A medial pivot kinematic pattern could be achieved in a significant proportion of patients with varus knees after primary total knee arthroplasty using functional positioning

Abstract

Abstract Purpose Physiological knee kinematics typically exhibit a medial pivot (MP) pattern and femoral rollback during flexion. There is a significant gap in the literature pertaining to the evaluation of kinematic patterns following total knee arthroplasty (TKA). The aim of this study was to evaluate the proportion of patients achieving a MP kinematic pattern following robotic‐arm‐assisted TKA using functional positioning. Methods Sixty consecutive patients who underwent primary robotic‐assisted TKA employing functional positioning were investigated. Following final positioning, sensor‐embedded tibial trials were used to assess the kinematic pattern. Two senior fellowship‐trained surgeons documented the kinematic tracking of the tibiofemoral articulation and centre of load on the sensor display monitor. The differential load pressure was captured intraoperatively at 10°, 45° and 90° to substantiate the kinematic pattern. Significance was for p ‐value < 0.05. Results A MP kinematic pattern was observed in 29 patients (48%). These patients exhibited a median medial load of 21.0 lbf at 10°, 15 lbf at 45° and 13 lbf at 90°, while the median lateral load was 13 lbf at 10°, 8 lbf at 45° and 6 lbf at 90°. The patients with MP kinematics were associated with significantly greater medial measured loads at 10° flexion (21 vs. 18 lbf; p < 0.001) and with lower measured loads in the lateral compartment at 10° (13 vs. 15 lbf; p = 0.011), 45° (8 vs. 13 lbf; p = 0.011) and 90° of flexion (6 vs. 10 lbf; p < 0.001). Mean differential load pressure between the compartments was <15 lbf at 10°, 45° and 90° in both groups. Conclusion In our cohort, using robotic arm assistance with functional positioning, we observed a MP kinematic pattern in approximately 50% of the cases. Further longer‐term studies are warranted to evaluate the impact of the kinematic pattern on clinical and patient‐reported outcomes. Level of Evidence Level III, retrospective cohort study.