Objective To investigate the early effectiveness of fixed-bearing unicompartmental knee arthroplasty (FBUKA) in patients with anterior cruciate ligament deficiency (ACLD), and to evaluate postoperative muscle strength and functional recovery through isokinetic muscle strength testing. Methods A retrospective analysis was performed on the clinical data of 181 patients with unilateral medial compartment knee osteoarthritis who underwent FBUKA treatment between January 2023 and June 2024 and met the selection criteria. According to the integrity of the anterior cruciate ligament, the patients were divided into the ACLD group (45 cases) and the anterior cruciate ligament intact (ACLI) group (136 cases). There was no significant difference in baseline data between the two groups (P>0.05), including age, gender, body mass index, affected side, disease duration, and preoperative Hospital for Special Surgery (HSS) score, Lysholm score, and visual analogue scale (VAS) score. A standardized rehabilitation protocol was adopted after surgery. Isokinetic muscle strength parameters [peak torque (PT) and total work (TW) of quadriceps and hamstring, and hamstring-to-quadriceps ratio (H/Q) at angular velocities of 60°/s and 180°/s] and HSS score, Lysholm score, and VAS score were measured preoperatively and at 6 weeks, 3 months, 6 months, and 12 months after operation; posterior tibial slope (PTS) was measured at 12 months after operation. Results All patients were followed up 12-18 months, with a mean of 13.6 months. No complication such as aseptic loosening of the prosthesis, dislocation of the mobile bearing insert, infection, or revision occurred after operation. Isokinetic muscle strength testing showed that at angular velocities of 60°/s and 180°/s, the PT and TW of quadriceps and hamstring significantly decreased and H/Q increased in both groups at 6 weeks after operation when compared with preoperative values (P<0.05); then PT and TW increased gradually, and H/Q decreased gradually. Except for no significant difference at 3 months after operation compared with preoperative values (P>0.05), all indicators were significantly different from preoperative values at 6 and 12 months after operation (P<0.05). There was no significant difference in isokinetic muscle strength parameters between the two groups at any time point before and after operation (P>0.05). The HSS score, Lysholm score, and VAS score at each postoperative time point in both groups significantly improved when compared with preoperative values (P<0.05), and there was no significant difference in each score between the two groups at each postoperative time point (P>0.05). At 12 months after operation, the PTS in the ACLD group was significantly smaller than that in the ACLI group (P<0.05). Conclusion For ACLD patients without anteroposterior knee instability, the isokinetic muscle strength recovery trajectory and clinical functional scores after FBUKA are comparable to those of ACLI patients. For such patients, FBUKA can achieve satisfactory muscle strength and functional recovery, and isokinetic muscle strength testing can provide objective quantitative evidence for postoperative rehabilitation evaluation.
