Innovative Design Methodology for Patient-Specific Short Femoral Stems

The biomechanical performance of hip prostheses is often suboptimal, which leads to problems such as strain shielding, bone resorption and implant loosening, affecting the long-term viability of these implants for articular repair. Different studies have highlighted the interest of short stems for preserving bone stock and minimizing shielding, hence providing an alternative to conventional hip prostheses with long stems. Such short stems are especially valuable for younger patients, as they may require additional surgical interventions and replacements in the future, for which the preservation of bone stock is fundamental. Arguably, enhanced results may be achieved by combining the benefits of short stems with the possibilities of personalization, which are now empowered by a wise combination of medical images, computer-aided design and engineering resources and automated manufacturing tools. In this study, an innovative design methodology for custom-made short femoral stems is presented. The design process is enhanced through a novel app employing elliptical adjustment for the quasi-automated CAD modeling of personalized short femoral stems. The proposed methodology is validated by completely developing two personalized short femoral stems, which are evaluated by combining in silico studies (finite element method (FEM) simulations), for quantifying their biomechanical performance, and rapid prototyping, for evaluating implantability.

Femoral Stems With Porous Lattice Structures: A Review

Cementless femoral stems are prone to stress shielding of the femoral bone, which is caused by a mismatch in stiffness between the femoral stem and femur. This can cause bone resorption and resultant loosening of the implant. It is possible to reduce the stress shielding by using a femoral stem with porous structures and lower stiffness. A porous structure also provides a secondary function of allowing bone ingrowth, thus improving the long-term stability of the prosthesis. Furthermore, due to the advent of additive manufacturing (AM) technology, it is possible to fabricate femoral stems with internal porous lattices. Several review articles have discussed porous structures, mainly focusing on the geometric design, mechanical properties and influence on bone ingrowth. However, the safety and effectiveness of porous femoral stems depend not only on the characteristic of porous structure but also on the macro design of the femoral stem; for example, the distribution of the porous structure, the stem geometric shape, the material, and the manufacturing process. This review focuses on porous femoral stems, including the porous structure, macro geometric design of the stem, performance evaluation, research methods used for designing and evaluating the femoral stems, materials and manufacturing techniques. In addition, this review will evaluate whether porous femoral stems can reduce stress shielding and increase bone ingrowth, in addition to analyzing their shortcomings and related risks and providing ideas for potential design improvements.

Selection Methodology of Femoral Stems According to the Cross Section and the Maximum Stresses

The maximum stresses on a femoral stem must be known for selecting the right size and shape of the shaft cross-sectional area for reducing the stress shielding effect generated after the total hip arthroplasty (THA) surgical procedure. The methodology proposed in this study provides the tools to the designers of femoral stems and orthopedic surgeons to select the adequate femoral stem cross section, decreasing the stiffness of the stem, thus reducing the stress shielding effect in the patient bones. The first contribution is the theoretical development of the maximum static stress calculation for 12 different femoral stem models with the beam theory, followed by the comparison with the static finite element analysis (FEA) simulations and finally the experimental corroboration of one femoral stem model measuring the strain with linear strain gages and transform it to stresses, the three different approaches provide comparable results, with a maximum average error of less than 8.5%. The second contribution is the formulation of a new selection methodology based on maximum stresses in the femoral stem and the cross-section area for decreasing the stress shielding effect, optimizing the area needed for withstand the loads and decreasing the overall stiffens of the stem.

Effects of Composition on Antibacterial and Antiviral Properties of Suspension Plasma-Sprayed Hydroxyapatite/Titania Coating

This study investigates the effect of composition on the antibacterial and antiviral properties of hydroxyapatite/titania composite coatings deposited by suspension plasma spraying. Hydroxyapatite is a bioceramic material used as a plasma-sprayed coating to promote osseointegration of femoral stems. TiO2 has promising photocatalytic activity and good efficiency in destroying bacteria, viral species, and parasites. Prior to coating, substrates were grit blasted, ultrasonically cleaned, and heated to enhance adhesion strength. The microstructure of the resulting coatings was then characterized using XRD and Raman spectroscopy. Test results indicated that SPS transformed Ti2O3 into TiO2 with mixed phases. Ti4O7 and Ti3O5 phases were also identified, which show photocatalytic activity due to oxygen vacancies. Antibacterial and antiviral tests were conducted as well.

Bioactive Borate-Based Glass Coatings For Titanium Alloy Femoral Stems

Hydroxyapatite (HA)-coated Ti6Al4V stems are currently used in total hip replacement (THR) surgeries. However, the residual stress in the HA coating due to mismatch in coefficient of thermal expansion (CTE) between HA and Ti6Al4V limits their application. Borate-based glasses can be promising alternatives to HA because of their similar CTEs to that of Ti6Al4V and excellent bioactivity that can promote bone repair. In this project, six borate-based glasses (Ly-B0, Ly-B1, Ly-B2, Ly-B3, Ly-B4, Ly-B5) from the B2O3-P2O5-CaO-Na2O-TiO2-SrO series were formulated by increasing the concentration of strontium oxide (SrO)from 0 to 25 in mol% at the expense of B2O3 in the glass series. Increased SrO content induced larger amounts of non-bridging oxygens and resulted in gradual increases in glass transition temperature (Tg). Discs of each glass powder were immersed in de-ionized water under 1, 7 and 30 days, and then the water extracts were used to determine the solubility and osteo-stimulatory effect of the glasses. Sr2+ doping retarded the dissolution rate of the glasses and the higher levels of Sr2+ doping (20 mol% and 25 mol%) promoted proliferation of osteoblasts. Except for Ly-B5 (containing 25 mol% SrO), discs of each glass powder exhibited bacteriostatic behavior against Staphylococcus aureus after 24 hours exposure. The glasses were enamelled onto Ti6Al4V substrates, and then bi-layer double cantilever beam (DCB) specimens were manufactured to measure the Mode I (GIC) and Mode II (GIIC) energy release rate of the glass coating/Ti6Al4V constructs. The mean GIC values increased from 6.56 ± 0.9 to 14.6 1 ± 2.1 J/m2 with increasing SrO content from Ly-B0 to Ly-B5, and the mean GIIC values increased from 36.07 ± 3.8 to 46.92 ± 3.3 J/m2 with increasing SrO content from Ly-B0 to Ly-B5, indicating that the incorporation of 15-25 mol% SrO significantly increased the fracture toughness of the construct. Moreover, the GIC and GIIC values of the coating/substrate system for all the six glasses significantly reduced (p ≤ 0.05) due to degradation in de-ionized water.