Stress transfer, stress shielding, and micro-movement analysis in the implanted femoral bone region with various hip implant stem materials: A finite element approach

Abstract

Listen

Translate article

This study analyzed stress distribution, stress shielding, and bone-implant micro-movement in different zones of implanted femur bone with hip implant stem composed of Inconel 718, 316 Stainless Steel, Ti6Al7Nb, Ti6Al4V, Ti-12Mo-6Zr-2Fe (TMZF), and Ti-33.6Nb-4Sn (TNS). A 3D model of a well-known hip implant “Summit” was placed in an adult femur bone, and walking, standing, and sitting load instances were simulated as loading conditions using a finite element model (FEM). Increasing hip implant material hardness reduces stress transmission in Gruen zones 1, 2, 5, 6, and 7 of the femur bone but increases it in Gruen zone 3. It also enhances stress holding in the implant body and elevates the Stress Shielding index (SSI) at seven Gruen zones for each load case. TMZF and TNS hip implants in Gruen regions 5 and 7 have negative SSI values under specific load situations. At Gruen zone 3, the SSI value for implanted femur bone increases with hip implant stem material hardness and SSI values variation in implanted femur bone for hip implants of different materials at each loading scenario is within 10 %. However, SSI values do not follow any pattern at Gruen zone 4. Less stiff implants demonstrate increased micro-movement in bone-implant contact zones 1 and 2 due to higher stress transfer. Greater stiffness (Inconel 718) caused increased micro-movement in zone 3. The overall micro-movement (Average and Highest) found an incremental trend for hip implants with higher stiffer to lower materials. The lowest stiff material (TNS) is still in the range of appropriate micro-movement for promoting osteointegration. This study indicates TNS as a superior hip implant stem material due to its enhanced stress distribution, reduced SSI in most Gruen zones on implanted femurs, and acceptable micro-movement over the implant-bone area of contact. Further research is required to minimize SSI, particularly in Gruen zone 3, when using TNS hip implants in implanted femurs.