Abstract
Introduction
Limb alignment after unicondylar knee arthroplasty (UKA) has a significant impact on surgical outcomes. The literature lacks studies that evaluate the limb alignment after lateral UKA or compare alignment outcomes between medial and lateral UKA. In this study, we retrospectively compare a single surgeon's alignment outcomes between medial and lateral UKA using a robotic-guided protocol.
Methods
All surgeries were performed by a single surgeon using the same planning software and robotic guidance for execution of the surgical plan. The senior surgeon's prospective database was reviewed to identify patients who had 1) undergone medial or lateral UKA for unicompartmental osteoarthritis; and 2) had adequate pre- and post-operative full-length standing radiographs. There were 229 medial UKAs and 37 lateral UKAs in this study. Mechanical limb alignment was measured in standing long limb radiographs both pre- and post-operatively. Intra-operatively, limb alignment was measured using the computer assisted navigation system. The primary outcome was over-correction of the mechanical alignment (i.e, past neutral). Our secondary outcome was the difference between the radiographic post-operative alignment and the intra-operative “virtual” alignment as measured by the computer navigation system. This allowed an assessment of the accuracy of our navigation system for predicting post-operative limb alignment after UKA.
Results
The percentage of overcorrection was significantly higher in the lateral UKA group (11%), when compared to the medial UKA group (4%), (p = 0.0001). In the medial UKA group, the mean difference between the intraoperative “virtual” alignment provided by the navigation system, and the post-operative, radiographically measured mechanical axis, was 1.33° (± 1.2°). This was significantly lower than the mean difference between these two parameters in the lateral UKA group, 1.86° (± 1.33°) (p = 0.019).
Conclusions
Our 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.
