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.

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 -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;  < 0.001) and with lower measured loads in the lateral compartment at 10° (13 vs. 15 lbf;  = 0.011), 45° (8 vs. 13 lbf;  = 0.011) and 90° of flexion (6 vs. 10 lbf; < 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.