Association between medial femoral resection thickness and postoperative pain after fixed-bearing unicompartmental knee arthroplasty: an exploratory cohort study.

BACKGROUND

Unicompartmental knee arthroplasty (UKA) is an established treatment for isolated compartment osteoarthritis and is associated with favorable functional outcomes and implant survivorship. However, determinants of achieving a near pain-free state after fixed-bearing (FB) UKA remain incompletely understood. This exploratory study investigated whether medial femoral resection thickness is associated with postoperative pain following medial FB-UKA.

METHODS

This retrospective single-surgeon cohort study included 40 consecutive patients who underwent medial fixed-bearing MOTO-UKA between March 2023 and June 2024. Pain was assessed one year postoperatively using the Numerical Rating Scale (NRS). Patients were categorized as near pain-free (NRS ≤ 1.0) or higher pain (NRS > 1.0). Medial femoral resection thickness was measured intraoperatively using calibrated calipers. Univariate analyses were performed. Receiver operating characteristic (ROC) analysis was conducted to explore discrimination.

RESULTS

At one year, 24 patients (60%) achieved NRS ≤ 1.0. In univariate analysis, greater medial femoral resection thickness was observed in the near pain-free group (6.9 ± 1.1 mm vs. 5.8 ± 0.7 mm; P = 0.001). ROC analysis demonstrated moderate discrimination (AUC 0.779; 95% CI 0.642-0.916), with an exploratory reference value of 6.5 mm.

CONCLUSIONS

In this exploratory single-surgeon cohort of medial fixed-bearing UKA, smaller medial femoral resection thickness was observed in patients reporting higher pain at one year. Resection thickness likely reflects medial compartment balance rather than representing a direct surgical target. Given the limited sample size, these findings should be considered hypothesis-generating and require prospective multicenter validation.