Functional alignment robotic-assisted total knee arthroplasty with tibial varus limited to 6° yields greater early postoperative pain improvement in patients with preoperative MPTA ≥84° compared with MPTA <84°.

BACKGROUND

Functional alignment (FA) in total knee arthroplasty (TKA) aims to restore native limb geometry while maintaining balanced soft-tissue tension within safe implant limits. Robotic-assisted FA-TKA typically limits tibial varus to 6° (preoperative medial proximal tibial angle [MPTA] 84°) to prevent tibial overload. This study investigates whether this varus limitation affects early 6-month outcomes in patients with preoperative tibia vara exceeding 6° (MPTA <84°).

METHODS

We retrospectively reviewed 93 consecutive CT-based robotic-assisted FA-TKAs performed between January 2024 and January 2025 in patients with varus deformity (preoperative MPTA ≤89°). Patients were stratified into preoperative MPTA <84° (n = 49) and MPTA ≥84-89° (n = 44). Six-month outcomes included Knee Society Knee and Function Scores (KSKS, KSFS), Oxford Knee Score (OKS), SF-36 scores, and achievement of minimal clinically important difference (MCID) for each patient-reported outcome (PRO).

RESULTS

Both groups showed significant improvements across all PROs with comparable overall satisfaction. Patients with preoperative MPTA ≥84° experienced greater SF-36 Bodily Pain improvement (49.4 ± 26.3 vs 32.6 ± 29.9; p = 0.017) and a trend toward higher MCID achievement (96.6% vs 81.0%; p = 0.05). Subgroup analysis of severe tibia vara (MPTA <81°) revealed no significant differences in pain or function compared with moderate deformities (MPTA 81-84°).

CONCLUSIONS

In conclusion, robotic-assisted FA-TKA yields comparable early clinical outcomes and patient satisfaction regardless of preoperative tibia vara severity, with only a modest difference in bodily pain improvement observed when native tibial alignment could be fully reproduced. Longer-term follow-up is warranted to evaluate implant survival and sustained functional outcomes.

LEVEL OF EVIDENCE: III.