Introduction. The exact mechanisms leading to tendinopathies and tendon ruptures remain poorly understood while their occurrence is clearly associated with exercise. Overloading is thought to be a major factor contributing to the development of tendon pathologies. However, as animal studies have shown, heavy loading alone won't cause tendinopathies. It has been speculated, that malfunctioning adaptation or healing processes might be involved, triggering tendon tissue degeneration. By analysing the expression of the entirety of degrading enzymes (degradome) in pathological and non-pathological, strained and non-strained tendon tissue, the aim of this study was to identify common or opposite patterns in gene regulation. This approach may generate new targets for future studies. Materials and Methods. RNA was extracted from different tendon tissues: normal (n=7), tendinopathic (n=4) and ruptured (n=4) Achilles tendon; normal (n=4) and tendinopathic (n=4) posterior tibialis tendon; normal hamstrings tendon with or without subjection to static strain (n=4). The RNA was reverse transcribed, then pooled per group The expression of 538 protease genes was analysed using Taqman low-density array quantitative RT-PCR. To be considered relevant, changes had to be at least 4fold and measurable at a level below 36 Cts. Results. In general, there was little common regulation when exercised was compared with pathological tissue. The expression of PAMR1 and TNFαIP3 was upregulated with exercise (169-fold and 78-fold), Achilles tendinopathy (9724-fold and 7-fold) and Achilles tendon rupture (1809-fold and 10-fold), while DDI1, PSMB11 and PSH2 which were down-regulated with exercise were upregulated with Achilles pathology. Discussion. The newly found targets may deliver insights into the initiation and progression of tendon pathologies: PAMR1, a regeneration associated muscle protease which has been shown to be downregulated in Duchenne muscular dystrophy and upregulated in regenerating muscle fibers, might also be involved in tendon regeneration; TNFαIP3, which negatively regulates the NF-κB/pro-inflammatory pathway, could have anti-inflammatory function in tendon regeneration. PSMB11 and PSH2 are for the first time shown to be expressed in tendon and regulated in tendon pathology. Using this approach we were able to generate new targets and to add information on function, regulation and expression sites of recently identified proteins

Despite the clinical relevance of back pain and intervertebral disc herniation, the lack of reliable models has strained their molecular understanding. We characterized the lumbar spinal phenotype of C57BL/6 and SM/J mice during aging. Interestingly, old SM/J lumbar discs evidenced accelerated degeneration, associated with high rates of disc herniation. SM/J AF's and degenerative human's AF transcriptomic profiles showed altered immune cell, inflammation, and p53 pathways. Old SM/J mice presented increased neuronal markers in herniated discs, thicker subchondral bone, and higher sensitization to pain. Dorsal root ganglia transcriptomic studies and spinal cord analysis exhibited increased pain and neuroinflammatory markers associated with altered extracellular matrix regulation. Immune system single-cell and tissue level analysis showed distinctive T-cell and B-cell modulation and negative correlation between mechanical allodynia and INF-α, IL-1β, IL2, and IL4, respectively. This study underscores the multisystemic network behind back pain and highlights the role of genetic background and the immune system in disc herniation disease. Acknowledgments: This study is supported by grants from the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) R01AR055655, R01AR064733, R01AR074813 to MVR

Prophylactic augmentation is meant to reinforce the vertebral body (VB), but in some cases it is suspected to actually weaken it. To elucidate the biomechanical efficacy of prophylactic augmentation, the full-field three-dimensional strain distributions were measured for the first time inside prophylactic-augmented vertebrae. Twelve thoracic porcine vertebrae were assigned to three groups: 4 were augmented with bone cement for vertebroplasty (Mendec-Spine, Tecres), 4 were treated with another bone cement for vertebroplasty (Calcemex-Spine, Tecres) while the other 4 were tested untreated as a control. Destructive tests were carried out under axial compression, in a step-wise fashion (unloaded, 5%, 10% and 15% compression). At each loading step, μCT-images were acquired. The internal strain distribution was investigated by means of DVC analysis. Some augmented specimens were stronger than the respective control, while others were weaker. In most of the specimens, the strain distribution in the elastic regime (5% compression) seemed to predict the location of the micro-damage initiation before it actually became identifiable (at 10% and 15% compression). The measured strain had the same order of magnitude for all groups. However, in the control vertebrae, the highest strain would unpredictably appear at any location inside the VB. Conversely, for both augmentation groups, the highest strains were measured in the regions adjacent to the injected cement mass, whereas the cement-interdigitated-bone was less strained. Localization of high strains and failure was consistent between specimens, but different between the two cement types: with Mendec-Spine failure the highest strains were mainly localized at mid-height and at the same level where the cement mass was localized; with Calcemex-Spine failure the highest strains were mainly cranial and caudal to the cement mass. Both the micro-CT images, and the DVC strain analysis highlighted that:. The cement mass was less strained than any other regions in the vertebra. Failure never started inside the cement mass. This can be explained with the additional stiffening and reinforcement associated with the infiltration of the cement inside the trabecular bone. The highest strains and failure were localized in the bone adjacent to the cement-bone interdigitated region. This can be explained by the strain concentration between the cement-interdigitated bone (stiffer and stronger), and the adjacent non-augmented trabecular bone. The strain maps in the elastic regime and the localization of failure was different in the augmented vertebrae, when compared to the natural controls. This suggests an alteration of the load sharing in the augmented structure where the load is mostly carried by the cement region. The different localization of failure initiation between the two augmented groups could be explained by the different mechanical properties of the two cements. This study has demonstrated the potential of DVC in measuring the internal strain and failure in prophylactic-augmented vertebrae. It has been shown that failure starts inside the augmented VB, next to the injected cement mass. This can help establishing better criteria (in terms of localization of the cement mass) in order to improve clinical protocols for vertebroplasty surgical procedures

Whilst lateral ankle sprain is often considered a benign injury it represents between 3–5% of all A&E visits in the UK. The mechanical characteristics of ankle ligaments under sprain-like conditions are scarcely reported. The lateral collateral ankle ligaments were dissected from n=6 human cadaveric specimens to produce individual bone-ligament-bone specimens. An Instron Electropuls E10000 was used to uni-axially load the ankle ligaments in tension. The ligaments were first preconditioned between 2 N and a load value corresponding to 3.5% strain for 15 cycles and then strained to failure at a rate of 100%/s. The mean ultimate failure loads and their standard deviations for the anterior talofibular (ATFL), calcaneofibular (CFL) and posterior talofibular (PTFL) ligaments are 351.4±105.6 N, 367.8±76.1 N and 263.6±156.6 N, respectively. Whilst the standard deviation values are high they align with those previously reported for ankle ligament characterisation. The large standard deviations are partly due to the inherent variability of human cadaveric tissue but could also be due to varying previous activity levels of participants or a prior unreported ankle sprain. Although the sample size is relatively small the results were stratified to identify any potential correlations of age, BMI and weight with ultimate load. A strong Pearson correlation (r=0.919) was found between BMI and ultimate load of the CFL but a larger sample size is required to confirm a link. The ligament failure modes were observed and categorised as avulsion or intra-ligamentous failure. The ATFL avulsed from the fibula in five instances and intra-ligamentous failure occurred once. The CFL avulsed from the fibula twice and failed four times through intra-ligamentous failure. Finally, the PTFL avulsed from the fibula once, avulsed from the talus once and failed through intra-ligamentous failure in four instances. The results identify the forces required to severely sprain the lateral collateral ankle ligaments and their failure modes

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

Summary. Canals are the preferential sites for failure in cortical bone and their architecture is able to dictate the mechanical behaviour of the bone: smaller and branched canals generate a high volume of bone failure even at low apparent tissue strain. Introduction. Osteogenesis imperfecta (OI), or brittle bone disease, is caused by mutations in the collagen genes and results in skeletal fragility. We recently showed that a mouse model of osteogenesis imperfecta (oim) has smaller and denser intracortical canals with a branched architecture compared to healthy wild type (WT) bones with similar cortical porosity [1]. We hypothesise this abnormal intracortical structure contributes to the increased fracture risk of the oim bones. Methods. Micro-architecture finite element (µFE) models of WT and oim cortical bone with the canals explicitly modelled as voids were developed (Mimics, Materialise) from 10 high resolution (700 nm) synchrotron-radiated computed tomography images previously collected at the Swiss Light Source, Switzerland. Bone was modelled as linear elastic, isotropic and homogeneous tissue with same material properties for WT and oim (E=17GPa, ν=0.3) in order to account for the solely contribute of the intracortical architecture to the mechanical properties of the bone. We estimated stresses and strains within the bone structure when under compression (0.1–0.5% apparent strain) (Abaqus, Simulia) and determined the bone failure per each element when the effective strain (. ε. e. f. f. =. 2. U. /. E. ) reached a level of 0.7%. We calculated the volume of bone above 0.7% at each strain level. Results. Visualization of the failure within the bone revealed that the high risk tissue is mainly located around the canals in both oim and WT bone structure. However, oim intracortical bone architecture presented a higher amount of bone strained at more than 0.7% than WT one. Discussion and Conclusions. Our μFE models of cortical bone showed that preferential site for bone failure is near canals, in agreement with previous experimental studies. However, our findings demonstrated that cortical bone with high canal density and branched canal architecture, as in oim, increases the volume of bone failure density and the chances for the entire bone to fail at a lower apparent tissue strain (when same material properties were used for WT and oim bone). Because cracks in mouse bone originate at the canal surface and propagate through osteocyte lacunae, it is possible that the increased lacunar porosity in oim bone additionally contributes to its fragility. Oim bone has also reduced stiffness compared to WT bone, which increases the strain around pores and may promote damage. Intracortical architecture and material properties can help explain why brittle bone fracture at a much smaller ultimate load and lower apparent tissue strain than WT bone. These findings are broader than just oim bone as provide an estimate of the influence of the intracortical canal structure on the strain distribution within the bone and a relationship with its mechanical integrity. Future treatment strategies should aim to reduce the number of canals and their braches within the cortical bone in order to reduce risk of fracture

Aims

The intra-articular administration of tranexamic acid (TXA) has been shown to be effective in reducing blood loss in unicompartmental knee arthroplasty and anterior cruciate reconstruction. The effects on human articular cartilage, however, remains unknown. Our aim, in this study, was to investigate any detrimental effect of TXA on chondrocytes, and to establish if there was a safe dose for its use in clinical practice. The hypothesis was that TXA would cause a dose-dependent damage to human articular cartilage.

In order to investigate the osteoinductive properties of allograft used in impaction grafting and the effect of strain during impaction on these properties, we designed an in vitro experiment to measure strain-related release of bone morphogenetic protein-7 (BMP-7) from fresh-frozen femoral head allograft. A total of 40 10 mm cubes of cancellous bone were cut from ten samples of fresh-frozen femoral head. The marrow was removed from the cubes and the baseline concentrations of BMP-7 were measured. Specimens from each femoral head were allocated to four groups and subjected to different compressive strains with a material testing machine, after which BMP-7 activity was reassessed. It was present in all groups. There was a linear increase of 102.1 pg/g (95% confidence interval 68.6 to 135.6) BMP-7 for each 10% increase in strain. At 80% strain the mean concentration of BMP-7 released (830.3 pg/g bone) was approximately four times that released at 20% strain. Activity of BMP-7 in fresh-frozen allograft has not previously been demonstrated. This study shows that the freezing and storage of femoral heads allows some maintenance of biological activity, and that impaction grafting provides a source of osteoinductive bone for remodelling.

We have shown that BMP-7 is released from fresh-frozen femoral head cancellous bone in proportion to the strain applied to the bone. This suggests that the impaction process itself may contribute to the biological process of remodelling and bony incorporation.

Ovine articular chondrocytes were isolated from cartilage biopsy and culture expanded in vitro. Approximately 30 million cells per ml of cultured chondrocytes were incorporated with autologous plasma-derived fibrin to form a three-dimensional construct. Full-thickness punch hole defects were created in the lateral and medial femoral condyles. The defects were implanted with either an autologous ‘chondrocyte-fibrin’ construct (ACFC), autologous chondrocytes (ACI) or fibrin blanks (AF) as controls. Animals were killed after 12 weeks. The gross appearance of the treated defects was inspected and photographed. The repaired tissues were studied histologically and by scanning electron microscopy analysis.

All defects were assessed using the International Cartilage Repair Society (ICRS) classification. Those treated with ACFC, ACI and AF exhibited median scores which correspond to a nearly-normal appearance. On the basis of the modified O’Driscoll histological scoring scale, ACFC implantation significantly enhanced cartilage repair compared to ACI and AF. Using scanning electron microscopy, ACFC and ACI showed characteristic organisation of chondrocytes and matrices, which were relatively similar to the surrounding adjacent cartilage.

Implantation of ACFC resulted in superior hyaline-like cartilage regeneration when compared with ACI. If this result is applicable to humans, a better outcome would be obtained than by using conventional ACI.