Long-term implant fixation and stress-shielding in total hip replacement

Comparison of cylindrical and tapered stem designs for femoral revision hip arthroplasty

Background

Both cylindrical and tapered stems are commonly used in revision total hip arthroplasty. However, whether the geometry of prosthesis stem has an effect on patient prognosis is unclear. We assume that the tapered stem results in better clinical outcome than the cylindrical stem.

Methods

A multicenter review of 120 femoral revisions with Paprosky I, II, and III defects using cobalt chrome cylindrical stem (54 hips) or titanium tapered stem (66 hips) was performed with an average follow-up of 6 years. Demographic data were comparable between groups.

Results

No significant group differences were found in surgery time, bleeding volume, postoperative Harris Hip Score, level of overall satisfaction, and 8-year cumulative survival. However, intraoperative fractures occurred significantly less in the tapered group (4.5%) than in the cylindrical group (14.8%), and stem subsidence was significantly less in the tapered group (2.17 mm) than in the cylindrical group (4.17 mm). A higher ratio of bone repair and lower bone loss were observed in the tapered group compared with the cylindrical group. The postoperative thigh pain rate was higher in the cylindrical group (12.9%) than in the tapered group (4.5%).

Conclusion

Both cylindrical stem and tapered stem can achieve satisfactory mid-term clinical results in revision total hip arthroplasty. The tapered stem has better bone restoration of proximal femur, lower incidence of intraoperative fractures, and lower postoperative thigh pain rate compared with the cylindrical stem.

An in vitro and in vivo comparison of Mg(OH)2-, MgF2- and HA-coated Mg in degradation and osteointegration

Magnesium hydroxide (Mg(OH)₂), magnesium fluoride (MgF₂), and hydroxyapatite (HA) films on Mg are widely studied owing to their easy preparation and favorable corrosion protection. Nevertheless, the most suitable film with the best performance for biomedical applications between the three films remains unknown. Therefore, the performance of the three coatings from in vitro to in vivo must be systematically investigated. In this study, Mg(OH)₂, MgF₂, and HA films were fabricated on pure Mg. Electrochemical analysis and the hydrogen evolution test suggested that the HA film showed the best in vitro corrosion resistance, followed by MgF₂ and Mg(OH)₂ films. In vitro cell culture indicated that the extract of the MgF₂-coated sample was most beneficial for the osteogenic differentiation of MC3T3-E1 cells and the vascularization of human umbilical vein endothelial cells (HUVECs), which might be ascribed to the existence of the F element in the film. The result of this subcutaneous implantation showed that the HA film exhibited the best in vivo corrosion resistance and induced the lightest inflammatory response. Femoral implantation data revealed that the HA film exhibited the best osseointegration. Furthermore, the major organs and blood indicators of all of the tested rats were normal in 8 weeks. In summary, though the in vitro biological performance of the MgF₂ film was the best among the three films, the HA film showed the best in vivo performance, suggesting that it is a more promising modification method for orthopedic applications.

Heat treatment dependent cytotoxicity of silicalite-1 films deposited on Ti-6Al-4V alloy evaluated by bone-derived cells

A silicalite-1 film (SF) deposited on Ti-6Al-4V alloy was investigated in this study as a promising coating for metallic implants. Two forms of SFs were prepared: as-synthesized SFs (SF-RT), and SFs heated up to 500 °C (SF-500) to remove the excess of template species from the SF surface. The SFs were characterized in detail by X-ray photoelectron spectroscopy (XPS), by Fourier transform infrared spectroscopy (FTIR), by scanning electron microscopy (SEM) and water contact angle measurements (WCA). Two types of bone-derived cells (hFOB 1.19 non-tumor fetal osteoblast cell line and U-2 OS osteosarcoma cell line) were used for a biocompatibility assessment. The initial adhesion of hFOB 1.19 cells, evaluated by cell numbers and cell spreading area, was better supported by SF-500 than by SF-RT. While no increase in cell membrane damage, in ROS generation and in TNF-alpha secretion of bone-derived cells grown on both SFs was found, gamma H2AX staining revealed an elevated DNA damage response of U-2 OS cells grown on heat-treated samples (SF-500). This study also discusses differences between osteosarcoma cell lines and non-tumor osteoblastic cells, stressing the importance of choosing the right cell type model.

Comparison of the osteoblastic activity of low elastic modulus Ti-24Nb-4Zr-8Sn alloy and pure titanium modified by physical and chemical methods

Ti-24Nb-4Zr-8Sn (Ti2448) alloy is a novel low elastic modulus β-titanium alloy without toxic elements. It also has the advantage of high strength, so it has potential application prospects for implantation. To develop its osteogenic effects, it can be modified by electrochemical, and physical processes. The main research aim of this study was to explore the bioactivity of Ti2448 alloy modified by sandblasted, large-grit, acid-etched (SLA), micro-arc oxidation (MAO) and anodic oxidation (AO), and to determine which of the three surface modifications is the best way for developing the osteogenesis of bone marrow mesenchymal stem cells (BMMSCs). In vitro studies, the cytoskeleton, focal adhesion and proliferation of BMMSCs showed that both pure titanium and Ti2448 alloy have good biocompatibility. The osteogenic differentiation of BMMSCs with the Ti2448 alloy were examined by detecting alkaline phosphatase (ALP), mineralization nodules and osteogenic proteins and were better than that with pure titanium. These results showed that the Ti2448 alloy treated by SLA has a better effect on osteogenesis than pure titanium, and AO is the best way of three surface treatments to improve osteogenesis in this study.

Effects of condensation and compressive strain on implant primary stability: A longitudinal, in vivo, multiscale study in mice

Aims

Surgeons and most engineers believe that bone compaction improves implant primary stability without causing undue damage to the bone itself. In this study, we developed a murine distal femoral implant model and tested this dogma.

Methods

Each mouse received two femoral implants, one placed into a site prepared by drilling and the other into the contralateral site prepared by drilling followed by stepwise condensation.

Results

Condensation significantly increased peri-implant bone density but it also produced higher strains at the interface between the bone and implant, which led to significantly more bone microdamage. Despite increased peri-implant bone density, condensation did not improve implant primary stability as measured by an in vivo lateral stability test. Ultimately, the condensed bone underwent resorption, which delayed the onset of new bone formation around the implant.

Conclusion

Collectively, these multiscale analyses demonstrate that condensation does not positively contribute to implant stability or to new peri-implant bone formation.

Cite this article:Bone Joint Res. 2020;9(2):60–70.

Palm readings: Manicaria saccifera palm fibers are biocompatible textiles with low immunogenicity

Plant-based fibers are a potential alternative to synthetic polymer fibers that can yield enhanced biocompatibility and mechanical properties matching those properties of tissue. Given the unique morphology of the bract of the Manicaria saccifera palm, being an interwoven meshwork of fibers, we believe that these fibers with this built-in structure could prove useful as a tissue engineering scaffold material. Thus, we first investigated the fiber's in vitro biocompatibility and immunogenicity. We cultured NIH/3T3 mouse fibroblasts, human aortic smooth muscle cells, and human adipose-derived mesenchymal stem cells on the fiber mats, which all readily attached and over 21 days grew to engulf the fibers. Importantly, this was achieved without treating the plant tissue with extracellular matrix proteins or any adhesion ligands. In addition, we measured the gene expression and protein secretion of three target inflammatory cytokines (IL-1β, IL-8, and TNFα) from THP-1 human leukemia monocytes cultured in the presence of the biotextile as an in vitro immunological model. After 24 h of culture, gene expression and protein secretion were largely the same as the control, demonstrating the low immunogenicity of Manicaria saccifera fibers. We also measured the tensile mechanical properties of the fibers. Individual fibers after processing had a Young's modulus of 9.51 ± 4.38 GPa and a tensile strength of 68.62 ± 27.93 MPa. We investigated the tensile mechanical properties of the fiber mats perpendicular to the fiber axis (transverse loading), which displayed upwards of 100% strain, but with a concession in strength compared to longitudinal loading. Collectively, our in vitro assessments point toward Manicaria saccifera as a highly biocompatible biotextile, with a range of potential clinical and engineering applications.

Altering the Course of Technologies to Monitor Loosening States of Endoprosthetic Implants

Musculoskeletal disorders are becoming an ever-growing societal burden and, as a result, millions of bone replacements surgeries are performed per year worldwide. Despite total joint replacements being recognized among the most successful surgeries of the last century, implant failure rates exceeding 10% are still reported. These numbers highlight the necessity of technologies to provide an accurate monitoring of the bone–implant interface state. This study provides a detailed review of the most relevant methodologies and technologies already proposed to monitor the loosening states of endoprosthetic implants, as well as their performance and experimental validation. A total of forty-two papers describing both intracorporeal and extracorporeal technologies for cemented or cementless fixation were thoroughly analyzed. Thirty-eight technologies were identified, which are categorized into five methodologies: vibrometric, acoustic, bioelectric impedance, magnetic induction, and strain. Research efforts were mainly focused on vibrometric and acoustic technologies. Differently, approaches based on bioelectric impedance, magnetic induction and strain have been less explored. Although most technologies are noninvasive and are able to monitor different loosening stages of endoprosthetic implants, they are not able to provide effective monitoring during daily living of patients.

Biocomposites based on hydroxyapatite matrix reinforced with nanostructured monticellite (CaMgSiO4) for biomedical application: Synthesis, characterization, and biological studies

In this study, a simple and facile strategy was developed for the synthesis of novel hydroxyapatite (HA)/nanostructured monticellite ceramic composites by mechanical method. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive x-ray spectroscopy (EDS) were used to peruse the phase structure, and morphology of soaked ceramic composites in simulated body fluid (SBF). The in vitro bioactivity of HA-based ceramic composites with nanostructured monticellite ranging from 0 to 50 wt% was evaluated via investigating the formation ability of bone-like calcium phosphates in SBF and the effect of obtained extracts from composites dissolution on osteoblast-like G-292 cell line. Moreover, In vitro cytocompatibility of the HA/monticellite ceramic composites was investigated by MTT, cell growth & adhesion and alkaline phosphatase (ALP) activity assays, and quantitative real-time PCR analysis. The results showed that HA/nanostructured monticellite ceramic composites could induce apatite formation in SBF. The cell proliferation and growth exposed to ceramic composites extracts were significantly stimulated and promoted at a certain concentration range compared to control for various time periods of cell culture. The optimized composite extract enhanced considerably gene expression of G-292 type X collagen (COLX) at different days. Also, G-292 cells were spread and adhered well on the ceramic composite disc. Furthermore, ALP activity of G-292 cells exposed to ceramic composites extracts was dramatically enhanced in comparison with pure HA extract (as control) at different concentrations for various time periods of cell culture. The results suggest that the optimized HA/nanostructured monticellite composite is promising biomaterial for clinical applications such as orthopedic and dentistry.

Silicalite-1 Layers as a Biocompatible Nano- and Micro-Structured Coating: An In Vitro Study on MG-63 Cells

Silicalite-1 is a purely siliceous form of zeolite, which does not contain potentially harmful aluminum in its structure as opposed to ZSM-5 aluminosilicate types of zeolite. This paper reports on a study of a silicalite-1 film, deposited on a silicon Si(100) substrate, as a potential anti-corrosive and biocompatible coating for orthopaedic implants. Silicalite-1 film was prepared in situ on the surface of Si(100) wafers using a reaction mixture of tetrapropyl-ammonium hydroxide (TPAOH), tetraethyl-orthosilicate (TEOS), and diH₂O. The physico-chemical properties of the obtained surface were characterized by means of X-ray photoelectron spectroscopy, water contact angle measurement, atomic force microscopy, and scanning electron microscopy. The biocompatibility was assessed by interaction with the MG-63 cell line (human osteosarcoma) in terms of cell adhesion, morphology, proliferation, and viability. The synthesized silicalite-1 film consisted of two layers (b- and a, b-oriented crystals) creating a combination of micro- and nano-scale surface morphology suitable for cell growth. Despite its hydrophobicity, the silicalite-1 film increased the number of initially adhered human osteoblast-like MG-63 cells and the proliferation rate of these cells. The silicalite-1 film also improved the cell viability in comparison with the reference Si(100) substrate. It is therefore a promising candidate for coating of orthopaedic implants.

Influence of design and postprocessing parameters on the degradation behavior and mechanical properties of additively manufactured magnesium scaffolds

Magnesium shows promising properties concerning its use in absorbable implant applications such as biodegradability, improved mechanical strength and plastic deformability. Following extensive research, the first fixation and compression screws composed of magnesium rare earth alloys were commercialised, notably in the field of orthopaedic surgery. Preclinical and clinical follow-up studies showed that the rapid degradation of unprotected metallic Magnesium surfaces and concomitant hydrogen gas bursts still raise concern regarding certain surgical indications and need to be further improved. In order to enlarge the scope of further applications, the development of future magnesium implants must aim at freedom of design and reduction of volume, hereby enabling higher functionalised implants, as e.g. plate systems or scaffold grafts for bone replacement therapy. In order to overcome the boundaries of conventional manufacturing methods such as turning or milling, the process of Laser Powder Bed Fusion (LPBF) for magnesium alloys was recently introduced. It enables the production of lattice structures, therefore allowing for reduction of implant material volume. Nevertheless, the concomitant increase of free surface of such magnesium scaffolds further stresses the aforementioned disadvantages of vast degradation and early loss of mechanical stability if not prevented by suitable postprocessing methods. Magnesium scaffold structures with different pore sizes were therefore manufactured by LPBF and consequently further modified either by thermal heat treatment or Plasma Electrolytic Oxidation (PEO). Implant performance was assessed by conducting degradation studies and mechanical testing. PEO modified scaffolds with small pore sizes exhibited improved long-term stability, while heat treated specimens showed impaired performance regarding degradation and mechanical stability. STATEMENT OF SIGNIFICANCE: Magnesium based scaffold structures offer wide possibilities for advanced functionalized bioabsorbable implants. By implementing lattice structures, big implant sizes and mechanically optimized implant geometries can be achieved enabling full bone replacement or large-scale plate systems, e.g. for orthopedic applications. As shape optimization and lattice structuring of such scaffolds consequently lead to enlarged surface, suitable design and postprocessing routines come into focus. The presented study addresses these new and relevant topics for the first time by evaluating geometry as well as heat and surface treatment options as input parameters for improved chemical and mechanical stability. The outcome of these variations is measured by degradation tests and mechanical analysis. Evaluating these methods, a significant contribution to the development of absorbable magnesium scaffolds is made. The findings can help to better understand the interdependence of high surface to volume ratio Magnesium implants and to deliver methods to incorporate such lattice structures into future large-scale implant applications manufactured from bioabsorbable Magnesium alloys.

Lamellar structure/processing relationships and compressive properties of porous Ti6Al4V alloys fabricated by freeze casting

Lamellar pores have superior biocompatibility due to their similarity to the lamellar structure of natural bones. In the present work, porous Ti6Al4V alloys with lamellar pores were successfully fabricated by directionally freeze casting. The lamellar structure/processing relationships were systematically studied through analyzing the interaction between ice front and alloy powders. The structural feature of translamella bridges is observed in the lamellar structure. The volume shrinkage of porous Ti6Al4V alloys is in the range of 44-60%. This is much higher compared with that of the porous ceramics. The solid content in the slurry exerts a strong influence on the porosity, while the freezing ice front velocity affects the structural wavelength and pore width. With the increase in ice front velocity, the structural wavelength decreases by an exponential function. The lamella formation mechanism and porosity gradient along the freezing direction were discussed. Young's modulus and yield stress of porous Ti6Al4V alloys fall in the range of 2-12 GPa and 40-300 MPa, respectively. The dominant compressive deformation mode is lamella buckling and splitting. The fabricated porous Ti6Al4V alloys possess higher relative yield stress.

Effects of femoral bone defect morphology on initial polished tapered stem stability in massive defect model: a biomechanical study

Background

Good outcomes have been reported in revision total hip replacement with massive segmental defects using impaction bone grafting with circumferential metal meshes. However, the morphology of defects that require a mesh is poorly defined. The purpose of this study was to evaluate the effects of a variety of segmental defects on load transmission to the proximal femur under both axial and rotational loads.

Methods

Initial stability of the Exeter stem was investigated in a composite bone model using three medial bone defect morphologies: Long (length 5 cm × width 2 cm), Short (2.5 cm × 2 cm), Square (3.2 cm × 3.2 cm), Square with mesh (3.2 cm × 3.2 cm defect covered with metal mesh), and with no defect as control. Specimens (5 per group) were axially loaded and internally rotated up to 20° or to failure. Strain distributions of the femora were measured using a strain gauge.

Results

All Square group specimens failed while rotation was increasing. In the other four groups, failure was not observed in any specimens. Mean torsional stiffness in the Long (4.4 ± 0.3 Nm/deg.) and Square groups (4.3 ± 0.3 Nm/deg.) was significantly smaller than in the Control group (4.8 ± 0.3 Nm/deg.). In the medio-cranial region, the magnitude of the maximum principal strain in the Square group (1176.4 ± 100.9) was significantly the largest (Control, 373.2 ± 129.5, p < 0.001; Long, 883.7 ± 153.3, p = 0.027; Short, 434.5 ± 196.8, p < 0.001; Square with mesh, 256.9 ± 100.8, p < 0.001). Torsional stiffness, and both maximum and minimum principal strains in the Short group showed no difference compared to the Control group in any region.

Conclusions

Bone defect morphology greatly affected initial stem stability and load transmission. If defect morphology is not wide and the distal end is above the lower end of the lesser trochanter, it may be acceptable to fill the bone defect region with bone cement. However, this procedure is not acceptable for defects extending distally below the lower end of the lesser trochanter or defects 3 cm or more in width.

Efficiency of Zoledronic Acid in Inhibiting Accelerated Periprosthetic Bone Loss After Cementless Total Hip Arthroplasty in Osteoporotic Patients: A Prospective, Cohort Study

OBJECTIVE

To investigate the influence of preoperative osteopenia/osteoporosis on periprosthetic bone loss after total hip arthroplasty (THA) and the efficiency of zoledronate (ZOL) treatment in periprosthetic bone preservation.

METHODS

This multicenter, prospective cohort study was conducted in four centers between April 2015 and October 2017. Patients were assigned to Normal BMD, Osteopenia, and Osteoporosis+ZOL groups. Patients with osteopenia received daily oral calcium (600 mg/d) and vitamin D (0.5 μg/d), while patients in the Osteoporosis+ZOL group received additional ZOL annually (5 mg/year). Periprosthetic bone mineral density (BMD) in seven Gruen zones, radiographic parameters, Harris hip score, EuroQol 5-Dimensions (EQ-5D) score, and BMD in hip and spine were measured within 7 days, 3 months, 12 months postoperation and annually thereafter.

RESULTS

A total of 266 patients were enrolled, while 81 patients that completed the first year follow-up were involved in the statistical analysis. The mean follow-up time was 1.3 years. There were significant decreases of mean BMD in total Gruen zones (-4.55%, P < 0.05) and Gruen zone 1 (-10.22%, P < 0.01) in patients with osteopenia during the first postoperative year. Patients in the Osteoporosis+ZOL group experienced a marked increase in BMD in Gruen zone 1 (+16%) at the first postoperative year, which had a significant difference when compared with the Normal BMD group (P < 0.05) and the Osteopenia Group (P < 0.001). Low preoperative BMD in hip and spine was predictive of bone loss in Gruen zone 1 at 12 months after THA in patients with normal BMD (R2 = 0.40, P < 0.05).

CONCLUSIONS

Patients with osteopenia are prone to higher bone loss in the proximal femur after cementless total hip arthroplasty (THA). ZOL, not solely calcium and vitamin D, could prevent the accelerated periprosthetic bone loss after THA in patients with osteopenia and osteoporosis.

The Electrochemical and Mechanical Behavior of Bulk and Porous Superelastic Ti‒Zr-Based Alloys for Biomedical Applications

Titanium alloys are well recognized as appropriate materials for biomedical implants. These devices are designed to operate in quite aggressive human body media, so it is important to study the corrosion and electrochemical behavior of the novel materials alongside the underlying chemical and structural features. In the present study, the prospective Ti‒Zr-based superelastic alloys (Ti-18Zr-14Nb, Ti-18Zr-15Nb, Ti-18Zr-13Nb-1Ta, atom %) were analyzed in terms of their phase composition, functional mechanical properties, the composition and structure of surface oxide films, and the corresponding corrosion and electrochemical behavior in Hanks’ simulated biological solution. The electrochemical parameters of the Ti-18Zr-14Nb material in bulk and foam states were also compared. The results show a significant difference in the functional performance of the studied materials, with different composition and structure states. In particular, the positive effect of the thermomechanical treatment regime, leading to the formation of a favorable microstructure on the corrosion resistance, has been revealed. In general, the Ti-18Zr-15Nb alloy exhibits the optimum combination of functional characteristics in Hanks’ solution, while the Ti-18Zr-13Nb-1Ta alloy shows the highest resistance to the corrosion environment. The Ti-18Zr-14Nb-based foam material exhibits slightly lower passivation kinetics as compared to its bulk equivalent.

Cerium Oxide Nanoparticle Incorporated Electrospun Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) Membranes for Diabetic Wound Healing Applications

Insufficient cell proliferation, cell migration, and angiogenesis are among the major causes for nonhealing of chronic diabetic wounds. Incorporation of cerium oxide nanoparticles (nCeO₂) in wound dressings can be a promising approach to promote angiogenesis and healing of diabetic wounds. In this paper, we report the development of a novel nCeO₂ containing electrospun poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) membrane for diabetic wound healing applications. In vitro cell adhesion studies, chicken embryo angiogenesis assay, and in vivo diabetic wound healing studies were performed to assess the cell proliferation, angiogenesis, and wound healing potential of the developed membranes. The experimental results showed that nCeO₂ containing PHBV membranes can promote cell proliferation and cell adhesion when used as wound dressings. For less than 1% w/w of nCeO₂ content, human mammary epithelial cells (HMEC) were adhered parallel to the individual fibers of PHBV. For higher than 1% w/w of nCeO₂ content, cells started to flatten and spread over the fibers. In ovo angiogenic assay showed the ability of nCeO₂ incorporated PHBV membranes to enhance blood vessel formation. In vivo wound healing study in diabetic rats confirmed the wound healing potential of nCeO₂ incorporated PHBV membranes. The study suggests that nCeO₂ incorporated PHBV membranes have strong potential to be used as wound dressings to enhance cell proliferation and vascularization and promote the healing of diabetic wounds.

Stress Relaxation and Targeted Nutrition to Treat Patellar Tendinopathy

Patellar tendinopathy is one of the most common afflictions in jumping sports. This case study outlines the rehabilitation of a professional basketball player diagnosed by magnetic resonance imaging (MRI) with a central core patellar tendinopathy within the proximal enthesis. The player undertook a nutrition and strength-based rehabilitation program combining gelatin ingestion and heavy isometric loading of the patellar tendon designed to produce significant stress relaxation as part of their competition schedule and a whole-body training plan. On follow-up one and a half years into the program an independent orthopedic surgeon declared the tendon normal on MRI. Importantly, the improved MRI results were associated with a decrease in pain and improved performance. This case study provides evidence that a nutritional intervention combined with a rehabilitation program that uses stress relaxation can improve clinical outcomes in elite athletes.

Prospective 5-year study with 96 short curved Fitmore™ hip stems shows a high incidence of cortical hypertrophy with no clinical relevance

Background

An increased occurrence of cortical hypertrophy (CH) was observed 1–2 years after implanting short curved Fitmore hip stems. There are no published data about either the clinical relevance or the progression of CH over the long term.

Methods

Ninety-six primary total hip arthroplasties were performed between 2008 and 2010 using the Fitmore hip stem. Clinical and radiological parameters were recorded preoperatively and at 1, 2, 3, and 5 year follow-up.

Results

CH appeared mainly on antero-posterior radiographs in Gruen Zones 2, 3, 5, and 6. After 1 year, the diameter was 10 ± 2 mm and remained constant thereafter. The CH rate after 1 year was 69% and after 5 years 71%. Subsidence after 1 year was 1.6 ± 1.55 mm and 1.93 ± 1.72 mm after 5 years. Cortical thinning was 46% after 1 year and 56% after 5 years, mainly in Gruen Zones 7 and 8. In the first year radiolucencies were found in 51% in all Gruen Zones, and in 20% after 5 years. Patient, implant, and surgical factors did not correlate with radiological outcomes except that larger stems had more CH. After 5 years, the Harris Hip Score had improved from 59 to 94 and the Oxford Hip Score from 22 to 41. Radiographic parameters, notably CH, were not associated with clinical outcomes except that cortical thinning correlated with lower outcome scores.

Conclusions

CH correlated neither with clinical outcome nor with patient, surgical or implant factors, except for a positive correlation with stem size. The Fitmore hip stems settled within the first year to a stable fixation and then remained almost unchanged. However, cortical thinning is common in Gruen Zone 7 and 8 meaning that there is stress-shielding.

Computed tomography porosity and spherical indentation for determining cortical bone millimetre-scale mechanical properties

The cortex of the femoral neck is a key structural element of the human body, yet there is not a reliable metric for predicting the mechanical properties of the bone in this critical region. This study explored the use of a range of non-destructive metrics to measure femoral neck cortical bone stiffness at the millimetre length scale. A range of testing methods and imaging techniques were assessed for their ability to measure or predict the mechanical properties of cortical bone samples obtained from the femoral neck of hip replacement patients. Techniques that can potentially be applied in vivo to measure bone stiffness, including computed tomography (CT), bulk wave ultrasound (BWUS) and indentation, were compared against in vitro techniques, including compression testing, density measurements and resonant ultrasound spectroscopy. Porosity, as measured by micro-CT, correlated with femoral neck cortical bone's elastic modulus and ultimate compressive strength at the millimetre length scale. Large-tip spherical indentation also correlated with bone mechanical properties at this length scale but to a lesser extent. As the elastic mechanical properties of cortical bone correlated with porosity, we would recommend further development of technologies that can safely measure cortical porosity in vivo.

Factors Influencing the Outcomes of Artificial Hip Replacements

Hip replacement is one of the most successful surgeries in the clinic for the removal of painful joints. Hip osteoarthritis and femoral head necrosis are the 2 main reasons for hip replacement. Several factors are associated with the outcomes of surgery. Nonsurgical factors include gender, age, body mass index, prosthetic material, and risk factors. Surgical factors are anesthesia, postoperative complications, and rehabilitation. Considering the increasing demand for hip arthroplasty and the rise in the number of revision operations, it is imperative to understand factor-related progress and how modifications of these factors promotes recovery following hip replacement. In this review, we first summarize recent findings regarding crucial factors that influence the outcomes of artificial hip replacement surgery. These findings not only show the time-specific effect for the treatment and recovery from hip arthroplasty in the clinic, but also provide suitable choices for different individuals for clinicians to consider. This, in turn, will help to develop the best possible postoperative program for specific patients.

Personalized Design of Functional Gradient Bone Tissue Engineering Scaffold

The porous structure of the natural bone not only has the characteristics of lightweight and high strength, but also is conducive to the growth of cells and tissues due to interconnected pores. In this paper, a novel gradient-controlled parametric modeling technology is presented to design bone tissue engineering (BTE) scaffold. First of all, the method functionalizes the pore distribution in the bone tissue, and reconstructs the pore distribution of the bone tissue in combination with the pathological analysis of the bone defect area of the individual patient. Then, based on the reconstructed pore distribution, the Voronoi segmentation algorithm and the contour interface optimization method are used to reconstruct the whole model of the bone tissue. Finally, the mechanical properties of the scaffold are studied by the finite element analysis (FEA) of different density gradient scaffolds. The results show that the method is highly feasible. BTE scaffold can be designed by irregular design methods and adjustment of pore distribution parameters, which is similar with natural bone in structural characteristics and biomechanical properties.

Biomechanical compatibility of high strength nickel free stainless steel bone plate under lightweight design

High nitrogen nickel-free stainless steel (HNNFSS) has excellent mechanical properties, corrosion resistance and biocompatibility, but its strength advantage is not fully used even though with one time higher than that of the conventional 316 L stainless steel. In this work, the lightweight design of HNNFSS bone plate was studied using finite element analysis, and the effect of lightweight plate fixation on histological and biomechanical behavior of healing bone were also researched on fractured rabbit femur. The finite element analysis results showed that the lightweight plate within 18.2% thickness reduction had higher bending strength and more homogeneous stress distribution compared with 316 L stainless steel plate. There was no obvious difference in radiography, histology analysis of callus and expression pattern of insulin like growth factor-1(IGF-1) of callus between the lightweight HNNFSS plate group and 316 L stainless steel plate group in animal test, and the IGF-1 concentrations of callus and the biomechanical bending test results also showed no statistical significance (p > 0.05), even though the data of the lightweight HNNFSS plate group were relatively better than that of 316 L stainless steel plate group. Therefore, the high nitrogen nickel-free stainless steel has the lightweight potential to keep good fixing function and improve bone healing compared with 316 L stainless steel plate.

Individual response variations in scaffold-guided bone regeneration are determined by independent strain- and injury-induced mechanisms

This study explored the regenerative osteogenic response in the distal femur of sheep using scaffolds having stiffness values within, and above and below, the range of trabecular bone apparent modulus. Scaffolds 3D-printed from stiff titanium and compliant polyamide were implanted into a cylindrical metaphyseal defect 15 × 15 mm. After six weeks, bone ingrowth varied between 7 and 21% of the scaffold pore volume and this was generally inversely proportional to scaffold stiffness. The individual reparative response considerably varied among the animals, which could be divided into weak and strong responders. Notably, bone regeneration specifically within the interior of the scaffold was inversely proportional to scaffold stiffness and was strain-driven in strongly-responding animals. Conversely, bone regeneration at the periphery of the defect was injury-driven and equal in all scaffolds and in all strongly- and weakly-responding animals. The observation of the strain-driven response in some, but not all, animals highlights that scaffold compliance is desirable for triggering host bone regeneration, but scaffold permanence is important for the load-bearing, structural role of the bone-replacing device. Indeed, scaffolds may benefit from being nonresorbable and mechanically reliable for those unforeseeable cases of weakly responding recipients.

Long-term hip loading in unilateral total hip replacement patients is no different between limbs or compared to healthy controls at similar walking speeds

Variation in hip joint contact forces directly influences the performance of total hip replacements (THRs). Measurement and calculation of contact forces in THR patients has been limited by small sample sizes, wide variation in patient and surgical factors, and short-term follow-up. This study hypothesised that, at long-term follow-up, unilateral THR patients have similar calculated hip contact forces compared to controls walking at similar (self-selected) speeds and, in contrast, THR patients walking at slower (self-selected) speeds have reduced hip contact forces. It was further hypothesised that there is no difference in calculated hip contact forces between operated and non-operated limbs at long-term follow-up for both faster and slower patients. Gait analysis data for THR patients walking at faster (walking speed: 1.29 ± 0.12 m/s; n = 11) and slower (walking speed: 0.72 ± 0.09 m/s; n = 11) speeds were used. Healthy subjects constituted the control group (walking speed: 1.36 ± 0.12 m/s; n = 10). Hip contact forces were calculated using static optimisation. There was no significant difference (p > 0.31) in hip contact forces between faster and control groups. Conversely, force was reduced at heel strike by 19% (p = 0.002), toe-off by 31% (p < 0.001) and increased at mid-stance by 15% (p = 0.02) for the slower group compared to controls. There were no differences between operated and non-operated limbs for the slower group or the faster group, suggesting good biomechanical recovery at long-term follow-up. Loading, at different walking speeds, presented here can improve the relevance of preclinical testing methods.

Comparative study on Ti-Nb binary alloys fabricated through spark plasma sintering and conventional P/M routes for biomedical application

The main purpose of this work is to obtain homogenous, single β phase in binary Ti-xNb (x = 18.75, 25, and 31.25 at.%) alloys by simple mixing of pure elemental powders using different sintering techniques such as spark plasma sintering (pressure-assisted sintering) and conventional powder metallurgy (pressure-less sintering). Synthesis parameters such as sintering temperature and holding time etc. are optimized in both techniques in order to get homogenous microstructure. In spark plasma sintering (SPS), complete homogeneous β phase is achieved in Ti25at.%Nb using 1300 °C sintering temperature with 60 min holding time under 50 MPa pressure. On the other hand, complete β phase is obtained in Ti25at.%Nb through conventional powder metallurgy (P/M) route using sintering temperature of 1400 °C for 120 min holding time which are adopted from the dilatometry studies. Nano-indentation is carried out for mechanical properties such as Young's modulus and nano-hardness. Elastic properties of binary Ti-xNb compositions are fallen within the range of 80-90 GPa. Cytotoxicity as well as cell adhesion studies carried out using MG63, osteoblast-like cells showed excellent biocompatibility of thus developed Ti25at.%Nb surface irrespective of fabrication route.

Measuring bone stiffness using spherical indentation

Objectives

Bone material properties are a major determinant of bone health in older age, both in terms of fracture risk and implant fixation, in orthopaedics and dentistry. Bone is an anisotropic and hierarchical material so its measured material properties depend upon the scale of metric used. The scale used should reflect the clinical problem, whether it is fracture risk, a whole bone problem, or implant stability, at the millimetre-scale. Indentation, an engineering technique involving pressing a hard-tipped material into another material with a known force, may be able to assess bone stiffness at the millimetre-scale (the apparent elastic modulus). We aimed to investigate whether spherical-tip indentation could reliably measure the apparent elastic modulus of human cortical bone.

Materials and methods

Cortical bone samples were retrieved from the femoral necks of nineteen patients undergoing total hip replacement surgery (10 females, 9 males, mean age: 69 years). The samples underwent indentation using a 1.5 mm diameter, ruby, spherical indenter tip, with sixty indentations per patient sample, across six locations on the bone surfaces, with ten repeated indentations at each of the six locations. The samples then underwent mechanical compression testing. The repeatability of indentation measurements of elastic modulus was assessed using the co-efficient of repeatability and the correlation between the bone elastic modulus measured by indentation and compression testing was analysed by least-squares regression.

Results

In total, 1140 indentations in total were performed. Indentation was found to be repeatable for indentations performed at the same locations on the bone samples with a mean co-efficient of repeatability of 0.4 GigaPascals (GPa), confidence interval (C.I): 0.33–0.42 GPa. There was variation in the indentation modulus results between different locations on the bone samples (mean co-efficient of repeatability: 3.1 GPa, C.I: 2.2–3.90 GPa). No clear correlation was observed between indentation and compression values of bone elastic modulus (r = 0.33, p = 0.17). The mean apparent elastic modulus obtained by spherical indentation was 9.9 GPa, the standard deviation for each indent cycle was 0.11 GPa, and the standard deviation between locations on the same sample was 1.01 GPa. The mean compression apparent elastic modulus was 4.42 GPa, standard deviation 1.02 GPa.

Discussion

Spherical-tip indentation was found to be a repeatable test for measuring the elastic modulus of human cortical bone, demonstrated by a low co-efficient of repeatability in this study. It could not, however, reliably predict cortical bone elastic modulus determined by platens compression testing in this study. This may be due to indentation only probing mechanical properties at the micro-scale while platens compression testing assesses millimetre length-scale properties. Improvements to the testing technique, including the use of a larger diameter spherical indenter tip, may improve the measurement of bone stiffness at the millimetre scale and should be investigated further.

A long-lasting bisphosphonate partially protects periprosthetic bone, but does not enhance initial stability of uncemented femoral stems: A randomized placebo-controlled trial of women undergoing total hip arthroplasty

Low bone quality may compromise the success of cementless total hip arthroplasty in high-risk patients such as elderly women. Zoledronic acid is a long-lasting antiresorptive agent, which is known to reduce short-term periprosthetic bone loss. However, its effect on femoral stem stability is not well known. Forty-nine female patients with a mean age of 68 years (range, 51-85 years) scheduled to undergo cementless total hip arthroplasty due to osteoarthritis were randomized in this double-blind, placebo-controlled trial to receive a single postoperative infusion of zoledronic acid or placebo. Patients were evaluated for up to four years postoperatively for femoral stem migration measured by radiostereometric analysis, bone mineral density (BMD) measured by dual X-ray absorptiometry, functional recovery, and patient-reported outcome scores. Implant survival was determined at nine years postoperatively. Zoledronic acid did not reduce the femoral stem migration that occurred predominantly during the settling period of the first 3-6 months. Subsequently, all femoral stems were radiographically osseointegrated. Zoledronic acid maintained periprosthetic BMD, while the expected loss of periprosthetic bone during the first 12 months was found in controls. Thereafter, periprosthetic BMD of Gruen zone 7 decreased even in the zoledronic acid group but remained 14.6% higher than that in the placebo group at four years postoperatively. Functional recovery was comparable across the groups. At nine years postoperatively, no revision arthroplasty had been performed. In conclusion, in women at high-risk for low BMD, zoledronic acid had a long-lasting, partially protective effect on periprosthetic bone loss, but the treatment did not enhance the initial femoral stem stability.

Validation of Material Algorithms for Femur Remodelling Using Medical Image Data

The aim of this study is the utilization of human medical CT images to quantitatively evaluate two sorts of "error-driven" material algorithms, that is, the isotropic and orthotropic algorithms, for bone remodelling. The bone remodelling simulations were implemented by a combination of the finite element (FE) method and the material algorithms, in which the bone material properties and element axes are determined by both loading amplitudes and daily cycles with different weight factor. The simulation results showed that both algorithms produced realistic distribution in bone amount, when compared with the standard from CT data. Moreover, the simulated L-T ratios (the ratio of longitude modulus to transverse modulus) by the orthotropic algorithm were close to the reported results. This study suggests a role for "error-driven" algorithm in bone material prediction in abnormal mechanical environment and holds promise for optimizing implant design as well as developing countermeasures against bone loss due to weightlessness. Furthermore, the quantified methods used in this study can enhance bone remodelling model by optimizing model parameters to gap the discrepancy between the simulation and real data.

Arthrotomy-based preclinical models of particle-induced osteolysis: A systematic review

We completed a systematic literature review of in vivo animal models that use arthrotomy-based methods to study particle-induced peri-implant osteolysis. The purpose of the review was to characterize the models developed to date, to determine the questions addressed, to assess scientific rigor and transparency, and to identify gaps in knowledge. We probed three literature databases (Medline, Embase, and Scopus) and found 77 manuscripts that fit the search parameters. In the most recent 10 years, researchers mainly used rat and mouse models, whereas in the previous 20 years, large animal, canine, and rabbit models were more common. The studies have demonstrated several pathophysiology pathways, including macrophage migration, particle phagocytosis, increased local production of cytokines and lysosomal enzymes, elevated bone resorption, and suppressed bone formation. The effect of variation in particle characteristics and concentration received limited attention with somewhat mixed findings. Particle contamination by endotoxin was shown to exacerbate peri-implant osteolysis. The possibility of early diagnosis was demonstrated through imaging and biomarker approaches. Several studies showed that both local and systemic delivery of bisphosphonates inhibits the development of particle-induced osteolysis. Other methods of inhibiting osteolysis include the use of anabolic agents and altering the implant design. Few studies examined non-surgical rescue of loosened implants, with conflicting results with alendronate. We found that the manuscripts often lacked the methodological detail now advocated by the ARRIVE guidelines, suggesting that improvement in reporting would be useful to maximize rigor and transparency. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2595-2605, 2017.

Numerical evaluation of bone remodelling and adaptation considering different hip prosthesis designs

BACKGROUND

The change in mechanical properties of femoral cortical bone tissue surrounding the stem of the hip endoprosthesis is one of the causes of implant instability. We present an analysis used to determine the best conditions for long-term functioning of the bone-implant system, which will lead to improvement of treatment results.

METHODS

In the present paper, a finite element method coupled with a bone remodelling model is used to evaluate how different three-dimensional prosthesis models influence distribution of the density of bone tissue. The remodelling process begins after the density field is obtained from a computed tomography scan. Then, an isotropic Stanford model is employed to solve the bone remodelling process and verify bone tissue adaptation in relation to different prosthesis models.

FINDINGS

The study results show that the long-stem models tend not to transmit loads to proximal regions of bone, which causes the stress-shielding effect. Short stems or application in the calcar region provide a favourable environment for transfer of loads to the proximal region, which allows for maintenance of bone density and, in some cases, for a positive variation, which causes absence of the aseptic loosening of an implant. In the case of hip resurfacing, bone mineral density changes slightly and is closest to an intact femur.

INTERPRETATION

Installation of an implant modifies density distribution and stress field in the bone. Thus, bone tissue is stimulated in a different way than before total hip replacement, which evidences Wolff's law, according to which bone tissue adapts itself to the loads imposed on it. The results suggest that potential stress shielding in the proximal femur and cortical hypertrophy in the distal femur may, in part, be reduced through the use of shorter stems, instead of long ones, provided stem fixation is adequate.

Diamond-like carbon coatings with zirconium-containing interlayers for orthopedic implants

Six types of diamond-like carbon (DLC) coatings with zirconium (Zr)-containing interlayers on titanium alloy (Ti-6Al-4V) were investigated for improving the biotribological performance of orthopedic implants. The coatings consist of three layers: above the substrate a layer stack of 32 alternating Zr and ZrN sublayers (Zr:ZrN), followed by a layer comprised of Zr and DLC (Zr:DLC), and finally a N-doped DLC layer. The Zr:ZrN layer is designed for increasing load carrying capacity and corrosion resistance; the Zr:DLC layer is for gradual transition of stress, thus enhancing layer adhesion; and the N-doped DLC layer is for decreasing friction, squeaking noises and wear. Biotribological experiments were performed in simulated body fluid employing a ball-on-disc contact with a Si₃N₄ ball and a rotational oscillating motion to mimic hip motion in terms of gait angle, dynamic contact pressures, speed and body temperature. The results showed that the Zr:DLC layer has a substantial influence on eliminating delamination of the DLC from the substrates. The DLC/Si₃N₄ pairs significantly reduced friction coefficient, squeaking noise and wear of both the Si₃N₄ balls and the discs compared to those of the Ti-6Al-4V/Si₃N₄ pair after testing for a duration that is equivalent to one year of hip motion in vivo.

Finite element analysis of cementless femoral stems based on mid- and long-term radiological evaluation

BACKGROUND

Femoral bone remodeling in response to stress shielding induces periprosthetic bone loss. Computerized finite element analysis (FEA) is employed to demonstrate differences in initial stress distribution. However, FEA is often performed without considering the precise sites at which the stem was fixed. We determined whether FEA reflects mid-term radiological examination exactly as predicted following long-term stress shielding.

METHODS

Femur-stem fixation sites were evaluated radiologically according to the location of spot welds in two anatomical cementless stem designs. Based on mid-term radiological results, four femur-stem bonding site conditions were defined as: (Condition A) no bonding; (Condition B) bonding within the 10 mm area proximal to the distal border of the porous area; (Condition C) bonding of the entire porous area; and (Condition D) bonding of the entire femoral stem, prior to conducting FEA analysis. Furthermore, we radiographically evaluated mid- and long-term stress shielding, and measured bone mineral density of the femur 10 years after total hip arthroplasty.

RESULTS

Spot welds appeared frequently around the border between the porous and smooth areas. FEA showed that, based on mid-term radiological evaluation, von Mises stress was reduced in condition B in the area proximal to the femur-stem bonding sites for both stem designs compared with condition A (no bonding). Conversely, von Mises stress at all areas of the femur-stem bonding sites in conditions C and D was higher than that in condition A. With respect to stress shielding progression, there was no significant difference between the two types of stem designs. However, stress shielding progressed and was significantly higher in the presence of spot welds (p = 0.001). In both stem designs, bone mineral density in zone VII was significantly lower than that in the contralateral hips.

CONCLUSIONS

These results indicate that FEA based on mid-term radiological evaluation may be helpful to predict the influence of long-term stress shielding more precisely.

New cosurface capacitive stimulators for the development of active osseointegrative implantable devices

Non-drug strategies based on biophysical stimulation have been emphasized for the treatment and prevention of musculoskeletal conditions. However, to date, an effective stimulation system for intracorporeal therapies has not been proposed. This is particularly true for active intramedullary implants that aim to optimize osseointegration. The increasing demand for these implants, particularly for hip and knee replacements, has driven the design of innovative stimulation systems that are effective in bone-implant integration. In this paper, a new cosurface-based capacitive system concept is proposed for the design of implantable devices that deliver controllable and personalized electric field stimuli to target tissues. A prototype architecture of this system was constructed for in vitro tests, and its ability to deliver controllable stimuli was numerically analyzed. Successful results were obtained for osteoblastic proliferation and differentiation in the in vitro tests. This work provides, for the first time, a design of a stimulation system that can be embedded in active implantable devices for controllable bone-implant integration and regeneration. The proposed cosurface design holds potential for the implementation of novel and innovative personalized stimulatory therapies based on the delivery of electric fields to bone cells.

In vitro implant-bone interface pressure measurements for a cementless femoral implant. A preliminary study

PURPOSE

Implants endurance as well as a good clinical tolerance depends on the recovery of a physiological stress distribution within bone after implantation. The purpose of the present work was to develop an alternative technique using Force Sensing Resistors (FSR) to gather in vitro pressure values at the implant-bone interface for a cementless implant.

METHOD

Eight cementless femoral stems were instrumented with six calibrated FSR bonded on each facet and then implanted in eight cadaver femurs. Compression tests were performed until failure and FSR pressure values were recorded.

RESULTS

The average failure load was 4241 N. The maximum contact pressure measured with the FSR averaged 1.965 MPa.

CONCLUSION

FSR reached many of the requirements for an ideal implant-bone interfacial sensor. This experimentation provided in vitro quantitative data on contact pressure at the implant-bone interface, which could help understanding stress shielding phenomenon and developing relevant numerical model.

In vivo monitoring of bone architecture and remodeling after implant insertion: The different responses of cortical and trabecular bone

The mechanical integrity of the bone-implant system is maintained by the process of bone remodeling. Specifically, the interplay between bone resorption and bone formation is of paramount importance to fully understand the net changes in bone structure occurring in the peri-implant bone, which are eventually responsible for the mechanical stability of the bone-implant system. Using time-lapsed in vivo micro-computed tomography combined with new composite material implants, we were able to characterize the spatio-temporal changes of bone architecture and bone remodeling following implantation in living mice. After insertion, implant stability was attained by a quick and substantial thickening of the cortical shell which counteracted the observed loss of trabecular bone, probably due to the disruption of the trabecular network. Within the trabecular compartment, the rate of bone formation close to the implant was transiently higher than far from the implant mainly due to an increased mineral apposition rate which indicated a higher osteoblastic activity. Conversely, in cortical bone, the higher rate of bone formation close to the implant compared to far away was mostly related to the recruitment of new osteoblasts as indicated by a prevailing mineralizing surface. The behavior of bone resorption also showed dissimilarities between trabecular and cortical bone. In the former, the rate of bone resorption was higher in the peri-implant region and remained elevated during the entire monitoring period. In the latter, bone resorption rate had a bigger value away from the implant and decreased with time. Our approach may help to tune the development of smart implants that can attain a better long-term stability by a local and targeted manipulation of the remodeling process within the cortical and the trabecular compartments and, particularly, in bone of poor health.

Biodegradable Materials for Bone Repair and Tissue Engineering Applications

This review discusses and summarizes the recent developments and advances in the use of biodegradable materials for bone repair purposes. The choice between using degradable and non-degradable devices for orthopedic and maxillofacial applications must be carefully weighed. Traditional biodegradable devices for osteosynthesis have been successful in low or mild load bearing applications. However, continuing research and recent developments in the field of material science has resulted in development of biomaterials with improved strength and mechanical properties. For this purpose, biodegradable materials, including polymers, ceramics and magnesium alloys have attracted much attention for osteologic repair and applications. The next generation of biodegradable materials would benefit from recent knowledge gained regarding cell material interactions, with better control of interfacing between the material and the surrounding bone tissue. The next generations of biodegradable materials for bone repair and regeneration applications require better control of interfacing between the material and the surrounding bone tissue. Also, the mechanical properties and degradation/resorption profiles of these materials require further improvement to broaden their use and achieve better clinical results.

Mechanics of Biological Tissues and Biomaterials: Current Trends

Investigation of the mechanical behavior of biological tissues and biomaterials has been an active area of research for several decades. However, in recent years, the enthusiasm in understanding the mechanical behavior of biological tissues and biomaterials has increased significantly due to the development of novel biomaterials for new fields of application, along with the emergence of advanced computational techniques. The current Special Issue is a collection of studies that address various topics within the general theme of “mechanics of biomaterials”. This editorial aims to present the context within which the studies of this Special Issue could be better understood. I, therefore, try to identify some of the most important research trends in the study of the mechanical behavior of biological tissues and biomaterials.