alignment in 241 patients who underwent medial (229 knees) or lateral (37 knees) UKA. Alignment was measured pre and postoperatively in radiographs and intra-operatively using a navigation system. We compared the percentage of over-correction and the difference between post-operative alignment and navigation measurement.ResultsPercentage of overcorrection was significantly higher in the lateral UKAs (11%) compared to the medial UKAs (4%). In medial UKAs, the mean difference between the intraoperative alignment and the post-operative was 1.33°. This was significantly lower than the mean 1.86° difference in the lateral UKAs.ConclusionsOur data demonstrated an increased risk of “overcorrection,” and greater difficulty in predicting postoperative alignment using computer navigation, when performing lateral UKAs compared to medial UKAs.