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

Abstract

Stress shielding secondary to bone resorption is one of the main causes of aseptic loosening, which limits the lifespan of hip prostheses and exacerbates revision surgery rates. In order to minimise post-hip replacement stress variations, this investigation proposes a low-stiffness, porous Ti6Al4V hip prosthesis, developed through selective laser melting (SLM). The stress shielding effect and potential bone resorption properties of the porous hip implant were investigated through both in vitro quasi-physiological experimental assays, together with finite element analysis. A solid hip implant was incorporated in this investigation for contrast, as a control group. The stiffness and fatigue properties of both the solid and the porous hip implants were measured through compression tests. The safety factor of the porous hip stem under both static and dynamic loading patterns was obtained through simulation. The porous hip implant was inserted into Sawbone/PMMA cement and was loaded to 2,300 N (compression). The proposed porous hip implant demonstrated a more natural stress distribution, with reduced stress shielding (by 70%) and loss in bone mass (by 60%), when compared to a fully solid hip implant. Solid and porous hip stems had a stiffness of 2.76 kN/mm and 2.15 kN/mm respectively. Considering all daily activities, the porous hip stem had a factor of safety greater than 2. At the 2,300 N load, maximum von Mises stresses on the hip stem were observed as 112 MPa on the medial neck and 290 MPa on the distal restriction point, whereby such values remained below the endurance limit of 3D printed Ti6Al4V (375 MPa). Overall, through the strut thickness optimisation process for a Ti6Al4V porous hip stem, stress shielding and bone resorption can be reduced, therefore proposing a potential replacement for the generic solid implant.

Study of cellular femoral stem for stress shielding and interface stability

“…This indicates that axial gradient stiffness increases stress in the medial regions of the femur, consistent with the results reported by recent studies on porous femoral stems. 11,12,14,22 Bone loss was more concentrated in Gruen zone 7 near the lesser trochanter region of the femur, 23,24 and the results showed that DAGS Gyroid has maximum stress transfer in the proximal medial section. Maximum stress shielding reduction is 14.42% in Gruen zone 6 and 13.37% in Gruen zone 7 for DAGS Gyroid design, according to Figure 5.…”

Advancement in total hip implant: a comprehensive review of mechanics and performance parameters across diverse novelties

“…This investigation involves fixed flexion angles ranging from 8 to 121 and abduction angles ranging from 6 to 12 degrees. [33][34][35][36][37][38][39][40][41][42][43][44][45] The loading condition plays a significant role in assessing the performance of hip implants. However, the mechanical performance of a hip implant stem within an implanted femur bone was evaluated following ISO-7206-08 guidelines in recent literature.…”

“…In those works, the analysis involved applying axial loads ranging from 600 N to 5 KN on the femoral head. 15,16,33,35,[37][38][39][41][42][43][46][47][48][49][50] In numerous recent studies, dynamic load component values have been utilized to assess the mechanical behaviour of hip implant stems within implanted bones. 12,34,43,45,47,[51][52][53] However, a German study group known as ''Orthoload'' has released dynamic force and moment data of daily activities in various environments.…”

“…34,45,51,52,[73][74][75][76][77] To generate the image and topology based Gyroid and Schwarz Diamond porous and lattice structure, the formula stated in en ( 6) and ( 7) were followed by recent research. 42,65,78 f Gðx;y;zÞ ¼ sin…”

“…A detailed theoretical discussion of porous and lattice structures with implicit-based unit cells is illustrated in recent literature. 42,65,78 The concept underlying the design of porous and lattice unit cells based on images involves the utilization of voxels. These voxels define an image by representing entities like cylinders, spheres, and similar shapes.…”