Introduction. BAG-S53P4 has similar mechanical properties as cortical bone tissue and can be used as an additive to bone allografts. The aim of this study was to evaluate the effect of adding BAG-S53P4 to chemically treated allografts with controlled grain size distribution. Methods. Allografts were prepared and chemically cleaned under sterile conditions. 30 samples were mixed with BAG-S53P4 additive (BG) and compared to a control group (CG) with similar grain size distribution and composition in weight. All samples underwent a uniaxial compression test after compaction with a dropped weight apparatus. The yield limit was determined by a uniaxial compression test and density was recorded. The two groups were tested for statistical differences with the student's t-Test. Results. Adding BAG-S53P4 to the chemically treated allografts with controlled grain size distribution did not affect the yield limit after compaction. No statistically significant difference regarding the yield limit could be found between CG and BG after compaction (p=0.432).). The yield limit yield limit showed an increase of approximately 96% in CG and 93 % in BG, which confirms the importance of impacting bone chips used for load bearing applications like in hip arthroplasty. Conclusions. Adding BAG-S53P4 seems to have a less profound impact on the yield stress limit. In BG particles smaller than 4 mm were substituted with BAG-S53P4. Achieving a high density may not be the major goal for the bone remodeling process as it may actually obstruct new osteocytes from growing into the allograft material. Adding BAG-S53P4 seems to have limited impact on the yield stress limit. From a biomechanical point of view, BAG-S53P4 can be used as a substitute in total hip replacement if access to bone allograft material is limited

Introduction. The increase in revision joint replacement surgery and fractures of bone around orthopaedic implants may be partly addressed by keeping bone healthy around orthopaedic implants by inserting implants with mechanical properties closer to the patient's bone properties. We do not currently have an accurate way of calculating a patient's bone mechanical properties. We therefore posed a simple question: can data derived from a micro-indenter be used to calculate bone stiffness?. Methods. We received ethical approval to retrieve femoral heads and necks from patients undergoing hip replacement surgery for research. Cortical bone from the medial calcar region of the femoral neck was cut into 3×3×6mm cuboid specimens using a diamond wafering blade. Micro-indentation testing was performed in the direction of loading of the bone using a MicroMaterials (MicroMaterials, UK) indenter, using the high load micro-indentation stage (see Figure 1). To simulate in vivo testing, the samples were kept hydrated and were not fixed or polished. From the unloading curve after indentation, the elastic modulus was calculated, using the Oliver-Pharr method using the indentation machine software. To assess which microindentation machine settings most precisely calculate the elastic modulus we varied the loading and unloading rates, load and indenter tip shape (diamond Berkovich tip, 1mm diameter Zirconia spherical tip and 1.5mm diameter ruby spherical tip). Following this, for 11 patients' bone, we performed compression testing of the same samples after they were indented with the 1.5mm diameter ruby spherical tip to assess if there was a correlation between indentation values of apparent elastic modulus and apparent modulus values calculated by compression testing (see Figure 2). Platens compression testing was performed using an Instron 5565 (Instron, USA) materials testing machine. Bluehill compliance correction software (Instron, USA) was used to correct for machine compliance. The strain rate was set at 0.03mm/s. The apparent elastic modulus was calculated from the slope of the elastic region of the stress-strain graph. The correlation between values of apparent modulus from compression testing and indentation were analyzed using IBM SPSS Statistics 22. Results. The most precise results were obtained using a spherical indenter tip (1.5 mm diameter ruby ball), rather than a sharp Berkovich tip, high load (10N), a loading rate of 100 mN/s and unloading rate of 300 mN/s with a pause of 60 seconds at maximum load. We also used multiple load cycles with a peak load of 10N (see Figure 3). Using these optimal settings we calculated the mean elastic modulus over 10 cycles of testing with six indents on one sample to be 11.8 GPa (+/− 1.01). There was a moderate correlation between indentation and compression values of apparent modulus (r=0.62, n=11, p=0.04). Discussion. By using a spherical indenter tip and fast unloading it was possible to get precise apparent modulus values. The apparent modulus derived from micro-indentation, correlated moderately with that derived from direct compression testing. This early data suggests that microindentation may become a clinically relevant test of bone quality in real time

Physical examination is critical to formation of a differential diagnosis in patients with ulnar-sided wrist pain. Although the specificity and sensitivity of some of those tests have been reported in the literature, the prevalence of positive findings of those provocative maneuvers has not been reported. The aim of the study is to find the prevalence of positive findings of the most commonly performed tests for ulnar sided wrist pain in a population presenting to UE surgeon clinics, and to correlate those findings with wrist arthroscopy findings. Patients with ulnar sided wrist pain were identified from a prospective database of patients presented with wrist pain from September 2014. Prevalence of positive findings for the following tests were gathered: ECU synergy test, ECU instability test (Ice cream and Fly Swatter), Lunotriquetral ballottement, Kleinman shear, triquetrum tenderness, triquetrum compression test, triquetral-hamate tenderness, pisotriquetral shuck test, ulnar fovea test, ulnocarpal impaction (UCI) maneuver, UCI maneuver with fovea pressure (ulnar carpal plus test), piano key sign. A subgroup was then created for those who underwent wrist arthroscopy, and analysis of the sensitivities, the specificities and the predictive values of these provocative tests was carried out with correlation to arthroscopic finding. Prevalence of ECU instability tests was t 1.13% (ice cream scoop) and 1.5% (fly swatter). Lunotriquetral ballottement test's positive findings range from 4.91% (excessive laxity) to 14.34% (pain reproducing symptoms. The Kleinman shear test yielded pain in 13.58% of patients, and instability in only 2.26%. Triquetrum compression test reproduces pain in 32.83% of patients, and triquetral-hamate tenderness reproduced pain in 13.21%. Pisotriquetral grind test yields 15.85% positive findings for pain, and 10.57% for crepitus with radioulnar translation. The ulnar fovea test revealed pain in 69.05% of cases. The UCI maneuver yielded pain in 70.19%. The UCI maneuver plus ulnar fovea test reproduced pain in 80.38% of cases. Finally, the piano key sign yields positive finding in 2.64% of cases. For patients who underwent surgery, sensitivities, specificities and predictive values were calculated based on arthroscopic findings. The lunotriquetral ballottement test has 59.6% sensitivity, 39.6% specificity, 20.3% positive predictive value and 85.4% negative predictive value. The sensitivity of Kleinman test was 62.4%, the specificity was 41.3%, the positive predictive value was 23.5%, and the negative predictive value was 83.2%. The sensitivity of fovea test was 94.3%, the specificity was 82.5%, the positive predictive value was 89.5% and the negative predictive value was 92.3%. The UCI maneuver plus ulnar fovea test has 96.5% sensitivity, 80.7% specificity 86.4% positive predictive value, and 95.3% negative predictive value. Among the provocative tests, the prevalence of positive findings is low in the majority of those maneuvers. The exceptions are the fovea test, the UCI maneuver, and the UCI plus maneuver. With regard to the sensitivity and the specificity of those tests, the current study reproduces the numbers reported in the literature. Of those patients who underwent wrist arthroscopy, the tests are better at predicting at the absence of injury rather than at predicting its presence

Introduction. A clinical case of catastrophic ring failure in a 13 year old autistic overweight patient during treatment for tibial lengthening and deformity using a Taylor Spatial Frame is reported. Ring failure was noted during the later stages of bone healing and the frame was removed. The clinical outcome was not affected by the catastrophic ring failure. The photograph of the deformed ring is presented below:. Materials and Methods. The patient's notes and X-rays were reviewed and a macroscopic examination of the deformed ring was performed. Mechanical tests of different Taylor Spatial frame constructs were performed in an attempt to simulate the deformity that was clinically observed. Different constructs of TSF of different ring sizes were fixed to polyurethane cylinders simulating bone, were mechanically tested to failure and load/deflection curves were produced. Results. Macroscopically the ring looked otherwise normal. Gradual mechanical compression tests of Taylor Spatial frame constructs showed that ring deformation increased by increasing the ring diameter and by using jointed rather than full joints without a ring. The ring deformation observed clinically was reproduced at the lab by applying high loads on frame constructs composed of large diameter jointed rings not rigidly fixed to bone. Conclusions. Taylor Spatial frame ring failure during treatment is a serious complication that has not been described in the literature. Possible causes are discussed. Clinicians are advised to use the smaller possible diameter rings. Where large diameter rings are required, these rings should preferably be not jointed. Half rings when used should be carefully and securely joined together by the operating surgeon in order to make a complete ring. For any figures or tables, please contact the authors directly

Introduction. The fixation of press-fit orthopaedic devices depends on the mechanical properties of the bone that is in contact with the implants. During the press-fit implantation, bone is compacted and permanently deformed, finally resulting in the mechanical interlock between implant and bone. For the development and design of new devices, it is imperative to understand these non-linear interactions. One way to investigate primary fixation is by using computational models based on Finite Element (FE) analysis. However, for a successful simulation, a proper material model is necessary that accurately captures the non-linear response of the bone. In the current study, we combined experimental testing with FE modeling to establish a Crushable Foam model (CFM) to represent the non-linear bone biomechanics that influences implant fixation. Methods. Mechanical testing of human tibial trabecular bone was done under uniaxial and confined compression configurations. We examined 62 human trabecular bone samples taken from 8 different cadaveric tibiae to obtain all the required parameters defining the CFM, dependent on local bone mineral density (BMD). The derived constitutive rule was subsequently applied using an in-house subroutine to the FE models of the bone specimens, to compare the model predictions against the experimental results. Results. The crushable foam model provided an accurate simulation of the experimental compression test, and was able to replicate the ultimate compression strength measured in the experiments [Figure 1]. The CFM was able to simulate the post-failure behavior that was observed in the experimental specimens up to strain levels of 50% [Figure 2]. Also, the distribution of yield strains and permanent displacement was qualitatively very similar to the experimental deformation of the bone specimens [Figure 3]. Conclusion. The crushable foam model developed in the current study was able to accurately replicate the mechanical behavior of the human trabecular bone under compression loading beyond the yield point. This advanced bone model enables realistic simulations of the primary fixation of orthopaedic devices, allowing for the analysis of the influence of interference fit and frictional properties on implant stability. In addition, the model is suitable for failure analysis of reconstructions, such as the tibial collapse of total knee arthroplasty. For any figures or tables, please contact the authors directly

Since artificial joints are expected to operate for more than decades in human body, animal and clinical studies are not suitable for evaluation of their durability. Instead, in-vitro mechanical tests have been employed, but they cannot fully reproduce complex in-vivo mechanical and biochemical environment. For instance, lipids in synovial fluid have been known to be absorbed in ultra-high molecular weight polyethylene (UHMWPE) components of artificial joints in vivo, and recently it was found that absorbed lipids have potential to degrade UHMWPE. In order to assure clinical relevance of the in-vitro mechanical tests, understanding of the effect of the in-vivo environment on mechanical properties is indispensable. However, well-developed mechanical tests cannot be applied to retrieved components, because they require large specimens. In this study, we attempted to develop methods to evaluate mechanical properties of retrieved UHMWPE components. We prepared five kinds of UHMWPE. Those are molded UHMWPE made from GUR 1020 resin without any further treatment, remelted highly crosslinked UHMWPE, annealed highly crosslinked UHMWPE, squalene absorbed UHMWPE which was prepared by immersing in squalene at 80°C for 7 days (SQ) and squalene absorbed and artificially aged UHMWPE which was prepared by artificially aging SQ at 80°C for 21 days in air (SQA). SQ and SQA were employed in this study to mimic lipid absorption and lipid induced degradation. These materials were tested by two well-established mechanical tests, namely, tensile tests and compression tests, and two proposed mechanical tests that can be applied to retrieved components, namely, tensile punch tests and micro indentation tests. It was possible to clearly identify the difference between materials by any of test methods used in this study. Stiffness obtained from tensile punch tests and elastic modulus obtained from micro indentation tests were shown to be highly correlated with elastic modulus obtained from compression tests except for SQA, which was inhomogeneous due to degradation at the surfaces. The results showed that the elastic modulus of the local surface could be evaluated by micro indentation tests, while the average of that of the entire specimen could be evaluated by compression tests. ield load, fracture load and maximum load obtained from tensile punch tests showed little correlation with yield stress, fracture stress and maximum stress obtained from tensile tests, respectively. These differences were considered to be attributed to the differences in a stress condition between these two test methods. It is multi-axial tension in tensile punch tests, while it is uniaxial in tensile tests. Although some of the parameters obtained by tensile punch tests showed no or limited correlation with those obtained by tensile tests, it was possible to clearly identify the difference between materials by these proposed test methods. In particular, micro indentation tests could evaluate the mechanical properties very locally. These proposed test methods have the potential to provide useful information on mechanical properties of retrieved UHMWPE components

Great strides have been made in the early detection and treatment of cancer which is resulting in improved survivability and more Canadians living with cancer. Approximately 80% of primary breast, lung, and prostate cancers metastasize to the spine. Poly-methyl methacrylate (PMMA) bone cement is one of the most commonly used bone substitutes in spine surgery. In clinical practice it can be loaded with various drugs, such as antibiotics or chemotheraputic drugs, as a means of local drug delivery. However, studies have shown that drugs loaded into PMMA cement tend to release in small bursts in the first 48–72 hours, and the remaining drug is trapped without any significant release over time. The objective of this study is to develop a nanoparticle-functionalized PMMA cement for use as a sustained doxorubicin delivery device. We hypothesize that PMMA cement containing mesoporous silica nanoparticles will release more doxorubicin than regular PMMA. High viscosity SmartSet ™ PMMA cement by DePuy Synthes was used in this study. The experimental group consisted of 3 replicates each containing 0.24 g of mesoporous silica nanoparticles, 1.76 g of cement powder, 1ml of liquid cement monomer and 1 mg of doxorubicin. The control group consisted 3 replicates each containing 2.0 g of cement powder, 1ml of liquid cement monomer and 1 mg of doxorubicin. The experimental group contained an average of 8.18 ± 0.008 % (W/W) mesoporous silica nanoparticles. Each replicate was casted into a cylindrical block and incubated in a PBS solution which was changed at predetermined intervals for 45 days. The concentration of eluted doxorubicin in each solution was measured using a florescent plate reader. The mechanical properties of cement were assessed by unconfined compression testing. The effect of the doxorubicin released from cement on prostate and breast tumor cell metabolic activity was assessed using the Alamar Blue test. After 45 days the experimental group released 3.24 ± 0.25 % of the initially loaded doxorubicin which was more than the 2.12 ± 0.005% released by the control group (p 0.03). There was no statistically significant difference in Young's elasticity modulus between groups (p 0.53). Nanoparticle functionalized PMMA suppressed the metabolic activity of prostate cancer by more than 50 percent but did not reach statistical significance. Nanoparticle functionalized PMMA suppressed the metabolic activity of breast cancer cells by 69 % (p < 0.05). Nanoparticle-functionalized PMMA cement can release up to 1.53 times more doxorubicin than the standard PMMA. The use of mesoporous silica nanoparticles to improve drug release from PMMA cement shows promise. In the future, in vivo experiments are required to test the efficacy of released doxorubicin on tumor cell growth

Introduction. Up to 60% of total hip arthroplasties (THA) in Asian populations arise from avascular necrosis (AVN), a bone disease that can lead to femoral head collapse. Current diagnostic methods to classify AVN have poor reproducibility and are not reliable in assessing the fracture risk. Femoral heads with an immediate fracture risk should be treated with a THA, conservative treatments are only successful in some cases and cause unnecessary patient suffering if used inappropriately. There is potential to improve the assessment of the fracture risk by using a combination of density-calibrated computed tomographic (QCT) imaging and engineering beam theory. The aim of this study was to validate the novel fracture prediction method against in-vitro compression tests on a series of six human femur specimens. Methods. Six femoral heads from six subjects were tested, a subset (n=3) included a hole drilled into the subchondral area of the femoral head via the femoral neck (University of Leeds, ethical approval MEEC13-002). The simulated lesions provided a method to validate the fracture prediction model with respect of AVN. The femoral heads were then modelled by a beam loaded with a single joint contact load. Material properties were assigned to the beam model from QCT-scans by using a density-modulus relationship. The maximum joint loading at which each bone cross-section was likely to fracture was calculated using a strain based failure criterion. Based on the predicted fracture loads, all six femoral heads (validation set) were classified into two groups, high fracture risk and low fracture risk (Figure 1). Beam theory did not allow for an accurate fracture load to be found because of the geometry of the femoral head. Therefore the predicted fracture loads of each of the six femoral heads was compared to the mean fracture load from twelve previously analysed human femoral heads (reference set) without lesions. The six cemented femurs were compression tested until failure. The subjects with a higher fracture risk were identified using both the experimental and beam tool outputs. Results. The computational tool correctly identified all femoral head samples which fractured at a significantly low load in-vitro (Figure 2). Both samples with a low experimental fracture load had an induced lesion in the subchondral area (Figure 3). Discussion. This study confirmed findings of a previous verification study on a disease models made from porcine femoral heads (Preutenborbeck et al. I-CORS2016). It demonstrated that fracture prediction based on beam theory is a viable tool to predict fracture. The tests confirmed that samples with a lesion in the weight bearing area were more likely to fracture at a low load however not all samples with a lesion fractured with a low load experimentally, indicating that a lesion alone is not a sufficient factor to predict fracture. The developed tool takes both structural and material properties into account when predicting the fracture risk. Therefore it might be superior to current diagnostic methods in this respect and it has the added advantage of being largely automated and therefore removing the majority of user bias. For any figures or tables, please contact the authors directly

Introduction. The ability to create patient-specific implants (PSI) at the point-of-care has become a desire for clinicians wanting to provide affordable and customized treatment. While some hospitals have already adopted extrusion-based 3D printing (fused filament fabrication; FFF) for creating non-implantable instruments, recent innovations have allowed for the printing of high-temperature implantable polymers including polyetheretherketone (PEEK). With interest in FFF PEEK implants growing, it is important to identify methods for printing favorable implant characteristics such as porosity for osseointegration. In this study, we assess the effect of porous geometry on the cell response and mechanical properties for FFF-printed porous PEEK. We also demonstrate the ability to design and print customized porous implants, specifically for a sheep tibial segmental defect model, based on CT images and using the geometry of triply periodic minimal surfaces (TPMS). Methods. Three porous constructs – a rectilinear pattern and gyroid/diamond TPMSs – were designed to mimic trabecular bone morphology and manufactured via PEEK FFF. TPMSs were designed by altering their respective equation approximations to achieve desired porous characteristics, and the meshes were solidified and shaped using a CAD workflow. Printed samples were mCT scanned to determine the resulting pore size and porosity, then seeded with pre-osteoblast cells for 7 and 14 days. Cell proliferation and alkaline phosphatase activity (ALP) were evaluated, and the samples were imaged via SEM. The structures were tested in compression, and stiffness and yield strength values were determined from resulting stress-strain plots. Roughness was determined using optical profilometry. Finally, our process of porous structure design/creation was modified to establish a proof-of-concept workflow for creating PSIs using geometry established from segmented sheep tibia CT images. Results. ALP activity measurements of the porous PEEK samples at 7 and 14 days were significantly greater than for solid controls (p < 0.001 for all three designs, 14 days). No difference between the porous geometries was found. SEM imaging revealed cells with flat, elongated morphology attached to the surface of the PEEK and into the pore openings, with filopodia and lamellipodia extensions apparent. mCT imaging showed average pore size to be 545 ± 43 µm (porosity 70%), 708 ± 64 µm (porosity 68%), and 596 ± 94 µm (porosity 69%) for the rectilinear, gyroid, and diamond structures, respectively. The average error between the theoretical and actual values was −16.3 µm (pore size) and −3.3 % (porosity). Compression testing revealed elastic moduli ranging from 210 to 268 MPa for the porous samples. Yield strengths were 6.6 ± 1.2 MPa for lattice, 14.8 ± 0.7 MPa for gyroid, and 17.1 ± 0.6 for diamond. Average roughness ranged from 0.8 to 3 µm. Finally, we demonstrated the ability to design and print a fully porous implant with the geometry of a sheep tibia segment. Assessments of implant geometrical accuracy and mechanical performance are ongoing. Discussion. We created porous PEEK with TPMS geometries via FFF and demonstrated a positive cellular response and mechanical characteristics similar to trabecular bone. Our work offers an innovative approach for advancing point-of-care 3D printing and PSI creation

Background. Processing of allografts, which are used to fill bone defects in orthopaedic surgery, includes chemical cleaning as well as gamma irradiation to reduce the risk of infection. Viable bone cells are destroyed and denaturing proteins present in the graft the osteoconductive and osteoinductive characteristics of allografts are altered. The aim of the study was to investigate the mechanical differences of chemical cleaned allografts by adding blood, clotted blood, platelet concentrate and platelet gel using a uniaxial compression test. Methods. The allografts were chemically cleaned, dried and standardized according to their grain size distribution. In group BL 4 ml blood, in CB 4 ml blood and 480 μl of 1 mol calcium chloride to achieve clotting, in PC 4 ml of concentrated platelet gel, in PG 4 ml of concentrated platelets and 666 μl of 1 mol calcium chloride were added. Uniaxial compression test was carried out for the four groups before and after compating the allografts. Results. No statistically significant decrease of the initial density was observed after compaction for BL and PC. In CB a statistical significant decrease of the initial density by 10% was observed, while PG decreased its initial density after compaction by 13%. Considering the density at the yield limit before and after compaction BL showed a statistically significant decrease of 13% and PG of 14%. In CB and PC no statistically significant decrease of the density at the yield limit could be observed. All groups showed a statistical significant difference when comparing the yield limit before and after compaction. BL and PC showed a ∼35% higher yield limit after compaction, while in the groups with the activation liquid CB and PG the yield limit increased by 15% for CB and 20% for PG. No statistically significant difference between groups was found for the density at the yield limit before compaction (p=0.157), for the initial density (p=0.523), the density at the yield limit (p=0.681) and the yield limit itself (p=0.423) after compaction. A statistically significant difference between the groups under investigation was found for the initial density before compaction (p=0.041) and for the yield limit before compaction (p=0.041). BL had a statistically significant lower initial density than PG (p=0.048). All other pairwise comparisons between groups did not reach statistically significance for the initial density before compaction. Conclusion. Adding blood, PRP or PC in allografts has shown in different studies to enhance bone ingrowth. The authors recommend to chemical clean allografts for large defects, optimize their grain size distribution and add platelet concentrate or platelet rich plasma for enhancing as well primary stability as well bone ingrowth. The recommended processing procedure has to be tested in an in-vivo study

The zonal organization of articular cartilage is crucial in providing the tissue with mechanical properties to withstand compression and shearing force. Current treatments available for articular cartilage injury are not able to restore the hierarchically organized architecture of the tissue. Implantation of zonal chondrocyte as a multilayer tissue construct could overcome the limitation of current treatments. However, it is impeded by the lack of efficient zonal chondrocyte isolation protocol and dedifferentiation of chondrocytes during expansion on tissue culture plate (TCP). This study aims to develop a protocol to produce an adequate number of high-quality zonal chondrocytes for clinical application via size-based zonal chondrocyte separation using inertial spiral microchannel device and expansion under dynamic microcarrier culture. Full thickness (FT) chondrocytes isolated from porcine femoral condyle cartilage were subjected to two serial of size-based sorting into three subpopulations of different cell sizes, namely small (S1), medium (S2), and large (S3) chondrocytes. Zonal phenotype of the three subpopulations was characterised. To verify the benefit of stratified zonal chondrocyte implantation in the articular cartilage regeneration, a bilayer hydrogel construct composed of S1 chondrocytes overlaying a mixture of S2 and S3 (S2S3) chondrocytes was delivered to the rat osteochondral defect model. For chondrocyte expansion, two dynamic microcarrier cultures, sort-before-expansion and sort-after-expansion, which involved expansion after or before zonal cells sorting, were studied to identify the best sort-expansion strategy. Size-sorted zonal chondrocytes showed zone-specific characteristics in qRT-PCR with a high level of PRG4 expression in S1 and high level of aggrecan, Type II and IX collagen expression in S2 and S3. Cartilage reformation capability of sorted zonal chondrocytes in three-dimensional fibrin hydrogel showed a similar trend in qRT-PCR, histology, extracellular matrix protein quantification and mechanical compression test, indicating the zonal characteristics of S1, S2 and S3 as superficial (SZ), middle (MZ) and deep (DZ) zone chondrocytes, respectively. Implantation of bilayered zonal chondrocytes resulted in better cartilage tissue regeneration in a rat osteochondral defect model than FT control group, with predominantly Type II hyaline cartilage tissue and significantly lower Type I collagen. Dynamic microcarrier expansion of sorted zonal chondrocytes was able to retain the zonal cell size difference that correlate to zonal phenotype, while maintaining the rounded chondrocyte morphology and F-actin distribution similar to that in mature articular cartilage. With the better retention of zonal cell size and zonal phenotype relation on microcarrier, zonal cells separation was achievable in the sort-after-expansion strategy with cells expanded on microcarrier, in comparison to cells expanded on TCP. Inertial spiral microchannel device provides a label-free and high throughput method to separate zonal chondrocytes based on cell size. Stratified implantation of zonal chondrocytes has the potential to improve articular cartilage regeneration. Dynamic microcarrier culture allows for size-based zonal chondrocyte separation to be performed on expanded chondrocytes, thus overcoming the challenge of limited tissue availability from the patients. Our novel zonal chondrocyte isolation and expansion protocol provide a translatable strategy for stratified zonal chondrocyte implantation that could improve articular cartilage regeneration of critical size defects

Introduction. The input mechanical properties of knee replacement bearing materials, such as elastic modulus and Poisson's ratio, significantly contribute to the accuracy of computational models. They should therefore be determined from independent experimental studies, under similar test conditions to the clinical and experimental conditions, to provide reliability to the models. In most cases, the reported values in the literature for the elastic modulus and Poisson's ratio of the bearing materials have been measured under tensile test conditions, in contrast to the compressive operating conditions of the total knee replacements (TKR). This study experimentally determined the elastic modulus and Poisson's ratio of conventional and moderately cross-linked ultra-high molecular weight polyethylene (UHMWPE) under compressive test conditions. These material parameters will be inputs to future computational models of TKR. Materials/Methods. To determine the Poisson's ratio of the conventional and moderately cross-linked UHMWPE, contact areas of 12mm diameter cylindrical specimens of 10.2mm length were measured experimentally under a compressive displacement of 1mm, at a strain rate of 12mm/min that was held for 10minutes. A computational model was developed in Abaqus, 6.14–1, to simulate this experimental test assuming different values for the Poisson's ratio of the UHMWPE cylindrical specimens. The curve fitted relationship between the computationally predicted contact area and Poisson's ratio was used to calculate the Poisson's ratio of the UHMWPE specimens, using the experimentally measured contact areas. Using a similar approach, the equivalent elastic modulus of the UHMWPE was calculated using the computationally calculated curve fitted contact area-elastic modulus relationship, from the computational simulation of a ball-on-flat compression test, and the experimentally measured contact area from a ball-on-flat dynamic compression test. This experiment used 10mm thick UHMWPE flat specimens against a 63.5mm rigid ball, under a compressive dynamic sinusoidal loading of 250N average load, and 6000 cycles. The applied test conditions maintained the stress level within the reported range for the TKR. Results. The predicted maximum contact stress was 26 and 35 [MPa] for the conventional and moderately cross-linked UHMWPE respectively. The measured Poisson's ratio was 0.33±0.04 (mean ± 95% confidence interval (CI), n=5) and 0.32±0.08 (mean ± 95% CI, n=3) for conventional and moderately cross-linked UHMWPE respectively. The corresponding values for the equivalent elastic modulus were 365±31 and 553±51 [MPa] (mean ± 95% CI, n=3) respectively (Fig.1). Discussion. The Poisson's ratios and elastic moduli for the conventional and moderately cross-linked UHMWPE materials were more than 20% lower than values reported in literature that have been measured under tensile test conditions [1–3]. Computational wear models adopting mechanical properties of the bearing materials delivered under more realistic compressive loading conditions are more appropriate. Conclusion. The current study presented a reverse engineering approach to characterise the mechanical properties of conventional and moderately cross-linked UHMWPE for TKR bearing materials, under realistic compressive test conditions. The measured mechanical properties, were lower than that reported in literature under tensile loading conditions, and should be adopted in future computational models of TKR for a more realistic and robust virtual modelling platform

Background. Antibiotic-loaded cement has been used over decades as a local antibiotic delivery for the treatment of bone and joint infections. However, there were some disadvantages such as unpredictable elution, insufficient local concentration and reduced mechanical strength. We developed hydrophilized bone cement and investigated whether it can improve consistent antibiotic release for extended periods to be effective in eradicating joint infection without any changes of mechanical strength. Methods. The experiments consists of preparation of the hydrophilized, vancomycin-loaded bone cement, In vitro test including drug release behavior, mechanical properties by compression test, cytotoxicity, antibacterial effect and animal study. In animal study, Antibiotic cement rod was implanted in the femur of rat osteomyelitis model. Sign of infections were assessed by gross observation, Micro CT and blood analysis at indicated period. Results. The hydrophilized Vancomycin-loaded bone cements showed that continuous release of Vancomycin even over 6 weeks in the drug release test, sufficient mechanical strengths in the compression test and also better anti-bacterial effect compared to other commercially available bone cement. The animal study demonstrated that it has superior inhibition of bacterial proliferation according to imaging and blood analysis compared to control group. Conclusion:. As a results from both in vitro test and animal study, hydrophilized antibiotic bone cement may provide favorable environment to control bone and joint infection by continuous antibiotic release for extended period

Artificial joints have been increasingly used in the treatment of physically disabled people who suffer from joint diseases such as osteoarthritis and rheumatoid arthritis. Ultra high molecular weight polyethylene (UHMWPE) is commonly used in hard-on-polymer joints as an impact-absorbing material for artificial hip joints because of its very low friction coefficient, high wear resistance, impact strength, and biocompatibility. However, particles generated by excessive wear and fatigue can cause osteolysis, which may lead to loosening. This has led to recent interest in metal-on-metal joints, which can provide better wear properties than hard-on-polymer joints, leading to reduced osteolysis. However, during gait, metal-on-metal joints are exposed to greater impacts than hard-on-polymer joints. These impacts can cause severe pain in patients who have undergone hip replacement arthroplasty. In previous work, we proposed a double-shell metal-on-metal artificial hip joint in which a single garter spring was inserted between the inner and outer acetabular shell of an impact relief device[1]. A garter spring is usually used by loading a compression stress from the outside to the center axis. The acetabular shell is composed of two layers as shown in Fig.1. In the current work, the performance of single and dual garter springs was investigated using static compression and free-fall type impact tests. Static compression tests were conducted on a conventional vise to examine the deformation of various kinds of garter springs under uniaxial loading. Free-fall impact tests, on the other hand, were conducted on a free-fall type impact test machine as shown in Fig. 2. The impact relief ability of the garter springs under impact loading was examined, and the maximum impact load and maximum impact load arriving-time were estimated[2]. The relief ability was also investigated for smaller and larger diameter garter springs with a three-pitch angle, and the maximum applied load was determined by taking into account the applied load on actual hip joints. Static compression test results indicated that some kinds of garter spring could withstand vertical loads of over 6000N, which is estimated to be equal to maximum vertical load during jumping. The pitch angle increased with an increase in the compression load and the shape of the coil ring deformed from a circular to ellipsoidal shape as the compression load increased, which may lead to a reduction in impact load and an increase in impact relief time. The impact test results for a single spring indicated that the maximum impact load decreased in reverse proportion to the maximum impact load arriving-time. A smaller diameter garter spring provided less maximum impact load and longer arriving maximum load time. In the case of dual garter springs, which have smaller and larger diameter garter springs, the springs offered a lower maximum impact load and a longer impact load arriving-time than a single spring

Introduction. Integrating additively manufactured structures, such as porous lattices into implants has numerous potential benefits, such as custom mechanical properties, porosity for osseointegration/fluid flow as well as improved fixation features. Component anisotropic stiffness can be controlled through varying density and lattice orientation. This is useful due to the influence of load on bone remodelling. Matching implant and bone anisotropy/stiffness may help reduce problems such as stress shielding and prevent implant loosening. It is therefore beneficial to be able to design AM parts with a desired anisotropic stiffness. In this study we present a method that predicts the anisotropic stiffness of an additively manufactured lattice structure from its CAD data, and validate this model with experimental testing. The model predicts anisotropic stiffness in terms of density (ρ), fabric (M) and fabric eigen values (m) and is matched to stiffness data of the structure in 3 principal directions, based on an orthotropic assumption. This model was described in terms of 10 constants and had the form shown in Equation 1. Eq.1. S. =. ∑. i. ,. j. =. 1.  .  .  .  . i. ,. j. =. 3. λ. (. i. ,. j. ). ρ. k. m. (. i. ). 1. (. i. ). m. (. j. ). 1. (. i. ). |. M. i. M. j. '. |. 2. Methods. A stochastic line structure was formed in CAD by joining pseudo-random points generated using the Poisson-disk method Lines at an angle lower than 30° to the x-y plane removed to allow for AM manufacturing. Lines were converted to struts with 330 µm diameter. Second order fabric tensors were determined from CAD files of the AM specimens using the mean intercept length (MIL), the gold standard for determining a measure of the ‘average orientation’ of material within trabecular bone structures. 10 × 10 × 12 mm specimens of the CAD model were manufactured on a Renishaw AM250 powder bed fusion machine. The structure was built in 10 different orientations to enable stiffness measurement in 10 different directions (n=5 for each direction). Compression testing in a servohydraulic materials testing machine was performed according to ISO13314 with LVDTs used to measure displacement to remove compliance effects. Stress-strain curves were obtained and elastic moduli were estimated from a hysteresis loop in the load application, from 70% to 20% of the plateau stress. Specimen density and fabric data were fit to the observed stiffnesses using least squares linear regression. Experimental stiffnesses of the structure in 10 directions were compared to the model to evaluate the accuracy of model predictions. Results & Discussion. The model predicted the stiffness of the structure across all 10 orientations to within 13% absolute error compared to the observed stiffness data, with an R. 2. value of 0.969. The three dimensional stiffness plot formed by the model was similar to the experimental data, displaying an hourglass shape. Our model is the first to predict the anisotropic stiffness of stochastic structures and will be highly useful in predicting stiffness of lattice structures and could also be applied to bone to measure anisotropic stiffness. For any figures or tables, please contact authors directly

Background. Calcium phosphate cement (CPC) is a promising biomaterial which can be used in numerous medical procedures for bone tissue repairing because of its excellent osteoconductivity. An injectable preparation and relatively short consolidation time are particularly useful characteristics of CPC. However, the low strength of CPC and its brittleness restrict its use. One method for toughening brittle CPC is to incorporate fibrous materials into its matrix to create a composite structure. Fibers are widely used to reinforce matrix materials in a variety of areas. Objective. We hypothesized that there must be an optimal fiber length and structure which can balance these conflicting aspects of fiber reinforcement. The purpose of this study is to prove our conjectures that adding a small amount of short fibers significantly improves the hardness and the toughness of CPC while maintaining its injectability with a syringe and that fiber morphologies that have crimps and surface roughness are favorable for reinforcing. Material and Methods. We used 3 types of short fibers of approximately 20–50 micrometer in diameter and 2 mm in length in this study: crimpy wool, crimpy polyethylene and straight polyethylene fibers. All of the materials were prepared by mixing a solvent with CPC powder with or without fiber. We grouped as follow, the control group, the wool group, the crimpy polyethylene group, the straight polyethylene group. After soaking in 37 degrees Celsius Simulated Body Fluid∗∗∗∗∗ for 1, 3, or 7 days, they were tested for each period. Impact strength test by the falling weight and compression test were performed. Result. In the impact strength test, after soaking for 1 day, impact resistance in the wool group was approximately 180 times greater than in the control group. When soaking for 3 days or more, impact resistance of wool group improve better than control group. The impact resistance of the wool group was the greatest among the four groups in soaking for 3 days. In the compression test, the yield strength and ultimate strength of the wool group were significantly higher than ultimate strength of the control group. The wool group has stress–strain curves that are typical of those of ductile materials, whereas the stress–strain curves of the control group resemble those of brittle materials. This indicates that fiber reinforcement drastically alters the physical properties of CPC converting it from brittle to ductile. Conclusion. In the present study, we sought to develop a method for producing injectable fiber-reinforced CPC. We focused on morphology and surface roughness of fiber in the reinforcement of CPC. This study clearly showed that CPC was substantially strengthened and toughened by crimpy short fiber reinforcement. CPC reinforced with short fibers which have morphology similar to wool should be a promising tool for orthopedic surgeons

Initial stability of cementless components in bone is essential for longevity of Total Hip Replacements. Fixation is provided by press-fit: seating an implant in an under-reamed bone cavity with mallet strikes (impaction). Excessive impaction energy has been shown to increase the risk of periprosthetic fracture of bone. However, if implants are not adequately seated they may lack the stability required for bone ingrowth. Ideal fixation would maximise implant stability but would minimise peak strain in bone, reducing the risk of fracture. This in-vitro study examines the influence of impaction energy and number of seating strikes upon implant push-out force (indicating stability) and peak dynamic strain in bone substitute (indicating likelihood of fracture). The ratio of these factors is given as an indicator of successful impaction strategy. A custom drop tower with simulated hip compliance was used to seat acetabular cups in 30 Sawbone blocks with CNC milled acetabular cavities. 3 impaction energies were selected; low (0.7j), medium (4.5j) and high (14.4j), representing the wide range of values measured during surgery. Each Sawbone was instrumented with strain gauges, secured on the block surface close to the acetabular cavity (Figure 1). Strain gauge data was acquired at 50 khz with peak tensile strain recorded for each strike. An optical tracker was used to determine the polar gap between the cup and Sawbone cavity during seating. Initially 10 strikes were used to seat each cup. Tracking data were then used to determine at which strike the cups progressed less than 10% of the final polar gap. This value was taken as number of strikes to complete seating. Tests were repeated with fresh Sawbone, striking each cup the number of times required to seat. Following each seating peak push-out forces of the cups were recorded using a compression testing machine. 10, 5 and 2 strikes were required to seat the acetabular cups for the low, medium and high energies respectively. It was found that strain in the Sawbone peaked around the number of strikes to complete seating and subsequently decreased. This trend was particularly pronounced in the high energy group. An increase in Sawbone strain during seating was observed with increasing energy (270 ± 29 µε [SD], 519 ± 91 µε and 585 ± 183 µε at low, medium and high energies respectively). The highest push-out force was achieved at medium strike energy (261 ± 46N). The ratio between push-out and strain was highest for medium strike energy (0.50 ± 0.095 N/µε). Push-out force was similar after 5 and 10 strikes for the medium energy strike. However push-out recorded at ten strikes for the high energy group was significantly lower than for 2 strikes (<40 ± 19 N, p<0.05). These results indicate that a medium strike energy with an appropriate number of seating strikes maximizes initial implant stability for a given peak bone strain. It is also shown that impaction with an excessive strike energy may greatly reduce fixation strength while inducing a very high peak dynamic strain in the bone. Surgeons should take care to avoid an excessive number of impaction strikes at high energy. For any figures or tables, please contact the authors directly

Background. Impaction bone grafting (IBG) using a circumferential metal mesh is one of the options that allow restoration of the femoral bone stock and stability of the implant in hip arthroplasty. Here we examined the clinical and radiographic outcome of this procedure with a cemented stem and analyzed experimentally the initial stability of mesh–grafted bone–cemented stem complexes. Methods. We retrospectively reviewed 6 hips (6 patients) that had undergone femoral revisions with a circumferential metal mesh, impacted bone allografts, and a cemented stem. The mean follow-up period was 2.9 years (range, 1.4–3.8 years). Hip joint function was evaluated with the Japanese Orthopaedic Association hip score, and radiographic changes were determined from radiographs. The initial resistance of cemented stem complexes to axial and rotational force was measured in a composite bone model with various segmental losses of the proximal femur. Results. The hip score improved from 50 (range, 10–84) preoperatively to a mean of 74 (range, 67–88) at the final follow-up. The overall implant survival rate was 100% at 4 years when radiological loosening or revision for any reason was used as the endpoint. No stem subsided more than 3 mm vertically within 1 year after implantation. Computed tomography showed reconstitution of the femoral canal in a metal mesh. In mechanical analyses, there was no influence on the stem stability to axial compression during the repeated axial compression test between IBG reconstruction rates. On the other hand, for IBG reconstruction rate of 66.7%, grafted bone-Sawbone juntion was buckled under the axial breaking force. In contrast, under rotational load, the rotation angles of the stainless mesh were strongly affected by the IBG reconstruction rate. Conclusions. The short-term results show good outcomes for reconstruction of proximal bone loss with impaction bone allografts and a circumferential mesh. The procedure should be applied in cases where the circumferential proximal bone loss is less than half of the stem length implanted

Orthopaedic reconstruction procedures to combat osteoarthritis, inflammatory arthritis, metabolic bone disease and other musculoskeletal disorders have increased dramatically, resulting in high demand on the advancement of bone implant technology. In the past, joint replacement operations were commonly performed primarily on elderly patients, in view of the prosthesis survivorship. With the advances in surgical techniques and prosthesis technology, younger patients are undergoing surgeries for both local tissue defects and joint replacements. This patient group is now more active and functionally more demanding after surgery. Today, implanted prostheses need to be more durable (load-bearing), they need to better match the patient's original biomechanics and be able to survive longer. Additive manufacturing (AM) provides new possibilities to further combat the problem of stress-shielding and promote better bone remodelling/ingrowth and thus long term fixation. This can be accomplished by matching the varying strain response (stiffness) of trabecular or subchondral bone locally at joints. The purpose of this research is therefore to determine whether a porous structure can be produced that can match the required behaviour and properties of trabecular bone regardless of skeletal location and can it be incorporated into a long-term implant. A stochastic structure visually similar to trabecular bone was designed and optimised for AM (Figure 1) and produced over a range of porosities in multiple materials, Stainless Steel 316, Titanium (Grade 23 – Ti6Al4V ELI) and Commercially Pure Titanium (Grade 2) using a Renishaw AM250 metal additive manufacturing system. Over 150 cylindrical specimens were produced per material and subjected to a compression test to determine the specimens' Elastic Modulus (Stiffness) and Compressive Yield Strength. Micro-CT scans and gravimetric analysis were also performed to determine and validate the specimens' porosity. Results were then graphed on a Strength vs. Stiffness Ashby plot (Figure 2) comparing the values to those of trabecular bone in the tibia and femur. It was found that AM can produce porous structures with an elastic modulus as low as 100 MPa up to 2.7 GPa (the highest stiffness investigated in this study). Titanium structures with a stiffness <500MPa had compressive strengths towards the bottom range of similar stiffness trabecular bone. Between 500 MPa − 1 GPa Titanium AM porous structures match the compressive strength of equivalent stiffness trabecular bone and from 1 GPa − 2 GPa the Ti structures exceed the strength of equivalent stiffness trabecular bone up to ∼2.5 times and consequently increase by a power law. These results show that AM can produce structures with similar stiffness to trabecular bone over a range of skeletal locations whilst matching or exceeding the compressive strength of bone. The results have not yet taken into account fatigue life with the fatigue life of these types of structures tending to be between 0.1 – 0.4 of their compressive strength. This means that a titanium porous structure would need to be 2.5 – 10 times stiffer or stronger than the portion of trabecular bone it is replacing. This data is highly encouraging for AM manufactured, bone stiffness matched implant technology

The disadvantage of removing a well-fixed femoral stem are multiple (operating time, risk of fracture, bone and blood loss, recovery time and post-op complications. Ceramic heads with titanium adapter sleeves (e.g. BIOLOX®OPTION, Ceramtec) are a possibility for putting a new ceramic head on slightly damaged used tapers. ‘Intolerable’ taper damages even for this solution are qualitatively specified by the manufacturers. The aim of this study was to determine the fracture strength of ceramic heads with adapter sleeves on stem tapers with such defined damage patterns. Pristine stem tapers (Ti-6Al-4V, 12/14) were damaged to represent the four major stem taper damage patterns specified by the manufacturers: . -. ‘Truncated’: Removal of 12.5% of the circumference along the entire length of the stem taper at a uniform depth of 0.5mm parallel to the taper slope. -. ‘Slanted’: Removal of 33.3% of the proximal diameter perimeter with decreasing damage down to 3.7mm from the proximal taper end. -. ‘Cut’: Removal of the proximal 25% (4mm) of the stem taper. -. ‘Scratched’: Stem tapers from a previous ceramic fracture test study with a variety of scratches and crushing around the upper taper edge from multiple ceramic head fractures. -. The ‘Control’ group consisted of three pristine tapers left undamaged. BIOLOX®OPTION heads (Ø 32mm, length M) with Ti adapter sleeves were assembled to the damaged stem tapers and subjected to ISO7206-10 ultimate compression strength testing. The forces required to fracture the head were high and caused complete destruction of the ceramic heads in all cases. The ‘Truncated’ group showed the lowest values (136kN ± 4.37kN; Fig. 3). Forces were higher and similar for the ‘Cut’ (170kN ± 8.89kN), ‘Control’ (171.8 ± 16.5kN) and ‘Slanted’ (173kN ± 21.9kN) groups, the ‘Scratched’ group showed slightly higher values (193kN ± 11.9kN). The Ti adapter sleeves were plastically deformed but did not fail catastrophically. The present study suggests that manufacturer's recommendations for removal of a well fixed femoral stem could be narrowed down to the ‘Truncated’ condition. Even this might not be necessary since the fracture load is still substantially higher than the ASTM standard requires. Surgeons should consider to keep stems with larger taper damages as previously thought and spare the patient from stem revision. The greatest reservation regarding adapter sleeves is the introduction of the new metal-on-metal interface between stem and sleeve, which could possibly facilitate fretting-corrosion, which is presently one of the major concerns for modular junctions (3). Clinically such problems have not been reported yet. Ongoing FE-simulations are performed to investigate whether micromotions between stem and head taper are altered by the investigated damages