Kinematic Performance of Medial Pivot Total Knee Arthroplasty

Background Total knee arthroplasty (TKA) implants have continued to evolve to accommodate new understandings of knee mechanics. The medial-pivot implant is a newer design, which is intended to limit anterior-posterior translation in the medial compartment while allowing lateral compartment translation. However, evidence for a generalized medial-pivot characteristic across all activities is limited. The purpose of the study was to quantify and compare in vivo knee joint kinematics using high-speed stereo radiography during activities of daily living in patients who have undergone a TKA with a cruciate sacrificing medial-pivot implant to age- and sex-matched native controls. Methods There were fifteen participants (7 patients, 4 women, mean age 70 years [range, 61 to 76] and 8 non-symptomatic controls, 4 women, mean age 64 years, [range, 56 to 81]) who performed 6 functional tasks in high-speed stereo radiography: deep-knee lunge; chair rise; step down; gait, gait with 90° turn; and seated knee extension. Translational differences between groups (surgical vs. control) were assessed for the medial and lateral condyle, while pivot location was normalized to subject-specific tibial plateau geometry. Results The emerging kinematic trend among the surgical cohort was a more constrained medial condyle that provided greater stability of the medial compartment and did not result in the paradoxical anterior translation at mid-flexion angles during weightbearing activities, but was associated with less condylar translation than native knees. Additionally, the transverse tibial pivot location occurs most commonly in the middle third of the tibial plateau and secondarily on the medial third. Conclusion Some variability in pivot location occurs between activities and is greater in non-symptomatic, native knee controls.