To analyze knee kinematic and kinetic parameters after mobile bearing unicompartmental knee arthroplasty (UKA) during postoperative squatting-standing activity, so as to evaluate the efficacy of UKA, guide the process of postoperative rehabilitation and predict complications.

This study was a clinical cohort study. Thirty-one patients were admitted to the Second Affiliated Hospital of Xi’an Jiaotong University from June 2016 to June 2018 diagnosed with medial knee OA with primary UKA were followed up. After case screening, Kellgren & Lawrence stage one or two, lower limb trauma, tumor, excessive body mass index (BMI), and other complications were excluded, then 26 patients were recruited to take gait tests. Squatting-standing activities were performed under the test of Vicon T40 10-Camera Motion Analysis System and Advanced Medical Technology Incorporated (AMTI) force plates preoperatively at different stages after UKA (12, 18, 24 months). Twenty-two healthy subjects were enrolled as the control group, and the difference of squatting pattern between the healthy group and the UKA patients was compared by double-tail t test.

The average duration of follow-up was (24.4±1.5)months. At one year follow-up, the peak values of varus angle (21.20±2.30) °, internal rotation angle (16.90±1.80) °, the torques of knee extension (0.310±0.040) N/kg and internal rotation (0.020±0.008) N/kg of the UKA knees were inferior to contralateral knees. The peak adductor moment (1.220±0.050) N/kg was superior to the contralateral knees.

Mobile UKA can improve the ROM and torques of the involved knee and don’t affect the biomechanical indicators of healthy limbs. OA knees show decreased torque of knee extension and increased torque of knee adduction during active deep flexion activity in early postoperative period. With rehabilitation time elongation, the patients can achieve better range of motion and more natural torques of knee extension and adduction, which may predict ideal functional outcome in medium and long terms.