Design of Titanium Alloy Femoral Stem Cellular Structure for Stress Shielding and Stem Stability: Computational Analysis

Abstract

The main objective of this study is to design titanium alloy femoral stems with cubic porous structures that will be able to reduce stress shielding and promote stem stability. These porous structure designs were introduced into titanium alloy femoral stems as homogeneous and functionally graded porous structures. First, the cubic cellular structures were simulated under compressive loading to measure the yield and modulus of elasticity for various porosity ranges. Based on the selected porosity range, fifteen different arrangements of radial geometrical functionally graded (FG) designs were developed with average porosities of 30, 50, and 70% respectively. Finite element models were developed with physiological loads presenting three different walking speeds (1, 3, and 5 km/h), where the average human body weight was assumed. Stresses at the bone Gruen zones were measured to check the percentage of stress transfer to the bone for each porous stem design and were compared with the bulk stem. Several FG stem designs were shortlisted for further investigation as candidates for hip implants.

A novel hybrid design and modelling of a customised graded Ti-6Al-4V porous hip implant to reduce stress-shielding: An experimental and numerical analysis

“…Hence, major factors -including the potting material and fixation orientation of the stems -were controlled, in order to ensure the validity of all comparative analyses performed during this study. The stiffness value of the porous stem (2.15 kN/mm) was comparable (0.42-2.18 kN/mm) to the previous developed porous hip stems in the literature (Harrysson et al, 2008;Mehboob et al, 2020b;Tan and van Arkel, 2021;Al Zoubi et al, 2022).…”

Additively manufactured controlled porous orthopedic joint replacement designs to reduce bone stress shielding: a systematic review

“…In contrast, Hedia et al (2019) compared the influence of porosity in their study but also material grading with a porosity decrease toward the distal end and reported a stress increase in the femur [ 48 ]. Al Zoubi et al (2022) compared radially graded and uniform designs with different porosities and found that designs with increasing porosity toward the center of the implant performed best in terms of stress transfer to bone, but also micromotion and mechanical strength [ 28 ]. Singh et al (2018) reported that a combination of both, radial and axial grading, could further enhance the decrease in stress shielding and the increase in bone ingrowth [ 49 ].…”

“…However, due to the multi-axial, dynamic, and high loading conditions at joints, the requirements of joint replacements differ from other bone-interfacing implants such as those for the treatment of large bone defects. Additionally, other factors besides stress shielding affecting implant longevity, including wear [ 54 , 70 ] and micromotion [ 14 , 15 , 28 , 35 , 44 , 46 , 50 , 59 – 61 , 63 , 70 , 84 ], were not considered in the analyses.…”

“…For the validation of the performance of hip implant designs, a setup following the ISO 7204-6 standard was used in four studies [25][26][27][28]. Other studies selected physiological or non-physiological loading conditions in their computational models or experiments.…”

Capability of auxetic femoral stems to reduce stress shielding after total hip arthroplasty

“…For the stem structure, using a slotted or grooved design or hollow and porous structures can reduce the local stiffness of the stem by reducing the material volume, which can increase the load transmitted to the bone [ 5 ]. Although such designs have been shown to reduce SS [ 4 , [6] , [7] , [8] , [9] , [10] ], several studies found that the stress on the femur after implantation is still less than on the intact femur, especially around the proximal lateral side near the greater trochanter [ 6 , 7 , 11 ].…”