Although 3D-printed porous dental implants may possess improved osseointegration potential, they must exhibit appropriate fatigue strength. Finite element analysis (FEA) has the potential to predict the fatigue life of implants and accelerate their development. This work aimed at developing and validating an FEA-based tool to predict the fatigue behavior of porous dental implants. Test samples mimicking dental implants were designed as 4.5 mm-diameter cylinders with a fully porous section around bone level. Three porosity levels (50%, 60% and 70%) and two unit cell types (Schwarz Primitive (SP) and Schwarz W (SW)) were combined to generate six designs that were split between calibration (60SP, 70SP, 60SW, 70SW) and validation (50SP, 50SW) sets. Twenty-eight samples per design were additively manufactured from titanium powder (Ti6Al4V). The samples were tested under bending compression loading (ISO 14801) monotonically (N=4/design) to determine ultimate load (F. ult. ) (Instron 5866) and cyclically at six load levels between 50% and 10% of F. ult. (N=4/design/load level) (DYNA5dent). Failure force results were fitted to F/F. ult. = a(N. f. ). b. (Eq1) with N. f. being the number of cycles to failure, to identify parameters a and b. The endurance limit (F. e. ) was evaluated at N. f. = 5M cycles. Finite element models were built to predict the yield load (F. yield. ) of each design. Combining a linear correlation between FEA-based F. yield. and experimental F. ult. with equation Eq1 enabled FEA-based prediction of F. e. . For all designs, F. e. was comprised between 10% (all four samples surviving) and 15% (at least one failure) of F. ult. The FEA-based tool predicted F. e. values of 11.7% and 12.0% of F. ult. for the validation sets of 50SP and 50SW, respectively. Thus, the developed FEA-based workflow could accurately predict endurance limit for different implant designs and therefore could be used in future to aid the development of novel porous implants. Acknowledgements: This study was funded by EU's Horizon 2020 grant No. 953128 (I-SMarD). We gratefully acknowledge the expert advice of Prof. Philippe Zysset

Summary. Lumbar spinal specimens exhibited high fatigue strength. The cycles to failure are not only dependent on the maximum peak load, but also on the load offset or the amplitude, respectably. Introduction. Spinal injury might be caused by whole body vibrations. The permitted exposure to vibration in the workplace is therefore limited. However, there is a lack in knowledge how external vibrations might cause internal damages. Numerical whole body models might provide the potential to estimate the dynamic spinal loading during different daily activities, but depends on knowledge about the corresponding fatigue strength. This study is aiming to determine the in vitro fatigue strength of spinal specimens from donors of working age. Patients & Methods. Lumbar functional spinal units (L2/L3 and L4/L5) from midlife donors (45–65 yrs, n = 24) and young donors (20–45 yrs, n = 6) were collected and stored deep frozen. CT scans were obtained to determine the endplate area and the bone mineral density of the vertebrae. Their product is referred to as vertebral capacity (VC). Muscles were removed from the thawed specimens, but apart from the transversal ligaments, all ligaments and the intervertebral disc were left intact. During the experiments, the specimens were immersed in saline solution (37°C) containing antibiotics (PAA, Austria) to reduce biological degeneration. After preconditioning (2.5 h) the specimens were exposed to continuous sinusoidal axial compression (5Hz, <300,000 cycles). Distinct changes in the characteristic creep curve of specimens’ height indicated fatigue failure. Specimens of midlife donors were equally assigned to three groups with different peak-to-peak loads (NORM: 0–2 kN; HIGH: 0–3 kN; OFFSET: 1–3 kN), while specimens from young donors were solely assigned to the HIGH group, since a previous study [1] had shown that young specimens hardly failed for NORM loading conditions. Findings from that previous study (midlife, n = 6; young, n = 6) were merged to NORM for analyses. Results. Within the NORM group, specimens only failed within 300,000 cycles when VC was below 2,000 cm. 2. mg K. 2. HPO. 4. /ml (8 of 20). Within the HIGH group, endplate failure occurred frequently within the test duration (10 of 13; 1 excluded). For the OFFSET group, specimen failure was occasionally observed (4 of 7; 1 excluded). Exponential regression of cycles to failure dependent on VC showed significant correlations for the specimen loaded in the NORM and HIGH group (r. 2. NORM. = 0.57, p = 0.029; r. 2. HIGH. = 0.47, p = 0.029; r. 2. OFFSET. = 0.83, p = 0.091). Discussion/Conclusion. Specimens’ fatigue failure strength depends on load offset and amplitude. The group with higher loading amplitudes (HIGH: 1.5 kN) resisted fewer loading cycles than those with the smaller amplitude (OFFSET: 1 kN), even though the maximum peak was the same (3 kN). The exponential regression is conservative, since several specimens did not fail within the predicted loading cycles. Vertebral capacity might suitable predict the fatigue strength of specimens. Together with numerical modelling, these findings might promote the appraisal of occupational diseases and might help to determine the duty cycles for new implants. The funding of FIOSH, Germany is thankfully acknowledged (project F2059 and F2069)

Introduction. Tendon disease and rupture are common in patients with diabetes and these are exacerbated by poor healing. although nanoscale changes in diabetic tendon are linked to increased strength and stiffness. The resistance to mechanical damage of a tissue may be measured using fatigue testing but this has not been carried out in diabetic tendon, although the toughness of diabetic bone is known to be reduced. The aim of this study was to measure the static fatigue behaviour of tendons from a streptozotocin (STZ)-induced rat model of diabetes, hypothesising that diabetes causes tendon to show lower resistance to mechanical damage than healthy tendon. Materials and Methods. Diabetic (n=3, 12 weeks post-STZ) and age-matched control (n=3) adult male Sprague Dawley rats were culled, tails harvested and stored at −80ºC. Following defrosting, fascicles (5 per animal) were carefully dissected, mean diameter measured using an optical micrometer and mounted in a Bose Biodynamics test machine using custom grips in a PBS bath. Static fatigue testing at 30 MPa to failure enabled both elastic modulus (initial ramp) and steady state creep rate (gradient at creep curve inflexion) to be measured. Data are reported as median ± interquartile range and pw0.05 using a Mann-Whitney U test was taken as significant. Results. Confirming previous reports, tendon from diabetic rats showed significantly higher elastic modulus (201 ± 68 MPa) than healthy (151 ± 62 MPa). Strain at failure showed no differences between groups. Tendon from diabetic rats showed significantly slower steady state creep (71 ± 44 μstrain s. −1. ) than healthy (691 ± 1000 μstrain s. −1. ). Discussion. These preliminary data show an order of magnitude larger resistance to mechanical damage in diabetic tendons, possibly associated with the previously reported increased packing and decreased fibril diameters. Energy-storing flexor tendons, the most commonly affected in diabetics, and the positional tendons tested here show similar fatigue behaviour when tested at the same fraction of “stress-in-life”. Further investigation is required into the cell tissue repair response in diabetes in order to link reduced rates of mechanical damage with the clinically increased risk of disease and rupture in diabetic patients

Summary Statement. Tendon micromechanics were investigated using 2 methods. When collagen deformation was measured directly, higher levels of inter-fibre sliding were observed than when tenocyte nuclei were tracked. This suggests that under high strain tenocytes become unattached from the collagen fibres. Introduction. Fibre extension and inter-fibre sliding have both been reported during tendon extension, but fibre sliding is believed to be the predominant mechanism in normal healthy tendon function. Fatigue damage is known to result in structural changes and reduced mechanical properties, but its influence on micromechanics is unknown. This work aimed:. 1. To investigate the effect of fatigue loading on bovine digital extensor fascicle micromechanics, comparing fibre extension and fibre sliding, hypothesising that the relative importance of these may change due to fatigue damage. 2. To compare two techniques for characterising micromechanics: bleaching of a grid to directly measure collagen deformation, and using the cells as fiducial markers of fibre movement. Methods. The tensional regions of healthy digital extensor tendons were removed within 24 hours of slaughter and frozen. Tendons were defrosted, hydrated and fascicles dissected and loaded into custom-designed chambers allowing the mechanical loading of fully hydrated tendon fascicles. Fascicles were loaded for 0, 300 or 900 cycles under creep conditions at a frequency of 1Hz and to a maximum applied stress of 25% of the mean UTS of the fascicles. Fascicles were stained using either Acridine Orange to stain the cell nuclei or DTAF solution to stain the collagen. After DTAF staining, a grid consisting of 4 squares of side 50 μm was photo-bleached using the FRAP system on a Leica TCS SP2 confocal scanning microscope. To investigate micromechanics, fascicles were secured in a uniaxial rig and strained in 2% increments to 10% total strain at a rate of 1%s. −1. Imaging was carried out at each increment and local strains calculated from grid deformation or nuclei movement. Results. No significant changes in micromechanics were observed with increasing numbers of creep cycles, as measured with either technique. This was despite quite significant matrix damage being observed particularly after 900 cycles. When using the grid deformation measure of strains, a continual increase in fibre sliding was seen above 4% applied strain, correlating with the levelling off of intra-fibre strains. This same move towards dominant fibre sliding was not observed with techniques using the nuclei as fiducial markers. Using the nuclei as markers consistently reported significantly lower levels of fibre sliding than those measured from grid deformation at strains of 6% and above, under all creep conditions. Discussion/Conclusion. The apparent absence of any effect of creep on the measured microstructural deformation may be a result of the localised nature of the measurement techniques. At sites where matrix structure broke down both the tracking of nuclei and the photo-bleaching of the grid proved problematic and it is these regions where the greatest degree of deformation would perhaps be expected, with remaining areas of the tissue stress-deprived. The smaller levels of fibre shear reported when measured through nuclei tracking suggests that the tenocytes may not be well adhered to the fibres and may be protected from some of the matrix deformation in response to loading

Abstract. Objectives. Additive manufacturing has led to numerous innovations in orthopaedic surgery: surgical guides; surface coatings/textures; and custom implants. Most contemporary implants are made from titanium alloy (Ti-6Al-4V). Despite being widely available industrially and clinically, there is little published information on the performance of this 3D printed material for orthopaedic devices with respect to regulatory approval. The aim of this study was to document the mechanical, chemical and biological properties of selective laser sintering (SLS) manufactured specimens following medical device (TOKA®, 3D Metal Printing LTD, UK) submission and review by the UK Medicines and Healthcare Products Regulatory Agency (MHRA). Methods. All specimens were additively manufactured in Ti-6Al-4V ELI (Renishaw plc, UK). Mechanical tests were performed according to ISO6892-1, ISO9585 and ISO12107 for tensile (n=10), bending (n=3) and fatigue (n=16) respectively (University of Bath, UK). Appropriate chemical characterisation and biological tests were selected according to recommendations in ISO10993 and conducted by external laboratories (Wickham Labs, UK; Lucideon, UK; Edwards Analytical, UK) in adherence with Good Lab Practise guidelines. A toxicological review was conducted on the findings (Bibra, UK). Results. The mechanical tests demonstrated that the material performed to the specification for conventionally manufactured titanium alloy of this type (ISO5832-3). The toxicology review concluded that there were no significant concerns for the health of the patients identified in this evaluation and implantation of the TOKA® device would not result in a significant health risk to patients. Conclusions. Reflecting on our MHRA experience, additive manufacture of orthopaedic devices is still considered to be a ‘novel’ process by regulatory bodies, requiring additional safety evidence. Despite this, our findings demonstrate that there is no difference, mechanically or chemically, to the traditionally manufactured alloy material. We hope to support the widening use of 3D printed titanium alloy orthopaedic devices by publishing our route to regulatory approval. Declaration of Interest. (a) fully declare any financial or other potential conflict of interest

Summary Statement. Fatigue loading has an age-specific effect on tendon fascicle micro-mechanics, with greater fibre sliding in aged samples indicating a decreased mechanical integrity, and a reduced ability to withstand cyclic loading, which may partially explain the age-related risk of tendon injury. Introduction. The human Achilles and equine superficial digital flexor (SDFT) tendons function as energy stores, experiencing large, repetitive stresses and strains. 1. and are therefore highly susceptible to injury, particularly in aged individuals. We have previously observed rotation within SDFT fascicles in response to applied strain, which indicates the presence of helical sub-structures within this tendon. Further, we have shown that this rotation decreases with ageing, suggesting alterations to the helix sub-structure and a difference in the extension mechanisms in aged tendons. We therefore hypothesise that cyclic fatigue loading (FL) will result in alterations in fascicle extension mechanisms which are age specific. Methods. Fascicles (n= 6–8/tendon) were dissected from the forelimb SDFTs of 6 young (aged 3–6 years) and 5 old horses (aged 18–20 years). Half the fascicles underwent 1800 cycles of FL to 60% of their predicted failure stress, while the remaining fascicles acted as unloaded controls. Following FL, fascicles were stained with 5-dicholorotriazynl fluorescein, secured in a straining rig and viewed under a confocal microscope. A grid was photobleached onto each fascicle and images were taken at 2% strain increments up to 10%. Deformation of the grid was quantified by measuring changes in longitudinal strain, deviation from the vertical gridline and rotation of the horizontal gridline. Statistical significance was set at p<0.05. Results. In agreement with previous studies, local longitudinal strains were smaller than the overall applied strain, and did not differ between FL and control groups or with ageing. Deviation of the vertical gridline, representing fibre sliding, did not differ between FL and control samples from young horses, but there was a significant increase in fibre sliding in FL samples from old horses (p<0.01). By contrast, grid rotation decreased significantly in FL samples from young horses, and with ageing (p<0.01) but showed no alteration with FL in aged samples. Discussion. The results support the hypothesis, showing that FL causes age-specific alterations in fascicle extension mechanisms. Our previous findings suggest that, in samples from young horses, extension is facilitated by the unwinding of helical sub-structures, which is indicated by the grid rotation observed. The results of the current study show that FL causes a significant decrease in this rotation, suggesting the helix sub-structures are altered by FL, which may reduce the ability of fascicles to extend and recoil. By contrast, in aged samples this rotation decreased, indicating ageing also causes alterations to the helical sub-structures. FL of aged samples resulted in increased fibre sliding, indicating that damage may be occurring between the collagen fibres, which is likely to decrease the mechanical integrity of the fascicles. The observed age-specific alterations in extension mechanisms after FL suggest that fascicles from aged tendons, where structure of the helix is already compromised, suffer increased fibre sliding. Fibre sliding may initiate a cell response predisposing aged tendons to degenerative changes and subsequent injury

The most common mode of failure observed in cemented orthopaedic implants is aseptic loosening of the prosthesis over time. This occurs as a result of fatigue failure of the bone cement under different loading conditions. Although a great deal of research has been carried out on the fatigue crack development of poly(methyl methacrylate) (PMMA) bone cements, the effects of different loading frequencies at low and high stress intensities are not well understood. Therefore, the aims of this study are to determine the effects of loading PMMA bone cement at different stress intensities and loading frequencies, as seen in-vivo, and the effects of changing these parameters on fatigue crack propagation. To achieve these aims, disc compact tension (DCT) samples with chevron notches were made and Krak Gages (Russenberger Prufmaschinen, Neuhausen am Rheinfall, Switzerland) were attached to monitor crack growth. The bone cement used in this study was the Cemex System, which uses a cement gun to mix and apply the material into the cavity. From standard compression and bending tests it was found that the cement made using this system had an average compressive strength of 86.66±5.52MPa, an average bending modulus of 3696.06±121.13MPa and an average bending strength of 51.95±4.14MPa. These values are within the normal range of acrylic resin cements for implants and above the minimum requirements of the ISO5833:2002 standard. A program has been written that loads the DCT samples with a stress intensity of 0.2MPam. 1/2. , 0.6MPam. 1/2. and 1.0MPam. 1/2. at a frequency of 1Hz, 2Hz, 5Hz, 10Hz and 20Hz. The crack was allowed to grow 0.2mm at each frequency and the frequencies were increased (1Hz to 20Hz) then decreased in magnitude (20Hz to 1Hz) for each of the stress intensities. This experimental design enables much more sensitive detection of small changes in crack growth rate than a conventional test where the crack grows through the entire range of δK at a single frequency. By repeatedly varying the loading within the same specimen the effects of variation between specimens can be removed, revealing significant differences in crack growth rate. The results provide important information on bone cement when loaded in conditions similar to those seen in-vivo and how frequency and stress intensities affect the fracture mechanics of PMMA

Abstract. Objectives. Total hip arthroplasty (THA) procedures are physically demanding for surgeons. Repetitive mallet swings to impact a surgical handle (impactions), can lead to muscle fatigue, discomfort and injuries. The use of an automated surgical hammer may reduce fatigue and increase surgical efficiency. The aim of this study was to develop a method to quantify user's performance, by recording surface electromyography (sEMG), for automated and manual impactions. Methods. sEMG signals were recorded from eight muscle compartments (arm and back muscles) of an orthopaedic surgeon during repetitions of manual and automated impaction tasks, replicating femoral canal preparation (broaching) during a THA. Each task was repeated, randomly, four times manually and four times with the automated impaction device. The mechanical outcomes (broaching efficiency and broach advancement) were quantified by tracking the kinematics of the surgical instrumentation. Root mean square (RMS) values and median frequency (MDF) were calculated for each task to, respectively, investigate which muscles were mostly involved (higher RMS) in each task and to quantify the decrease in MDF, which is an indicator of muscle fatigue. Results. RMS for arm muscles was significantly higher (p-value=0.002) during manual impactions than during automated impactions and muscle fatigue was significantly reduced (p-value=0.011), for the same muscles, when the same tasks were performed with the automated surgical hammer. The time required to achieve the same mechanical outcome, in terms of broaching efficiency and broach advancement, was significantly reduced with the automated surgical hammer (p=0.019). Conclusions. Results from this study showed how with this methodology it was possible to discern muscle performance and fatigue, between impaction modalities. Moreover, the reduction in exposure time to automated impactions, could be a factor in muscle fatigue decrease. These results could therefore provide useful insights into the study of surgical ergonomic improvements, to reduce surgeons muscle fatigue and, potentially, injuries. Declaration of Interest. (a) fully declare any financial or other potential conflict of interest

Abstract. Objective. Bi-condylar tibia plateau fractures are one of challenging injuries due to multi-planar fracture lines. The risk of fixation failure is correlated with coronal splits observed in CT images, although established fracture classifications and previous studies disregarded this critical split. This study aimed to experimentally and numerically compare our innovative fracture model (Fracture C), developed based on clinically-observed morphology, with the traditional Horwitz model (Fracture H). Methods. Fractures C and H were realized using six samples of 4th generation tibia Sawbones and fixed with Stryker AxSOS locking plates. Loading was introduced through unilateral knee replacements and distributed 60% medially. Loading was initiated with six static ramps to 250 N and continued with incremental fatigue tests until failure. Corresponding FE models of Fractures C and H were developed in ANSYS using CT scans of Sawbones and CAD data of implants. Loading and boundary conditions similar to experimental situations were applied. All materials were assumed to be homogenous, isotropic, and linear elastic. Von-Mises stresses of implant components were compared between fractures. Results. Fracture C showed 46% lower static stiffness than Fracture H, and it was 38–59% laxer than Fracture H during cyclic loading. Fractures C and H failed at 368±63N and 593±159N, respectively. Von-Mises stress distributions of locking plates indicated that for Fracture C peak stresses, observed around the proximal-inferior and proximal-threadless holes, were 55% higher than Fracture H's, which occurred around the kick-stand hole. The Kick-stand screw of Fracture C demonstrated 65% higher stress than Fracture H's. Conclusions. Experimental outcomes revealed that coronal splits significantly reduced structural stability. Von-Mises stress distributions demonstrated that potential fatigue failure points of implant components depend on the fracture geometry. Therefore, coronal fracture lines should be counted to precisely assess different fixation methods and find the optimum option for this problematic trauma

Type-2 Diabetic (T2D) patients experience up to a 3-fold increase in bone fracture risk[1]. Paradoxically, T2D-patients have a normal or increased bone mineral density when compared to non-diabetic patients. This implies that T2D has a deleterious effect on bone quality, whereby the intrinsic material properties of the bone matrix are altered. Creating clinical challenges as current diagnostic techniques are unable to accurately predict the fracture probability in T2D-patients. To date, the relationship between cyclic fatigue loading, mechanical properties and microdamage accumulation of T2D-bone tissue has not yet been examined and thus our objective is to investigate this relationship. Ethically approved femoral heads were obtained from patients, with (n=8) and without (n=8) T2D. To obtain the mechanical properties of the sample, one core underwent a monotonic compression test to 10% strain, the other core underwent a cyclic compression test at a normalized stress ratio between 0.0035mm/mm and 0.016mm/mm to a maximum strain of 3%. Microdamage was evaluated by staining the tissue with barium sulfate precipitate [2] and conducting microcomputed tomography scanning with a voxel size of 10μm. The monotonically tested T2D-group showed no statistical difference in mechanical properties to the non-T2D-group, even when normalised against BV/TV. There was also no difference in BV/TV. For the cyclic test, the T2D-group had a significantly higher initial modulus (p<0.01) and final modulus (p<0.05). There was no difference in microdamage accumulation. Previous population-level studies have found that T2D-patients have been shown to have an increased fracture risk when compared to non-T2D-patients. This research indicates that T2D does not impair the mechanical properties of trabecular bone from the femoral heads of T2D-patients, suggesting that other mechanisms may be responsible for the increased fracture risk seen in T2D-patients

Orthopaedic impaction-instruments are used to drive implants into the bone of the patient. Pre-clinical experimental testing protocols and computer models of those are used to assess robustness and functional efficiency of such instruments. This generally involves impaction of the instrument mounted on a substrate that should represent the mechanics of the patient. In this study, the effects of the substrate on stressing of the impaction-instruments were investigated using dynamic finite element analysis. Model results were compared with experimental data from lab protocols, which have been derived to recreate the mechanics of cadaveric implantations, which represent clinical conditions. FEA models of selected experimental protocols were created in which a simplified instrument was impacted on substrates with varying material properties and boundary conditions. After impaction, the instrument settled into a modal vibration which then decayed over time. The resulting axial strain data from the computational model was compared to strain-gauge data collected from experimental measurements. Strain signal amplitude, frequency and decay were compared. The damping-ratio was derived from the decay of the strain signal. The computational model slightly over-predicted the initial experimental strain amplitudes in all cases, but the frequency of the cyclic strain signals matched. However, the model underestimated the experimentally measured rate of signal decay. Inclusion of implant seating and soft-tissue conditions had little effect on decay. Clinical failures of impaction-instruments may be related to multiple fatigue cycles for each impaction and should be modelled accurately to allow failure prediction. Any soft substrate results in an impedance mismatch at the instrument interface, which reflects the pressure wave and causes vibration with a frequency related to the speed-of-sound in the instrument, and its geometry. While this could be accurately modelled computationally, signal decay was underestimated. Further experimental quantification of energy losses will be important to understand vibration decay

Variations in component positioning of total hip replacements can lead to edge loading of the liner, and potentially affect device longevity. These effects are evaluated using ISO 14242:4 edge loading test results in a dynamic system. Mediolateral translation of one of the components during testing is caused by a compressed spring, and therefore the kinematics will depend on the spring stiffness and damping coefficient, and the mass of the translating component and fixture. This study aims to describe the sensitivity of the liner plastic strain to these variables, to better understand how tests using different simulator designs might produce different amounts of liner rim deformation. A dynamic explicit deformable finite element model with 36mm Pinnacle metal-on-polyethylene bearing geometry (DePuy Synthes, Leeds, UK) was used with material properties for conventional UHMWPE. Setup was 65° clinical inclination, 4mm mismatch, 70N swing phase load, and 100N/mm spring. Fixture mass was varied from 0.5-5kg, spring damping coefficient was varied from 0-2Ns/mm. They were changed independently, and in combination. Maximum separation values were relatively insensitive to changes in the mass, damping coefficient, or both. The sensitivity of peak plastic strain, to this range of inputs, was similar to changing the swing phase load from 70N to approximately 150N – 200N. Increasing the fixture mass and/or damping coefficient increased the peak plastic strain, with values from 0.15-0.19. Liner plastic deformation was sensitive to the spring damping and fixture mass, which may explain some of the differences in fatigue and deformation results in UHMWPE liners tested on different machines or with modified fixtures. These values should be described when reporting the results of ISO14242:4 testing. Acknowledgements. Funded by EPSRC grant EP/N02480X/1; CAD supplied by DePuy Synthes

Introduction. Today TKR is considered one of the most successful operative procedures in orthopedic surgery. Nevertheless, failure rates of 2 – 10% depending on the length of the study and the design are still reported. This provides evidence for further development in knee arthroplasty. Particularly the oxide ceramics used now in THA show major advantages due to their excellent tribological properties, their significantly reduced third-body wear as well as their high corrosion resistance. A further advantage of ceramic materials is their potential use in patients with metal allergy. Metallic wear induces immunological reactions resulting in hypersensitivity, pain, osteolysis and implant loosening. The purpose of our study was to examine the safety of the tibial component of a novel all-ceramic TKR. Materials and Methods. We tested the tibial components of the primary knee implant BPK-S Integration Ceramic. Both the tibial and the femoral component consist of BIOLOX®delta ceramic The standards ISO 14879-1 and ASTM F1800-07 describe the test set-up for the experimental fatigue strength testing of tibial components from knee implants. We conducted the testing with a significantly increased maximum load of 5,300 N (900 N are required). A final burst strength test was carried out after the fatigue load testing in the same embedding and with the same test set-up. Results. No specimen failed during fatigue load testing. The subsequent post-fatigue burst strength testing showed a maximum strength against fracture of at least 9.7 kN for size 3 and at least 12.1 kN for size 6. Discussion. The good results of the strength testing of the tibial component of the BPK-S Integration Ceramic tibial plateau supported the good initial clinical outcome without any implant specific complications of this knee design. Further clinical studies have to show if this design fulfills the high expectations over long periods of time

Introduction and Objective. Slipped Capital Femoral Epiphysis (SCFE) is one of the most common hip disorders in children and is characterized by a proximal femoral deformity, resulting in early osteoarthritis. Several studies have suggested that SCFE patients after in situ fixation show an altered gait pattern. Early identification of gait alterations might lead to earlier intervention programs to prevent osteoarthritis. The aim of this study is to analyse gait alterations in SCFE patients after in situ fixation compared to typically developed children, using the Computer Assisted Rehabilitation Environment (CAREN) system. Materials and Methods. This is a cross-sectional, multi-center case-control study in the Netherlands. Eight SCFE patients and eight age- and sex-matched typically developed were included from two hospitals. Primary outcomes were kinematic parameters (absolute joint angles), studied with gait analysis using statistical parametric mapping (SPM). Secondary outcomes were spatiotemporal parameters, the Notzli alpha angle, muscle activation patterns (EMG), and clinical questionnaires (VAS, Borg CR10, SF-36, and HOOS), analyzed using non-parametric statistical methods. Results. Patients (mean BMI=28±9 kg/m. 2. ) showed altered gait patterns, with significantly increased external hip rotation and decreased downward pelvic obliquity during the pre-swing phase of the gait cycle compared to typically developed (mean BMI=22±3 kg/m. 2. ). Walking speed, cadence, % stance time, and step length were reduced in SCFE patients. Coefficient of variances of cadence, stance time, and step length were increased. Patients had a mean alpha angle of 64, SD=7.9. Clinical questionnaires showed that general health (SF-36) was 80±25, energy/fatigue (SF-36) was 67±15, pain (VAS) was 0±1.5, and total HOOS score was 85±18. Conclusions. SCFE patients after in situ fixation appear to have developed a compensation mechanism, showing slight alterations in gait parameters, good general health, little functional limitations of the hip, and no self-reported pain. Cam deformities, altered joint loading, and this compensation mechanism might influence long-term early osteoarthritis. BMI reduction should be implemented in care plans, as obesity might also play a role in unfavorable long-term outcomes

Introduction and Objective. The surgical strategy for acetabular component revision is determined by available host bone stock. Acetabular bone deficiencies vary from cavitary or segmental defects to complete discontinuity. For segmental acetabular defects with more than 50% of the graft supporting the cup it is recommended the application of reinforcement ring or ilioischial antiprotrusio devices. Acetabular reconstruction with the use of the antiprotrusion cage (APC) and allografts represents a reliable procedure to manage severe periprosthetic deficiencies with highly successful long-term outcomes in revision arthroplasty. Objective. We present our experience, results, critical issues and technical innovations aimed at improving survival rates of antiprotrusio cages. Materials and Methods. From 2004 to 2019 we performed 69 revisions of the acetabulum using defrosted morcellized bone graft and the Burch Schneider anti-protrusion cage. The approach was direct lateral in 25 cases, direct anterior in 44. Patients were re-evaluated with standard radiography and clinical examination. Results. Eight patients died from causes not related to surgery, and two patients were not available for follow up. Five patients were reviewed for, respectively, non-osseointegration of the ring, post-traumatic loosening with rupture of the screws preceded by the appearance of supero-medial radiolucency, post-traumatic rupture of the distal flange, post-traumatic rupture of the cemented polyethylene-ceramic insert, and dislocation treated with new dual-mobility insert. Among these cases, the first three did not show macroscopic signs of osseointegration of the ring, and the only areas of stability were represented by the bone-cement contact at the holes in the ring. Although radiographic studies have shown fast remodeling of the bone graft and the implant survival range from 70% to 100% in the 10-year follow up, the actual osseointegration of the ring has yet to be clarified. To improve osseointegration of the currently available APC whose metal surface in contact with the bone is sandblasted, we combined the main features of the APC design long validated by surgical experience with the 3D-Metal Technology for high porosity of the external surface already applied to and validated with the press fit cups. The new APC design is produced with the 3D-Metal technology using Titanium alloy (Ti6Al4V ELI) that Improves fatigue resistance, primary stability and favorable environment for bone graft ingrowth. We preview the results of the first cases with short-term follow up. Conclusions. Acetabular reconstruction with impacted morcellized bone graft and APC is a current and reliable surgical technique that allows the restoration of bone loss with a high survival rate of the implant in the medium to long term. The new 3D Metal Cage is designed to offer high friction for the initial stability. The high porosity of the 3D Metal structure creates a favorable environment for bone growth, thus providing valid secondary fixation reproducing the results achieved with the 3D metal press fit cup

Formation of micro-cracks occurs in bone due to daily activities. Through a mechanism of self-repair, these micro-cracks are detected, and the damaged areas are restored, avoiding further propagation. The Scissors Model suggests that the osteocyte processes that cross the micro-cracks break as consequence of the cyclic displacements of the micro-crack faces, due to fatigue, and this triggers the remodelling processes. A fresh bovine tibia bone was cut in sections oriented 20° from the transversal direction. The cortical bone was sliced using a circular saw and shaped to the dimensions: 20 × 10 × 1 (mm) and the surfaces were polished. µCT images were obtained from all the samples (μCT 40, Scanco Medical, Brüttisellen, Switzerland). From the DICOM files, the geometries were reconstructed and meshed using tetrahedrons, in ICEM CFD. The Elasticity Modulus (E) was determined in Bonemat, by applying an empirical relationship Elasticity-Density from the literature. The parts were then imported into ANSYS APDL to simulate micro-crack propagation in bone. This model will be validated with further experimental work where the micro-crack will be initiated in the prepared samples and propagated due to fatigue loading, and the osteocyte processes will be visualized in the Scanning Electron Microscope (SEM). This investigation aims to study how cyclic loading in bones and failure of osteocyte processes can trigger target the mechanism of bone remodelling. The resulting model can later contribute for the investigation of treatments for bone diseases such as osteoporosis and the response of bone to the presence of orthopaedic implants

Fracture fixation has advanced significantly with the introduction of locked plating and minimally invasive surgical techniques. However, healing complications occur in up to 10% of cases, of which a significant portion may be attributed to unfavorable mechanical conditions at the fracture. Moreover, state-of-the-art plates are prone to failure from excessive loading or fatigue. A novel biphasic plating concept has been developed to create reliable mechanical conditions for timely bone healing and simultaneously improve implant strength. The goal of this study was to test the feasibility and investigate the robustness of fracture healing with a biphasic plate in a large animal experiment. Twenty-four sheep underwent a 2mm mid-diaphyseal tibia osteotomy stabilized with either the novel biphasic plate or a control locking plate. Different fracture patterns in terms of defect location and orientation were investigated. Animals were free to fully bear weight during the post-operative period. After 12 weeks, the healing fractures were evaluated for callus formation using micro-computer tomography and strength and stiffness using biomechanical testing. No plate deformation or failures were observed under full weight bearing with the biphasic plate. Osteotomies stabilized with the biphasic plate demonstrated robust callus formation. Torsion tests after plate removal revealed no statistical difference in peak torsion to failure and stiffness for the different fracture patterns stabilized with the biphasic plate. However, the biphasic plate group specimens were 45% stronger (p=0.002) and 48% stiffer (p=0.007) than the controls. The results of this large animal study demonstrate the clinical potential of this novel stabilization concept

We investigated the effect of pre-heating a femoral component on the porosity and strength of bone cement, with or without vacuum mixing used for total hip replacement. Cement mantles were moulded in a manner simulating clinical practice for cemented hip replacement. During polymerisation, the temperature was monitored. Specimens of cement extracted from the mantles underwent bending or fatigue tests, and were examined for porosity. Pre-heating the stem alone significantly increased the mean temperature values measured within the mantle (+14.2°C) (p < 0.001) and reduced the mean curing time (−1.5 min) (p < 0.001). The addition of vacuum mixing modulated the mean rise in the temperature of polymerisation to 11°C and reduced the mean duration of the process by one minute and 50 seconds (p = 0.01 and p < 0.001, respectively). In all cases, the maximum temperature values measured in the mould simulating the femur were < 50°C. The mixing technique and pre-heating the stem slightly increased the static mechanical strength of bone cement. However, the fatigue life of the cement was improved by both vacuum mixing and pre-heating the stem, but was most marked (+ 280°C) when these methods were combined. Pre-heating the stem appears to be an effective way of improving the quality of the cement mantle, which might enhance the long-term performance of bone cement, especially when combined with vacuum mixing

Most cases of tendinopathy are believed to be overuse injuries rather than the result of a chronic event. The investigation of the fatigue properties of tendon is therefore of critical importance. This work considered the cyclic stress-relaxation and creep behaviour of two contrasting bovine tendon types – the largely postional digital extensor and the more energy storing deep digital flexor tendon. Fascicles were cyclically loaded (1Hz), to 1800 cycles of stress relaxation or to failure in creep, stopping some tests at 300, 900 or 1200 cycles to perform quasi-static failure tests or confocal imaging using a highly concentrated Acridine Orange solution. Creep tests were cycled to 60% of the ultimate tensile strength (UTS), while for stress relaxation, cyclic deformation to the strain associated with 60% UTS was used. Flexor tendon fascicles were found to exhibit reduced stress relaxation at all time points compared to the extensor fascicles and also showed an increase in the mean cycles to failure during creep testing. Evidence of fatigue damage was clear in the confocal images with breakdown of the collagen fibre alignment evident from 300 cycles; however it appears that some damage could occur without effect on the UTS of the fascicle. Despite what appears to be superior fatigue resistance in the flexor tendon fascicles, the matrix damage, certainly at early time points, appeared visually to be as severe as that observed with the extensor tendon fascicles

Mismatch of bearing component centres and tension of soft tissues surrounding the hip joint can lead to component separation during gait cycle and cause the femoral head to contact the rim of an acetabular liner, which could increase wear and shorten lifespan of an implant. This study aims to investigate the contact and wear mechanics of a metal-on-polyethylene hip joint under dynamic separation by using Finite Element Analysis (FEA). A Pinnacle® cup with a Marathon neutral liner 36×56mm with a 45° inclination was constrained by a spring element in the medial-lateral axis. The spring was pre-compressed by 4mm to represent the corresponding translational mismatch of a simulator testing. Archard's law was used to predict wear over one ISO 14242-1 gait cycle. Contact pressure is proportional to the load input during the stance phase, associated with concentric contact condition; it increases threefold just before the swing phase (time C), reaching 46.2MPa, where edge loading occurs. Consequently, separation climbs to 3.54mm, which is comparable to the mathematical prediction (3.34mm) and dynamic FEA (3.2mm). The predicted volumetric wear after this gait cycle is 1.22 × 10–5 mm3. Dynamic separation between femoral head and acetabular liner can result in edge loading, consequently high contact pressure on the edge of a liner. In combination with cyclic loading, fatigue damage could take place and may be worth investigating in the future