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. 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. 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. 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.