Autologous cancellous bone graft is the gold standard in large bone defect repair. However, studies using autologous bone grafting in rats are rare and donor sites as well as harvesting techniques vary. The aim of this study was to determine the feasibility of autologous cancellous bone graft harvest from 5 different anatomical sites in rats and compare their suitability as donor sites for autologous bone graft. 13 freshly euthanised rats were used to describe the surgical approaches for autologous bone graft harvest from the humerus, iliac crest, femur, tibia and tail vertebrae (n=4), determine the cancellous bone volume and microstructure of those five donor sites using µCT (n=5), and compare their cancellous bone collected qualitatively by looking at cell outgrowth and osteogenic differentiation using an ALP assay and Alizarin Red S staining (n=4). It was feasible to harvest cancellous bone graft from all 5 anatomical sites with the humerus and tail being more surgically challenging. The microstructural analysis showed a significantly lower bone volume fraction, bone mineral density, and trabecular thickness of the humerus and iliac crest compared to the femur, tibia, and tail vertebrae. The harvested volume did not differ between the donor sites. All donor sites apart from the femur yielded primary osteogenic cells confirmed by the presence of ALP and Alizarin Red S stain. Bone samples from the iliac crest showed the most consistent outgrowth of osteoprogenitor cells. The tibia and iliac crest may be the most favourable donor sites considering the surgical approach. However, due to the differences in microstructure of the cancellous bone and the consistency of outgrowth of osteoprogenitor cells, the donor sites may have different healing properties, that need further investigation in an in vivo study

Remodeling of the cancellous bone is more active than that of the cortical bone. It is known that the remodeling is governed by the intracancellous fluid pressure. Particularly, the lacunocanalicular pore (PLC) fluid pressure (FP) is essential for survival of the osteocyte and communication of remodeling signals between the PLC and intertrabecular pore (PIT). As a result, knowledge about the PLCFP generation of trabeculae is required to understand human cancellous bone biology. At this moment, the PLCFP measurement of human trabeculae is not reported. The purpose of this study was a direct measurement of PLCFP generation of human proximal femoral trabeculae in the direction of superior-to-fovea. Twenty one microscopic cylindrical trabecular specimens from trabeculae of five fresh human proximal femur (75 to 77 years) were fabricated using a micro-milling machine composed of the laser (Teemphotonics: 532nm), 3-dimensional PZT stage (PI Gmbh, resolution: 0.5nm), and microscope (lens: Navitar, and CCD: Hitachi) with the image processor. The fabrication resolution of the micro-milling machine was 0.4 um. Based on the trabecular trajectory of femoral head, the specimens were obtained in the direction of superior-to-fovea. The cylindrical specimen size had 120 um in diameter and 240 um in length. The test methods described in the previous study were utilized. The used undrained uniaxial strain condition could induce the maximum PLCFP within the trabecular elastic limit. The measured trabecular PLCFP (±SD) at the strain of 0.4% was 693.7±79.1 kPa. Since this experiment is equivalent to the instantaneous response of PLCFP with free flow boundaries after application of an extremely fast loading speed such an ideal step loading, a PLCFP generation in the physiological condition will be much less than the results obtained in this study. Base on the linear isotropic poroelasticity, the obtained Skempton's coefficient is almost 0. Thus, the load bearing capability by trabecular PLC fluid is negligible. The Biot coefficient is 0.35 which is higher than that of the cortical tissue (0.14). As a result, the intraosseous fluid communication through trabecular surfaces is active compared to that through Haversian canal surfaces. This imply that mass transports from the trabecular PLC into the PIT and from the PIT into the trabecular PLC could be significantly affected by the PITFP (the physiological blood systolic and diastolic pressure: 16 and 11 kPa, respectively) that acts as the FP boundary condition for the PLC flow. It is known that the PLC flow generates the electrical charges on the trabecular surface (‘+’ for being spouted into the PIT and ‘−’ for being flown into the PLC), which control differentiation and proliferation of the osteoblast and mesenchymal stem cell. Thus, significant changes in the PITFT could cause changes in the intra-trabecular PLC flow characteristics, mass transports between the PLC and PIT, and electrical charges on the trabeculae. Eventually, these could result in pathologies related to the trabecular remodeling

We obtained medial and lateral subchondral cancellous bone specimens from ten human postmortem proximal tibiae with early osteoarthritis (OA) and ten normal age- and gender-matched proximal tibiae. The specimens were scanned by micro-CT and the three-dimensional microstructural properties were quantified. Medial OA cancellous bone was significantly thicker and markedly plate-like, but lower in mechanical properties than normal bone. Similar microstructural changes were also observed for the lateral specimens from OA bone, although there had been no sign of cartilage damage. The increased trabecular thickness and density, but relatively decreased connectivity suggest a mechanism of bone remodelling in early OA as a process of filling trabecular cavities. This process leads to a progressive change of trabeculae from rod-like to plate-like, the opposite to that of normal ageing. The decreased mechanical properties of subchondral cancellous bone in OA, which are due to deterioration in architecture and density, indicate poor bone quality

Summary. At the clinical CT image resolution level, there is no influence of the image voxel size on the derived finite element human cancellous bone models. Introduction. Computed tomography (CT)-based finite element (FE) models have been proved to provide a better prediction of vertebral strength than dual-energy x-ray absorptiometry [1]. FE models based on µCTs are able to provide the golden standard results [2], but due to the sample size restriction of the µCT and the XtremeCT machines, the clinical CT-based FE models is still the most promising tool for the in vivo prediction of vertebrae's strength. It has been found [3] that FE predicted Young's modulus of human cancellous bone increases as the image voxel size increases at the µCT resolution level [3]. However, it is still not clear whether the image voxel size in the clinical range has an impact on the predicted mechanical behavior of cancellous bone. This study is designed to answer this question. Methods. For this study, 6 thoracolumbar vertebrae (Th12) obtained from the female donors were scanned in the non-dissected cadavers under 2 different resolutions – group A: 120 kVp, 100 mAs, with a resolution of 0.29×0.29×1.3 mm. 3. ; group B: 120 kVp, 360 mAs, with a resolution of 0.18×0.18×0.6 mm. 3. A solid calibration phantom (QRM-BDC) was placed beneath the cadavers during the scans. Cuboids with the size of 12.3×12.3×14.3 mm. 3. were cropped from the center of each vertebral body. The FE model was created by converting each image voxel into hexahedron (C3D8). Inhomogeneous material property was defined for the cuboid [4], i.e. the image greyscale value were firstly calibrated into the bone mineral density (BMD), then the Young's modulus and yield stress were calculated from the BMD [5] for each element. Statistical analysis was performed to compare the FE predicted mechanical properties between the groups and the significance level was set to 95% (α=0.05). Results. The trabecular structure is more clearly mimicked in the models from group B than those from group A. The modulus (mean ± SE) in group A is 5.9% higher than that in group B (193.33 ± 31.67 MPa vs. 182.50 ± 27.07 MPa). The yield strength (mean ± SE) in group A is 6.4% higher than that in group B (0.99 ± 0.21MPa vs. 0.93 ± 0.17MPa). However, the paired t-test shows there is no significant difference of the mechanical properties in the two groups (p=0.109 for the modulus and p=0.234 for the yield strength). Discussion. This study shows that there is no influence of the voxel size on the clinical CT derived FE cancellous bone models. This finding can help choose a better, less invasive CT protocol for the patient when creating a clinical CT image based FE model. Acknowledgements. This study is financially supported by the Federal Ministry of Education and Research and the state of Hamburg, Germany

Previous studies have shown that low-density, rod-like trabecular structures develop in regions of low stress, whereas high-density, plate-like trabecular structures are found in regions of high stress. This phenomenon suggests that there may be a close relationship between the type of trabecular structure and mechanical properties. In this study, 160 cancellous bone specimens were produced from 40 normal human tibiae aged from 16 to 85 years at post-mortem. The specimens underwent micro-CT and the microstructural properties were calculated using unbiased three-dimensional methods. The specimens were tested to determine the mechanical properties and the physical/compositional properties were evaluated. The type of structure together with anisotropy correlated well with Young’s modulus of human tibial cancellous bone. The plate-like structure reflected high mechanical stress and the rod-like structure low mechanical stress. There was a strong correlation between the type of trabecular structure and the bone-volume fraction. The most effective microstructural properties for predicting the mechanical properties of cancellous bone seem to differ with age

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

Intermittent treatment with parathyroid hormone (PTH) has an anabolic effect on both intact cancellous and cortical bone. Very little is known about the effect of the administration of PTH on the healing of fractures or the incorporation of orthopaedic implants. We have investigated the spontaneous ingrowth of callus and the formation of bone in a titanium chamber implanted at the medioproximal aspect of the tibial metaphysis of the rat. Four groups of ten male rats weighing approximately 350 g were injected with human PTH (1-34) in a dosage of 0, 15, 60 or 240 μg/kg/day, respectively, for 42 days from the day of implantation of the chamber.

During the observation period the chamber became only partly filled with callus and bone and no difference in ingrowth distance into the chamber was found between the groups. The cancellous density was increased by 90%, 132% and 173% in the groups given PTH in a dosage of 15, 60 or 240 μg/kg/day, respectively. There was a linear correlation between bone density and the log PTH doses (r²= 0.6).

Our findings suggest that treatment with PTH may have a potential for enhancement of the incorporation of orthopaedic implants as well as a beneficial effect on the healing of fractures when it is given in low dosages.

Tourniquet is widely used in extremity surgery. In order to prevent surgical site infection, correct timing of antimicrobial prophylaxis and tourniquet inflation is important. We aimed to evaluate the time for which the free drug concentration of cefuroxime is maintained above the minimal inhibitory concentration (T>MIC) in subcutaneous tissue and calcaneal cancellous bone during three clinically relevant tourniquet application scenarios. Twenty-four female pigs were included. Microdialysis catheters were placed for sampling of cefuroxime concentrations bilaterally in calcaneal cancellous bone and subcutaneous tissue, and a tourniquet cuff was applied on a randomly picked leg of each pig. Subsequently, the pigs were randomized into three groups to receive 1.5 g of cefuroxime by intravenous injection 15 min prior to tourniquet inflation (Group A), 45 min prior to tourniquet inflation (Group B), and at the tourniquet release (Group C). The tourniquet duration was 90 min in all groups. Dialysates and venous blood samples were collected eight-hours postcefuroxime administration. Cefuroxime concentrations were maintained above the clinical breakpoint MIC for Staphylococcus aureus (4 μg/mL) in calcaneal cancellous bone and subcutaneous tissue throughout the 90 min tourniquet duration in Group A and B. Cefuroxime administration at tourniquet release (Group C) resulted in concentrations above 4 μg/mL for a minimum of 3.5 hours in the tissues on the tourniquet side. There were no significant differences in the T>MIC (4 μg/mL) in subcutaneous tissue or calcaneal cancellous bone between the three groups. However, Group A tended toward shorter T>MIC in tourniquet calcaneal cancellous bone compared to Group C (p=0.08). We conclude that administration of cefuroxime (1.5 g) in the 15–45 min window prior to tourniquet inflation resulted in sufficient calcaneal cancellous bone and subcutaneous tissue concentrations throughout the 90 min tourniquet application. If the target is to maintain postoperative cefuroxime concentrations above relevant MIC values, our results suggest that a second dose of cefuroxime should be administered at tourniquet release

To analyse bone stresses in humerus-megaprosthesis construct in response to axial loading under varying implant lengths in proximal humeral replacement following tumour excision. CT scans of 10 cadaveric humeri were processed in 3D Slicer to obtain three-dimensional (3D) models of the cortical and cancellous bone. Megaprostheses of varying body lengths (L) were modelled in FreeCAD to obtain the 3D geometry. Four FE models: group A consisting of intact bone; groups B (L=40mm), C (L=100mm) and D (L=120mm) comprising of humerus-megaprosthesis constructs were created. Isotropic linear elastic behaviour was assigned for all materials. A tensile load of 200N was applied to the elbow joint surface with the glenohumeral joint fixed with fully bonded contact interfaces. Static analysis was performed in Abaqus. The bone was divided at every 5% bone length beginning distally. Statistical analysis was performed on maximum von Mises stresses in cortical and cancellous bone across each slice using one-way ANOVA (0-45% bone length) and paired t-tests (45-70% bone length). To quantify extent of stress shielding, average percentage change in stress from intact bone was also computed. Maximum stress was seen to occur distally and anteriorly above the coronoid fossa. Results indicated statistically significant differences between intact state and shorter megaprostheses relative to longer megaprostheses and proximally between intact and implanted bones. Varying levels of stress shielding were recorded across multiple slices for all megaprosthesis lengths. The degree of stress shielding increased with implant lengthening being 2-4 times in C and D compared to B. Axial loading of the humerus can occur with direct loading on outstretched upper limbs or indirectly through the elbow. Resultant stress shielding effect predicted in longer megaprosthesis models may become clinically relevant in repetitive axial loading during activities of daily living. It is recommended to use shorter megaprosthesis to prevent failure

Objectives. Osteophytes are products of active endochondral and intramembranous ossification, and therefore could theoretically provide significant efficacy as bone grafts. In this study, we compared the bone mineralisation effectiveness of osteophytes and cancellous bone, including their effects on secretion of growth factors and anabolic effects on osteoblasts. Methods. Osteophytes and cancellous bone obtained from human patients were transplanted onto the calvaria of severe combined immunodeficient mice, with Calcein administered intra-peritoneally for fluorescent labelling of bone mineralisation. Conditioned media were prepared using osteophytes and cancellous bone, and growth factor concentration and effects of each graft on proliferation, differentiation and migration of osteoblastic cells were assessed using enzyme-linked immunosorbent assays, MTS ((3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium)) assays, quantitative real-time polymerase chain reaction, and migration assays. Results. After six weeks, the area of mineralisation was significantly higher for the transplanted osteophytes than for the cancellous bone (43803 μm. 2. , . sd. 14660 versus 9421 μm. 2. , . sd. 5032, p = 0.0184, one-way analysis of variance). Compared with cancellous bone, the conditioned medium prepared using osteophytes contained a significantly higher amounts of transforming growth factor (TGF)-β1 (471 pg/ml versus 333 pg/ml, p = 0.0001, Wilcoxon rank sum test), bone morphogenetic protein (BMP)-2 (47.75 pg/ml versus 32 pg/ml, p = 0.0214, Wilcoxon rank sum test) and insulin-like growth factor (IGF)-1 (314.5 pg/ml versus 191 pg/ml, p = 0.0418, Wilcoxon rank sum test). The stronger effects of osteophytes towards osteoblasts in terms of a higher proliferation rate, upregulation of gene expression of differentiation markers such as alpha-1 type-1 collagen and alkaline phosphate, and higher migration, compared with cancellous bone, was confirmed. Conclusion. We provide evidence of favourable features of osteophytes for bone mineralisation through a direct effect on osteoblasts. The acceleration in metabolic activity of the osteophyte provides justification for future studies evaluating the clinical use of osteophytes as autologous bone grafts. Cite this article: K. Ishihara, K. Okazaki, T. Akiyama, Y. Akasaki, Y. Nakashima. Characterisation of osteophytes as an autologous bone graft source: An experimental study in vivo and in vitro. Bone Joint Res 2017;6:73–81. DOI: 10.1302/2046-3758.62.BJR-2016-0199.R1

To quantify bone-nail fit in response to varying nail placements by entry point translation in straight antegrade humeral nailing using three-dimensional (3D) computational analysis. CT scans of ten cadaveric humeri were processed in 3D Slicer to obtain 3D models of the cortical and cancellous bone. The bone was divided into individual slices each consisting of 2% humeral length (L) with the centroid of each slice determined. To represent straight antegrade humeral nail, a rod consisting of two cylinders with diameters of 9.5mm and 8.5mm and length of 0.22L mm and 0.44L mm respectively joined at one end was modelled. The humeral head apex (surgical entry point) was translated by 1mm in both anterior-posterior and medio-lateral directions to generate eight entry points. Total nail protrusion surface area, maximum nail protrusion distance into cortical shell and top, middle, bottom deviation between nail and intramedullary cavity centre were investigated. Statistical analysis between the apex and translated entry points was conducted using paired t-test. A posterior-lateral translation was considered as the optimal entry point with minimum protrusion in comparison to the anterior-medial translation experiencing twice the level of protrusion. Statistically significant differences in cortical protrusion were found in anterior-medial and posterior-lateral directions producing increased and decreased level of protrusion respectively compared to the apex. The bottom anterior-posterior deviation distance appeared to be a key predictor of cortical breach with the distal nail being more susceptible. Furthermore, nails with anterior translation generated higher anterior-posterior deviation (>4mm) compared to posterior translation (<3mm). Aside from slight posterolateral translation of the entry point from the apex, inclusion of a distal posterior-lateral bend into current straight nail design could improve nail fitting within the curved humeral bone, potentially improving distal working length within the flat and narrow medullary canal of the distal humeral shaft

The success of cementless orthopaedic implants relies on bony ingrowth and active bone remodelling. Much research effort is invested to develop implants with controllable surface roughness and internal porous architectures that encourage these biological processes. Evaluation of these implants requires long-term and costly animal studies, which do not always yield the desired outcome requiring iteration. The aim of our study is to develop a cost-effective method to prescreen design parameters prior to animal trials to streamline implant development and reduce live animal testing burden. Ex vivo porcine cancellous bone cylinders (n=6, Ø20×12mm) were extracted from porcine knee joints with a computer-numerically-controlled milling machine under sterile conditions within 4 hours of animal sacrifice. The bone discs were implanted with Ø6×12mm additive manufactured porous titanium implants and were then cultured for 21days. Half underwent static culture in medium (DMEM, 10% FBS, 1% antibiotics) at 37°C and 5% CO. 2. The rest were cultured in novel high-throughput stacked configuration in a bioreactor that simulated physiological conditions after surgery: the fluid flow and cyclic compression force were set at 10ml/min and 10–150 N (1Hz,5000 cycles/day) respectively. Stains were administered at days 7 and 14. Samples were evaluated with widefield microscopy, scanning electron microscopy (SEM) and with histology. More bone remodelling was observed on the samples cultured within the bioreactor: widefield imaging showed more remodelling at the boundaries between the implant-bone interface, while SEM revealed immature bone tissue integration within the pores of the implant. Histological analysis confirmed these results, with many more trabecular struts with new osteoid formation on the samples cultured dynamically compared to static ones. Ex vivo bone can be used to analyse new implant technologies with lower cost and ethical impact than animal trial. Physiological conditions (load and fluid flow) promoted bone ingrowth and remodelling

Tourniquet is widely used in orthopedic surgery to reduce intraoperative bleeding and improve visualization. We evaluated the effect of tourniquet application on both peri- and postoperative cefuroxime concentrations in subcutaneous tissue, skeletal muscle, calcaneal cancellous bone, and plasma. The primary endpoint was the time for which the free drug concentration of cefuroxime was maintained above the clinical breakpoint minimal inhibitory concentration (T>MIC) forStaphylococcus aureus (4 µg/mL). Ten patients scheduled for hallux valgus or hallux rigidus surgery were included. Microdialysis catheters were placed for sampling of cefuroxime concentrations bilaterally in subcutaneous tissue, skeletal muscle, and calcaneal cancellous bone. A tourniquet was applied on the thigh of the leg scheduled for surgery. Cefuroxime (1.5 g) was administered intravenously as a bolus 15 minutes prior to tourniquet inflation, followed by a second dose 6 hours later. The mean tourniquet duration (range) was 65 (58; 77) minutes. Dialysates and venous blood samples were collected for 12 hours. For cefuroxime the T>MIC (4 μg/mL) ranged between 4.8–5.4 hours across compartments, with similar results for the tourniquet and non-tourniquet leg. Comparable T>MIC and penetration ratios were found for the first and second dosing intervals. We concluded that administration of cefuroxime (1.5 g) 15 minutes prior to tourniquet inflation is safe in order to achieve tissue concentrations above 4 µg/mL throughout surgery. A tourniquet application time of approximately 1 hour did not affect the cefuroxime tissue penetration in the following dosing interval

Introduction and Objective. Curative resection of proximal humerus tumours is now possible in this era of limb salvage with endoprosthetic replacement considered as the preferred reconstructive option. However, it has also been linked with mechanical and non-mechanical failures such as stem fracture and aseptic loosening. One of the challenges is to ensure that implants will endure the mechanical strain under physiological loading conditions, especially crucial in long surviving patients. The objective is to investigate the effect of varying prosthesis length on the bone and implant stresses in a reconstructed humerus-prosthesis assembly after tumour resection using finite element (FE) modelling. Methods. Computed tomography (CT) scans of 10 humeri were processed in Mimics 17 to create three-dimensional (3D) cortical and cancellous solid bone models. Endoprostheses of different lengths manufactured by Stryker were modelled using Solidworks 2020. The FE models were divided into four groups namely group A consisting of the intact humerus and groups B, C and D composed of humerus-prosthesis assemblies with a body length of 40, 100 and 120 mm respectively and were meshed using linear 4-noded tetrahedral elements in 3matic 13. The models were then imported into Abaqus CAE 6.14. Isotropic linear elastic behaviour with an elastic modulus of 13400, 2000 and 208 000 MPa were assigned to the cortical bone, cancellous bone and prosthesis respectively and a Poisson's ratio of 0.3 was assumed for each material. To represent the lifting of heavy objects and twisting motion, a tensile load of 200 N for axial loading and a 5 Nm torsional load for torsional loading was applied separately to the elbow joint surface with the glenohumeral joint fixed and with all contact interfaces defined as fully bonded. A comparative analysis against literature was performed to validate the intact model. Statistical analysis of the peak von Mises stress values collected from predicted stress contour plots was performed using a one-way repeated measure of analysis of variance (with a Bonferroni post hoc test) using SPSS Statistics 26. The average change in stress of the resected models from the intact state were then determined. Results. The validation of the intact humerus displayed a good agreement with literature values. The peak bone stress occurred distally above the coronoid and olecranon fossa closer to the load application region in the intact and resected bone models with a significant amount of loading borne by the cortical bone, while the peak implant stress occurred at the bone-prosthesis contact interface under both loading conditions. Based on the results obtained, a statistically significant difference (p =.013) in implant stress was only seen to occur between groups B and C under tension. Results illustrate initiation of stress shielding with the bone bearing lesser stress with increasing resection length which may eventually lead to implant failure by causing bone resorption according to Wolff's law. The peak implant stress under torsion was 3–5 times the stress under tension. The best biomechanical behaviour was exhibited in Group D, having the least average change in stress from the intact model, 5% and 3.8% under tension and torsion respectively. It can be deduced that the shorter the prosthesis length, the more pronounced the effect on cortical bone remodelling. With the maximum bone and implant stresses obtained being less than their yield strength, it can be concluded that the bone-implant construct is safe from failure. Conclusions. The developed FE models verified the influence of varying the prosthesis length on the bone and implant stresses and predicted signs of stress shielding in longer endoprostheses. By allowing for 2 cm shortening in the upper extremity and post-surgical scarring, it is beneficial to err towards a shorter endoprosthesis

Introduction. The crescent sign is thought to be an early indicator of collapse in osteonecrosis of the femoral head. However, the formation mechanism of the crescent sign is still not quite clear. The purpose of this study was to utilize the two-dimensional finite element model analysis (FEA) technique to analyze mechanical function of different structures and intraosseous fluid in the femoral head under the stress of physiological loading. We wished to answer the following question: which structure or structures' failure are the main causes of collapse in osteonecrosis of the femoral head (ONFH)?. Methods. Based on two femoral head specimens obtained during THA (one with osteonecrosis of the femoral head with crescent sign formation and the other with most of the cancellous bone eroded by tumor cells without collapse), three groups of ten models were designed. Group A were standard femoral heads composed of subchondral plate, cancellous bone, intraosseous fluid, and cortical bone with 50 mm in diameter, Group B included ONFH, and Group C was based on a tumor-eroded femoral head. Previously reported mechanical property parameters were used in the FEA calculation. The strain and Von Mieses stress mechanics parameters of fifteen points (with the same coordinates) in the junction between subchondral plate and cancellous bone were harvested and compared. Results. In the model, Group B3 (around the fissure region), had strains 12 times and Von Mieses' stresses 4.5 times higher than the values in same region of Group A1. Strain and Von Mieses stresses were concentrated in the fissure region and in the junction of the subchondral plate and the cancellous bone of the necrotic region. Conclusion. All three; the subchondral plate, cancellous bone, and intraosseous fluid, together played an important role for the femoral head to bear physiological loads. It is the fissure in the subchondral plate caused by the resorption that; 1) provides a channel for the intraosseous fluid to outflow and makes the necrotic region in both the subchondral plate and the cancellous bone lose mechanical support from the intraosseous fluid, and 2) destroys the function of the subchondral plate as a thin shell structure, making the stress and strain concentrate in the junction of the subchondral plate and the cancellous bone of the necrotic region. Concentrated stress leads to fracture of the junction between the subchondral plate and the cancellous bone and the formation of a crescent sign

Abstract. Objectives. Additive manufacturing (AM) enables fine control over the architecture of porous lattice structures, and the resulting mechanical performance. Orthopaedic implants may benefit from the tailored stiffness/elastic modulus of these AM biomaterials, as the stiffness can be made to closer match the properties of the replaced trabecular bone. Methods. This study used laser powder bed fusion (PBF) to create stochastic porous lattice structures in stainless steel (SS316L) and titanium alloy (Ti6Al4V), with modifications that aimed to overcome PBF manufacturing limitations of build angles. The structures were tested in uni-axial compression (n = 5) in 10 load orientations relative to the structure, including the three orthogonal axes. Results. The testing verified that no hidden peaks in elastic modulus existed in the stochastic structure. The standard deviation of the 10 elastic modulus values in the final structure decreased from 249 MPa to 101 MPa when made in SS316L and from 95.9 MPa to 52.5 MPa for Ti6Al4V, indicating the structures were more isotropic. Conclusions. These modified stochastic lattices have similar stiffness to cancellous bone and have controllable anisotropy, giving them the potential to be used within implants which match the stiffness of trabecular bone. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

Introduction and Objective. The choice of appropriate characteristics is crucial to favor a firm bonding between orthopedic implants and the host bone and to permit bone regeneration. In particular, the morphology and composition of the biointerface plays a crucial role in orchestrating precise cellular responses. Here, to modulate the biointerface, we propose new biomimetic coatings, having multi-scale nano- to micro- morphological cues and a composition mimicking the mineral phase of bone. Materials and Methods. Films on various substrates are obtained by Ionized Jet Deposition (IJD), by ablation of biogenic apatite and annealing at 400°C for 1 hour. Films are proposed for functionalization of metallic implants, but application to heat sensitive porous (3D printed) substrates is also shown, as it permits to further boost biomimicry (by addition of collagen/gelatin), thus reproducing the architecture of cancellous bone. In IJD, coatings thickness can be selected by tuning deposition duration. Here, a 450 nm thickness is selected based on preliminary results. Micro-rough titanium alloy (Ti6Al4V) disks (roughness 5 μm) are used as a substrate for the deposition and as a control. The coatings are characterized in terms of composition (GI-XRD, EDS, FT-IR microscopy), morphology (FEG-SEM, AFM, data processing by ImageJ), mechanical properties (micro-scratch test) and dissolution profile in medium (pH 7.4, FEG-SEM). Then, their behavior is characterized in vitro (human bone marrow-derived mesenchymal stromal cells - hMSCs), by studying cells early adhesion (focal adhesion by vinculin staining), viability (Alamar Blue), morphology (SEM) and differentiation (expression of RUNX2, ALPL, SPARC and COL1A1, BMP2, BGLAP, osteocalcin, alkaline phosphatase, collagen type I) at 3, 7 and 14 days. Results. Films exhibit a biomimetic composition, as they are constituted by a nanocrystalline multi-doped carbonated hydroxyapatite. EDS indicates the presence of trace ions sodium (0,11 ± 0,02 wt%) and magnesium (0,47 ± 0,05 wt%), uniformly distributed in the coating in a percentage close to native bone. These ion-substitutions are crucial, as each ion modifies apatite solubility and ion-release in the peri-implant environment and has important biological role. Films have a high adhesion to the substrates and a suitable dissolution profile. The morphology is highly rough, as films are composed by nanosized grains (minimum diameter 40 nm) aggregated in multi-scale clusters (diameter range: 100 nm-2 μm). Morphology of the aggregates can be tuned by selecting deposition duration and also depends on the morphology, roughness and composition of the substrate. Because of the nanoscale thickness of the films, they do not alter the microscale features of the implants. For fibrous substrates, films grow onto the fibers surface, with no pore occlusion or damage to substrate composition. Coatings do not alter the metabolic activity of MSCs but influence their early adhesion, morphology and differentiation. More in detail, MSCs on coated disks show a branched shape, while those on the controls show a more spindle and elongated morphology. Coatings increase hMSCs early adhesion, as a higher density and a greater area of focal adhesions are observed at 24 hours. Finally, they can trigger a signaling pathway that promotes the osteogenic differentiation of hMSCs, as confirmed by quantification of osteocalcin, alkaline phosphatase and collagen, even in the absence of osteogenesis-inducing factors. Conclusions. The topographical and chemical cues of the biomimetic nanostructured coating are perceived by hMCSs, showing that combining morphological and biomimetic cues is a promising route for the development of cells-instructive biomaterials for orthopedics. In vivo tests on rabbit models are in progress

Summary. The negative impact of NSAIDs on fracture healing appears not to pertain to fractures in cancellous bone. Possibly this is because of a higher prevalence of MSCs in cancellous bone, making recruitment of distant cells via inflammatory signals less important. Introduction. It is well established that cox inhibitors (NSAIDs) impair fracture healing, also in humans. However, as they provide good pain relief it is unclear when to avoid these drugs. The healing process in cortical and cancellous fractures differs regarding progenitor cell sources, and inflammation might be involved in the recruitment of cells from distant sources. We therefore hypothesised that fractures in cancellous bone are less sensitive to reduced inflammation due to cox inhibitors. Methods. Indomethacin was used to study the role of an NSAID on shaft and metaphyseal fracture healing. 40 male 10 week old C57/bl6 mice were used, 20 of which received a stabilised mid-shaft femur fracture, whilst the other 20 received a screw inserted into the cancellous bone of the proximal tibia on one side, and a drill hole in the same area on the contralateral side. Half of the mice received injections of 1 mg/kg bodyweight of Indomethacin, twice daily for 14 days. The other half received saline. The effect of the treatment on the fracture healing was evaluated with mechanical testing, µCT, and histology. Results. Biomechanical testing (pull-out force for the screws) could detect no significant effect of indomethacin on the cancellous fracture healing. A reduction in force by more than 21 % could be excluded with 95 % confidence. The drill holes contained new bone, but µCT of this bone showed no effect of treatment on BMD, BV/TV, trabecular thickness, or trabecular number. Analysis of shaft healing is not yet completed. µCT of the first 12 femurs is available. A difference between the groups was obvious on visual inspection: Blind sorting, based on amount of callus, could identify all 6 indomethacin treated femurs and none of the controls as having an inferior callus response. More data will follow. Discussion/Conclusion. NSAIDs had no visible effect on metaphyseal healing, but a dramatic effect on the shaft fractures. Possibly, prostaglandin signaling is important for recruitment of progenitor cells to the shaft callus, whereas such cells are already present within the metaphyseal marrow

Abstract. Introduction. The long-term biological success of cementless orthopaedic prostheses is highly dependent on osteointegration. Pre-clinical testing of new cementless implant technology however, requires live animal testing, which has anatomical, loading, ethical and cost challenges. This proof-of-concept study aimed to develop an in vitro model to examine implant osteointegration under known loading/micromotion conditions. Methods. Fresh cancellous bone cylinders (n=8) were harvested from porcine femur and implanted with additive manufactured porous titanium implants (Ø4 × 15 mm). To simulate physiological conditions, n=3 bone cylinders were tested in a bioreactor system with a cyclic 30 µm displacement at 1Hz for 300 cycles every day for 15 days in a total of 21 days culture. The chamber was also perfused with culture medium using a peristaltic pump. Control bone cylinders were cultured under static conditions (n=5). Samples were calcein stained at day 7. Post-testing, bone cylinders were formalin fixed and bony ingrowth was measured via microscopy. Results. Viability of the freshly harvested ex vivo bone cylinders was maintained for up to 28 days. Two samples remain unanalysed due to COVID lockdown, one in each group. Similar to osteointegration seen in live animal models, evidence of bony ingrowth was seen more markedly at the bone-implant interface under dynamic conditions. This was evident by a greater intensity of calcein staining, confirming the deposition of new bone, at the bone-implant interface. In comparison, under static conditions, calcein staining was observed randomly all over the cylinder. Conclusion. This proof-of-concept study demonstrates that implant bony adaptation and ingrowth can be measured in vitro under known cyclic micromotion/loading conditions. This comparatively low cost, low ethical impact, controlled loading laboratory method has potential to accelerate the rate of implant development whilst conforming with the principles of NC3Rs. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

Abstract. Objective. To compare the periprosthetic fracture mechanics between a collared and collarless fully coated cementless femoral stem in a composite femur. Methods. Two groups of six composite femurs (‘Osteoporotic femur’, SawBones, WA USA) were implanted with either a collared (collared group) or collarless (collarless group) cementless femoral stem which was otherwise identical by a single experienced surgeon. Periprosthetic fractures of the femur were simulated using a previously published technique. High speed video recording was used to identify fracture mechanism. Fracture torque and angular displacement were measured and rotational work and system stiffness were estimated for each trial. Results were compared between collared and collarless group and the comparison was evaluated against previously published work using fresh frozen femurs and the same protocol. Results. In composite femur testing median fracture torque (IQR) was greater with a collared versus collarless implant (48.41 [42.60 to 50.27] Nm versus 45.12 [39.13 to 48.09] Nm, p= 0.4). Median rotational displacement (IQR) was less with a collared versus collarless implant (0.29 [0.27 to 0.31] radians versus 0.33 [0.32 to 0.34] radians, p= 0.07). Estimated rotary work was similar between groups (5.76 [4.92 to 6.64] J versus 5.21 [4.25 to 6.04] J, p= 0.4). Torsional stiffness was greater with a collared versus collarless implant (158.36 [152.61, 163.54] Nm per radian versus 138.79 [122.53, 140.59] Nm per radian, p= 0.5). Collarless stems were seen to move independently of the femur and fracture patterns originated at the calcar. Conclusions. Testing with composite femurs using an established protocol produced similar results to previously published studies using human femurs, but the difference between collared and collarless stems was smaller. The internal homogenous foam material in composite femurs does not accurately represent the heterogeneous cancellous bone which supports a femoral stem in vivo and may lead to overestimation of implant stability. Declaration of Interest. (a) fully declare any financial or other potential conflict of interest