Correction to: Compressive loading of the murine tibia reveals site-specific micro-scale differences in adaptation and maturation rates of bone.

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Compressive loading of the murine tibia reveals site-specific micro-scale differences in adaptation and maturation rates of bone.

Loading increases bone mass and strength in a site-specific manner; however, possible effects of loading on bone matrix composition have not been evaluated. Site-specific structural and material properties of mouse bone were analyzed on the macro- and micro/molecular scale in the presence and absence of axial loading. The response of bone to load is heterogeneous, adapting at molecular, micro-, and macro-levels. INTRODUCTION: Osteoporosis is a degenerative disease resulting in reduced bone mineral density, structure, and strength. The overall aim was to explore the hypothesis that changes in loading environment result in site-specific adaptations at molecular/micro- and macro-scale in mouse bone. METHODS: Right tibiae of adult mice were subjected to well-defined cyclic axial loading for 2 weeks; left tibiae were used as physiologically loaded controls. The bones were analyzed with µCT (structure), reference point indentation (material properties), Raman spectroscopy (chemical), and small-angle X-ray scattering (mineral crystallization and structure). RESULTS: The cranial and caudal sites of tibiae are structurally and biochemically different within control bones. In response to loading, cranial and caudal sites increase in cortical thickness with reduced mineralization (-14 and -3%, p < 0.01, respectively) and crystallinity (-1.4 and -0.3%, p < 0.05, respectively). Along the length of the loaded bones, collagen content becomes more heterogeneous on the caudal site and the mineral/collagen increases distally at both sites. CONCLUSION: Bone structure and composition are heterogeneous, finely tuned, adaptive, and site-specifically responsive at the micro-scale to maintain optimal function. Manipulation of this heterogeneity may affect bone strength, relative to specific applied loads.

Fast plasma sintering delivers functional graded materials components with macroporous structures and osseointegration properties.

We explored the osseointegration potential of two macroporous titanium surfaces obtained using fast plasma sintering (FPS): Ti macroporous structures with 400-600 µmØ pores (TiMac400) and 850-1000 µmØ pores (TiMac850). They were compared against two surfaces currently in clinical use: Ti-Growth® and air plasma spray (Ti-Y367). Each surface was tested, once placed over a Ti-alloy and once onto a CoCr bulk substrate. Implants were placed in medial femoral condyles in 24 sheep. Samples were explanted at four and eight weeks after surgery. Push-out loads were measured using a material-testing system. Bone contact and ingrowth were assessed by histomorphometry and SEM and EDX analyses. Histology showed early osseointegration for all the surfaces tested. At 8 weeks, TiMac400, TiMac850 and Ti-Growth® showed deep bone ingrowth and extended colonisation with newly formed bone. The mechanical push-out force was equal in all tested surfaces. Plasma spray surfaces showed greater bone-implant contact and higher level of pores colonisation with new bone than FPS produced surfaces. However, the void pore area in FPS specimens was significantly higher, yet the FPS porous surfaces allowed a deeper osseointegration of bone to implant. FPS manufactured specimens showed similar osseointegration potential to the plasma spray surfaces for orthopaedic implants. FPS is a useful technology for manufacturing macroporous titanium surfaces. Furthermore, its capability to combine two implantable materials, using bulk CoCr with macroporous titanium surfaces, could be of interest as it enables designers to conceive and manufacture innovative components. FPS delivers functional graded materials components with macroporous structures optimised for osseointegration.

Ageing does not result in a decline in cell synthetic activity in an injury prone tendon.

Advancing age is a well-known risk factor for tendon disease. Energy-storing tendons [e.g., human Achilles, equine superficial digital flexor tendon (SDFT)] are particularly vulnerable and it is thought that injury occurs following an accumulation of micro-damage in the extracellular matrix (ECM). Several authors suggest that age-related micro-damage accumulates due to a failure of the aging cell population to maintain the ECM or an imbalance between anabolic and catabolic pathways. We hypothesized that ageing results in a decreased ability of tendon cells to synthesize matrix components and matrix-degrading enzymes, resulting in a reduced turnover of the ECM and a decreased ability to repair micro-damage. The SDFT was collected from horses aged 3-30 years with no signs of tendon injury. Cell synthetic and degradative ability was assessed at the mRNA and protein levels. Telomere length was measured as an additional marker of cell ageing. There was no decrease in cellularity or relative telomere length with increasing age, and no decline in mRNA or protein levels for matrix proteins or degradative enzymes. The results suggest that the mechanism for age-related tendon deterioration is not due to reduced cellularity or a loss of synthetic functionality and that alternative mechanisms should be considered.

A biodegradable antibiotic-impregnated scaffold to prevent osteomyelitis in a contaminated in vivo bone defect model.

Open fractures are at risk of serious infection and, if infected, require several surgical interventions and courses of systemic antibiotics. We investigated a new injectable formulation that simultaneously hardens in vivo to form a porous scaffold for bone repair and delivers antibiotics at high concentrations to the local site of infection. Duration of antimicrobial activity against Staphylococcus aureus was determined using the serial plate transfer test. Ultimate compressive strength and porosity of the material was measured with and without antibiotics. The material was evaluated in vivo in an ovine medial femoral condyle defect model contaminated with S. aureus. Sheep were sacrificed at either 2 or 13 weeks and the defect and surrounding bone assessed using micro-computed tomography and histology. Antimicrobial activity in vitro persisted for 19-21 days. Sheep with antibiotic-free material and bacteria became infected, while those with antibiotic-containing material and bacteria did not. Similarly, new bone growth was seen in uninoculated animals with plain polymer, and in those with antibiotic polymer with bacteria, but not in sheep with plain polymer and bacteria. The antibiotic-impregnated scaffolds were effective in preventing S. aureus infections whilst supporting bone growth and repair. If translated into clinical practice, this approach might reduce the need for systemic antibiotics.

Cell-based therapies for tendon and ligament injuries.

Tendon and ligament injuries have proved difficult to treat effectively. Cell-based therapies offer the potential to harness the complex protein synthetic machinery of the cell to induce a regenerative response rather than fibrous scarring. This article reviews the current state of play with respect to the clinically used cell preparations for the treatment of tendon and ligaments overstrain injuries.

The relationship between in vivo limb and in vitro tendon mechanics after injury: a potential novel clinical tool for monitoring tendon repair.

REASONS FOR PERFORMING THE STUDY: Highly prevalent superficial digital flexor tendon (SDFT) injury results in compromised tendon function through fibrosis and high frequency of re-injury due to altered biomechanical function. This study investigated the consequences of SDF tendinopathy on limb mechanics in relation to the mechanical properties of injured tendon. OBJECTIVES: To develop and validate a noninvasive in vivo assessment of tendon mechanics to investigate the effect of recent SDFT injury on limb stiffness index, providing an objective method to assess quality of healing. HYPOTHESES: Limb stiffness index would reduce as a consequence of SDFT injury and progressively increase during tendon healing and correlate with in vitro mechanical properties of the respective SDFTs. METHODS: Kinematic analysis was performed at walk in 10 horses that had sustained career-ending SDFT injury. Stiffness index was derived from limb force recorded via a series of force plates and measurement of change in metacarpophalangeal joint angle using 3D motion analysis software. Horses were subjected to euthanasia 7 months after injury, the SDFTs removed and subjected to nondestructive in vitro mechanical testing. RESULTS: Limb stiffness index was reduced following SDFT injury in comparison with the contralateral limb and increased during the convalescent period, approximating that of the contralateral limb by 7 months post injury. There was a significant positive correlation between in vivo limb stiffness index and in vitro SDFT stiffness. CLINICAL RELEVANCE: The ability to assess and monitor SDFT mechanical competence through limb stiffness measurement techniques in horses recovering from SDFT injury and the possibility of corroborating this with functional tendon healing may permit a more objective and accurate assessment of optimal tendon repair in the horse. This technique may be a useful method for assessing the efficacy of treatment regimens for tendinopathy and could be utilised to predict time to safe return to performance or re-injury.

Optimisation of bone marrow aspiration from the equine sternum for the safe recovery of mesenchymal stem cells.

REASONS FOR PERFORMING STUDY: Mesenchymal stem cell (MSC) therapy for orthopaedic disease is being used with increasing frequency; there is a need to define a safe, reliable and effective technique for the recovery of MSCs from the sternum of the horse. OBJECTIVES: To describe an optimised safe technique for obtaining bone marrow-derived MSCs from the sternum of the Thoroughbred horse. METHODS: The anatomical relationship of the sternum with the heart and internal anatomy was demonstrated in cadavers. Sternal anatomy was evaluated ultrasonographically and after midline sectioning. Sternebrae were examined histologically after aspiration to determine the effect of needle insertion. The quality of the aspirate was evaluated as the number of colony-forming units from sequential and separately aspirated 5 ml aliquots and assessed for their multipotency using trilineage differentiation. RESULTS: The optimal safe location for the needle was the 5th sternebra because it had a safe dorsoventral thickness and was cranial to the apex of the heart. This sternebra could be reliably identified ultrasonographically. Aspirates could also be obtained from the 4th and 6th sternebrae, although the former is between the front limbs and the latter closer to the heart. Minimal disruption of the internal bony architecture was seen after needle insertion through the thin outer cortex and the first 5 ml aliquot contained the greatest number of colony-forming units of mesenchymal stem cells with trilineage capabilities. CONCLUSIONS: Accurate placement of a Jamshidi needle into the medullary cavity of the 4th-6th individual sternebrae is facilitated by the use of ultrasonography and enables aspiration of bone marrow reliably with minimal damage to the sternum and risk to the horse. POTENTIAL CLINICAL RELEVANCE: Sternal marrow aspiration as described is a safe and reliable technique to obtain MSCs for orthopaedic cell-based therapies.

A novel closed-loop electromechanical stimulator to enhance osseointegration with immediate loading of dental implant restorations.

The degree of osseomechanical integration of dental implants is acutely sensitive to their mechanical environment. Bone, both as a tissue and structure, adapts its mass and architecture in response to loading conditions. Therefore, application of predefined controlled loads may be considered as a treatment option to promote early maturation of bone/implant interface prior to or in conjunction with crown/prosthesis attachment. Although many studies have established that the magnitude, rate of the applied strain, and frequency have significant effects on the osteogenic response, the actual specific relationships between strain parameters and frequency have not yet been fully defined. The purpose of this study was to develop a stimulator to apply defined mechanical stimuli to individual dental implants in vivo immediately after implantation, exploring the hypothesis that immediate controlled loading could enhance implant integration. An electromechanical device was developed, based on load values obtained using a two-dimensional finite element analysis of the bone/implant interface generating 1000 to 4000 pe and operated at 30 and 3 Hz respectively. The device was then tested in a cadaveric pig mandible, and periosteal bone surface strains were recorded for potential future comparison with a three-dimensional finite element model to determine loading regimens to optimize interface strains and iterate the device for clinical use.

Mechanical properties of the equine superficial digital flexor tendon relate to specific collagen cross-link levels.

REASONS FOR PERFORMING STUDY: Damage to the flexor tendons, particularly the superficial digital flexor tendon (SDFT), is one of the most common musculoskeletal injuries sustained by horses competing in all disciplines. Our previous work has shown that SDFTs from different individuals show a wide variation in mechanical strengths; this is important clinically as it may relate to predisposition to injury. The high mechanical strength of tendon relies on the correct orientation of collagen molecules within fibrils and stabilisation by the formation of chemical cross-links between collagen molecules. It is not known whether the variation in SDFT mechanical properties between individuals relates to differences in collagen cross-link levels. HYPOTHESIS: Enzyme-derived, intermolecular cross-linking of tendon collagen correlates with mechanical properties of the SDFT. METHODS: SDFTs were collected from 38 horses and mechanically tested to failure. Structural and material properties were calculated from the load/deformation plot and cross-sectional area for each tendon. Following mechanical testing, pyrrolic cross-link levels were measured using a spectrophotometric assay for Ehrlich's reactivity and pyridinoline levels were quantified by HPLC. Cross-link levels were correlated with mechanical properties and statistical significance tested using a Pearson's correlation test. RESULTS: Pyrrole cross-link levels showed a significant positive correlation with ultimate stress (P = 0.004), yield stress (P = 0.003) and elastic modulus (P = 0.018) of the tendons, despite being a minor cross-link in these tendons. There was no significant correlation of mechanical properties with either hydroxylysyl- or lysyl-pyridinoline levels. CONCLUSIONS: Given the low absolute levels of pyrrole, we suggest that the correlation with high mechanical strength is through an indirect mechanism. Understanding the nature of the relationships between pyrrole cross-links, other matrix characteristics and tendon material properties may allow development of strategies to identify horses at risk from tendon injury and be of value in informing training practices.

The relationship between physical activity and leg health in the broiler chicken.

1. The relationship between the physical activity and leg health of broiler chickens was assessed on a semi-commercial scale. 2. Three batches of birds (2128 per batch) were raised under two lighting regimes during the photoperiod; either a step-wise change of light intensity alternating between an illuminance of 200 and 10 lx or a constant illuminance of 10 lx. The activity of focal individuals (24 per batch) was observed at 2, 4 and 6 weeks of age, and leg health assessed weekly, based on gait score, the prevalence of burns on the hock and foot pad, and angulation and rotation of the leg at the intertarsal joint. Cortical bone density and thickness and area moments of inertia of the mid-physis tibiotarsus were measured post mortem at 6 weeks of age. 3. The step-wise change in light intensity did not affect overall performance, activity or leg health. 4. An individual bird's activity did not affect its gait score, the prevalence of hock burn or foot pad burn, cortical density or thickness or shape of the tibiotarsus. Sex of the bird was the only factor to affect significantly the area moment of inertia in the horizontal and vertical planes of the tibiotarsus, with females showing a lower moment of inertia for both. No variable had a significant effect on cortical density or thickness. Mean cortical density was low across all birds and may indicate that, when allowed to move freely as much or as little as they choose, broiler chickens do not exercise enough or do not perform the higher impact activities required to affect bone quality. 5. These findings imply that the activity of broiler chickens raised on a semi-commercial scale is unaffected by step-wise changes in light intensity and that other husbandry measures are needed to raise activity and hence improve leg health.

Maturational alterations in gap junction expression and associated collagen synthesis in response to tendon function.

Energy-storing tendons including the equine superficial digital flexor tendon (SDFT) contribute to energetic efficiency of locomotion at high-speed gaits, but consequently operate close to their physiological strain limits. Significant evidence of exercise-induced microdamage has been found in the SDFT which appears not to exhibit functional adaptation; the degenerative changes have not been repaired by the tendon fibroblasts (tenocytes), and are proposed to accumulate and predispose the tendon to rupture during normal athletic activity. The anatomically opposing common digital extensor tendon (CDET) functions only to position the digit, experiencing significantly lower levels of strain and is rarely damaged by exercise. A number of studies have indicated that tenocytes in the adult SDFT are less active in collagen synthesis and turnover than those in the immature SDFT or the CDET. Gap junction intercellular communication (GJIC) is known to be necessary for strain-induced collagen synthesis by tenocytes. We postulate therefore that expression of GJ proteins connexin 43 and 32 (Cx43; Cx32), GJIC and associated collagen expression levels are high in the SDFT and CDET of immature horses, when the SDFT in particular grows significantly in cross-sectional area, but reduce significantly during maturation in the energy-storing tendon only. The hypothesis was tested using tissue from the SDFT and CDET of foetuses, foals, and young adult Thoroughbred horses. Cellularity and the total area of both Cx43 and Cx32 plaques/mm(2) of tissue reduced significantly with maturation in each tendon. However, the total Cx43 plaque area per tenocyte significantly increased in the adult CDET. Evidence of recent collagen synthesis in the form of levels of neutral salt-soluble collagen, and collagen type I mRNA was significantly less in the adult compared with the immature SDFT; procollagen type I amino-propeptide (PINP) and procollagen type III amino-propeptide (PIIINP) levels per mm(2) of tissue and PINP expression per tenocyte also decreased with maturation in the SDFT. In the CDET PINP and PIIINP expression per tenocyte increased in the adult, and exceeded those in the adult SDFT. The level of PINP per mm(2) was greater in the adult CDET than in the SDFT despite the higher cellularity of the latter tendon. In the adult SDFT, levels of PIIINP were greater than those of PINP, suggesting relatively greater synthesis of a weaker form of collagen previously associated with microdamage. Tenocytes in monolayers showed differences in Cx43 and Cx32 expression compared with those in tissue, however there were age- and tendon-specific phenotypic differences, with a longer time for 50% recovery of fluorescence after photobleaching in adult SDFT cells compared with those from the CDET and immature SDFT. As cellularity reduces following growth in the SDFT, a failure of the remaining tenocytes to show a compensatory increase in GJ expression and collagen synthesis may explain why cell populations are not able to respond to exercise and to repair microdamage in some adult athletes. Enhancing GJIC in mature energy-storing tendons could provide a strategy to increase the cellular synthetic and reparative capacity.

The influence of the mechanical environment on remodelling of the patellar tendon.

An understanding of the remodelling of tendon is crucial for the development of scientific methods of treatment and rehabilitation. This study tested the hypothesis that tendon adapts structurally in response to changes in functional loading. A novel model allowed manipulation of the mechanical environment of the patellar tendon in the presence of normal joint movement via the application of an adjustable external fixator mechanism between the patella and the tibia in sheep, while avoiding exposure of the patellar tendon itself. Stress shielding caused a significant reduction in the structural and material properties of stiffness (79%), ultimate load (69%), energy absorbed (61%), elastic modulus (76%) and ultimate stress (72%) of the tendon compared with controls. Compared with the material properties the structural properties exhibited better recovery after re-stressing with stiffness 97%, ultimate load 92%, energy absorbed 96%, elastic modulus 79% and ultimate stress 80%. The cross-sectional area of the re-stressed tendons was significantly greater than that of stress-shielded tendons. The remodelling phenomena exhibited in this study are consistent with a putative feedback mechanism under strain control. This study provides a basis from which to explore the interactions of tendon remodelling and mechanical environment.

The influence of exercise during growth on ultrasonographic parameters of the superficial digital flexor tendon of young Thoroughbred horses.

REASON FOR PERFORMING STUDY: Conditioning by early training may influence the composition of certain musculoskeletal tissues, but very few data exist on its effect during growth on tendon structure and function. OBJECTIVES: To investigate whether conditioning exercise in young foals would lead to any ultrasonographically detectable damage to the superficial digital flexor tendon or an increase in cross-sectional area (CSA). METHODS: Thirty-three Thoroughbred foals reared at pasture were allocated to 2 groups: control (PASTEX) allowed exercise freely at pasture; and CONDEX, also at pasture, began conditioning exercise from mean age 21 days over 1030 m on a purpose-built oval grass track, for 5 days/week until mean age 18 months. Foals were observed daily, and underwent orthopaedic examination monthly. Ultrasonographic images of the superficial digital flexor tendon (SDFT) at the mid-metacarpal level of both forelimbs were obtained in all foals at ages 5, 8, 12, 15 and 18 months. CSA was validated (r(2) = 0.89) by determining CSA from digital photographs of the transected SDFT surface from 12 of the horses necropsied at age 17.1 months. RESULTS: here was no clinical or ultrasonographic evidence of tendonopathy in either group and the greatest increase in mean CSA in both groups occurred between age 5 and 8 months. Across all age categories, there was no significant difference in mean CSA between the left and right limbs, or colts and fillies; there was a trend towards a larger CSA in the CONDEX group (P = 0.058). CONCLUSIONS: There was no conclusive evidence for a structural adaptive hypertrophy of the SDFT, probably because the regimen was insufficiently rigorous or because spontaneous pasture exercise may induce maximal development of energy storing tendons. POTENTIAL RELEVANCE: A moderate amount of early conditioning exercise against a background of constant exercise at pasture is not harmful to the development of the flexor tendons.

Effects of exercise on tenocyte cellularity and tenocyte nuclear morphology in immature and mature equine digital tendons.

REASON FOR PERFORMING STUDY: The injury-prone, energy-storing equine superficial digital flexor tendon (SDFT) of the mature performance horse has a limited ability to respond to exercise in contrast with the noninjury-prone, anatomically opposing common digital extensor tendon (CDET). Previous studies have indicated low levels of cellular activity in the mature SDFT, but in foal tendons the tenocytes may still have the ability to adapt positively to increased exercise. OBJECTIVES: To measure tenocyte densities and types in histological sections from the SDFT and CDET of horses from controlled long-term, short-term and foal exercise studies. METHODS: Specimens were collected from mid-metacarpal segments of the CDET and SDFT for each horse and processed for histology; central and peripheral regions of the SDFT cross-section were analysed separately (SDFTc, SDFTp). Tenocyte nuclei were counted in a total area of 1.59 mm(2) for each tendon region in each horse. Each nucleus was classified as type 1 (elongate and thin), type 2 (ovoid and plump) or type 3 (chondrocyte-like); type 1 cells are proposed to be less synthetically active than type 2 cells. RESULTS: No significant differences were noted between exercise and control groups in any of the studies, with the exception of an exercise-related reduction in the proportion of type 1 tenocytes for all tendons combined in the long-term study. There were tendon- and site-specific differences in tenocyte densities and proportions of type 1 and 2 cells in all 3 studies. CONCLUSIONS AND POTENTIAL RELEVANCE: There was no indication that exercise increased tenocyte density or proportions of the (theoretically) more active type 2 cells in immature horses (short-term and foal studies), perhaps because the training regimens did not achieve certain threshold strain levels. In the foal study these findings can still be interpreted positively as evidence that the training regimen did not induce subclinical damage.

Evaluation of a new strategy to modulate skeletal development in racehorses by imposing track-based exercise during growth: the effects on 2- and 3-year-old racing careers.

REASON FOR PERFORMING STUDY: No data exist on the effects of conditioning exercise at foal age on workload and subsequent clinical injury rate during their 2- and 3-year-old racing careers. OBJECTIVES: To investigate the effects of subjecting TB foals to conditioning exercise prior to the start of race training on: the workload required to reach a level of fitness sufficient to compete; and the prevalence of orthopaedic injury during the first 2 seasons of their racing careers. METHODS: Twenty 18-month-old TBs, 12 subjected to conditioning exercise at foal age (CONDEX) and 8 exercised spontaneously at pasture only (PASTEX) were trained and entered in competitive events. Workload was quantified using the cumulative workload index (the product of average velocity and distance at a specific gait) and the animals were monitored clinically and radiographically for signs of musculoskeletal disorders. RESULTS: Workload to reach the desired fitness level was similar for CONDEX and PASTEX. CONDEX performed more prerace training sessions as 2-year-olds (P<0.05). The incidence of orthopaedic injuries was low in both groups and there were no differences in the occurrence of orthopaedic ailments. PASTEX animals tended to show signs of musculoskeletal disorders earlier than CONDEX animals. This time difference was significant for metacarpophalangeal joint pain on flexion, reduced carpal flexion and hindlimb lameness (P<0.05). CONCLUSIONS: Subjecting TB foals to conditioning exercise early in life does not have adverse effects on racing careers at ages 2 and 3 years, and does not influence the workload needed to reach a fitness level that is sufficient for racing. POTENTIAL RELEVANCE: The lack of negative effects and the indications of some positive effects of early conditioning exercise in the Thoroughbred encourage further large-scale comparative studies.

Evaluation of a new strategy to modulate skeletal development in Thoroughbred performance horses by imposing track-based exercise during growth.

REASON FOR PERFORMING STUDY: No data exist on the intensity of exercise required or on possible harmful effects of increasing exercise in foals over the natural level when free at pasture. OBJECTIVES: To investigate whether an increase in workload over free pasture exercise in the period from directly after birth to the start of training is tolerated by Thoroughbred (TB) foals without increasing injury rate or producing other undesired side effects. METHODS: Thirty-three TB foals were allocated to one of 2 exercise groups directly after birth. One group (PASTEX) was raised on pasture and the other (CONDEX) kept under identical circumstances, but was additionally subjected to an exercise protocol of gradually increasing intensity. Foals were monitored periodically and scored for the presence of clinical signs related to the musculoskeletal system (joint effusion, pain at flexion, occurrence of physeal swelling), and radiographs taken at the end of the conditioning phase. Also, behavioural studies were performed to detect any changes in behaviour related to the exercise programme. Cortisol levels were measured in both groups, to assess the level of stress. RESULTS: Workload in the CONDEX group was significantly higher than in the PASTEX group (approximately 30%). Conditioning increased the likelihood for joint effusion in the antebrachiocarpal joint, but reduced tarsocrural effusion and physeal swelling at the lateral distal radius, the third metacarpal bone (medial aspect) and lateral and medial aspects of the third metatarsal bone. CONCLUSIONS: The 30% increase in workload did not affect the animals' welfare, effects of conditioning exercise on clinical musculoskeletal health were few and there were no adverse effects. POTENTIAL RELEVANCE: This study supports the feasibility of imposing early conditioning exercise in horses and is a benchmark for its effects on the development of equine musculoskeletal tissues.

Can exercise modulate the maturation of functionally different immature tendons in the horse?

Tendons can be considered in two functional groups, those contributing to energetics of locomotion and those acting solely to position the limb. The energy-storing tendons in both human and equine athletes have a high frequency of injury with similar pathophysiology. In previous studies, high-intensity exercise appears to induce a disruption of the matrix rather than functional adaptation in adults. Here we explore the hypothesis that the introduction of controlled exercise during growth would result in an adaptive response without deleterious effects. Young horses were given a controlled exercise program similar to that previously shown to induce matrix changes in energy-storing tendons of skeletally mature animals. The tendons were assessed in relation to mechanical properties, molecular composition, and morphology. Results showed a significant increase in cartilage oligomeric matrix protein (COMP) in the positional tendon but not in the energy-storing tendon. Other matrix properties and mechanical properties were not significantly changed. While the imposition of high-strain-rate exercise in immature horses failed to augment the development of the energy-storing tendon over and above that induced by normal pasture exercise, it did not induce deleterious changes, supporting an earlier introduction of athletic training in horses.

How does exercise intensity and type affect equine distal tarsal subchondral bone thickness?

Adaptation of osteochondral tissues is based on the strains experienced during exercise at each location within the joint. Different exercise intensities and types may induce particular site-specific strains, influencing osteochondral adaptation and potentially predisposing to injury. Our hypotheses were that patterns of equine distal tarsal subchondral bone (SCB) thickness relate to the type and intensity of exercise, and that high-intensity exercise leads to site-specific increases in thickness. SCB thickness was measured at defined dorsal and plantar locations on magnetic resonance images of cadaver tarsi collected from horses with a history of low [general purpose (n=20) and horse walker (n=6)] or high [elite competition (n=12), race training (n=15), and treadmill training (n=4)] exercise intensity. SCB thickness was compared between sites within each exercise group and between exercise groups. SCB thickness in elite competition and race training, but not treadmill training, was greater than low-intensity exercise. For general purpose horses, lateral SCB thickness was greater than medial throughout. Horse walker exercise led to relatively thicker lateral and medial SCB compared with the midline. Elite competition was associated with increased SCB thickness of the proximal small tarsal bones medially and the distal bones laterally. For race training and treadmill training, there were minimal differences between sites overall, although the lateral aspect was greater than medial, and medial greater than midline at a few sites for race training. In conclusion, different types of high-intensity exercise were associated with different patterns of SCB thickness across the joints from medial to lateral and proximal to distal, indicating that both exercise intensity and type of exercise affect the SCB response at any particular site within the equine distal tarsal joints.