The effect of mechanical axis correction on clinical outcomes after unicondylar knee arthroplasty

The optimal degree of postoperative mechanical axis correction following unicondylar knee arthroplasty (UKA) remains controversial. This study aimed to evaluate the relationship between postoperative alignment after UKA and clinical outcomes.

The study included 43 knees from 41 patients who underwent medial UKA. Preoperative full-length standing radiographs and postoperative radiographs obtained at the final follow-up visit were used to assess mechanical axis alignment and posterior tibial slope. Patients were grouped according to postoperative mechanical axis zone and by the amount of varus correction (<5° and ≥5°). Clinical outcomes were assessed using the Knee Society Score (KSS), the visual analog scale (VAS), the SF-36, and patient satisfaction scores.

Patients whose postoperative alignment fell in the central zone had significantly higher KSS (2011) - Functional score (85.0 ± 5.1 vs. 77.0 ± 5.7 and 79.5 ± 6.0; p = 0.003) and KSS (2011) - Objective score (81.7 ± 4.8 vs. 75.0 ± 6.1 and 75.7 ± 7.5; p = 0.013). Patients with varus correction ≥5° demonstrated higher KSS (2011) - Functional score (83.6 ± 5.6 vs. 75.5 ± 4.2; p < 0.001), KSS (2011) - Objective score (79.7 ± 6.5 vs. 73.6 ± 6.3; p = 0.007), SF-36 physical functioning (79.5 ± 8.6 vs. 72.3 ± 7.2; p = 0.004), and KSS (2011) - Patient satisfaction (32.1 ± 3.7 vs. 29.8 ± 2.3; p = 0.004).

Restoration of the mechanical axis toward the central zone and greater varus correction were associated with improved functional outcomes after UKA. These findings should be interpreted with caution due to the retrospective design and relatively limited sample size. Within these limitations, the results suggest that patient-specific, functionally oriented alignment strategies may be more considered than rigid alignment targets in UKA.