Assessment of subchondral bone microdamage quantification using contrast-enhanced imaging techniques.

Bone microdamage is common at subchondral bone (SCB) sites subjected to repeated high rate and magnitude of loading in the limbs of athletic animals and humans. Microdamage can affect the biomechanical behaviour of bone under physiological loading conditions. To understand the effects of microdamage on the mechanical properties of SCB, it is important to be able to quantify it. The extent of SCB microdamage had been previously estimated qualitatively using plain microcomputed tomography (µCT) and a radiocontrast quantification method has been used for trabecular bone but this method may not be directly applicable to SCB due to differences in bone structure. In the current study, SCB microdamage detection using lead uranyl acetate (LUA) and quantification by contrast-enhanced µCT and backscattered scanning electron microscopy (SEM) imaging techniques were assessed to determine the specificity of the labels to microdamage and the accuracy of damaged bone volume metrices. SCB specimens from the metacarpus of racehorses, with the hyaline articular cartilage (HAC) removed, were grouped into two with one group subjected to ex vivo uniaxial compression loading to create experimental bone damage. The other group was not loaded to preserve the pre-existing in vivo propagated bone microdamage. A subset of each group was stained with LUA using an established or a modified protocol to determine label penetration into SCB. The µCT and SEM images of stained specimens showed that penetration of LUA into the SCB was better using the modified protocol, and this protocol was repeated in SCB specimens with intact hyaline articular cartilage. The percentage of total label localised to bone microdamage was determined on SEM images, and the estimated labelled bone volume determined by µCT in SCB groups was compared. Label was present around diffuse and linear microdamage as well as oblique linear microcracks present at the articular surface, except in microcracks with high-density mineral infills. Bone surfaces lining pores with recent mineralisation were also labelled. Labelled bone volume fraction (LV/BV) estimated by µCT was higher in the absence of HAC. At least 50% of total labels were localised to bone microdamage when the bone area fraction (B.Ar/T.Ar) of the SCB was greater than 0.85 but less than 30% when B.Ar/T.Ar of the SCB was less than 0.85. To adjust for LUA labels on bone surfaces, a measure of the LV/BV corrected for bone surface area (LV/BV BS-1) was used to quantify damaged SCB. In conclusion, removal of HAC and using a modified labelling protocol effectively stained damaged SCB of the metacarpus of racehorses and represents a technique useful for quantifying microdamage in SCB. This method can facilitate future investigations of the effects of microdamage on joint physiology.

Prolonged cyclical loading induces Haversian remodeling in mandibles of growing rabbits.

Bone adaptation to mechanical loading happens predominantly via modeling and remodeling, but the latter is poorly understood. Haversian remodeling (cortical bone replacement resulting in secondary osteons) is thought to occur in regions of low strain as part of bone maintenance or high strain in response to microdamage. However, analyses of remodeling in primates have revealed an unappreciated association with the number of daily load cycles. We tested this relationship by raising 30 male domestic rabbits (Oryctolagus cuniculus) on disparate diets from weaning to adulthood (48 weeks), facilitating a naturalistic perspective on mandibular bone adaptation. A control group consumed only rabbit pellets and an 'overuse' group ate hay in addition to pellets. To process hay, which is tougher and stiffer, rabbits increase chewing investment and duration without increasing bite force (i.e. corpus mean peak strain is similar for the two foods). Corpus remodeling in overuse rabbits was ∼1.5 times that of controls, measured as osteon population density and percentage Haversian bone. In the same subjects, there was a significant increase in overuse corpus bone formation (ratio of cortical area to cranial length), consistent with previous reports on the same dietary manipulation and bone formation in rabbits. This is the first evidence that both modeling and remodeling are simultaneously driven by the number of load cycles, independent of strain magnitude. This novel finding provides unique data on the feeding apparatus, challenges traditional thought on Haversian remodeling, and highlights the need for experimental studies of skeletal adaptation that examine mechanical factors beyond strain magnitude.

A Three-Dimensional Mechanical Loading Model of Human Osteocytes in Their Native Matrix.

Osteocytes are mechanosensory cells which are embedded in calcified collagenous matrix. The specific native matrix of osteocytes affects their regulatory activity, i.e., transmission of signaling molecules to osteoclasts and/or osteoblasts, in the mechanical adaptation of bone. Unfortunately, no existing in vitro model of cortical bone is currently available to study the mechanosensory function of human osteocytes in their native matrix. Therefore, we aimed to develop an in vitro three-dimensional mechanical loading model of human osteocytes in their native matrix. Human cortical bone explants containing osteocytes in their three-dimensional native matrix were cultured and mechanically loaded by three-point bending using a custom-made loading apparatus generating sinusoidal displacement. Osteocyte viability and sclerostin expression were measured 1-2 days before 5 min loading and 1 day after loading. Bone microdamage was visualized and quantified by micro-CT analysis and histology using BaSO4 staining. A linear relationship was found between loading magnitude (2302-13,811 µÉ›) and force (1.6-4.9 N) exerted on the bone explants. At 24 h post-loading, osteocyte viability was not affected by 1600 µÉ› loading. Sclerostin expression and bone microdamage were unaffected by loading up to 8000 µÉ›. In conclusion, we developed an in vitro 3D mechanical loading model to study mechanoresponsiveness of viable osteocytes residing in their native matrix. This model is suitable to study the effect of changed bone matrix composition in metabolic bone disease on osteocyte mechanoresponsiveness.

Damage to the human lumbar cartilage endplate and its clinical implications.

The cartilaginous endplate (CEP) is a thin layer of hyaline cartilage, and plays an important role in the diffusion of nutrients into the intervertebral discs. Its damage may seriously affect the disc degeneration, and result in low back pain (LBP). However, the structural features of damaged CEPs have not been well characterized, and this hinders our understanding of the etiology of disc degeneration and pain. To present the structural features of micro-damaged CEPs in patients with disc degeneration and LBP that might even be regarded as an initial factor for disc degeneration, we performed a histological study of micro-damaged CEPs harvested from human lumbar intervertebral discs and analyzed its clinical implications. Human lumbar CEPs were excised from 35 patients (mean age 60.91 years) who had disc degeneration and LBP. Control tissue was obtained from 15 patients (mean age 54.67 years) with lumbar vertebral burst fractures. LBP and disability were assessed clinically, and all patients underwent anterior vertebral body fusion surgery. CEPs together with some adjacent nucleus pulposus (NP) were sectioned at 4 µm, and stained using H&E, Safranin O/Fast Green, and Alcian Blue. Immunostaining and PCR were used to identify various markers of degeneration, innervation, and inflammation. Histology demonstrated physical micro-damage in 14/35 CEPs from the disc degeneration group. Six major types of damage could be distinguished: fissure, traumatic nodes, vascular mimicry, incorporation of NP tissue within the CEP, incorporation of bone within the CEP, and incorporation of NP and bone within the CEP. Pain and disability scores (ODI: p = 0.0190; JOA: p = 0.0205; JOABPEQ: p = 0.0034) were significantly higher in those with micro-damaged CEPs (N = 14) than in those with non-damaged CEPs (N = 21). CEP damage was significantly associated with elevated MMP3 (p = 0.043), MMP13 (p = 0.0191), ADAMTS5 (p = 0.0253), TNF-α (p = 0.0011), and Substance P (p = 0.0028), and with reduced Sox9 (p = 0.0212), aggrecan (p = 0.0127), and type II collagen (p = 0.0139). In conclusion, we presented a new classification of human lumbar micro-damaged CEPs. Furthermore, we verify disc degeneration, innervation, and discogenic pain in micro-damaged CEPs.

Spatiotemporal characterization of microdamage accumulation and its targeted remodeling mechanisms in diabetic fatigued bone.

The skeleton of type 1 diabetes mellitus (T1DM) has deteriorated mechanical integrity and increased fragility, whereas the mechanisms are not fully understood. Load-induced microdamage naturally occurs in bone matrix and can be removed by initiating endogenous targeted bone remodeling. However, the microdamage accumulation in diabetic skeleton and the corresponding bone remodeling mechanisms remain poorly understood. Herein, streptozotocin-induced T1DM rats and age-matched non-diabetic rats were subjected to daily uniaxial ulnar loading for 1, 4, 7, and 10 days, respectively. The SPECT/CT and basic fuchsin staining revealed significant higher-density spatial accumulation of linear and diffuse microdamage in diabetic ulnae than non-diabetic ulnae. Linear microcracks increased within 10-day loading in diabetic bone, whereas peaked at Day 7 in non-diabetic bone. Moreover, diabetic fatigued ulnae had more severe disruptions of osteocyte canaliculi around linear microcracks. Immunostaining results revealed that diabetes impaired targeted remodeling in fatigued bone at every key stage, including increased apoptosis of bystander osteocytes, decreased RANKL secretion, reduced osteoclast recruitment and bone resorption, and impaired osteoblast-mediated bone formation. This study characterizes microdamage accumulation and abnormal remodeling mechanisms in the diabetic skeleton, which advances our etiologic understanding of diabetic bone deterioration and increased fragility from the aspect of microdamage accumulation and bone remodeling.

Diffuse microdamage in bone activates anabolic response by osteoblasts via involvement of voltage-gated calcium channels.

INTRODUCTION: Matrix damage sustained by bone tissue is repaired by the concerted action of bone cells. Previous studies have reported extracellular calcium ([Ca2+]E) efflux to originate from regions of bone undergoing diffuse microdamage termed as "diffuse microdamage-induced calcium efflux" (DMICE). DMICE has also been shown to activate and increase intracellular calcium ([Ca2+]I) signaling in osteoblasts via the involvement of voltage-gated calcium channels (VGCC). Past studies have assessed early stage (< 1 h) responses of osteoblasts to DMICE. The current study tested the hypothesis that DMICE has longer-term sustained effect such that it induces anabolic response of osteoblasts. MATERIALS AND METHODS: Osteoblasts derived from mouse calvariae were seeded on devitalized bovine bone wafers. Localized diffuse damage was induced in the vicinity of cells by bending. The response of osteoblasts to DMICE was evaluated by testing gene expression, protein synthesis and mineralized nodule formation. RESULTS: Cells on damaged bone wafers showed a significant increase in RUNX2 and Osterix expression compared to non-loaded control. Also, RUNX2 and Osterix expression were suppressed significantly when the cells were treated with bepridil, a non-selective VGCC inhibitor, prior to loading. Significantly higher amounts of osteocalcin and mineralized nodules were synthesized by osteoblasts on diffuse damaged bone wafers, while bepridil treatment resulted in a significant decrease in osteocalcin production and mineralized nodule formation. CONCLUSION: In conclusion, this study demonstrated that DMICE activates anabolic responses of osteoblasts through activation of VGCC. Future studies of osteoblast response to DMICE in vivo will help to clarify how bone cells repair diffuse microdamage.

Once-Weekly Teriparatide Treatment Prevents Microdamage Accumulation in the Lumbar Vertebral Trabecular Bone of Ovariectomized Cynomolgus Monkeys.

The effect of teriparatide treatment on microdamage accumulation has yet to be examined in animal studies. The purpose of this study was to investigate the effect of once-weekly teriparatide treatment on bone microdamage accumulation and the relationship between microdamage parameters and bone mass, architecture, turnover, and collagen cross-linking in the lumbar vertebral trabecular bone of ovariectomized (OVX) cynomolgus monkeys. Female monkeys were divided into four groups (n = 18-20 per group): (1) SHAM group, (2) OVX group, (3) OVX with 1.2 µg/kg once-weekly teriparatide group (LOW group), (4) OVX with 6.0 µg/kg once-weekly teriparatide group (HIGH group). After 18 months, all animals were double-labeled with calcein for histomorphometry. L3 and L7 lumbar vertebrae were harvested and analyzed for differences in histomorphometry, microdamage, and collagen cross-linking. The iliac crest was also analyzed for differences in bone turnover. In the OVX group, cancellous bone mass was reduced and microdamage accumulation was increased as compared with the SHAM control. Once-weekly teriparatide at both doses prevented the decrease in bone mass and increase in microdamage accumulation, and improved the distribution of collagen cross-linkage types. Regression analyses indicated that decreased microdamage accumulation was associated with reduced non-enzymatic cross-link pentosidine rather than increased cancellous bone mass or enzymatic cross-links. These findings suggest that once-weekly teriparatide treatment decreases microdamage accumulation by recovering the balance in collagen cross-links.

Accumulation of microdamage and low bone mass in the femoral head as a cause of subchondral insufficiency fracture in a patient with osteogenesis imperfecta.

Subchondral insufficiency fractures of the femoral head are generally considered to be osteoporosis-related fragility fractures. There have been reports of microfractures being found in subchondral bone on pathological examination. However, the mechanism of these microfractures is not known. In this report, we describe a patient with osteogenesis imperfecta who developed a subchondral insufficiency fracture of the femoral head after a fall that had resulted in a subcapital femoral neck fracture. Bipolar hemiarthroplasty was performed, and bone at the femoral head and neck was sampled for pathophysiological examination. Hematoxylin and eosin staining revealed microfractures and microcallus in the subchondral bone in the femoral head, indicating healing of a subchondral insufficiency fracture before the subcapital femoral neck fracture. Moreover, decreased bone volume and accumulated microdamage were observed in the subchondral bone but not in the cancellous bone in the femoral neck. These findings suggest that subchondral insufficiency fracture of the femoral head is a stress fracture caused by accumulation of microdamage in fragile subchondral bone.

Accumulation of microdamage in subchondral bone at the femoral head in patients with end-stage osteoarthritis of the hip.

In end-stage osteoarthritis (OA) of the hip, the effect of bone metabolism with and without cartilage is unclear. In this study, we aimed to investigate histomorphology and microdamage in the subchondral bone of the femoral head in areas with and without articular cartilage in patients with end-stage OA. Nineteen femoral heads were evaluated in 10 women who underwent total hip arthroplasty for OA and in nine cadaveric controls (CNT). Chondral thickness and subchondral bone plate thickness (SBP.Th) were measured in 5-mm-wide areas where cartilage was lost (area A) or preserved (area B) in OA and in corresponding areas in the load-bearing portion of the femoral head in the CNT. Histomorphometry and microdamage in 5 × 5-mm areas of cancellous bone were assessed. SBP.Th and bone volume were significantly greater in area A than in area B or in the CNT. Osteoid volume was significantly greater in area A than in area B or in the CNT. There was no significant difference in eroded surface between area A and CNT. Microcrack density was significantly greater in area A than in area B or in the CNT. Although accumulation of microdamage was caused by concentration of stress on the subchondral bone in the cartilage loss area in end-stage OA, remodeling for microdamage repairing mechanism was not enhanced. It was considered that the subchondral cancellous bone volume was increased because of modeling, not remodeling, by stress concentration due to articular cartilage loss.

Microcrack-associated bone remodeling is rarely observed in biopsies from athletes with medial tibial stress syndrome.

The pathology of medial tibial stress syndrome (MTSS) is unknown. Studies suggest that MTSS is a bony overload injury, but histological evidence is sparse. The presence of microdamage, and its potential association with targeted remodeling, could provide evidence for the pathogenesis of MTSS. Understanding the pathology underlying MTSS could contribute to effective preventative and therapeutic interventions for MTSS. Our aim was to retrospectively evaluate biopsies, previously taken from the painful area in athletes with MTSS, for the presence of linear microcracks, diffuse microdamage and remodeling. Biopsies, previously taken from athletes with MTSS, were evaluated at the Department of Anatomy and Cell Biology at the Indiana University. After preparing the specimens by en bloc staining, one investigator evaluated the presence of linear microcracks, diffuse microdamage and remodeling in the specimens. A total of six biopsies were evaluated for the presence of microdamage and remodeling. Linear microcracks were found in 4 out of 6 biopsies. Cracking in one of these specimens was artefactual due to the biopsy procedure. No diffuse microdamage was seen in any of the specimens, and only one potential remodeling front in association with the microcracks. We found only linear microcracks in vivo in biopsies taken from the painful area in 50% of the athletes with MTSS, consistent with the relationship between linear cracks and fatigue-associated overloading of bone. The nearly universal absence of a repair reaction was notable. This suggests that unrepaired microdamage accumulation may underlie the pathophysiological basis for MTSS in athletes.

Bone Microdamage in Acute Knee Injury.

PURPOSE OF REVIEW: This review summarizes what is known about how bone tissue responds to microdamage, and how this applies to the subchondral region. This has significant relevance to acute joint injury, and is related to the occurrence of bone marrow lesions (BMLs) which are seen by MRI in 80% of acute knee joint injuries. Here, we review what is known about these phenomena (microcracks and BMLs) in the literature and discuss potential mechanisms by which they may be linked. RECENT FINDINGS: The recent findings in this field have shown that microcracks in bone initiate targeted remodeling via RANKL expression in osteocytes. Other work has shown that subchondral microcracks co-localize with BMLs as viewed by MRI. Finally, BMLs are associated with pain and structural joint degeneration. This paper demonstrates that subchondral microcracks likely occur during acute joint injury, and are closely linked to BML that are seem by clinical MRI and thus are potentially involved in the subsequent joint degeneration that occurs after injury.

Effects of Shape and Orientation of Pore Canals on Mechanical Behaviors of Lobster Cuticles.

The work is to investigate the relationships between the microstructures and mechanical behaviors of lobster cuticles and reveal the inner mechanisms of the anisotropic mechanical properties of the cuticles and give the helpful guidance for the design of high-performance man-made composites. First, the tensile mechanical properties of the longitudinal and transverse specimens of the cuticles of American lobsters were tested with a mechanical-testing instrument. It is was found that the fracture strength and elastic modulus of the longitudinal specimens are distinctly larger than those of the transverse specimens. Then, the microstructural characteristics of the fracture surfaces of the specimens were observed with scanning electron microscope. It was observed that the pore canals in the cuticles are elliptic and their orientations are along the longitudinal orientation of the cuticles. Furthermore, the stresses and micro-damage of the longitudinal and transverse specimens were calculated with the rule of progressive damage by finite element method. It was revealed that the shape and orientation of the pore canals in the cuticles give rise to the anisotropic mechanical property of the cuticles and ensure that the cuticles possess the largest fracture strength and elastic modulus along their largest main-stress orientation.

A novel rat model for subchondral microdamage in acute knee injury: a potential mechanism in post-traumatic osteoarthritis.

OBJECTIVE: Subchondral microdamage may play an important role in post-traumatic osteoarthritis (PTOA) development following anterior cruciate ligament (ACL) rupture. It remains unknown whether this injury mechanism causes subchondral microdamage, or whether its repair occurs by targeted osteoclast-mediated remodeling. If so these events may represent a mechanism by which subchondral bone is involved in PTOA. Our objective was to test the hypothesis that subchondral microdamage occurs, and is co-localized with remodeling, in a novel rat model of ACL rupture. DESIGN: We developed a novel non-invasive rat animal model for ACL rupture and subchondral microdamage generation. By inducing ACL rupture noninvasively rather than surgically, this more closely mimics the clinical injury. MicroCT, MRI and histological methods were used to measure microstructural changes, ligament damage, and cellular/matrix degeneration, respectively. RESULTS: We reproducibly generated ACL rupture without damage to other soft joint tissues. Immediately after injury, increased microdamage was found in the postero-medial aspect of the tibia. Microstructural parameters showed increased resorption at 2 weeks, which returned to baseline. Dynamic histomorphometry showed increased calcein label uptake in the same region at 4 and 8 weeks. Chondrocyte death and protease activity in cartilage was also noted, however whether this was directly linked to subchondral changes is not yet known. Similarly, cartilage scoring showed degradation at 4 and 8 weeks post-injury. CONCLUSIONS: This study shows that our novel model can be used to study subchondral microdamage after ACL-rupture, and its association with localized remodeling. Cartilage degeneration, on a similar time-scale to other models, is also a feature of this system.

Rebound-associated vertebral fractures after discontinuation of denosumab-from clinic and biomechanics.

UNLABELLED: Rebound-associated vertebral fractures may follow treatment discontinuation of highly potent reversible bone antiresorptives, resulting from the synergy of rapid bone resorption and accelerated microdamage accumulation in trabecular bone. INTRODUCTION: The purposes of this study are to characterize rebound-associated vertebral fractures following the discontinuation of a highly potent reversible antiresorptive therapy based on clinical observation and propose a pathophysiological rationale. METHODS: This study is a case report of multiple vertebral fractures early after discontinuation of denosumab therapy in a patient with hormone receptor-positive non-metastatic breast cancer treated with an aromatase inhibitor. RESULTS: Discontinuation of highly potent reversible bone antiresorptives such as denosumab may expose patients to an increased fracture risk due to the joined effects of absent microdamage repair during therapy followed by synchronous excess activation of multiple bone remodelling units at the time of loss-of-effect. We suggest the term rebound-associated vertebral fractures (RVF) for this phenomenon characterized by the presence of multiple new clinical vertebral fractures, associated with either no or low trauma, in a context consistent with the presence of high bone turnover and rapid loss of lumbar spine bone mineral density (BMD) occurring within 3 to 12 months after discontinuation (loss-of-effect) of a reversible antiresorptive therapy in the absence of secondary causes of bone loss or fractures. Unlike atypical femoral fractures that emerge from failure of microdamage repair in cortical bone with long-term antiresorptive treatment, RVF originate from the synergy of rapid bone resorption and accelerated microdamage accumulation in trabecular bone triggered by the discontinuation of highly potent reversible antiresorptives. CONCLUSIONS: Studies are urgently needed to i) prove the underlying pathophysiological processes suggested above, ii) establish the predictive criteria exposing patients to an increased risk of RVF, and iii) determine appropriate treatment regimens to be applied in such patients.

Characterizing microcrack orientation distribution functions in osteonal bone samples.

Prefailure microdamage in bone tissue is considered to be the most detrimental factor in defining its strength and toughness with respect to age and disease. To understand the influence of microcracks on bone mechanics it is necessary to assess their morphology and three-dimensional distribution. This requirement reaches beyond classic histology and stereology, and methods to obtain such information are currently missing. Therefore, the aim of the study was to develop a methodology that allows to characterize three-dimensional microcrack distributions in bulk bone samples. Four dumbbell-shaped specimens of human cortical bone of a 77-year-old female donor were loaded beyond yield in either tension, compression or torsion (one control). Subsequently, synchrotron radiation micro-computed tomography (SRµCT) was used to obtain phase-contrast images of the damaged samples. A microcrack segmentation algorithm was developed and used to segment microcrack families for which microcrack orientation distribution functions were determined. Distinct microcrack families were observed for each load case that resulted in distinct orientation distribution functions. Microcracks had median areas of approximately 4.7 µm2 , 33.3 µm2 and 64.0 µm2 for tension, compression and torsion. Verifying the segmentation algorithm against a manually segmented ground truth showed good results when comparing the microcrack orientation distribution functions. A size dependence was noted when investigating the orientation distribution functions with respect to the size of the volume of interest used for their determination. Furthermore, a scale separation between tensile, compressive and torsional microcracks was noticeable. Visual comparison to classic histology indicated that microcrack families were successfully distinguished. We propose a methodology to analyse three-dimensional microcrack distributions in overloaded cortical bone. Such information could improve our understanding of bone microdamage and its impact on bone failure in relation to tissue age and disease.

Multiscale imaging of bone microdamage.

Bone is a structural and hierarchical composite that exhibits remarkable ability to sustain complex mechanical loading and resist fracture. Bone quality encompasses various attributes of bone matrix from the quality of its material components (type-I collagen, mineral and non-collagenous matrix proteins) and cancellous microarchitecture, to the nature and extent of bone microdamage. Microdamage, produced during loading, manifests in multiple forms across the scales of hierarchy in bone and functions to dissipate energy and avert fracture. Microdamage formation is a key determinant of bone quality, and through a range of biological and physical mechanisms, accumulates with age and disease. Accumulated microdamage in bone decreases bone strength and increases bone's propensity to fracture. Thus, a thorough assessment of microdamage, across the hierarchical levels of bone, is crucial to better understand bone quality and bone fracture. This review article details multiple imaging modalities that have been used to study and characterize microdamage; from bulk staining techniques originally developed by Harold Frost to assess linear microcracks, to atomic force microscopy, a modality that revealed mechanistic insights into the formation diffuse damage at the ultrastructural level in bone. New automated techniques using imaging modalities, such as microcomputed tomography are also presented for a comprehensive overview.

Tendon overload results in alterations in cell shape and increased markers of inflammation and matrix degradation.

Tendon injury is thought to involve both damage accumulation within the matrix and an accompanying cell response. While several studies have characterized cell and matrix response in chronically injured tendons, few have assessed the initial response of tendon to overload-induced damage. In this study, we assessed cell response to cyclic loading. Fascicle bundles from the equine superficial digital flexor tendon were exposed to cyclic loading in vitro, designed to mimic a bout of high-intensity exercise. Changes in cell morphology and protein-level alterations in markers of matrix inflammation and degradation were investigated. Loading resulted in matrix damage, which was accompanied by cells becoming rounder. The inflammatory markers cyclooxygenase-2 and interleukin-6 were increased in loaded samples, as were matrix metalloproteinase-13 and the collagen degradation marker C1,2C. These results indicate upregulation of inflammatory and degradative pathways in response to overload-induced in vitro, which may be initiated by alterations in cell strain environment because of localized matrix damage. This provides important information regarding the initiation of tendinopathy, suggesting that inflammation may play an important role in the initial cell response to tendon damage. Full understanding of the early tenocyte response to matrix damage is critical in order to develop effective treatments for tendinopathy.

Microstructural changes in cartilage and bone related to repetitive overloading in an equine athlete model.

The palmar aspect of the third metacarpal (MC3) condyle of equine athletes is known to be subjected to repetitive overloading that can lead to the accumulation of joint tissue damage, degeneration, and stress fractures, some of which result in catastrophic failure. However, there is still a need to understand at a detailed microstructural level how this damage progresses in the context of the wider joint tissue complex, i.e. the articular surface, the hyaline and calcified cartilage, and the subchondral bone. MC3 bones from non-fractured joints were obtained from the right forelimbs of 16 Thoroughbred racehorses varying in age between 3 and 8 years, with documented histories of active race training. Detailed microstructural analysis of two clinically important sites, the parasagittal grooves and the mid-condylar regions, identified extensive levels of microdamage in the calcified cartilage and subchondral bone concealed beneath outwardly intact hyaline cartilage. The study shows a progression in microdamage severity, commencing with mild hard-tissue microcracking in younger animals and escalating to severe subchondral bone collapse and lesion formation in the hyaline cartilage with increasing age and thus athletic activity. The presence of a clearly distinguishable fibrous tissue layer at the articular surface immediately above sites of severe subchondral collapse suggested a limited reparative response in the hyaline cartilage.

Zoledronate reduces loading-induced microdamage in cortical ulna of ovariectomized rats.

As a daily physiological mechanism in bone, microdamage accumulation dissipates energy and helps to prevent fractures. However, excessive damage accumulation might bring adverse effects to bone mechanical properties, which is especially problematic among the osteoporotic and osteopenic patients treated by bisphosphonates. Some pre-clinical studies in the literature applied forelimb loading models to produce well-controlled microdamage in cortical bone. Ovariectomized animals were also extensively studied to assimilate human conditions of estrogen-related bone loss. In the present study, we combined both experimental models to investigate microdamage accumulation in the context of osteopenia and zoledronate treatment. Three-month-old normal and ovariectomized rats treated by saline or zoledronate underwent controlled compressive loading on their right forelimb to create in vivo microdamage, which was then quantified by barium sulfate contrast-enhanced micro-CT imaging. Weekly in vivo micro-CT scans were taken to evaluate bone (re)modeling and to capture microstructural changes over time. After sacrifice, three-point-bending tests were performed to assess bone mechanical properties. Results show that the zoledronate treatment can reduce cortical microdamage accumulation in ovariectomized rats, which might be explained by the enhancement of several bone structural properties such as ultimate force, yield force, cortical bone area and volume. The rats showed increased bone formation volume and surface after the generation of microdamage, especially for the normal and the ovariectomized groups. Woven bone formation was also observed in loaded ulnae, which was most significant in ovariectomized rats. Although all the rats showed strong correlations between periosteal bone formation and microdamage accumulation, the correlation levels were lower for the zoledronate-treated groups, potentially because of their lower levels of microdamage. The present study provides insights to further investigations of pharmaceutical treatments for osteoporosis and osteopenia. The same experimental concept can be applied in future studies on microdamage and drug testing.

Morphological human bone features and demography controlling damage accumulation and fracture: a finite element study.

Prediction of bone fracture risk is clinically challenging. Computational modeling plays a vital role in understanding bone structure and diagnosing bone diseases, leading to novel therapies. The research objectives were to demonstrate the anisotropic structure of the bone at the micro-level taking into consideration the density and subject demography, such as age, gender, body mass index (BMI), height, weight, and their roles in damage accumulation. Out of 438 developed 3D bone models at the micro-level, 46.12% were female. The age distribution ranged from 23 to 95 years. The research unfolds in two phases: micro-morphological features examination and stress distribution investigation. Models were developed using Mimics 22.0 and SolidWorks. The anisotropic material properties were defined before importing into Ansys for simulation. Computational simulations further uncovered variations in maximum von-Misses stress, highlighting that young Black males experienced the highest stress at 127.852 ± 10.035 MPa, while elderly Caucasian females exhibited the least stress at 97.224 ± 14.504 MPa. Furthermore, age-related variations in stress levels for both normal and osteoporotic bone micro models were elucidated, emphasizing the intricate interplay of demographic factors in bone biomechanics. Additionally, a prediction equation for bone density incorporating demographic variables was proposed, offering a personalized modeling approach. In general, this study, which carefully examines the complexities of how bones behave at the micro-level, emphasizes the need for an enhanced approach in orthopedics. We suggest taking individual characteristics into account to make therapeutic interventions more precise and effective.