Similar kinematic patterns in posterior-stabilized and condylar constrained knee prostheses in revision knee arthroplasty: a prospective cohort study.

Abstract

The rising incidence of primary total knee arthroplasty (pTKA) is expected to lead to more revision TKAs (rTKA), which pose greater challenges and poorer outcomes, burdening both patients and healthcare systems. Knee kinematics play a key role in pTKA outcomes, but less is known about rTKA, where high-constraint implants and joint line elevation (JLE) may affect knee kinematics. The study aimed to: (1) Compare kinematic patterns between posterior-stabilized (PS) and condylar constrained (CCK) implants during open- and closed-chain exercises in rTKA; (2) Assess the impact of JLE on anteroposterior translation and post-cam engagement. Thirty patients (19 with PS implants and 11 with CCK implants) who underwent rTKA between 2022 and 2024 were tested at a minimum six-month follow-up. Tibiofemoral kinematics during open-chain flexion-extension (FE) and closed-chain exercises (sit-to-stand (STS) and squatting (SQ)) were analyzed using fluoroscopy. (1) Kinematic patterns were compared between PS and CCK implants, focusing on AP translation, internal-external (IE) rotation, varus-valgus (VV) rotation, range of motion (ROM) and post-cam engagement. (2) Joint line elevation was defined as a ≥4 mm increase compared to the native knee on a weight-bearing radiograph, and comparisons were made between patients with and without JLE. (1) No significant differences were observed in kinematic patterns between PS and CCK implants in rTKA. (2) A JLE ≥4 mm led to instability during squatting, particularly in early- and mid-flexion, with a significantly more anterior position in the medial compartment (0-30°: p = 0.037; 30-60°: p = 0.021). Although post-cam engagement was delayed in patients with JLE, the difference was not statistically significant (p = 0.173). (1) CCK implants have a kinematic pattern similar to PS implants in revision setting, supporting their use when appropriate, (2) JLE is associated with instability during squatting in early- and mid-flexion.