Factors influencing the insertion of a size 1 minimum-sized tibial baseplate in fixed-bearing unicompartmental knee arthroplasty for Japanese patients.

Abstract

An overhang of the tibial baseplate in unicompartmental knee arthroplasty (UKA) has been associated with postoperative pain and impaired function. There are significant patient factors that influence the insertion of a size 1 minimum-sized tibial baseplate in fixed-bearing (FB) UKA for Japanese patients with varus knee osteoarthritis (KOA). This study investigated the above-hypothesized factors. We conducted a retrospective study of 74 consecutive patients who underwent FB-UKA between March 2023 and July 2025. The endpoints were the Kellgren and Lawrence (KL) grade; patient height (m); weight (kg); body mass index (BMI, kg/m²); preoperative extension and flexion range of motion (ROM); preoperative hip-knee angle (HKA); and preoperative and postoperative medial proximal tibial angle (MPTA) and posterior tibial slope (PTS). Following surgery, calipers were used to measure the medial resection amounts of the distal and dorsal femur and the proximal tibia. The sizes of the femoral and tibial components that were actually inserted were recorded. Logistic regression analyses were performed to clarify the factors influencing the insertion of a size 1 minimum-sized tibial baseplate. Univariate analysis revealed significant difference between the group concerning patient height (1.47 ± 0.1 in Group 1 and 1.57 ± 0.1 in Group O, P < 0.001). Logistic regression demonstrated that shorter height (OR: 3.07e-19, 95 % CI: 7.54e-35- 1.25e-03, P = 0.020), the size of the femoral component that were actually inserted (OR: 9.16e-3, 95 % CI: 1.48e-4-0.57, P = 0.026). ROC analysis identified cutoff values of <1.51 m for patient height (AUC: 0.872, 95 % CI: 0.765-0.980), and size 2 femoral component (AUC: 0.832, 95 % CI: 0.748-0.917). Patient height and femoral component size were significant factors that influence the insertion of a size 1 minimum-sized tibial baseplate in FB-UKA for Japanese patients with varus KOA.