Abstract
Introduction
Controversy still exists as to whether total knee arthroplasty (TKA) provides reproducible knee kinematics during activities. In this study, we evaluated the in vivokinematics of stair-climbing after TKA using a 3D-to-2D model-to-image registration technique.
Patients and Methods
A total of twenty four knees in nineteen patients following cruciate-retaining (CR) or posterior-stabilized (PS) TKA were randomly included in the study. The twenty-four knees included 22 female knees and 2 male knees in patients aged 73 years. The pre-operative diagnosis was osteoarthritis in 22 knees and rheumatoid arthritis in 2 knees. The average follow-up period after surgery was 29 months, and average post-operative knee extension/flexion angle was 2°/121°. The average knee score was 93 and the average functional score was 77. Continuous sagittal radiological images were obtained during stair-climbing for each patient using a large flat panel detector. Anteroposterior (AP) tibiofemoral position, implant flexion, and axial rotation angles were determined in three dimensions using a 3D-to-2D model-to-image registration technique. In CR TKA, the minimum distances between the femoral trochlea and the intercondylar eminence of the tibial insert were measured using a CAD software program. In PS TKA, the minimum distances between the femoral cam and the posterior aspect of the tibial post and between the femoral trochlea and the anterior aspect of the tibial post were measured.
Results
The average implant flexion angle at foot strike/toe off during stair-climbing was 65.6°/−5.9° after CR TKA and 72.3°/−0.5° after PS TKA. The average AP tibiofemoral position from the center of the tibial insert at foot strike/toe off was 9.2mm posterior/1.0mm posterior after CR TKA and 8.6mm posterior/1.0mm posterior after PS TKA. The average tibiofemoral rotation angle at foot strike/toe off was −6.0°/−2.1° after CR TKA and −8.6°/2.7° after PS TKA. In CR TKA, the average of the minimum distance between the intercondylar notch of the femoral trochlea and the intercondylar eminence of the tibial insert at foot strike/toe off was 26.9mm/4.6mm. No knees demonstrated impingement of the femoral trochlea on the tibial insert (Fig. 1). In PS TKA, the average of the minimum post-cam and femoral trochlea-anterior post distances at foot strike/toe off were 4.0 ± 1.9 mm/18.2 ± 4.1 mm and 19.3mm/1.6mm. No knees demonstrated post-cam engagement, but four knees demonstrated anterior tibial post impingement from −0.5° of implant flexion (Fig. 2).
Discussion
This study characterized knee kinematics during stair-climbing after two different types of total knee prostheses. Mid-flexion AP stability was demonstrated in all knees after CR TKA during stair-climbing. It could be assumed that the retained posterior cruciate ligament was functioning. However, paradoxical femoral translation and/or reverse axial rotation due to deficiency of the anterior cruciate ligament were shown in 75% of knees at low flexion. The post-cam mechanism did not function during stair-climbing after PS TKA and 33% of knees demonstrated forward sliding of the femur at mid-flexion. The post-cam mechanism should be configured to function at mid-flexion. Unintended anterior tibial post impingement, which was observed in 33% of knees at knee extension, provided anterior femoral position.
