A new technique to measure micromotion distribution around a cementless femoral stem

The interfacial micromotion is closely associated to the long-term success of cementless hip prostheses. Various techniques have been proposed to measure them, but only a few number of points over the stem surface can be measured simultaneously. In this paper, we propose a new technique based on micro-Computer Tomography (μCT) to measure locally the relative interfacial micromotions between the metallic stem and the surrounding femoral bone. Tantalum beads were stuck at the stem surface and spread at the endosteal surface. Relative micromotions between the stem and the endosteal bone surfaces were measured at different loading amplitudes. The estimated error was 10 μm and the maximal micromotion was 60 μm, in the loading direction, at 1400 N. This pilot study provided a local measurement of the micromotions in the 3 direction and at 8 locations on the stem surface simultaneously. This technique could be easily extended to higher loads and a much larger number of points, covering the entire stem surface and providing a quasi-continuous distribution of the 3D interfacial micromotions around the stem. The new measurement method would be very useful to compare the induced micromotions of different stem designs and to optimize the primary stability of cementless total hip arthroplasty.     

Dehydrocostus lactone attenuates osteoclastogenesis and osteoclast‐induced bone loss by modulating NF‐κB signalling pathway

Osteolysis is characterized by overactivated osteoclast formation and potent bone resorption. It is enhanced in many osteoclast‐related diseases including osteoporosis and periprosthetic osteolysis. The shortage of effective treatments for these pathological processes emphasizes the importance of screening and identifying potential regimens that could attenuate the formation and function of osteoclasts. Dehydrocostus lactone (DHE) is a natural sesquiterpene lactone containing anti‐inflammatory properties. Here, we showed that DHE suppressed receptor activator of nuclear factor‐κB ligand (RANKL)‐induced osteoclast formation and osteoclast marker gene expression. It also inhibited F‐actin ring formation and bone resorption in a dose‐dependent manner in vitro. Moreover, DHE inhibited the RANKL‐induced phosphorylation of NF‐κB, mitigated bone erosion in vivo in lipopolysaccharide‐induced inflammatory bone loss model and particle‐induced calvarial osteolysis model. Together, these results suggest that DHE reduces osteoclast‐related bone loss via the modulation of NF‐κB activation during osteoclastogenesis indicating that it might be a useful treatment for osteoclast‐related skeletal disorders.     

Stachydrine prevents LPS‐induced bone loss by inhibiting osteoclastogenesis via NF‐κB and Akt signalling

Osteoclast overactivation‐induced imbalance in bone remodelling leads to pathological bone destruction, which is a characteristic of many osteolytic diseases such as rheumatoid arthritis, osteoporosis, periprosthetic osteolysis and periodontitis. Natural compounds that suppress osteoclast formation and function have therapeutic potential for treating these diseases. Stachydrine (STA) is a bioactive alkaloid isolated from Leonurus heterophyllus Sweet and possesses antioxidant, anti‐inflammatory, anticancer and cardioprotective properties. However, its effects on osteoclast formation and function have been rarely described. In the present study, we found that STA suppressed receptor activator of nuclear factor‐κB (NF‐κB) ligand (RANKL)‐induced osteoclast formation and bone resorption, and reduced osteoclast‐related gene expression in vitro. Mechanistically, STA inhibited RANKL‐induced activation of NF‐κB and Akt signalling, thus suppressing nuclear factor of activated T cells c1 induction and nuclear translocation. In addition, STA alleviated bone loss and reduced osteoclast number in a murine model of LPS‐induced inflammatory bone loss. STA also inhibited the activities of NF‐κB and NFATc1 in vivo. Together, these results suggest that STA effectively inhibits osteoclastogenesis both in vitro and in vivo and therefore is a potential option for treating osteoclast‐related diseases.     

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.     

Primary Rotational Stability of Various Megaprostheses in a Biomechanical Sawbone Model with Proximal Femoral Defects Extending to the Isthmus

Purpose

Fixation of proximal femoral megaprostheses is achieved in the diaphyseal isthmus. We hypothesized that after extended bone resection including the proximal part of the isthmus a reduced length of fixation will affect the stability and fixation characteristics of these megaprostheses. The aim of this study was to analyze in a validated sawbone model with extended proximal femoral defects which types of implants have sufficient primary stability to allow osteointegration and to describe their fixation characteristics.

Methods

Four different cementless megaprostheses were implanted into 16 Sawbones with an AAOS type III defect after resection 11cm below the lesser trochanter involving the proximal isthmus. To determine the primary implant stability relative micromotions between bone and implant were measured in relation to a cyclic torque of 7Nm applied on the longitudinal axis of the implant. We determined the fixation characteristics of the different implant designs by comparing these relative micromotions along the longitudinal stem axis.

Results

In the tested sawbones all studied implants showed sufficient primary stability to admit bone integration with relative micromotions below 150µm after adapting our results to physiologic hip joint loadings. Different fixation characteristics of the megaprostheses were determined, which could be explained by their differing design and fixation concepts.

Conclusions

Cementless megaprostheses of different designs seem to provide sufficient primary stability to bridge proximal femoral defects if the diaphyseal isthmus is partially preserved. In our sawbone model the different implant fixation patterns can be related to their stem designs. No evidence can be provided to favor one of the studied implants in this setting. However, femoral morphology is variable and in different isthmus configurations specific implant designs might be appropriate to achieve the most favorable primary stability, which enables bone integration and consequently long term implant stability.     

PDGFBB promotes PDGFRα-positive cell migration into artificial bone in vivo

Bone defects caused by traumatic bone loss or tumor dissection are now treated with auto- or allo-bone graft, and also occasionally by artificial bone transplantation, particularly in the case of large bone defects. However, artificial bones often exhibit poor affinity to host bones followed by bony union failure. Thus therapies combining artificial bones with growth factors have been sought. Here we report that platelet derived growth factor bb (PDGFBB) promotes a significant increase in migration of PDGF receptor α (PDGFRα)-positive mesenchymal stem cells/pre-osteoblastic cells into artificial bone in vivo. Growth factors such as transforming growth factor beta (TGFβ) and hepatocyte growth factor (HGF) reportedly inhibit osteoblast differentiation; however, PDGFBB did not exhibit such inhibitory effects and in fact stimulated osteoblast differentiation in vitro, suggesting that combining artificial bones with PDGFBB treatment could promote host cell migration into artificial bones without inhibiting osteoblastogenesis.     

Porphyromonas gingivalis GroEL Induces Osteoclastogenesis of Periodontal Ligament Cells and Enhances Alveolar Bone Resorption in Rats

Porphyromonas gingivalis is a major periodontal pathogen that contains a variety of virulence factors. The antibody titer to P. gingivalis GroEL, a homologue of HSP60, is significantly higher in periodontitis patients than in healthy control subjects, suggesting that P. gingivalis GroEL is a potential stimulator of periodontal disease. However, the specific role of GroEL in periodontal disease remains unclear. Here, we investigated the effect of P. gingivalis GroEL on human periodontal ligament (PDL) cells in vitro, as well as its effect on alveolar bone resorption in rats in vivo. First, we found that stimulation of PDL cells with recombinant GroEL increased the secretion of the bone resorption-associated cytokines interleukin (IL)-6 and IL-8, potentially via NF-κB activation. Furthermore, GroEL could effectively stimulate PDL cell migration, possibly through activation of integrin α1 and α2 mRNA expression as well as cytoskeletal reorganization. Additionally, GroEL may be involved in osteoclastogenesis via receptor activator of nuclear factor κ-B ligand (RANKL) activation and alkaline phosphatase (ALP) mRNA inhibition in PDL cells. Finally, we inoculated GroEL into rat gingiva, and the results of microcomputed tomography (micro-CT) and histomorphometric assays indicated that the administration of GroEL significantly increased inflammation and bone loss. In conclusion, P. gingivalis GroEL may act as a potent virulence factor, contributing to osteoclastogenesis of PDL cells and resulting in periodontal disease with alveolar bone resorption.     

Characterization of bone-implant fixation using modal analysis: Application to a press-fit implant model

Orthopaedic implant fixation is strongly dependant upon the effective mechanical properties of newly formed tissue. In this study, we evaluated the potential of modal analysis to derive viscoelastic properties of periprosthetic tissue. We hypothesized that Young's modulus and loss factor could be obtained by a combined theoretical, computational and experimental modal analysis approach. This procedure was applied to ex vivo specimens from a cylindrical experimental implant placed in cancellous bone in an unloaded press-fit configuration, obtained after a four week observation period. Four sections each from seven textured titanium implants were investigated. The first resonant frequency and loss factor were measured. Average experimentally determined loss factor was 2% (SD 0.4%) and average first resonant frequency was 2.1 KHz (SD: 50). A 2D axisymmetric finite element (FE) model identified effective Young's modulus of tissue using experimental resonant frequencies as input. Average value was 42 MPa (SD: 2.4) and no significant difference between specimens was observed.In this pilot study, the non-destructive method allowed accurate measure of dynamic loss factor and resonant frequency and derivation of effective Young's modulus. Prior to implementing this dynamic protocol for broader mechanical evaluation of experimental implant fixation, further work is needed to determine if this affects results from subsequent destructive shear push-out tests.     

Bone ingrowth simulation for a concept glenoid component design

Glenoid component loosening is the major problem of total shoulder arthroplasty. It is possible that uncemented component may be able to achieve superior fixation relative to cemented component. One option for uncemented glenoid is to use porous tantalum backing. Bone ingrowth into the porous backing requires a degree of stability to be achieved directly post-operatively. This paper investigates the feasibility of bone ingrowth with respect to the influence of primary fixation, elastic properties of the backing and friction at the bone prosthesis interface. Finite element models of three glenoid components with different primary fixation configurations are created. Bone ingrowth into the porous backing is modelled based on the magnitude of the relative interface micromotions and mechanoregulation of the mesenchymal stem cells that migrated via the bonded part of the interface. Primary fixation had the most influence on bone ingrowth. The simulation showed that its major role was not to firmly interlock the prosthesis, but rather provide such a distribution of load, that would result in reduction of the peak interface micromotions. Should primary fixation be provided, friction has a secondary importance with respect to bone ingrowth while the influence of stiffness was counter intuitive: a less stiff backing material inhibits bone ingrowth by higher interface micromotions and stimulation of fibrous tissue formation within the backing.     

MiR-138-5p Targets MACF1 to Aggravate Aging-related Bone Loss

Senile osteoporosis is one of the major health problems in an aging society. Decreased bone formation due to osteoblast dysfunction may be one of the causes of aging-related bone loss. With increasing evidence suggesting that multiple microRNAs (miRNAs) play important roles in osteoblast function, the relationship between miRNAs and senile osteoporosis has become a popular research topic. Previously, we confirmed that mechanoresponsive miR-138-5p negatively regulated bone anabolic action. In this study, the miR-138-5p level was found to be negatively correlated with BMD and osteogenic markers in bone specimens of senile osteoporotic patients by bioinformatic analysis and experimental verification. Furthermore, high miR-138-5p levels aggravated the decrease of aged osteoblast differentiation in vitro and led to worse bone loss in aged osteoblastic miR-138-5p transgenic mice in vivo. We also previously identified that the target of miR-138-5p, microtubule actin cross-linking factor 1 (MACF1), could attenuate senile osteoporosis. Here, miR-138-5p was demonstrated to regulate aged osteoblast differentiation by targeting MACF1. Finally, the therapeutic inhibition of miR-138-5p counteracted the decrease in bone formation and aging-related bone loss in aged mice. Overall, our results highlight the crucial roles and the molecular mechanism of miR-138-5p in aging-related bone loss and may provide a powerful therapeutic target for ameliorating senile osteoporosis.     

Sensitivity of periprosthetic stress-shielding to load and the bone density-modulus relationship in subject-specific finite element models

Subject-specific finite element (FE) computer models of the proximal femur in hip replacement could potentially predict stress-shielding and subsequent bone loss in individual patients. Before such predictions can be made, it is important first to determine if between subject differences in stress-shielding are sensitive to poorly defined parameters such as the load and the bone material properties. In this study we investigate if subject-specific FE models provide consistent stress-shielding patterns in the bone, independent of the choice of the loading conditions and the bone density-modulus relationship used in the computer model. FE models of two right canine femurs with and without implants were constructed based on contiguous computed tomography (CT) scans so that subject-specific estimates of stress-shielding could be calculated. Four different loading conditions and two bone density-modulus relationships were tested. Stress-shielding was defined as the decrease of strain energy per gram bone mass in the femur with the implant in place relative to the intact femur.The analyses showed that for the four loading conditions and two bone density-modulus relationships the difference in stress-shielding between the two subjects was essentially constant (1% variation) when the same loading condition and density-modulus relationship was used for both subjects. The severity of stress-shielding within a subject was sensitive to these input parameters, varying up to 20% in specific regions with a change in loading conditions and up to 10% for a change in the assumed density-modulus relationship. We conclude that although the choice of input parameters can substantially affect stress-shielding in an individual, this choice had virtually no effect on the relative differences in femoral periprosthetic stress-shielding between individuals. Thus, while care should be taken in the interpretation of the absolute value of stress-shielding calculated with these type of models, subject-specific FE models may be useful for explaining the variation in bone adaptation responsiveness between different subjects in experimental or clinical studies.     

Yeast AEP3p Is an Accessory Factor in Initiation of Mitochondrial Translation

Initiation of protein synthesis in mitochondria and chloroplasts normally uses a formylated initiator methionyl-tRNA (fMet-tRNA_f^Met). However, mitochondrial protein synthesis in Saccharomyces cerevisiae can initiate with nonformylated Met-tRNA_f^Met, as demonstrated in yeast mutants in which the nuclear gene encoding mitochondrial methionyl-tRNA formyltransferase (FMT1) has been deleted. The role of formylation of the initiator tRNA is not known, but in vitro formylation increases binding of Met-tRNA_f^Met to translation initiation factor 2 (IF2). We hypothesize the existence of an accessory factor that assists mitochondrial IF2 (mIF2) in utilizing unformylated Met-tRNA_f^Met. This accessory factor might be unnecessary when formylated Met-tRNA_f^Met is present but becomes essential when only the unformylated species are available. Using a synthetic petite genetic screen in yeast, we identified a mutation in the AEP3 gene that caused a synthetic respiratory-defective phenotype together with Δfmt1. The same aep3 mutation also caused a synthetic respiratory defect in cells lacking formylated Met-tRNA_f^Met due to loss of the MIS1 gene that encodes the mitochondrial C₁-tetrahydrofolate synthase. The AEP3 gene encodes a peripheral mitochondrial inner membrane protein that stabilizes mitochondrially encoded ATP6/8 mRNA. Here we show that the AEP3 protein (Aep3p) physically interacts with yeast mIF2 both in vitro and in vivo and promotes the binding of unformylated initiator tRNA to yeast mIF2. We propose that Aep3p functions as an accessory initiation factor in mitochondrial protein synthesis.     

Experimental and computational analysis of micromotions of an uncemented femoral knee implant using elastic and plastic bone material models

It is essential to calculate micromotions at the bone-implant interface of an uncemented femoral total knee replacement (TKR) using a reliable computational model. In the current study, experimental measurements of micromotions were compared with predicted micromotions by Finite Element Analysis (FEA) using two bone material models: linear elastic and post-yield material behavior, while an actual range of interference fit was simulated. The primary aim was to investigate whether a plasticity model is essential in order to calculate realistic micromotions. Additionally, experimental bone damage at the interface was compared with the FEA simulated range.TKR surgical cuts were applied to five cadaveric femora and micro- and clinical CT- scans of these un-implanted specimens were made to extract geometrical and material properties, respectively. Micromotions at the interface were measured using digital image correlation. Cadaver-specific FEA models were created based on the experimental set-up. The average experimental micromotion of all specimens was 53.1 ± 42.3 µm (mean ± standard deviation (SD)), which was significantly higher than the micromotions predicted by both models, using either the plastic or elastic material model (26.5 ± 23.9 µm and 10.1 ± 10.1 µm, respectively; p-value < 0.001 for both material models). The difference between the two material models was also significant (p-value < 0.001). The predicted damage had a magnitude and distribution which was comparable to the experimental bone damage. We conclude that, although the plastic model could not fully predict the micro motions, it is more suitable for pre-clinical assessment of a press-fit TKR implant than using an elastic bone model.     

Disrupted Bone Remodeling Leads to Cochlear Overgrowth and Hearing Loss in a Mouse Model of Fibrous Dysplasia

Normal hearing requires exquisite cooperation between bony and sensorineural structures within the cochlea. For example, the inner ear secretes proteins such as osteoprotegrin (OPG) that can prevent cochlear bone remodeling. Accordingly, diseases that affect bone regulation can also result in hearing loss. Patients with fibrous dysplasia develop trabecular bone overgrowth resulting in hearing loss if the lesions affect the temporal bones. Unfortunately, the mechanisms responsible for this hearing loss, which could be sensorineural and/or conductive, remain unclear. In this study, we used a unique transgenic mouse model of increased G_s G-protein coupled receptor (GPCR) signaling induced by expression of an engineered receptor, Rs1, in osteoblastic cells. These ColI(2.3)⁺/Rs1⁺ mice showed dramatic bone lesions that histologically and radiologically resembled fibrous dysplasia. We found that ColI(2.3)⁺/Rs1⁺ mice showed progressive and severe conductive hearing loss. Ossicular chain impingement increased with the size and number of dysplastic lesions. While sensorineural structures were unaffected, ColI(2.3)⁺/Rs1⁺ cochleae had abnormally high osteoclast activity, together with elevated tartrate resistant acid phosphatase (TRAP) activity and receptor activator of nuclear factor kappa-B ligand (Rankl) mRNA expression. ColI(2.3)⁺/Rs1⁺ cochleae also showed decreased expression of Sclerostin (Sost), an antagonist of the Wnt signaling pathway that normally increases bone formation. The osteocyte canalicular networks of ColI(2.3)⁺/Rs1⁺ cochleae were disrupted and showed abnormal osteocyte morphology. The osteocytes in the ColI(2.3)⁺/Rs1⁺ cochleae showed increased expression of matrix metalloproteinase 13 (MMP-13) and TRAP, both of which can support osteocyte-mediated peri-lacunar remodeling. Thus, while the ossicular chain impingement is sufficient to account for the progressive hearing loss in fibrous dysplasia, the deregulation of bone remodeling extends to the cochlea as well. Our findings suggest that factors regulating bone remodeling, including peri-lacunar remodeling by osteocytes, may be useful targets for treating the bony overgrowths and hearing changes of fibrous dysplasia and other bony pathologies.     

Exposure to omega-3 fatty acids at early age accelerate bone growth and improve bone quality

Omega-3 fatty acids (FAs) are essential nutritional components that must be obtained from foods. Increasing evidence validate that omega-3 FAs are beneficial for bone health, and several mechanisms have been suggested to mediate their effects on bone, including alterations in calcium absorption and urinary calcium loss, prostaglandin synthesis, lipid oxidation, osteoblast formation and inhibition of osteoclastogenesis. However, to date, there is scant information regarding the effect of omega-3 FAs on the developing skeleton during the rapid growth phase. In this study we aim to evaluate the effect of exposure to high levels of omega-3 FAs on bone development and quality during prenatal and early postnatal period. For this purpose, we used the fat-1 transgenic mice that have the ability to convert omega-6 to omega-3 fatty acids and the ATDC5 chondrogenic cell line as models. We show that exposure to high concentrations of omega-3 FAs at a young age accelerates bone growth through alterations of the growth plate, associated with increased chondrocyte proliferation and differentiation. We further propose that those effects are mediated by the receptors G-protein coupled receptor 120 (GPR120) and hepatic nuclear factor 4α, which are expressed by chondrocytes in culture. Additionally, using a combined study on the structural and mechanical bone parameters, we show that high omega-3 levels contribute to superior trabecular and cortical structure, as well as to stiffer bones and improved bone quality. Most interestingly, the fat-1 model allowed us to demonstrate the role of maternal high omega-3 concentration on bone growth during the gestation and postnatal period.     

Estrogen improves the proliferation and differentiation of hBMSCs derived from postmenopausal osteoporosis through notch signaling pathway

Estrogen deficiency is the main reason of bone loss, leading to postmenopausal osteoporosis, and estrogen replacement therapy (ERT) has been demonstrated to protect bone loss efficiently. Notch signaling controls proliferation and differentiation of bone marrow-derived mesenchymal stem cells (BMSCs). Moreover, imperfect estrogen-responsive elements (EREs) were found in the 5′-untranslated region of Notch1 and Jagged1. Thus, we examined the molecular and biological links between estrogen and the Notch signaling in postmenopausal osteoporosis in vitro. hBMSCs were obtained from healthy women and patients with postmenopausal osteoporosis. Notch signaling molecules were quantified using real-time polymerase chain reaction (real-time PCR) and Western Blot. Luciferase reporter constructs with putative EREs were transfected into hBMSCs and analyzed. hBMSCs were transduced with lentiviral vectors containing human Notch1 intracellular domain (NICD1). We also used N-[N-(3, 5-diflurophenylacetate)-l-alanyl]-(S)-phenylglycine t-butyl ester, a γ-secretase inhibitor, to suppress the Notch signaling. We found that estrogen enhanced the Notch signaling in hBMSCs by promoting the expression of Jagged1. hBMSCs cultured with estrogen resulted in the up-regulation of Notch signaling and increased proliferation and differentiation. Enhanced Notch signaling could enhance the proliferation and differentiation of hBMSCs from patients with postmenopausal osteoporosis (OP-hBMSCs). Our results demonstrated that estrogen preserved bone mass partly by activating the Notch signaling. Because long-term ERT has been associated with several side effects, the Notch signaling could be a potential target for treating postmenopausal osteoporosis.