Method for determining the effect of nonspherical head geometry in hip joint implants on contact pressures

• Published in: Research on biomedical engineering Vol. 38; no. 4; pp. 1029 - 1035
• Main Author: Chernets, Myron
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 01.12.2022
• Subjects: Biomaterials; Biomedical Engineering and Bioengineering; Biomedical Engineering/Biotechnology; Engineering; Original Article; Hip joint implant; Metal-on-plastic; Contact pressures; Small ovality of head geometry; Contact angle; Analytical method
• ISSN: 2446-4740; 2446-4740
• DOI: 10.1007/s42600-022-00236-w

Purpose The main purpose of the publication is the presentation of a new analytical method for calculating the contact parameters considering the deviation from the sphericity (cross-sectional circularity) of the femoral head in the metal-plastic hip implants. The influence of the ovality of the femoral head and its position on the maximum contact pressures and the contact angle at the average load on the implant and the accepted nominal diameters and radial clearance is investigated. Methods The developed analytical method is based on the classical propositions of the elasticity theory and mechanics of contact interaction of close radii cylindrical bodies in internal contact. Its peculiarity is that, within the classical formulation of such a contact problem, a small difference between the real non-sphericity of the femoral head (cross-sectional circularity) and the ideal shape is taken into account. Results Quantitative and qualitative changes of contact parameters at the accepted date in the metal-on-plastic (MoP) hip joint implant due to the ovality of the femoral head are determined. The femoral head is made of thermodiffusion nitrided (TDN) titanium 2 and the acetabular cup is made of ultra-high-molecular-weight polyethylene (UHMWPE). Conclusion The regularities of the influence of the femoral head nonsphericity of the MoP hip joint implant on the maximum contact pressure have been established. It has been confirmed that it can be reduced by up to 33% if the oval femoral head is positioned appropriately relative to the acetabular cup. That is, the non-spherical (ovaloid) femoral head in a hip implant is useful. The presented non-spherical model of the endoprosthesis of the hip joint and the research method can be effectively applied in its modeling and prosthetics design.