Correction: Răzvan et al. Selective Laser Sintering of PA 2200 for Hip Implant Applications: Finite Element Analysis, Process Optimization, Morphological and Mechanical Characterization. Materials 2021, 14, 4240

The authors wish to make the following correction to their paper [...]

Topology Optimisation for Compliant Hip Implant Design and Reduced Strain Shielding

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.

In-vitro & In-vivo Investigation of the Silicon Nitride Ceramic Hip Implant’s Safety and Effectiveness Evaluation

Background: With regard to the ceramic hip joint implant, given the concerns in ceramic about the alumina brittleness and zirconia instability, is there any alternative material solution for the orthopaedic implant? Beyond the metastable oxide ceramics, along the echelon of advanced technical ceramics, looking at the non-oxide ceramic, the silicon nitride could be an excellent candidate for the joint implant’s application. The purpose of this study is to investigate the safety, effectiveness and to demonstrate the potential of this silicon nitride hip implant. Methods: According to the related ISO (International Organization for Standardization) standards, a series of in-vitro (nine) & in-vivo (five) tests, which had been accomplished for the aforementioned aim. Especially, the total hip replacement in pigs had been achieved, as per the authors’ knowledge, this is the first time to apply the THA (Total Hip Arthroplasty) in the big animal. Results: Refer to the ISO 6474-2, in comparison with the current monopolized German product, this silicon nitride ceramic hip implant has high strength, high hardness, excellent fracture toughness, lower density, better wear resistance, good biocompatibility, inherent stability, corrosion resistance and bioactivity, bone integration capability. Conclusions: This silicon nitride ceramic will be an admirable alternative solution with superior comprehensive property that can withstand the toughest conditions in the most demanding applications like in orthopedic and beyond.

Creation and finite-element analysis of multi-lattice structure design in hip stem implant to reduce the stress-shielding effect

The term stress-shielding is frequently used to mention the reduction in mechanical stimulus in the surrounding bone due to the presence of a biomaterial inert implant whose mechanical properties are superior to bone. As the natural consequence of this, mineral loss occurs in the bone over time and creating subsequent weakness. One of the methods to reduce stress-shielding problem is to develop hip-stem implant designs that will transfer the load more to the bone. Therefore, in this study, multi-lattice designs were developed to reduce the stress-shielding effect in hip implant applications. For this, the proximal part of the hip implant stems has been divided into three parts. Simple cubic, body centered cubic, and face centered cubic lattice structures were created on the upper parts. Inner vertical and inner vertical + inner horizontal beams were added to the lattice structure of the upper part for middle and lower parts, respectively. Due to the multi-lattice designs, the maximum von Mises stress values on the hip implant stem were reduced from 289 to 189 MPa, as well as a weight reduction of up to 25.89%. Stress-shielding signals were obtained by determining the change in strain energy per unit bone mass caused by the presence of the femoral hip implant stem and its ratio to intact bone. In the case of using hip-stems having multi-lattice designs, there is a significant increase (max. 150.47%) in stress-shielding signals from different zones of the femur.

Effect of Stem Positioning on Biomechanical Performance of a Novel Cementless Short-Stem Canine Total Hip Implant

Objective The aim of this study was to evaluate the effect of stem positioning on the biomechanical performance of a novel, collared, short-stem total hip implant under compression and torsion ex vivo. Study Design Six canine cadaveric femurs were implanted with a collared short-stem femoral implant. Canal flare index (CFI), stem angle, absolute and relative cut heights and relative size were measured radiographically and used as independent variables. Biomechanical performance of the construct was evaluated using physiologic loading (loading) and supraphysiologic loading (failure) protocols. Results During loading protocols, compressive stiffness was influenced by absolute cut height (p = 0.018). During failure protocols, peak torque was influenced by CFI (p = 0.004) and craniocaudal relative size (p = 0.005). Peak load and torsional stiffness were not impacted by any of the radiographic variables (p > 0.05). Three of six femurs developed longitudinal fractures originating at the medial calcar at the time of failure. Conclusion The biomechanical performance of the collared short-stem implant was positively impacted by preserving more of the femoral neck, having a higher CFI and using a smaller implant size relative to the femoral neck isthmus.