Does preoperative varus alignment impact functional outcomes in robotic assisted medial unicompartmental knee arthroplasty? mid-term analysis.

The aims of our study are (1) to evaluate clinical outcomes of robotic-assisted medial unicompartmental knee arthroplasty (UKA) in varying degrees of varus deformities (2) what should be the target for correction of the varus deformities? (3) to validate intraoperative robotic hip-knee-ankle (HKA) axis (dynamic HKA) against HKA obtained from long leg radiographs (LLR) (static HKA). 212 fixed-bearing medial UKA performed from 2017 to 2024 with the help of a burr-based robot platform, were evaluated with a mean follow-up of 56 months. All the patients were classified on the basis of static HKA and dynamic HKA into three groups of varus deformities: mild (> 172°), moderate (168° to 172°), and severe (< 168°). The functional outcome was assessed using the Oxford Knee Score (OKS) and the modified Kujala Score (MKS). 85 (40.2%) had a mild, 94 (44.3%) moderate, and 33 (15.5%) had a severe varus preoperatively. All the patients demonstrated a significant increase in OKS, MKS after surgery (p < 0.001) with no difference between the three groups (p > 0.05). There was poor correlation between preoperative dynamic HKA and postoperative OKS, MKS (r = 0.06, r = 0.41). A good agreement was noted between the static and dynamic HKAs (96.2% preoperatively, 97.7% postoperatively). Degree of preoperative varus deformity does not negatively impact the functional outcomes to achieve satisfactory functional outcomes. The target postoperative HKA shouldbe correcting  50% of the preoperative varus deformity. Preoperative LLRs represent static alignment of the limb and can be safely done away with in high volume robotic centres.