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. 2020 Nov;9(11):768-777.
doi: 10.1302/2046-3758.911.BJR-2020-0019.R2.

Effect of material selection on tibial post stresses in posterior-stabilized knee prosthesis

Chang-Hung Huang  1   2   3 , Yung-Chang Lu  1   4   5 , Lin-I Hsu  1   6 , Jiann-Jong Liau  7 , Ting-Kuo Chang  1   4   5 , Chun-Hsiung Huang  4   5   8
Affiliations

Effect of material selection on tibial post stresses in posterior-stabilized knee prosthesis

Chang-Hung Huang et al. Bone Joint Res. 2020 Nov.

Abstract

Aims: The material and design of knee components can have a considerable effect on the contact characteristics of the tibial post. This study aimed to analyze the stress distribution on the tibial post when using different grades of polyethylene for the tibial inserts. In addition, the contact properties of fixed-bearing and mobile-bearing inserts were evaluated.

Methods: Three different grades of polyethylene were compared in this study; conventional ultra high molecular weight polyethylene (UHMWPE), highly cross-linked polyethylene (HXLPE), and vitamin E-stabilized polyethylene (VEPE). In addition, tibial baseplates with a fixed-bearing and a mobile-bearing insert were evaluated to understand differences in the contact properties. The inserts were implanted in neutral alignment and with a 10° internal malrotation. The contact stress, von Mises stress, and equivalent plastic strain (PEEQ) on the tibial posts were extracted for comparison.

Results: The stress and strain on the tibial post for the three polyethylenes greatly increased when the insert was placed in malrotation, showing a 38% to 56% increase in von Mises stress and a 335% to 434% increase in PEEQ. The VEPE insert had the lowest PEEQ among the three materials. The mobile-bearing design exhibited a lower increase in stress and strain around the tibial posts than the fixed-bearing design.

Conclusion: Using VEPE for the tibial component potentially eliminates the risk of material permanent deformation. The mobile-bearing insert can help to avoid a dramatic increase in plastic strain around the tibial post in cases of malrotation. The mobility allows the pressure to be distributed on the tibial post and demonstrated lower stresses with all three polyethylenes simulated. Cite this article: Bone Joint Res 2020;9(11):768-777.

Keywords: Highly cross-linked; Malposition; Polyethylene; Stress-strain distribution; Vitamin E-stabilized.

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Figures

Fig. 1
Fig. 1
Typical elastoplastic stress-strain curves of ultra high molecular weight polyethylene (UHMWPE), highly cross-linked polyethylene (HXLPE), and vitamin E-stabilized polyethylene (VEPE).
Fig. 2
Fig. 2
Finite element models of a) fixed-bearing and b) mobile-bearing knee prostheses.
Fig. 3
Fig. 3
Convergence test of the contact area, peak contact pressure, and von Mises stress on the tibial post.
Fig. 4
Fig. 4
Graphs of a) contact pressure, b) von Mises stress, and c) equivalent plastic strain (PEEQ) of ultra high molecular weight polyethylene (UHMWPE), highly cross-linked polyethylene (HXLPE), and vitamin E-stabilized polyethylene (VEPE) posts in fixed-bearing and mobile-bearing knee prostheses under neutral and malrotation contact.
Fig. 5
Fig. 5
The maximum tensile stress was observed at the base of the tibial post and maximum compressive stress at the anteroinferior portion of the tibial post during post-cam engagement.
Fig. 6
Fig. 6
Plastic deformation at the posterior surface and the base of the tibial post. Vitamin E-stabilized polyethylene (VEPE) had a smaller equivalent plastic strain (PEEQ) around the post than highly cross-linked polyethylene (HXLPE).
Fig. 7
Fig. 7
Contact pattern of the post-cam contact surface in a) neutral contact of fixed-bearing, b) malrotation contact of fixed-bearing, c) neutral contact of mobile-bearing, and d) malrotation of mobile-bearing. Note: CPRESS indicates compression pressure.
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