Abstract

Background

Unicompartmental knee arthroplasty (UKA) is effective in the treatment of symptomatic unicompartmental knee osteoarthritis. However, ideal limb alignment and acceptable changes of alignment remains contentious.

Purpose

The purpose of this study is to look at the impact of post-operative mechanical limb alignment on short term functional outcomes in an Asian population.

Methods

We performed a retrospective review of all mobile bearing, Oxford UKAs performed from July 2016 to January 2019 by a single-surgeon (43 patients, 47 knees).  Pre- and post-operative weight bearing radiographic parameters were measured, as well as functional assessments via Oxford knee society (OKS) scores and the original Knee society score (KSS).

Results

The post-operative mechanical axis mean was varus 4.3° (range valgus 2° to varus 10°), with a mean correction of 4.4° towards valgus. All our patients had an improvement in functional scores and range of movement post-operatively, however, patients with pre-operative alignment of varus 15° did not meet the cut off for minimal important change (MIC) in OKS scores. More varus pre-operative alignment resulted in a larger degree of change in limb alignment post-operatively. A larger change in alignment was also associated with higher satisfaction scores in patients.

Conclusion

Post-operative limb alignment of up to 10° varus does not compromise short term functional outcome scores in medial UKA. Caution is advised when selecting patients with varus 15° and above for UKA as they may not be able to achieve a minimal important change in functional scores post-operatively. 

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