In vitro assessment of Function Graded (FG) artificial Hip joint stem in terms of bone/cement stresses: 3D Finite Element (FE) study

Abstract

BackgroundStress shielding in the cemented hip prosthesis occurs due to the mismatching in the mechanical properties of metallic stem and bone. This mismatching in properties is considered as one of the main reasons for implant loosening. Therefore, a new stem material in orthopedic surgery is still required. In the present study, 3D finite element modeling is used for evaluating the artificial hip joint stem that is made of Function Graded (FG) material in terms of joint stress distributions and stem length.Method3D finite element models of different stems made of two types of FG materials and traditional stems made of Cobalt Chromium alloy (CoCrMo) and Titanium alloy (Ti) were developed using the ANSYS Code. The effects on the total artificial hip joint stresses (Shear stress and Von Mises stresses at bone cement, Von Mises stresses at bone and stem) due to using the proposed FG materials stems were investigated. The effects on the total artificial hip joint system stresses due to using different stem lengths were investigated.ResultsUsing FG stem (with low stiffness at stem distal end and high stiffness at its proximal end) resulted in a significant reduction in shear stress at the bone cement/stem interface. Also, the Von Mises stresses at the bone cement and stem decrease significantly when using FG material instead of CoCrMo and Ti alloy. The stresses’ distribution along the bone cement length when using FG material was found to be more uniform along the whole bone cement compared with other stem materials. These more uniform stresses will help in the reduction of the artificial hip joint loosening rate and improve its short and long term performance.ConclusionFE results showed that using FG stem increases the resultant stresses at the femur bone (reduces stress shielding) compared to metallic stem. The results showed that the stem length has significant effects on the resultant shear and Von Mises stresses at bone, stem and bone cement for all types of stem materials.

Musculoskeletal-based finite element analysis of femur after total hip replacement

“…With titanium alloy, stress of 77 MPa was obtained whereas when used CoCrMo as implant material, stress of 88 MPa was obtained. 27 Regarding stem length, the stresses increased with increase in stem length. Research is being done by many authors on the effect of neck length on implant stresses and contradictory observations are reported.…”

Lattice Structures and Functionally Graded Materials Applications in Additive Manufacturing of Orthopedic Implants: A Review

“…All numerical results pointed toward a reduction in stress shielding. Low modulus at the distal end and high modulus at the proximal end was suggested by Al-Jassir et al [107] to improve the performance of the femoral stem. The proposed material combination was titanium alloy and cobalt chromium alloy, which may be challenging to grade together.…”

Recent development in modeling and analysis of functionally graded materials and structures

“…Bahraminasab et al [55,56] investigated advantages of FGMs over other material like titanium alloys, stainless steel or cobalt chromium molybdenum (CoCrMo) and concluded that using FGMs results reduction in stress developed in the neighboring part of tibia tray. FGMs is also using in the artificial hip joint replacement [57][58][59]. Jassir et al [59] suggested that using FGMs instead of CoCrMo and Ti alloy results reduction in stress in bone cement and stem which is the main parts of total hip replacement.…”

“…FGMs is also using in the artificial hip joint replacement [57][58][59]. Jassir et al [59] suggested that using FGMs instead of CoCrMo and Ti alloy results reduction in stress in bone cement and stem which is the main parts of total hip replacement.…”