Purpose: Use of a mobile tibial plateau for total knee arthroplasty (TKA) is designed to reduce wear and improve prosthetic kinetics. The purposes of this study were: 1) to compare the kinetics of a posterior stabilised TKA implanted with a fixed plateau (FP) or a mobile plateau (MP) and, 2) to determine whether the mobile plateau improves axial rotation.

Material and methods: Ten patients with a unilateral TKA (HLS) with a fixed or mobile plateau were selected for this study according to the following criteria: arthroplasty for degenerative knee disease, healthy contralateral knee, age < 80 years, pain-free prosthesis, IKS > 80/100, flexion > 90°, follow-up > 1 year. There were five patients with a fixed plateau and five patients with the same prosthesis except with a mobile plateau. Knee movement (flexion-extension, axial rotation, valgus-varus) were measured with an electromagnetic goniometer on the implanted and healthy sides. Four movements were recorded: walking, standing up sitting down, flexion-extension without loading. Amplitudes were compared with non-parameteric statistical tests between the healthy side and the implanted side and between the two types of implants

Results: The FP knees were more mobile in valgus-varus due to greater residual frontal laxity than the MP knees. This extra laxity generated excessive axial rotation on the FP during non-loaded movements. Conversely, when loaded, axial rotation of the MP knees was 10° greater (mean, p < 0.05) than for the FP knees, giving better stability in the frontal plane. This study did not demonstrate any difference in flexion between FP and MP. Patients with an MP prosthesis did not have significantly different amplitudes of the three movements for the healthy versus implanted knee. For the patients with a FP prosthesis, axial rotation and frontal plane movement was lower in the implanted knee than in the healthy knee (p< à.05).

Discussion: This study devoted to the design of a single prosthesis demonstrated the usefulness of the mobile plateau for axial rotation during loaded movement. The kinetics of MP prostheses is similar to that of the healthy knee. Better axial rotation with MP prostheses during loaded movements suggests the persistence of the plateau mobility which should be confirmed with a cinematographic study.