Medial-pivot inserts are associated with less periprosthetic bone mineral density reduction than that associated with posterior-stabilized inserts with identical geometries for total knee arthroplasty.

Abstract

Few studies have compared periprosthetic bone mineral density (BMD) changes associated with total knee arthroplasty (TKA) according to the insert design. Additionally, few have investigated BMD around medial-pivot prostheses. This study compared periprosthetic BMD changes associated with medial-pivot and posterior-stabilized TKA inserts comprising femoral and tibial components with identical geometries. This retrospective analysis of prospectively collected data included 85 procedures performed using a primary TKA system comprising femoral and tibial components with identical geometries (medial-pivot inserts: 38 procedures; posterior-stabilized inserts: 47 procedures) conducted between 2015 and 2020. Dual-energy X-ray absorptiometry was used to measure BMD in six regions of interest (ROIs) around the femur and tibia. The primary outcome was periprosthetic BMD changes, which were defined as the BMD percentage at 1 and 2 years postoperatively based on the BMD 3 weeks postoperatively. Clinical and radiographic outcomes of the groups were assessed and compared. Two years postoperatively, the medial-pivot group exhibited significantly less BMD loss in the anterior femoral ROI (-5.7 ± 9.2 %) compared with that of the posterior-stabilized group (-10.6 ± 12.0 %; P = 0.04). However, no significant differences in BMD changes in the other femoral ROIs or tibial ROIs were observed between groups. All postoperative clinical and radiographic outcomes, except for the knee flexion angle, were comparable between groups. Compared with posterior-stabilized inserts, medial-pivot inserts attenuated anterior femoral BMD loss. Medial-pivot inserts provide the potential advantage of a reduced long-term risk of TKA-related complications.