Influencing factors in knee kinematics following posteriorly stabilized knee arthroplasty: a comprehensive analysis.

Purpose: Numerous papers present in-vivo knee kinematics data following total knee arthroplasty (TKA) from fluoroscopic testing. Comparing data is challenging given the large number of factors that could potentially affect the reported kinematics. This paper aims to understand the effects of some of the most pertinent factors: 1. What is the role of post-cam interaction and implant geometry in total knee kinematics? 2. Do tibiofemoral kinematics vary with different activities? 3. Is there a correlation between landmark-based and contact points kinematics?

Methods: Thirty patients who underwent TKA between 2014 and 2016 were assessed at a minimum follow-up period of six months. Given the use of three different posterior stabilized implants in the hospital, the first ten patients per implant who attended follow-up consultations and demonstrated a minimum of 90° knee flexion, were included in the study. The tibiofemoral kinematics during both open kinetic chain flexion-extension and closed kinetic chain exercises, such as rising from a chair and squatting, were examined using fluoroscopy. Single-plane fluoroscopic analysis (2D) was used to record the data, which was subsequently converted to 3D implant positions to evaluate the tibiofemoral contact points and landmark-based kinematic parameters.

Results: Significantly different anteroposterior translations and internal-external rotations were observed between the considered implants. Comparing the activities, a significantly more posterior position was observed for both the medial and lateral compartments in the closed chain activities during mid-flexion. A strong and significant correlation was found between the contact points and landmark-based analysis methods. However, large individual variations were also observed, yielding a difference of up to 25% in anteroposterior position between both methods.

Conclusion: In conclusion, all three evaluated factors significantly affect the obtained tibiofemoral kinematics.

Level of evidence: Diagnostic, Level IV Case series.