Early Clinical Outcomes of a New Posteriorly Stabilized Total Knee Arthroplasty Prosthesis: Comparisons with Two Established Prostheses

Abstract

Purpose: We sought to determine whether early clinical performance of new posterior stabilized (PS) knee system, the Vega-PS (Aesculap), is better than that of two established total knee arthroplasty (TKA) prostheses, the E.motion-PS (Aesculap) and the Genesis II (Smith & Nephew) in terms of functional outcomes, patient satisfaction, and incidence of adverse events.

Materials and methods: We compared the clinical outcomes of 206 consecutive TKAs using Vega-PS with those of 205 TKAs using E.motion-PS and 216 TKAs using Genesis II at 2 years of follow-up.

Results: Overall, the knees with the Vega-PS had better functional outcome scores than the knees with the E.motion-PS, but had similar outcome scores to the knees with the Genesis II, as evident from the American Knee Society knee score (94.2 vs. 92.5 vs. 93.2), Western Ontario McMaster Universities Osteoarthritis (WOMAC) stiffness index (1.8 vs. 2.3 vs. 2.0), WOMAC function index (11.8 vs. 16.8 vs. 18.5), Short Form 36 (SF-36) physical component summary score (41.9 vs. 39.3 vs. 41.6), and SF-36 mental component summary score (50.0 vs. 45.8 vs. 46.9). Patient satisfaction was higher in the Vega-PS and Genesis II groups than the E.motion-PS group. No notable group differences were found in terms of the incidence of adverse events.

Conclusions: The Vega-PS, a newly developed PS fixed bearing prosthesis, had comparable or superior clinical performance in comparison with the two established fixed or mobile bearing PS prostheses.

Keywords: Arthroplasty; Knee; Outcome assessment; Prosthesis design; Replacement.

Fig. 1

The photographs show the Vega-PS prosthesis. The anterior and posterior narrowing of the femoral component with a low profile intercondylar box minimizes interference with the surrounding soft tissues. Fifty-five degrees posterior inclination of the post acts to avoid post-edge loading for better load distribution, prevents impingement with the extensor mechanism, and increases resistance to dislocation. The deepened anterior cutout of the insert allows smooth articulation with the patellar tendon.

Fig. 2

(A) The radiograph shows the preoperative mechanical tibiofemoral angle (MTFA). (B) The radiograph shows the postoperative MTFA. (C)The radiograph shows the femoral component lateral angle (FCLA), defined as the lateral angle between the femoral mechanical axis and a line connecting the most distal points of the medial and lateral condyles of the femoral component. (D) The radiograph shows the the tibial component lateral angle (TCLA), defined as the lateral angle between the tibial mechanical axis and a line parallel to the top surface of the tibial component. (E) The radiograph shows the femoral component flexion angle. To assess the sagittal alignment of the femoral component, we measured the angle between the line perpendicular to the tangent line of the femoral component box (a) and the line connecting the anterior cortical point of 10 cm proximal to the joint line and the anterior point of the meta-epiphysis junction before metaphyseal diverging (b). (F) The radiograph shows the tibial component posterior slope. To assess the sagittal alignment of the tibial component, we measured the angle between the line parallel to the upper surface of the tibial tray (b) and the line perpendicular to the tangent line of the anatomical axis (the posterior cortical line of tibia at two points, 5 cm and 15 cm distal to the joint line) of the proximal tibia (a).