In vivo three-dimensional kinematics in unicompartmental knee arthroplasty: A sports activity cluster analysis

The specific kinematics relevant to sports activities after unicompartmental knee arthroplasty (UKA) remain unclear. We aimed to clarify the kinematic factors associated with sports activities after UKA.

Twenty-five knees that had undergone UKA were examined fluoroscopically during squatting (weight-bearing [WB]) and active-assisted knee flexion (non-weight-bearing [NWB]). Patients who were able to perform deep squatting were included. A two-dimensional/three-dimensional registration technique was used to evaluate tibiofemoral kinematics, including flexion angle, axial rotation angle, varus-valgus angle, and anteroposterior translation (APT) of the femur relative to the tibia. Patients were divided into two groups using hierarchical cluster analysis based on 1-year postoperative sports scores from the Knee Injury and Osteoarthritis Outcome Score and the 2011 Knee Society Score (low-to-moderate score group [n = 15] and high score group [n = 10]).

The sports subscale Knee Injury and Osteoarthritis Outcome Scores, except for jumping, were significantly higher in the high-score group than in the low-score group. During WB, the flexion angle was significantly greater in the high-score group (136.2 ± 8.5°) than in the low-score group (126.3 ± 14.2°). In contrast, no significant difference in flexion angle was observed during NWB. Regarding lateral APT, the high-score group showed a more posterior position than the low-score group throughout the flexion range during WB. No significant between-group differences were observed in terms of axial rotation, varus-valgus angle, or medial APT.

The ability to achieve greater flexion during weight-bearing activities is an important factor for sports performance after UKA.

Level III.