Topology Optimisation for Compliant Hip Implant Design and Reduced Strain Shielding

Abstract

Stiff total hip arthroplasty implants can lead to strain shielding, bone loss and complex revision surgery. The aim of this study was to develop topology optimisation techniques for more compliant hip implant design. The Solid Isotropic Material with Penalisation (SIMP) method was adapted, and two hip stems were designed and additive manufactured: (1) a stem based on a stochastic porous structure, and (2) a selectively hollowed approach. Finite element analyses and experimental measurements were conducted to measure stem stiffness and predict the reduction in stress shielding. The selectively hollowed implant increased peri-implanted femur surface strains by up to 25 percentage points compared to a solid implant without compromising predicted strength. Despite the stark differences in design, the experimentally measured stiffness results were near identical for the two optimised stems, with 39% and 40% reductions in the equivalent stiffness for the porous and selectively hollowed implants, respectively, compared to the solid implant. The selectively hollowed implant’s internal structure had a striking resemblance to the trabecular bone structures found in the femur, hinting at intrinsic congruency between nature’s design process and topology optimisation. The developed topology optimisation process enables compliant hip implant design for more natural load transfer, reduced strain shielding and improved implant survivorship.

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).…”

“…The percentage reduction of SSI values of the porous stem compared to solid stem in Gruen zones 1, 6 and 7 were 50%, 74% and 41% respectively. In a previous study by Tan and van Arkel (2021) SSI reduction in Gruen zones 6 and 7 were reported as 15% and 25%, respectively. Corresponding values in Al Zoubi et al (2022) were 22% and 65%, and for Cortis et al (2022) were 11% and 25% for Gruen zones 6 and 7 respectively.…”

“…This is followed by bone re-modelling which results in either bone formation or resorption ( Huiskes et al, 2000 ). In the case of stress shielding, a large portion of the natural load is removed from the cortical bone, resulting in a loss of the mechanical stimulus that drives bone formation, leading to bone loss over time ( Tan and van Arkel, 2021 ). This consequently weakens the implant support and increases the risk of elevated micromotion at the interface of implant and bone, leading to aseptic loosening of the implant.…”

Stress Shielding and Bone Resorption of Press-Fit Polyether–Ether–Ketone (PEEK) Hip Prosthesis: A Sawbone Model Study

“…Gross and Abel designed a hip implant with a hollow structure and evaluated its advantages in the reduction in stress shielding (15–32%) by finite element analysis [ 15 ]. Tan et al [ 16 ] studied two topology-optimized 316L stainless steel hip stems, based upon stochastic porous structure and a selectively hollowed approach. Concerning the hollowed stem, stress shielding of the femoral bone was reduced by 15% in Gruen zone 6, and by 25% in Gruen zone 7.…”

Special Issue “Design and Application of Additive Manufacturing”

“…In [9], the authors optimized a hip implant that reduced the strain shielding effect, using the solid isotropic material with penalization (SIMP) topology optimization method. Finite element analyses and experimental measurements (hip manufactured with 316L-0407 stainless steel in PBF technology) were conducted to measure stem stiffness and predict the reduction in stress shielding.…”