Influence of Congruency Design on the Contact Stress of a Novel Hinged Knee Prosthesis Using Finite Element Analysis.

Objectives: To investigate the contact stress and the contact area o tibial inserts and bushings with respect to different congruency designs in a spherical center axis and rotating bearing hinge knee prosthesis under gait cycle loading conditions using finite element analysis.

Methods: Nine prostheses with different congruency (different degrees of tibiofemoral conformity and different distances between the spherical center and the bushing) designs were developed with the same femoral and tibial components. The models were transferred to finite element software. The peak contact stresses and contact areas on tibial inserts and bushings under the gait cycle loading conditions were investigated and compared.

Results: For tibial insert, the peak contact stress was the highest in the low conformity-long group (61.4486 MPa), and it was 1.88 times higher than that in the group with the lowest stress (moderate conformity-short group, 32.754 MPa). The contact area was the largest in the low conformity-long group (420.485 mm ), and it was 1.19 times larger than that in the group with the smallest area (moderate conformity-middle group, 352.332 mm ). For bushing, the peak contact stress was the highest in the high conformity-long group (72.8093 MPa), and it was 3.21 times higher than that in the group with the lowest stress (high conformity-short group, 22.6928 MPa). The contact area was the largest in the low conformity-short group (2.41 mm ), and it was 2.27 times larger than that in the group with the smallest area (high conformity-middle group, 1.063 mm ).

Conclusion: The results of our study showed that the congruency of the tibiofemoral surface and bushing surface should be considered carefully in the design of the spherical center axis and rotating bearing hinge knee prosthesis. Different levels of contact performance were observed with different congruency designs. In addition, the influence of contact stress and contact area on the polyethylene wear of rotating hinge knee prostheses should be confirmed with additional laboratory tests.