Objectives. There remains conflicting evidence regarding cortical bone strength following bisphosphonate therapy. As part of a study to assess the effects of bisphosphonate treatment on the healing of rat tibial fractures, the mechanical properties and radiological density of the uninjured contralateral tibia was assessed. Methods. Skeletally mature aged rats were used. A total of 14 rats received 1µg/kg ibandronate (iban) daily and 17 rats received 1 ml 0.9% sodium chloride (control) daily. Stress at failure and toughness of the tibial diaphysis were calculated following four-point bending tests. Results. Uninjured cortical bone in the iban group had a significantly greater mean (standard deviation (. sd. )), p < 0.001, stress at failure of 219.2 MPa (. sd. 45.99) compared with the control group (169.46 MPa (. sd. 43.32)) following only nine weeks of therapy. Despite this, the cortical bone toughness and work to failure was similar. There was no significant difference in radiological density or physical dimensions of the cortical bone. Conclusions. Iban therapy increases the stress at failure of uninjured cortical bone. This has relevance when normalising the strength of repair in a limb when comparing it with the unfractured limb. However, the 20% increase in stress at failure with iban therapy needs to be interpreted with caution as there was no corresponding increase in toughness or work to failure. Further research is required in this area, especially with the increasing clinical burden of low-energy diaphyseal femoral fractures following prolonged use of bisphosphonates. Cite this article: Bone Joint Res 2015;4:99–104

Background

High re-rupture rates following repairs of rotator cuff tears (RCTs) have resulted in the increased use of repair grafts to act as temporary scaffolds to support tendon healing. It has been estimated that thousands of extracellular matrix repair grafts are used annually to augment surgical repair of rotator cuff tears. The only mechanical assessment of the suitability of these grafts for rotator cuff repair has been made using tensile testing only, and compared grafts to canine infraspinatus. As the shoulder and rotator cuff tendons are exposed to shearing as well as uniaxial loading, we compared the response of repair grafts and human rotator cuff tendons to shearing mechanical stress. We used a novel technique to study material deformation, dynamic shear analysis (DSA).

Introduction. In vivo, UHMWPE bearing surfaces are subject to wear and oxidation that can lead to bearing fatigue or fracture. A prior study in our laboratory of early antioxidant (AO) polyethylene retrievals, compared to gamma-sterilized and highly cross-linked (HXL) retrievals, showed them to be more effective at preventing in vivo oxidation. The current analysis expands that early study, addressing the effect of:. manufacturing-variables on as-manufactured UHMWPE;. in vivo time on these initial properties;. identifying important factors in selecting UHMWPE for the hip or knee. Methods. After our prior report, our IRB-approved retrieval laboratory received an additional 96 consecutive AO-retrievals (19 hips, 77 knees: in vivo time 0–6.7 years) of three currently-marketed AO-polyethylenes. These retrievals represented two different antioxidants (Vitamin E and Covernox) and two different delivery methods: blending-prior-to and diffusing-after irradiation cross-linking. Consecutive HXL acetabular and tibial inserts, received at retrieval, with in vivo time of 0–6.7 years (260 remelted, 170 annealed) were used for comparison with AO-retrievals. All retrievals were analyzed for oxidation and trans-vinylene index (TVI) using a Thermo-Scientific iN10 FTIR microscope. Mechanical properties were evaluated for 35 tibial inserts by uniaxial tensile testing using an INSTRON load frame. Cross-link density (n=289) was measured using a previously published gravimetric gel swell technique. Oxidation was reported as maximum ketone oxidation index (KOI) measured for each bearing. TVI was reported as the average of all scans for each material. Cross-link density and mechanical properties were evaluated as a function of both TVI and oxidation. Results. Minimal increase in oxidation was seen in these AO-retrievals, out to almost 7 years in vivo. In contrast, HXL-retrievals showed increasing KOI with time in vivo (annealed-HXL = 0.127/year, remelted-HXL = 0.036/year, p<0.001). HXL oxidation rate was higher in knees (0.091/year) than in hips (0.048/year), p<0.001. Cross-link density (XLD) correlated positively with TVI for both HXL (Pearson's correlation=0.591, p<0.001) and AO (Pearson's correlation=0.598, p<0.001) retrievals. AO-materials had higher TVI for the same or similar XLD than did HXL polyethylene. XLD correlated negatively with KOI for HXL retrievals (Pearson's correlation=−0.447, p<0.001). Mechanical properties varied by material across all materials evaluated, with tensile toughness correlating negatively with increasing TVI (Pearson Correlation=−0.795, p<0.001). Discussion. Irradiation cross-linking has been used effectively to improve wear resistance. Residual free radicals from irradiation are the target of AO-polyethylene, to prevent loss of UHMWPE XLD, resulting from in vivo oxidation of free radicals as seen in HXL retrievals, and toughness, resulting from oxidation or initial remelting. Despite different manufacturing variables, AO-polyethylene retrievals in this cohort had minimal oxidation and no change in XLD or toughness due to oxidation. However, toughness did vary with irradiation dose as did cross-link density. To achieve the same level of cross-linking as HXL-polyethylene required a higher irradiation dose in blended AO-polyethylene. AO-polyethylenes evaluated in this study had toughness that decreased with irradiation dose, but avoided loss of toughness due to remelting. Because AO-polyethylenes did not oxidize, they did not show the decrease of cross-link density, and potential loss of wear resistance, seen in HXL-polyethylene. For any figures or tables, please contact authors directly

Introduction. Bone fracture toughness is an important parameter in resistance of bone to monotonic and fatigue failure. Earlier studies on bone fracture toughness were focused on either cortical or cancellous bone, separately [1, 2]. Reported fracture toughness values indicated that cortical bone is tougher to break as compared to cancellous bone. In order to understand complete fracture of a whole bone, the interface between cortical and cancellous bone (named as corticellous bone) might play a crucial role and is interesting topic of research. The goal of this study was to identify fracture toughness in terms of J integral and fracture mechanism of the corticellous bone. Material and Methods. Corticellous bone samples (single edge notch bend specimen or SENB) were prepared from bovine proximal femur according to ASTM E399-90 standard (Fig.1). For corticellous bone, samples were prepared in such way that approximately half of the sample width consist of cortical bone and another half is cancellous bone. Precaution was taken while giving notch and pre-crack to corticellous bone that pre-crack should not enter from cortical to cancellous portion. All specimens were tested using a universal testing machine (Tinius Olsen, ± 100 N) under displacement rate of 100 µm/min until well beyond yield point. The fracture toughness parameter in terms of critical stress intensity (K. IC. ) was calculated according to ASTM E399-90 as given by, . (1). K. IC. =. PS. /. BW. 1.5. *. f. (. a. /. W. ). …. Where, P = applied load in kN, S = loading span in cm, B = specimen thickness in cm, W = specimen width in cm, a = total crack length, f(a/W) = geometric function. After the fracture test the J integral of each specimen was calculated using following equation. [ASTM E1820]. . (2). J. total. =. J. el. +. J. pl. =. K. IC. 2. /. E. ′. +. 2. A. pl. /. Bb. 0. …. Where, J. el. is J integral of the elastic deformation, J. pl. is J integral of the plastic deformation, E′=E for plane stress condition and E′= E/(1−ν. 2. ) for plane strain condition (E is elastic modulus; ν is Poisson's ratio), b. o. = W−a. o. , height of the un-cracked ligament, and A. pl. is the area of the plastic deformation part in the load–displacement curve. Result and Discussion. The fracture toughness in terms of critical stress intensity (K. IC. ) of corticellous bone was found to be 2.45 MPa.m. 1/2. The plastic part of J integral, J. pl. value of corticellous specimen was 9310 Jm. −2. , and shown to be 27 times of the J. el. value, 341 Jm. −. 2. Total J integral of corticellous bone was found to be 9651 Jm. −2. When crack travels through cortical portion and reaches at the interface, crack branching occurred and further it slows down (Fig.2). Indeed, more energy is required in plastic than elastic deformation. Conclusion. J integral of corticellous bone is found to higher which is due to plastic deformation and crack branches at the interface between cortical and cancellous bone. For any figures or tables, please contact the authors directly

Introduction. The in vivo evolution of surface material properties is important in determining the longevity of bioceramics. Fracture toughness is particularly relevant because of its role in wear resistance. Some bioceramics, such as zirconia (ZrO2) undergo in vivo phase transformation, resulting in a marked reduction in toughness and commensurate increased wear. Here, we investigated the effect of accelerated aging on the surface toughness of alumina (Al2O3), zirconia-toughened alumina (ZTA), and silicon nitride (Si3N4) femoral heads, in order to identify the optimal ceramic material for in vivo implantation and long-term durability. Materials. A newly developed Raman microprobe-assisted indentation method was applied to evaluate and compare surface fracture toughness mechanisms operative in Si3N4 (Amedica Corporation, Salt Lake City, UT, USA), Al2O3 and ZTA (BIOLOX® forte, and delta, respectively, CeramTec, GmbH, Plochingen, Germany) bioceramics. The Al2O3 and ZTA materials have long established histories in total hip arthroplasty; whereas Si3N4 has been newly developed for this purpose. The improved method proposed here consisted in coupling the “traditional” indentation technique with quantitative assessments of microscopic stress fields by confocal Raman microprobe piezo-spectroscopy. Concurrently, crack opening displacement (COD) profiles were also monitored by Raman spectroscopy. Toughness measurements were determined using both as-received and hydrothermally exposed (100–121°C for up to 300 hours) femoral heads. Results. The Raman microprobe visualized two main toughening mechanisms operative in Si3N4 and ZTA bioceramics, namely crack-face bridging by acicular Si3N4 grains and polymorphic transformation of ZrO2 dispersoids. Both mechanisms elevated the resistance to crack propagation above the brittle behavior of Al2O3, which experienced a low crack resistance of ∼1.5 MPaâ��m1/2 independent of crack length. The as-received Si3N4 showed a sharply rising R-curve, up to ∼7 MPaâ��m1/2 within a propagation distance of ∼110 µm. A rising R-curve was also observed in the as-received ZTA, although its increase was less pronounced, ∼4 MPaâ��m1/2 within ∼120 µm. After hydrothermal exposure, surface toughness values decreased by ∼5%, ∼10%, and ∼42% for Si3N4, Al2O3, and ZTA, respectively. Substantial embrittlement was particularly noted at the surface of the ZTA material, with its toughness value reduced to the level of Al2O3. At the micromechanical scale, such embrittlement is obviously related to decreased availability of transformable (metastable) tetragonal ZrO2dispersoids at the surface. In ZTA, the hydrothermal attack annihilated any rising R-curve effect; whereas this degradation mechanism was not present in either Al2O3 or Si3N4 (Fig. 1). Discussion. Empowered by the Raman microprobe, the indentation micro-fracture method was shown capable of providing reliable surface toughness measurements in dissimilar biomaterials. Different from bulk toughness, surface toughness is the most relevant parameter in designing bioceramic microstructures for use as hip arthroplasty bearing couples for improved tribological performance. It was demonstrated that the environmentally driven phase transformation in ZTA is detrimental to surface toughness. On the other hand, Si3N4 experienced surface toughness values conspicuously independent of hydrothermal attack. Conclusions. Unlike transformation toughening (which is operative in ZTA), crack-face bridging (which is the toughening mechanism in Si3N4) proved to be the most durable surface toughening effect for a biomaterial to be employed in joint arthroplasty

Introduction. The optimum UHMWPE orthopaedic implant bearing surface must balance wear, oxidation and fatigue resistance. Antioxidant polyethylene addresses free radicals, resulting from irradiation used in cross-linking, that could oxidize and potentially lead to fatigue damage under cycles of in vivo use. Assessing the effectiveness of antioxidant (AO) polyethylene compared to conventional gamma-sterilized or remelted highly cross-linked (HXL) polyethylene is necessary to set realistic expectations of the service lifetime of AO polyethylene in the knee. This study evaluates what short-term antioxidant UHMWPE retrievals can reveal about: (1) oxidation-resistance, and (2) fatigue-resistance of these new materials. Methods. An IRB-approved retrieval laboratory received 25 AO polyethylene tibial insert retrievals from three manufacturers with in vivo time of 0–3 years. These were compared with 20 conventional gamma-inert sterilized and 30 HXL (65-kGray, remelted) tibial inserts of the same in vivo duration range. The retrievals were. (1) analyzed for oxidation and trans-vinylene index (TVI) using an FTIR microscope, and (2) inserts of sufficient size and thickness were evaluated for mechanical properties by uniaxial tensile testing using an INSTRON load frame. Oxidation was reported as maximum oxidation measured in the scan from the articular surface to the backside of each bearing. TVI was reported as the average of all scans for each material. Average ultimate tensile strength (UTS), ultimate elongation (UE), and toughness were the reported mechanical properties for each material. Results. Maximum oxidation values differed significantly across material types (p=0.018, Figure 1). No antioxidant retrieval exhibited a subsurface oxidation peak, in contrast to conventional gamma-sterilized (55%) and highly cross-linked (37%) retrievals that exhibited subsurface oxidation peaks over the same in vivo time (Figure 2). Trans-vinylene index (TVI) correlated positively with nominal irradiation dose (p<0.001). Mechanical properties varied by material, with tensile toughness correlating negatively with increasing TVI (p<0.001, Figure 3). Discussion. AO polyethylene was developed to address the problem of free radicals in polyethylene resulting from irradiation used in cross-linking or sterilization. Each manufacturer used a different antioxidant or method of supplying the antioxidant. However, all of the antioxidant materials appeared to be effective at minimizing oxidation over the in vivo period of this study. The antioxidant materials prevented in vivo oxidation more effectively than both conventional gamma-sterilized and remelted HXL polyethylene, at least over the in vivo period represented. The toughness, or ability of the material to resist fatigue damage, decreased with increasing irradiation cross-linking dose (increasing TVI). The AO polyethylenes evaluated in this study had lower toughness than conventional gamma-sterilized polyethylene, but they avoided the loss of toughness due to remelting. Clinical relevance. Antioxidant polyethylene tibial retrievals showed superior oxidation resistance to conventional gamma-inert and remelted HXL inserts. Material toughness varied with the irradiation dose used to produce the material. Comparison of antioxidant retrieval tensile properties can be used as a guide for clinicians in choosing appropriate materials for the applications represented by their patients

The aim of this study is to print 3D polycaprolactone (PCL) scaffolds at high and low temperature (HT/LT) combined with salt leaching to induced porosity/larger pore size and improve material degradation without compromising cellular activity of printed scaffolds. PCL solutions with sodium chloride (NaCl) particles either directly printed in LT or were casted, dried, and printed in HT followed by washing in deionized water (DI) to leach out the salt. Micro-Computed tomography (Micro-CT) and scanning electron microscope (SEM) were performed for morphological analysis. The effect of the porosity on the mechanical properties and degradation was evaluated by a tensile test and etching with NaOH, respectively. To evaluate cellular responses, human bone marrow-derived mesenchymal stem/stromal cells (hBMSCs) were cultured on the scaffolds and their viability, attachment, morphology, proliferation, and osteogenic differentiation were assessed. Micro-CT and SEM analysis showed that porosity induced by the salt leaching increased with increasing the salt content in HT, however no change was observed in LT. Structure thickness reduced with elevating NaCl content. Mass loss of scaffolds dramatically increased with elevated porosity in HT. Dog bone-shaped specimens with induced porosity exhibited higher ductility and toughness but less strength and stiffness under the tension in HT whereas they showed decrease in all mechanical properties in LT. All scaffolds showed excellent cytocompatibility. Cells were able to attach on the surface of the scaffolds and grow up to 14 days. Microscopy images of the seeded scaffolds showed substantial increase in the formation of extracellular matrix (ECM) network and elongation of the cells. The study demonstrated the ability of combining 3D printing and particulate leaching together to fabricate porous PCL scaffolds. The scaffolds were successfully printed with various salt content without negatively affecting cell responses. Printing porous thermoplastic polymer could be of great importance for temporary biocompatible implants in bone tissue engineering applications

This study aims to assess the fracture mechanics of type-2 diabetic (T2D) femoral bone using innovative site-specific tests, whilst also examining the cortical and trabecular bone microarchitecture from various regions using micro-computed tomography (CT) of the femur as the disease progresses. Male [Zucker Diabetic Fatty (ZDF: fa/fa) (T2D) and Zucker Lean (ZL: fa/+) (Control)] rats were euthanized at 12-weeks of age, thereafter, right and left femora were dissected (Right femora: n = 6, per age, per condition; Left femora: n=8-9, per age, per condition). Right femurs were notched in the posterior of the midshaft. Micro-CT was used to scan the proximal femur, notched and unnotched femoral midshaft (cortical) of the right femur and the distal metaphysis (trabecular) of the left femur to investigate microarchitecture and composition. Right femurs were fracture toughness tested to measure the stress intensity factor (Kic) followed by a sideways fall test using a custom-made rig to investigate femoral neck mechanical properties. There was no difference in trabecular and cortical tissue material density (TMD) between T2D and control rats. Cortical thickness was unchanged, but trabeculae were thinner (p<0.01) in T2D rats versus controls. However, T2D rats had a greater number of trabeculae (p<0.05) although trabecular spacing was not different to controls. T2D rats had a higher connectivity distribution (p<0.05) and degree of anisotropy (p<0.05) in comparison to controls. There was no difference in the mechanical properties between strains. At 12-weeks of age, rats are experiencing early-stage T2Ds and the disease impact is currently not very clear. Structural and material properties are unchanged between strains, but the trabecular morphology shows that T2D rats have more trabecular struts present in order to account for the thinner trabeculae

Introduction. Radiation cross-linked UHMWPE is preferred in total hip replacements due to its wear resistance [1]. In total knees, where stresses are higher, there is concern of fatigue damage [2]. Antioxidant stabilization of radiation cross-linked UHMWPE by blending vitamin E into the polymer powder was recently introduced [3]. Vitamin E greatly hinders radiation cross-linking in UHMWPE [4]. In contrast peroxide cross-linking of UHMWPE is less sensitive to vitamin E concentration [5]. In addition, exposing UHMWPE to around 300°C, increases its toughness by inducing controlled chain scission and enhanced intergranular diffusion of chains, simultaneously [6]. We present a chemically cross-linked UHMWPE with high vitamin E content and improved toughness by high temperature melting. Methods and Materials. Medical grade GUR1050 UHMWPE was blended with vitamin E and with 2,5-Di(tert-butylperoxy)-2,5-dimethyl-3-hexyne or P130 (0.5% Vitamin-E and 0.9% P130). The mixed powder was consolidated into pucks. The pucks were melted for 5 hours in nitrogen at 300, 310 and 320°C. One set of pucks melted at 310°C was accelerated aged at 70°C at 5 atm. oxygen for 2 weeks. Tensile mechanical properties were determined using ASTM D638. Izod impact toughness was determined using ASTM D256 and F648. Wear rate was determined using a bidirectional pin-on-disc (POD) tester with cylindrical pins of UHMWPE against polished CoCr discs in undiluted, preserved bovine serum. Results. The vinyl index increased as a function of temperature (Fig 1a). Cross-link density steadily decreased and impact strength increased with increasing vinyl index (Fig 1b). The ultimate tensile strength (UTS) was not affected by HTM (Table 2). Impact strength was significantly improved for all treatment temperatures (P<0.05) and wear was significantly increased only for the sample melted at 320°C (Table 2). Discussion. High temperature melting (HTM) was shown to increase toughness of UHMWPEs presumably due to controlled chain scissioning and increased intergranular diffusion of chains [6]. For radiation cross-linked UHMWPE, it was shown that an increase in elongation-at-break and impact strength could be obtained without sacrificing wear resistance up to an elongation of about 500% [7]. This vitamin E-blended, peroxide cross-linked, high temperature melted UHMWPE has very high oxidation resistance due to its high antioxidant content, high wear resistance due to cross-linking and much improved toughness, representing an optimum joint replacement surface. For figures/tables, please contact authors directly.

Rotator cuff tears are common, with failure rates of up to 94% for large and massive tears. 1. For such tears, reattachment of the musculotendinous unit back to bone is problematic, and any possible tendon-bone repair heals through scar tissue rather than the specially adapted native enthesis. We aim to develop and characterise a novel soft-hard tissue connector device, specific to repairing/bridging the tendon-bone injury in significant rotator cuff tears, employing decellularised animal bone partially demineralised at one end for soft tissue continuation. Optimisation samples of 15×10×5mm. 3. , trialled as separate cancellous and cortical bone samples, were cut from porcine femoral condyles and shafts, respectively. Samples underwent 1-week progressive stepwise decellularisation and a partial demineralisation process of half wax embedding and acid bathing. Characterisations were performed histologically for the presence/absence of cellular staining in both peripheral and central tissue areas (n=3 for each cortical/cancellous, test/PBS control and peripheral/central group), and with BioDent reference point indentation (RPI) for pre- and post-processing mechanical properties. Histology revealed absent cellular staining in peripheral and central cancellous samples, whilst reduced in cortical samples compared to controls. Cancellous samples decreased in wet mass after decellularisation by 45.3% (p<0.001). RPI measurements associated with toughness (total indentation depth, indentation depth increase) and elasticity (1st cycle unloading slope) showed no consistent changes after decellularisation. X-rays confirmed half wax embedding provided predictable control of the mineralised-demineralised interface position. Initial optimisation trials show proof-of-concept of a soft-hard hybrid scaffold as an immune compatible xenograft for irreparable rotator cuff tears. Decellularisation did not appreciably affect mechanical properties, and further biological, structural and chemical characterisations are underway to assess validity before in vivo animal trials and potential clinical translation

In this study, we developed biocompatible adhesive which enables implanted chondrogenic-enhanced hASCs being strongly fixed to the lesion site of defected cartilage. The bioengineered mussel adhesive protein (MAP) was produced and purified using a bacterial expression system as previously reported. The cell encapsulated coacervate was formulated with two polyelectrolyte, the MAP and 723kDa hyaluronic acid (HA). MAP formed liquid microdroplets with HA and subsequently gelated into microparticles, which is highly viscous and strongly adhesive. The MAP with chondro-induced hASCs were implanted on the osteochondral defect created in the patellar groove/condyle of OA-induced rabbits. Rabbits were allocated to three different groups as follows: Group1 – Fibrin only; Group2 – Fibrin with hASCs (1.5×10. 6. chondro-induced hASCs); Group3; MAP with hASCs. The implanted cells were labeled with a fluorescent dye for in vivo visualization. After 35 days, fluorescent signals were more potently detected for MAP with hASCs group than Fibrin with hASCs group in osteochondral defect model. Moreover, histological assessment showed that MAP with hASCs group had the best healing and covered with hyaline cartilage-like tissue. The staining image shows that MAP with hASCs group were filled with perfectly differentiated chondrocytes. Although Fibrin with hASCs group had better healing than fibrin only group, it was filled with fibrous cartilage which owes its flexibility and toughness. As MAP with hASCs group has higher possibility of differentiating to complete cartilage, Fibrin only group and Fibrin with hASCs group have failed to treat OA by rehabilitating cartilage. In order to clarify the evidence of remaining human cell proving efficacy of newly developed bioadhesive, human nuclear staining was proceeded with sectioned rabbit cartilage tissue. The results explicitly showed MAP with hASCs group have retained more human cells than Fibrin only and Fibrin with hASCs groups. We investigated the waterproof bioadhesive supporting transplanted cells to attach to defect lengthily in harsh environment, which prevents cells from leaked to other region of cartilage. Collectively, the newly developed bio-adhesive, MAP, could be successfully applied in OA treatment as a waterproof bioadhesive with the capability of the strong adhesion to target defect sites

Combined techniques of fracture mechanics and confocal Raman microprobe spectroscopy were applied to characterize, after increasing periods of environmental exposure, bulk and surface toughness values in an advanced alumina/zirconia composite. This material is used in joint prostheses (BIOLOX. ®. delta femoral heads, manufactured by CeramTec AG). Besides conventional fracture mechanics characterizations, including different types of fracture toughness test, Raman and fluorescence microprobe spectroscopy provided a microscopic insight into the effect of environmentally assisted processes of zirconia phase transformation at the surface on the fracture toughness of the material. We have found that the tetragonal-to-monoclinic polymorphic transformation occurs in the studied composite material as a consequence of an environmentally assisted process, although severe exposures are needed for to obtain a substantial increase of the monoclinic content. Such severe exposures in vitro correspond to exposures in human body of several lifetimes. The effect of an exposure of 10 h in autoclave (in vitro accelerated test) was carefully examined, because this span of time corresponds:. to the period of time recommended for testing in vitro by ISO standard; and,. to approximately the lifetime expected for a prosthesis in vivo. The main experimental outcomes of confocal Raman spectroscopy and fracture mechanics assessments can be summarized as follows:. the crack-tip toughness level measured in the as-received material was comprehensive of a tangible contribution by transformation toughening, thus showing that phase transformation in the zirconia dispersoids plays a positive role in the toughening behavior of the material;. after the material was environmentally aged in vitro for periods of the order of hundreds of hours, its surface toughness was reduced by about one-third; but, even in the case of such a severe exposure, the surface toughness of the composite was at least the same as that of monolithic alumina;. the observed decrease of fracture toughness by about one-third was limited to the very surface of the material (i.e., to a layer of the order of the tens of microns) and did not affect the bulk fracture behavior of the composite. It appears that concerns arising from the brittleness of alumina-based materials and, thus, from their vulnerability to fracture due to unexpected load situation, can be successfully counteracted by properly adding a dispersion of zirconia particles to the alumina matrix. Such an addition enables the obtainment of a composite material, whose fracture resistance is greatly enhanced by a crack-shielding effect due to phase-transformation processes occurring in the zirconia dispersoids

Osteoporosis (OP) results in a reduction in the mechanical competence of the bone tissue of the sufferers. In skeletal sites such as the proximal femur and the vertebrae, OP manifests itself in low trauma fragility fractures which are debilitating for the patient. The relationships between the compressive strength of cancellous tissue and its apparent density are well established in studies of the past. Recently the authors have presented a method able to assess the fracture toughness properties of cancellous bone (1), a challenging cellular material which can exhibit large elasto-plastic deformations. The in-vitro measurement of fracture toughness alongside the customary compressive strength can provide a comprehensive assessment of the mechanical capacity of cancellous bone, which will reflect closer its ability to resist crack initiation. The aims of the present study were: (1) to examine whether the observed fracture toughness deterioration can also be detected by non-invasive quantitative ultrasound (QUS); and (2) to provide rational evidence for the well proven ability of QUS to predict directly ‘risk of fracture’. 20 femoral heads were obtained from donors undergoing emergency surgery for a fractured neck of femur. QUS investigations of the calcaneus, proximal phalanx and distal radius were undertaken within 72 hours of surgery. 128 fracture toughness samples and 20 compression cores were manufactured and tested. Two clinical QUS systems were used to obtain in-vivo scan data and then directly compared those to the density, porosity and the fracture mechanics of tissue extracted from the same individuals. The results demonstrated not only that there was a significant link between in-vivo determined QUS values for the calcaneus and finger to the density of the density of the femoral head; but that there was also a significant link between the QUS results from the calcaneus and the fracture toughness of the cancellous bone from the femoral head. These results point towards a systemic effect of osteoporosis which affects similarly different parts of the skeleton and supports the use of clinical QUS systems as a diagnostic tool for the prediction of fracture risk

Complex spinal deformities can cause pain, neurological symptoms and imbalance (sagittal and/or coronal), severely impairing patients’ quality of life and causing disability. Their treatment has always represented a tough challenge: prior to the introduction of modern internal fixation systems, the only option was an arthrodesis to prevent worsening of the deformity. Then, the introduction of pedicle screws allowed the surgeons to perform powerful corrective manoeuvres, distributing forces over multiple levels, to which eventually associate osteotomies. In treating flexible coronal deformities, in-ternal fixation and corrective manoeuvres may be sufficient: the combination of high density pedicle screws and direct vertebral rotation revolutionized surgical treatment of scoliosis. However, spinal osteotomies are needed for correcting complex rigid deformities; the type of osteot-omy must be chosen according to the aetiology, type and apex of the deformity. When dealing with large radius deformities, spread over multiple levels and without fusion, multiple posterior column os-teotomies such as Smith-Petersen and Ponte (asymmetric, when treating scoliosis) can be performed, dissipating the correction over many levels. Conversely, the management of a sharp, angulated de-formity that involves a few vertebral levels and/or with bony fusion, requires more aggressive 3 col-umn osteotomies such as Pedicle Subtraction Osteotomies (PSO), Bone Disc Bone Osteotomies (BDBO) or Vertebral Column Resection (VCR). Sometimes the deformity is so severe that cannot be corrected with only one osteotomy: in this scenario, multilevel osteotomies can be performed

Multiple biological and mechanical factors may be responsible for the failure of fixation in cemented total hip replacements (THRs). Although the eventual failure of THRs may appear to be biological, the initiation of the failure during early period post operation may well be mechanical. It is in this area that mechanistic analysis is of particular significance. This study builds on work by Rapperport et al, Dals-tra and Huiskes on stress analysis of implanted acetabulum, while focuses on fracture mechanics analyses of fracture of cement and of bone-cement interface. Specifically, finite element models were developed where cracks of most favourable orientations in the cement mantle were simulated. Possible crack path selections were explored. A simplified multilayer experimental model was also developed to represent the implanted acetabulum, and fatigue tests were carried out on the model. The experimental results were compared with those from the FE model. Furthermore, interfacial crack growth at bone-cement interface was simulated from the superior edge of the acetabulum, as suggested from the clinical observations. The strain energy release rates were computed for typical hip contact forces during gait and as a function of crack length. Associated phase angles were also computed to account for the materials mismatch. The results were evaluated against the interfacial fracture toughness of the bone-cement interface, measured using sandwich Brazilian disk specimens. The results show that although interfacial fracture seems to be unlikely for large phase angles where shear component is most active, the strain energy release rates are comparable with the values of the interfacial fracture toughness when mode I is predominant, suggesting interfacial fracture. The study also shows that the fracture toughness of cement is much higher than the interfacial fracture toughness of bone-cement, this may explain the reason why interfacial fracture is favoured even if the crack driving force at bone-cement interface appears to be weaker than that in the cement mantle

The long-term stability of total hip replacements (THRs) critically depends on the lasting integrity of the bond between the implant and the bone. Late failure in the absence of infection is known as ‘aseptic loosening’, a process characterised by the formation and progressive thickening of a continuous layer of fibrous tissue at the interface between the prosthesis and the bone. Aseptic loosening has been identified as the most common cause for long-term instability leading to the failure of ace-tabular cups. There is clearly a need to study the failure mechanisms in the acetabular fixation if the long-term stability of THR is to be significantly improved. The bonding strength in the presence of defects is measured using interfacial fracture toughness, and this information is not available currently. In this work, interfacial fracture toughness of synthetic and bovine bone-cement interface has been studied using sandwiched Brazilian disk specimens. Experiments were carried out using a common bone cement, CMW, and polyurethane foam under selected loading angles from 0 to 25 degrees to achieve full loading conditions from tensile (mode I) to shear (mode II). Finite element analyses were carried out to obtain the solutions for strain energy release rate at a given phase angle (ratio of shear and tensile stress) associated with the experimental models. The effects of crack length on the measured interfacial fracture toughness were examined. Microscopic studies were also carried out to obtain the morphology of the fractured interfaces at selected loading angles. The results show that both polyurethane foam and bovine cancellous bone seem to produce a similar type of interfacial failure of bone-cement interface, with cement pedicles being ‘pull-out’ of the pores of the foam/ bone. Damage sustained by the cement pedicles seems to increase progressively as the increase of shear loading component. The measured values of fracture toughness are a function of crack length and phase angle, and are comparable with those published in the literature on cortical bone and cement interface. The implication of these results on the assessment of fixation in acetabular replacements is discussed, particularly in the light of results from bovine cancellous bone-cement interface

Introduction: Patients who are prescribed bisphosphonates are still at risk to endure a fracture from weak and brittle bones. The question is what pharmacologic strategy should be taken to accelerate fracture healing when the patient is currently taking a bisphosphonate. Ibandronate, was tested in an osteoporotic rat model to determine how it modified the callus healing and resistance to torsion after a transverse fracture was produced in a femur. Materials and Methods: 36 female rats were divided into 3 groups; ovariectomized (OVX) placebo control, non-OVX control and Ibandronate. Prior to the osteotomy, the Ibandronate treatment group was injected with the drug over 21 days healing. Each sample was scanned by the SCANCO uCT 80 to measure volume of the callus and quality of the trabeculae in the proximal femur. Instron testing recorded the modulus of rigidity and torque until failure. Yield point and toughness were also calculated. Results: uCT images taken over the fracture gap showed that the Ibandronate rats had greater bone volume fraction of woven callus by ANOVA compared to control groups (p< 0.05). Significant in total callus volume for Ibandronate, were shown to be 32% larger than the non-OVX control group and 45% larger than the placebo group. Ibandronate also increased BMD of woven bone in the callus by 14%. Ibandronate showed the highest polar moment of inertia as well. The torsion testing in Ibandronate had 51% greater toughness than placebo and 69% greater than the non-OVX group. Ibandronate increased trabecular number significantly over the placebo and was not significantly different from the non-OVX group. Trabecular separation was less in Ibandronate compared to the placebo group. Volume in the trabecular neck increased by 35% for the Ibandronate over the placebo. Discussion: Ibandronate had an anabolic effect to produce more callus tissue at the fracture site, most likely by suppressing osteoclast remodelling activity. A large callus with more bone would increase fracture stability and reduce risk of non union. This is supported by a larger polar moment of inertia. Ibandronate had greater resistance to torsion, which could indicate better healing. However increased rigidity would not entirely benefit the healing unless the bone could handle load plastically. The toughness results showed that Ibandronate can absorb more energy than the control groups before refracturing. Continued treatment with this drug after a fracture could form a larger callus with greater mechanical toughness while also treating the disease of osteoporosis in other fracture risk sites of the body

Introduction: Alumina exhibits excellent hardness and wear properties, however it is a brittle material with an inherent risk of fracture. Therefore, the feasibility of a new family of Alumina based ceramics with improved toughness for hip joint articulation applications was investigated. Materials and methods: The addition of 25% Zirconia to Alumina during the manufacturing process to achieve the objective has been proposed. Two types of Zirconia Toughened Alumina (ZTA) ceramics were analysed; one binary and the other pentary by composition. Following tests were used: structural analysis, mechanical testing of components, determination of hardness (HV), fl exural strength (ASTM C1161), indentation fracture toughness, X-ray diffraction (XRD), aging (accelerated and real-time) and wear simulator testing. The test data was analysed by descriptive statistics. Results: The structure of the two ZTAs is similar with small-grained Zirconia dispersed in a matrix of larger grained Alumina. X-ray diffraction analysis showed no phase transformation after accelerated and real-time aging and the strength values did not change. Flexural strength was statistically significant increased by > 50% over Alumina. The indentation fracture toughness was also increased by up to 50% while the hardness of the ZTA ceramics was not affected. The wear testing showed that ZTA – ZTA couples articulating against themselves produce not significant lower wear than Alumina – Alumina couples, but the combination of ZTA ball-heads with Alumina inserts produced significantly lower wear rates, also in micro-separation. Conclusions: The toughness and bending strength of the Alumina was successfully increased while all other properties of the Alumina were maintained. No change in properties after aging was observed and the wear properties of the ZTA were lower wear than for Alumina. Zirconia Toughened Alumina looks promising for the next generation of fracture and wear resistant ceramic bearings

INTRODUCTION. Ceramics are excellently suited for applications in arthroplasty, mainly total hip, knee and shoulder replacement. As the most prominent representative of this demanding type of material, BIOLOX. ®. delta is widely used and very successful in the market for more than 10 years. The ability of zirconia phase transformation (t-ZrO. 2. →m-ZrO. 2. ) in zirconia-platelet toughened alumina (ZPTA) ceramics is an indispensable prerequisite for their excellent mechanical properties. The degree of stabilization of the zirconia tetragonal phase at body temperature is essential for the desired toughening mechanism. Y. 2. O. 3. is the most widely used t-ZrO. 2. chemical stabilizer; also microstructure and grain size contribute to t-ZrO. 2. phase stabilization. Stabilization must be achieved such that no material degradation will occur in body environment, i.e. in aqueous liquid (synovia), which is known to potentially trigger phase transformation at the surface of ceramic components. In this study, it is shown how phase stabilization in BIOLOX. ®. delta as a reference material is excellently balanced by means of optimal mechanical performance and environmental stability. OBJECTIVES. To assess the influence of t-ZrO. 2. chemical stabilization on ZPTA properties, in terms of fracture toughness (i.e. the ability to resist crack extension), wear resistance and environmental stability. METHODS. Three ZPTA compositions with increasing yttria content (Y. 2. O. 3. /ZrO. 2. 2–4mol%) were produced and compared to the reference. Hardness and fracture toughness were assessed by Vickers indentation method. A micro scratch tester (CSM Instruments, Peseux Switzerland) loaded with a Rockwell C diamond tip with 50µm radius was used to assess the scratch resistance of the ceramic compositions. The scratch load was linearly increased from 0 to 30N, which simulates extremely heavy local wear conditions. The morphology and depth of the scratches as well as local damage has been analysed with a laser microscope (Olympus LEXT-OLS4000) and scanning electron microscope (Hitachi S4700). The hydrothermal aging resistance was measured by autoclaving the compositions up to 150 hours at 134°C and 2.2bar and the monoclinic zirconia volume fraction measured by XRD using the Garvie formula at each time interval (i.e. 0, 10, 50, 100 and 150h). Surface roughness after hydrothermal ageing was also evaluated by atomic force microscopy. RESULTS. As expected, t-ZrO. 2. stabilization improved with increasing yttria content. Consequently, hydrothermal aging resistance increased and fracture toughness decreased strongly to almost monolithic alumina values. The scratch resistance performances also decreased showing gradually lower critical load Lc1, where grain pull-out phenomenon appeared earlier with the higher zirconia stabilization composition. The materials kept almost the same hardness (about 18GPa). Surface roughness also remained unchanged for all compostions, even in extreme hydrothermal conditions. CONCLUSIONS. Higher tetragonal zirconia stabilization leads to the suppression of zirconia phase transformation toughening and consequently of low temperature degradation; annihilating almost all the improvements of ZPTA over the monolithic alumina material. It was demonstrated that the best performance is achieved by properly triggering the tetragonal zirconia transformation. This result is explaining the successful performance of BIOLOX. ®. delta bearing couples already observed in the clinical setting

Today, hip prostheses are validated with Standards for fatigue testing: The Standard ISO 7206-4 requires to test 6 components at 230daN during 5 × 10. 6. cycles without crack. For the neck region of stemmed femoral components, the Standard ISO 7206-6 requires 6 tests at 534daN during 10 × 10. 6. cycles without crack. But these tests don't provide provide any indication on reliability level for an implantation in population. At the same time, the number of hip prosthesis implantation is growing, patients are implanted younger and younger and they want to be able to maintain a “normal” life. This way the average “loading spectrum” is getting tougher and tougher, due to this modification of the use of prosthesis in comparison with some years ago. On the other hand, there is new materials, new processes (additive manufacturing), new methods (customized stems…) with no feedback on reliability. A method is then necessary to manage the reliability in fatigue for actual and new products. The objective of this study is to establish a statistical distribution of loading of hip prosthesis in order to define at best a minimum value of strength required for a good fatigue design. To define this strength, the Stress-Strength (well known in automotive sector) approach is applied (fig 1). This approach will allow better assess the reliability in a population, depending on the mean strength and the scattering in fatigue. The first step is to establish the distribution of the loads for a hip prosthesis. Then, for a given risk level, the required strength can be defined, knowing the scattering of this strength. The strategy to have the distribution is based on:. In vivo load recordings on hip prosthesis (find on . Orthoload.com. ),. Analysis of frequency of everyday activities,. Activity level of different category of the population,. Statistical distribution of key parameters, like weight, age…. All these data are collected in the literature, and combined, then processed with the software DEFFI. ®. The goal is first to assess the reliability reached by a “nominal” stem and compare it to the reliability described in implant registers. Another goal is to analyse the stress distribution and compare it to standard requests (ISO 7206-6), in order to assess the reliability of an implant that succeeded this standard. A last, this method is a way to define the minimum strength for implants dedicated to particular populations: young and active patients, patients with high Body Weight, etc…. For any figures or tables, please contact authors directly (see Info & Metrics tab above).