Abstract: BACKGROUND: The knee osteoarthritis, a major cause of disability in the elderly, is currently treated with surgical procedures including unicompartmental knee arthroplasty in end-stage patients, but the recovery of muscle strength in patients after unicompartmental knee arthroplasty is not well understood. 
OBJECTIVE: To analyze the short-term and medium-term knee isometric muscle strength characteristics of patients with unilateral knee osteoarthritis after unicompartmental knee arthroplasty, to compare with those of the unaffected side, and to analyze the recovery of muscle strength in the affected limb. 
METHODS: Patients undergoing unicompartmental knee arthroplasty in the Qingdao Municipal Hospital from June to December 2023 were recruited to undergo standardized functional rehabilitation exercises. The A8-2M multi-joint isokinetic training and testing system was used to detect the peak torque and the maximum one-repetition work of the extensor muscle of the unaffected side and the affected side of the knee joint at the angular velocity of 60 (°) /s and the range of joint motion of 0°-90° before, 1 and 3 months after surgery. 
RESULTS AND CONCLUSION: (1) At an angular velocity of 60 (°)/s, the peak moment and maximum one-repetition work of the flexor and extensor muscles of the affected side were lower than those of the unaffected side preoperatively (P < 0.05). (2) The peak moment and maximum one-repetition work of the flexor and extensor muscles were significantly lower than those of the unaffected side 1 month postoperatively (P < 0.05). Meanwhile, the peak moment of the flexor and extensor muscles and the maximum one-repetition work of the flexor and extensor muscles on the affected side at 1 month postoperatively were significantly lower than those on the affected side preoperatively (P < 0.05). (3) The peak moment of the flexor and extensor muscles and the maximum one-repetition work of the flexor and extensor muscles on the affected side at 3 months postoperatively had no significant difference from those on the unaffected side. The peak flexor-extensor moment of the flexor-extensor muscles on the affected side was higher than that preoperatively (P < 0.05). (4) It is indicated that after unicompartmental knee arthroplasty, the muscle strength on the affected side is poor after 1 month after standard functional rehabilitation. However, after 3 months, there was no significant difference between the affected side and the unaffected side.  

Key words: unicompartmental knee arthroplasty, total knee arthroplasty, knee osteoarthritis, degenerative lesions, isometric counting, muscle strength, peak torque, maximum one-repetition work