Measured Resection as Gap Balance Method in Mobile-Bearing Medial Unicompartmental Knee Arthroplasty: A Randomized Controlled Trial

Objective: Gap balancing is a vital process during mobile-bearing unicompartmental knee arthroplasty (MB-UKA). However, this process commonly depends on the surgeon's experience and lacks specific unified standards. This study aimed to propose and evaluate a novel "measured resection" method for gap balance in MB-UKA.

Methods: This prospective study included 49 consecutive patients (52 knees) who underwent MB-UKA from February 1, 2023, to September 1, 2023. Gap balance was achieved by the traditional "two-finger" method (Group 1, 26 knees) or the measured resection method (Group 2, 26 knees). The novel "measured resection" method was performed by measuring the thickness of the resected posterior femoral condyle and resected medial posterior tibial plateau to assess proper meniscal bearing thickness. Data were collected at baseline and the 6-month follow-up. Prosthetic angles, range of motion (ROM), visual analog scale (VAS) score, Oxford knee score (OKS), and Global Perceived Scale (GPE) were used to evaluate clinical outcomes. Independent samples t-test and Mann-Whitney U test were used to compare the differences.

Results: There were significant improvements in all measured outcomes at the 6-month follow-up from baseline in both groups (p < 0.01). Patients using measured resection method showed better ROM (130° vs. 120°, p = 0.007), VAS score (1 vs. 2, p = 0.013), and OKS scores (39.9 vs. 38.1, p = 0.013) at 6-month follow-up than the traditional "two-finger" method group. The prosthetic angles, ROM improvement, and GPE showed no significant difference between the groups (p > 0.05).

Conclusions: The measured resection method is a reliable method for assisting surgeons in choosing the ideal meniscal bearing thickness in MB-UKA to achieve proper gap balance and gain better clinical outcomes.

Trial registration: ClinicalTrials.gov (NCT03815448).