High-intensity exercise induces structural, compositional and metabolic changes in cuboidal bones--findings from an equine athlete model

Review of the Mechanism of Action and Use of Bisphosphonates in Horses

Bisphosphonates are a group of drugs that can reduce bone resorption by incorporating into the crystal structure of exposed hydroxyapatite where they are taken up by osteoclasts. Bisphosphonates have several other mechanisms of action including reducing pain and inflammation and altering macrophage function. There are two types of bisphosphonates - nitrogenous and non-nitrogenous, the latter of which is used in horses. This article provides a literature-based review of the proposed mechanisms of action and therapeutic uses of bisphosphonates including a brief review of bone response to disease. A review of the literature available in horses including safety data and current rules and regulations is also provided.

Multibody Computer Model of the Entire Equine Forelimb Simulates Forces Causing Catastrophic Fractures of the Carpus during a Traditional Race

Simple Summary

Palios are traditional horseraces held in the main square of few Italian cities. Due to peculiar features of such circuits, adapted to the square architecture and thus characterized by tight curves and unconventional footing surface, horses involved are at particular risk of accidents. Prevention of catastrophic musculoskeletal injuries is a significant issue and matter of debate during these events. In particular, the negotiation of the curves in the city circuits is a significative concern. An experiment was set up to build a model of entire forelimb at the point of failure in the context of a turn comparable to that in a Palio circuit. The model was informed by live data and the output compared to post-mortem findings obtained from a horse that sustained a catastrophic fracture of the carpus during this competition. The objective of this study is to determine the magnitude and distribution of internal forces generated across the carpus under which the catastrophic injury has occurred and describe related post-mortem findings.

Abstract

A catastrophic fracture of the radial carpal bone experienced by a racehorse during a Palio race was analyzed. Computational modelling of the carpal joint at the point of failure informed by live data was generated using a multibody code for dynamics simulation. The circuit design in a turn, the speed of the animal and the surface characteristics were considered in the model. A macroscopic examination of the cartilage, micro-CT and histology were performed on the radio-carpal joint of the limb that sustained the fracture. The model predicted the points of contact forces generated at the level of the radio-carpal joint where the fracture occurred. Articular surfaces of the distal radius, together with the proximal articular surface of small carpal bones, exhibited diffuse wear lines, erosions of the articular cartilage and subchondral bone exposure. Even though the data in this study originated from a single fracture and further work will be required to validate this approach, this study highlights the potential correlation between elevated impact forces generated at the level of contact surfaces of the carpal joint during a turn and cartilage breakdown in the absence of pre-existing pathology. Computer modelling resulted in a useful tool to inversely calculate internal forces generated during specific conditions that cannot be reproduced in-vivo because of ethical concerns.

Comparing racing performance following arthroscopic surgery of metacarpophalangeal/metatarsophalangeal and carpal joints in Thoroughbred racehorses rehabilitated using conventional and underwater treadmill therapies

BACKGROUND

Rehabilitation of horses using underwater treadmill therapy has been shown to improve joint range of motion, joint mobility, stride length and proprioceptive parameters with experimental studies. However, studies investigating the prognosis and return to function following rehabilitation are lacking.

METHODS

A retrospective study of Thoroughbred racehorses treated with arthroscopic surgery for osteochondral fragments of the metacarpophalangeal (MCP) or metatarsophalangeal (MTP) joints or carpal joints undergoing conventional rehabilitation or underwater treadmill assisted rehabilitation at the same facility were included. The objective of the current study was to investigate if underwater treadmill assisted rehabilitation following arthroscopy in the Thoroughbred racehorse was positively associated with returning to racing, time to return to racing and postoperative racing performance including Beyer Speed Figures.

RESULTS

Surgery was performed on 165 horses on 174 surgical occasions; 70 (40.2 per cent) underwent underwater treadmill rehabilitation, with the remainder undergoing conventional rehabilitation. The time to return to racing was a median of 227 (IQR 185-281) days and 239 (IQR 205-303) days for underwater treadmill and conventional rehabilitation, respectively (P=0.16). Of the horses that raced presurgery, 83 per cent (58/70) of underwater treadmill rehabilitated horses and 61 per cent (63/104) of horses undergoing conventional rehabilitation returned to racing following surgery (P=0.02).

CONCLUSION

Underwater treadmill rehabilitation is superior in returning a Thoroughbred racehorse to racing following arthroscopic surgery of the carpus and/or MCP/MTP joints.

Fatigue behavior of subchondral bone under simulated physiological loads of equine athletic training

Fatigue-induced subchondral bone (SCB) injuries are prevalent among athletes due to the repetitive application of high magnitude loads on joints during intense physical training. Existing fatigue studies on bone utilize a standard fatigue test approach by applying loads of a constant magnitude and frequency even though physiological/realistic loading is a combination of various load magnitudes and frequencies. Metal materials in implant and aerospace applications have been studied for fatigue behavior under physiological or realistic loading, however, no such study has been conducted on biological materials like bones. In this study, we investigated fatigue behavior of SCB under the range of loads likely to occur during a fast-workout of an equine athlete in training. A loading protocol was developed by simulating physiological loads occurring during a fast-workout of a racehorse in training, which consisted of a sequence of compression-compression load cycles, including a warm-up (32, 54, 61 MPa) and cool-down (61, 54, 32 MPa) before and after the slow/fast/slow gallop phase of training, also referred to as a training loop. This loading protocol/training loop was applied at room temperature in load-control mode to cylindrical SCB specimens (n = 12) harvested from third metacarpal medial condyles (MCIII) of twelve thoroughbred racehorses and repeated until fatigue failure. The mean ± standard deviation for total time-to-failure (TTF) was 76,393 ± 64,243 s (equivalent to 18.3 ± 15.7 training workouts) for n = 12 specimens. We observed the highest relative energy loss (REL, hysteresis loss normalized to energy absorbed in a load cycle) under loads equivalent to gallop speeds and all specimens failed under these gallop loads. This demonstrates the importance of the gallop speeds in the development of SCB injury, consistent with observations made in live racehorses. Moreover, specimens with higher mean REL and lower mean stiffness during the first loop had a shorter fatigue life which further confirms the detrimental effect of high energy loss in SCB. Further studies are required to reconcile our results with fatigue injuries among equine athletes and understand the influence of different training programs on the fatigue behavior of subchondral bone.

Needle arthroscopy of the radiocarpal and middle carpal joints in standing sedated horses

OBJECTIVE

To develop a technique for standing diagnostic needle arthroscopy of the radiocarpal and middle carpal joints in standing sedated horses.

STUDY DESIGN

Experimental study.

ANIMALS

Six cadaveric forelimbs (phase 1) and six healthy horses (phase 2).

METHODS

In phase 1, six cadaveric forelimbs were used to assess needle arthroscopic evaluation of both joints. Six healthy horses were subsequently enrolled in phase 2 to validate the procedure in live animals. The joint was maintained in flexion with a custom-made splint and base.

RESULTS

In phase 1, needle arthroscopy allowed thorough evaluation of the dorsal and palmar recesses of both joints with traditional arthroscopic portals. In phase 2, joint evaluation was also thorough but only dorsal approaches were performed. All horses underwent radiocarpal joint arthroscopy, whereas the middle carpal joint was evaluated in only three of six horses because of limb movement. The technique was quickly performed and well tolerated by all horses. Complications included moderate movement, mild iatrogenic cartilage damage, and mild hemarthrosis.

CONCLUSION

Standing needle arthroscopy allowed thorough evaluation of the dorsal aspect of both joints, although only three of six middle carpal joints were assessed because of movement limitations.

CLINICAL SIGNIFICANCE

The proposed technique offers an alternative diagnostic tool for radiographically silent intra-articular lesions of the carpus while initially avoiding the cost and risks associated with general anesthesia. Arthroscopy of a single joint is recommended to minimize risks associated with movement during the procedure.

Radiographic and arthroscopic features of third carpal bone slab fractures and their impact on racing performance following arthroscopic repair in a population of racing Thoroughbreds in the UK

BACKGROUND

Slab fractures of the third carpal bone (C3) are a common injury of Thoroughbred racehorses. Results of arthroscopically guided repair have not been reported since the initial description of the technique in 1986. Additionally, fracture details and racing outcomes in a population of Thoroughbreds racing under UK jurisdiction have not previously been described.

OBJECTIVES

To report the frequency distribution of C3 slab fractures and to determine the impact on racing performance following arthroscopically guided repair in a population of Thoroughbred racehorses.

STUDY DESIGN

Retrospective case series.

METHODS

Case records of Thoroughbred racehorses undergoing arthroscopically guided repair of C3 slab fractures at Newmarket Equine Hospital between 2006 and 2015 were retrieved. Radiographs and arthroscopic studies were reviewed. The effect of demography and fracture morphology on racing outcome was evaluated.

RESULTS

C3 slab fractures occurred most commonly through the radial facet in a frontal plane (45/71 63.4%). Comminution was identified during arthroscopy in 42/71 (59.2%) fractures and occurred most frequently at the palmar margin of the fracture. Forty-one out of 65 horses (63.1%) raced at least once post-operatively. Females were less likely to return to racing compared to males (P<0.001). Horses that had raced before injury were more likely (OR 4.4, 95% CI 1.4-13.5, P = 0.01) to race after injury compared to horses that were unraced at the time of injury. After injury horses had a small but significant reduction in racing performance.

MAIN LIMITATIONS

The series is a preselected population of Thoroughbred racehorses which referring veterinary surgeons considered potential candidates for surgical repair.

CONCLUSION

Fracture configurations can be identified radiographically but is not a reliable predictor of comminution or other intra-articular lesions. Arthroscopy not only directs repair but also identifies and facilitates management of concurrent lesions. The results reported should assist in formulating appropriate prognoses for Thoroughbred horses racing in the UK.

A 10-year study of arthroscopic surgery in racing Thoroughbreds and Quarter Horses with osteochondral fragmentation of the carpus

BACKGROUND

Osteochondral fragmentation of the carpus is a common cause of lameness in racehorses. Prognosis following arthroscopic removal of the fragments was reported in 1987, but little is known of recent success rates.

OBJECTIVE

To identify associations between the severity and location of osteochondral fragments in the carpus, and to describe the racing performance of horses pre- and post-surgery in Thoroughbreds and Quarter Horses. To identify factors associated with a horse racing post-surgery.

STUDY DESIGN

Retrospective study of clinical records (2006-2016).

METHODS

Surgical and racing records for racehorses undergoing arthroscopic surgery of the carpus were collated during the 10-year study period. Signalment, location of osteochondral fragmentation and grade of defect left after removal and debridement identified and racing performance pre- and post-surgery were described, stratified by breed. Logistic regression analysis was used to identify factors associated with unsuccessful return to racing.

RESULTS

In total, 828 horses (n = 416 Quarter Horses; n = 412 Thoroughbreds) underwent 880 carpal arthroscopies after fragments were found on radiography. Sixty-five percent (n = 289) and 27% (n = 118) of the lesions were bilateral in Quarter Horses and Thoroughbreds respectively (P<0.001). In both breeds, the most commonly affected bone was the dorsodistal radial carpal bone (n = 320/659; 48.6%). Overall, 82% (n = 686; n = 358 Quarter Horses, n = 328 Thoroughbreds) of horses raced post-surgery, with 69.5% (n = 476; n = 228 Quarter Horses, n = 248 Thoroughbreds) racing at the same or a higher level of competition. Factors associated with horses not returning to racing post-surgery were increasing horse age, female horses, and a lesion grade of 4, while racing pre-surgery was protective.

MAIN LIMITATIONS

This study does not include a control population for comparison.

CONCLUSIONS

There were significant differences between the location and severity of lesions in Quarter Horses, when compared to Thoroughbreds. The majority of horses return to racing following surgery, although performance was influenced by lesion severity. The Summary is available in Portuguese - see Supporting information.

A diagnostic pathologist's guide to carpal disease in racehorses

As a pathologist, postmortem examination of the equine carpus can be daunting. The anatomy is complex and oftentimes, small or subtle lesions have significant impact on lameness and secondary lesions such as catastrophic musculoskeletal fractures and other injuries. In performance horses, particularly racehorses, the carpus is a common site of injury and source of lameness. Given the predisposition of racehorses to developing carpal disease, familiarity with clinically relevant anatomy and common developmental, degenerative, traumatic, and inflammatory processes are imperative for thorough postmortem examination. Our aim is (1) to provide a concise summary of clinically relevant anatomy and function that serves as a guide for postmortem evaluation of the equine carpus, and (2) to review common carpal injuries and diseases in actively training, racing, or retired racehorses, including developmental lesions (incomplete ossification, osteochondromata), infectious and inflammatory lesions (septic arthritis and tenosynovitis), and degenerative and traumatic lesions (degenerative and traumatic osteoarthritis, osteochondral fragmentation, and polyostotic catastrophic "breakdown" fractures). Representative gross and histologic images are presented along with corresponding antemortem and postmortem diagnostic images, and a review of current scientific literature pertaining to the pathogenesis of these equine carpal lesions.

Does subchondral bone of the equine proximal phalanx adapt to race training?

Sagittal fractures of the first phalanx are a common, potentially catastrophic injury in racehorses. These fractures are often linked to an acute, one time, biomechanical event; however, recent evidence implies that chronic exposure to stress can lead to the accumulation of bony changes that affect the structural integrity of the bone and increase the likelihood of fracture. The aim of the study was to compare variations of two common metrics of bone adaptation - subchondral bone density and thickness across the proximal articular surface of the first phalanx in Thoroughbred horses that (1) raced but never experienced a first phalanx fracture (Raced Control); (2) raced and had experienced fracture of the contralateral first phalanx (Contralateral to Fracture); (3) had never raced or experienced a first phalanx fracture (Unraced Control). A total of 22 first phalangeal bones were sampled post-mortem and imaged using micro-computed tomography calibrated for mineral density measures. Measurements of volumetric subchondral bone mineral density and thickness were taken from images at five sites from medial to lateral, in three coronal planes (25, 50 and 75% dorsal-palmar). At each of the 15 sites, measurements were repeated and averaged across 10 adjacent micro-computed tomography slices of bone, spanning 0.75 mm. The magnitude and variance of these measurements were compared between sites and between cohorts with non-parametric statistical tests. Across the proximal osteochondral surface of the first phalanx, the pattern of subchondral bone volumetric bone mineral density and thickness varied with each coronal section studied. The subchondral bone thickness was greater for the central and dorsal coronal sections, compared with the palmar section. For the race-fit groups (Raced Control and Contralateral to Fracture), the highest volumetric bone mineral density was in the central sagittal groove. The volumetric bone mineral density was significantly greater in the sagittal groove in the central coronal section in the raced than the unraced group. The Contralateral to Fracture group demonstrated significantly greater variance of volumetric bone mineral density compared with the Raced Control and Unraced Control (P < 0.0001), with no difference in variance noted between the Raced Control and Unraced Control groups. There was a small (R rank = 0.3) but significant correlation between subchondral bone volumetric bone mineral density and thickness in the Contralateral to Fracture group (P = 0.005). The findings demonstrate that differences exist in subchondral bone volumetric bone mineral density and thickness across the proximal osteochondral surface of the equine first phalanx in horses with different training histories. The findings also demonstrate that the subchondral bone of the sagittal groove of the equine first phalanx adapts to race-training in the race-fit groups (Raced Control and Contralateral to Fracture) with an increase in volumetric bone mineral density relative to unraced controls. Within the race-trained groups, the Contralateral to Fracture bones had a greater variance of volumetric bone mineral density, suggesting that stress-induced bone adaptation had become more erratic, potentially contributing to the aetiology of sagittal fractures of the first phalanx in the Thoroughbred racehorse.

Osteoclasts are recruited to the subchondral bone in naturally occurring post-traumatic equine carpal osteoarthritis and may contribute to cartilage degradation

The role of osteoclasts in osteochondral degeneration in osteoarthritis (OA) has rarely been investigated in spontaneous disease or animal models of OA.

OBJECTIVE

The objectives of the current study were to investigate osteoclast density and location in post-traumatic OA (PTOA) and control specimens from racehorses.

METHOD

Cores were harvested from a site in the equine third carpal bone, that undergoes repetitive, high intensity loading. Histological and immunohistochemical (Cathepsin K and Receptor-activator of Nuclear Factor kappa-β ligand (RANKL)) stained sections were scored (global and subregional) and the osteoclast density calculated. The cartilage histological scores were compared with osteoclast density and RANKL scores.

RESULTS

There was a greater density of osteoclasts in PTOA samples and they were preferentially located in the subchondral bone plate. RANKL scores positively correlated to the scores of cartilage degeneration and the osteoclast density. The relationship between hyaline articular cartilage RANKL score and osteoclast density was stronger than that of the subchondral bone RANKL score suggesting that cartilage RANKL may have a role in recruiting osteoclasts. The RANKL score in the articular calcified cartilage correlated with the number of microcracks also suggesting that osteoclasts recruited by RANKL may contribute to calcified cartilage degeneration in PTOA.

CONCLUSION

Our results support the hypothesis that osteoclasts are recruited during the progression of spontaneous equine carpal PTOA by cartilage RANKL, contributing to calcified cartilage microcracks and focal subchondral bone loss.

Influence of Exercise and Intra-articular Site on Canals in Articular Calcified Cartilage of Equine Third Carpal Bones

The third carpal bone (C3) responds to exercise by adaptive modeling of bone and articular calcified cartilage along the dorsal load path. Canals penetrating articular calcified cartilage, thought to contain vascular tissue, are reported in numerous species. Their significance remains unclear. Our objective was to determine if the number of canals was significantly different in strenuously exercised and control young horses and in a site of intermittent high loading compared to sites sustaining lower habitual loads. Volumetric bone mineral density in the radial facet of C3 of strenuously exercised and gently exercised (control) 19-month-old thoroughbred horses ( n = 6/group) was determined by peripheral quantitative computed tomography. The hyaline cartilage was corroded to expose the surface of articular calcified cartilage. The number of canals penetrating the articular calcified cartilage surface in en face scanning electron microscopy images was compared in 4 regions. Volumetric bone mineral density of C3 was significantly greater ( P = .004) in strenuously exercised horses. There were 2 morphologically distinct groups of canals and significantly fewer ( P = .006) large canals in the dorsal than in the palmar aspect of C3 in control but not in exercised horses. Roughly circular depressions in the articular calcified cartilage surface around apparently forming canals were visible in some samples and have not been previously described in the literature. The canals may be evidence of chondroclastic activity reaching the interface of hyaline and calcified cartilage. Further work is needed to elucidate the relationships between presence of canals and the responses to exercise and to joint disease.

Skeletal maturation substantially affects elastic tissue properties in the endosteal and periosteal regions of loaded mice tibiae

Although it is well known that the bone adapts to changes in the mechanical environment by forming and resorbing the bone matrix, little is known about the influence of mechanical loading on tissue material properties of the pre-existing and newly formed bone. In this study, we analyzed the newly formed and pre-existing tissue after two weeks of controlled in vivo axial compressive loading in tibia of young (10 week-old) and adult (26 week-old) female mice and compared to the control contralateral limb, by means of scanning acoustic microscopy. Additionally, we used quantitative backscattered electron imaging to determine the bone mineral density distribution within the newly formed and pre-existing bone of young mice. No significant differences were found in tissue stiffness or mineral density in the pre-existing bone tissue as a result of external loading. In the endosteal region, 10 and 26 week loaded animals showed a 9% reduction in bone tissue stiffness compared to control animals. An increase of 200% in the mineral apposition rate in this region was observed in both age groups. In the periosteal region, the reduction in bone tissue stiffness and the increase in bone mineral apposition rate as a result of loading were two times higher in the 10 compared to the 26 week old animals. These data suggest that, during growth and skeletal maturation, the response of bone to mechanical loading is a deposition of new bone matrix, where the tissue amount but not its mineral or elastic properties are influenced by animal age.

Musculoskeletal Pathology

The current understanding of pathology as it relates to common diseases of the equine musculoskeletal system is reviewed. Conditions are organized under the fundamental categories of developmental, exercise-induced, infectious, and miscellaneous pathology. The overview of developmental pathology incorporates the new classification system of juvenile osteochondral conditions. Discussion of exercise-induced pathology emphasizes increased understanding of the contribution of cumulative microdamage caused by repetitive cyclic loading. Miscellaneous musculoskeletal pathology focuses on laminitis, which current knowledge indicates should be regarded as a clinical syndrome with a variety of possible distinct mechanisms of structural failure that are outlined in this overview.

Effect of in vivo loading on bone composition varies with animal age

Loading can increase bone mass and size and this response is reduced with aging. It is unclear, however how loading affects bone mineral and matrix properties. Fourier Transform Infrared Imaging and high resolution synchrotron scanning small angle X-ray scattering were used to study how bone’s microscale and nanoscale compositional properties were altered in the tibial midshaft of young, adult, and elderly female C57Bl/6J mice after two weeks of controlled in vivo compressive loading in comparison to physiological loading. The effect of controlled loading on bone composition varied with animal age, since it predominantly influenced the bone composition of elderly mice. Interestingly, controlled loading led to enhanced collagen maturity in elderly mice. In addition, although the rate of bone formation was increased by controlled loading based on histomorphometry, the newly formed tissue had similar material quality to new bone tissue formed during physiological loading. Similar to previous studies, our data showed that bone composition was animal and tissue age dependent during physiological loading. The findings that the new tissue formed in response to controlled loading and physiological loading had similar bone composition and that controlled loading enhanced bone composition in elderly mice further supports the use of physical activity as a noninvasive treatment to enhance bone quality as well as maintain bone mass in individuals suffering from age-related bone loss.

Relationship between cartilage and subchondral bone lesions in repetitive impact trauma-induced equine osteoarthritis

OBJECTIVE

To correlate degenerative changes in cartilage and subchondral bone in the third carpal bone (C3) of Standardbred racehorses with naturally occurring repetitive trauma-induced osteoarthritis.

DESIGN

Fifteen C3, collected from Standardbred horses postmortem, were assessed for cartilage lesions by visual inspection and divided into Control (CO), Early Osteoarthritis (EOA) and Advanced Osteoarthritis (AOA) groups. Two osteochondral cores were harvested from corresponding dorsal sites on each bone and scanned with a micro-computed tomography (CT) instrument. 2D images were assembled into 3D reconstructions that were used to quantify architectural parameters from selected regions of interest, including bone mineral density and bone volume fraction. 2D images, illustrating the most severe lesion per core, were scored for architectural appearance by blinded observers. Thin sections of paraffin-embedded decalcified cores stained with Safranin O-Fast Green, matched to the micro-CT images, were scored using a modified Mankin scoring system.

RESULTS

Subchondral bone pits with deep focal areas of porosity were seen more frequently in AOA than EOA but never in CO. Articular cartilage damage was seen in association with a reduction in bone mineral and loss of bone tissue. Histological analyses revealed significant numbers of microcracks in the calcified cartilage of EOA and AOA groups and a progressive increase in the score compared with CO bones.

CONCLUSION

The data reveal corresponding, progressive degenerative changes in articular cartilage and subchondral bone, including striking focal resorptive lesions, in the third carpal bone of racehorses subjected to repetitive, high impact trauma.

Innovative approach to investigating the microstructure of calcified tissues using specular reflectance Fourier transform-infrared microspectroscopy and discriminant analysis

Although bone fracture has become a serious global health issue, current clinical assessments of fracture risk based on bone mineral density are unable to accurately predict whether an individual is likely to suffer a fracture. There is increasing recognition that the chemical structure and composition, or microstructure, of mineralized tissues has an important role to play in determining the fracture resistance of bone. The objective of this preliminary study was to evaluate the use of specular reflectance Fourier transform infrared (SR FT-IR) microspectroscopy in conjunction with discriminant analysis as an innovative technique for providing future insights into the origins of orthopedic abnormalities. The impetus for this approach was that SR FT-IR microspectroscopy would offer several advantages over conventional transmission methods. Bone samples were obtained from young racehorses at known fracture predilection sites and spectra were successfully obtained from calcified cartilage and subchondral bone for the first time. By applying discriminant analysis to the spectral data set in biologically relevant regions, microstructural differences between groups of individuals were found to be related to features associated with both the mineral and organic components of the bone. The preliminary findings also suggest that differences in bone microstructure may exist between healthy individuals of the same age, raising important questions around the normal limits of individual variation and whether individuals may be predisposed to later fracture as a result of detrimental microstructural changes during early growth and development.

Regulation of osteoarthritis by omega-3 (n-3) polyunsaturated fatty acids in a naturally occurring model of disease

OBJECTIVE

To examine effects of high omega-3 (n-3) polyunsaturated fatty acid (PUFA) diets on development of osteoarthritis (OA) in a spontaneous guinea pig model, and to further characterise pathogenesis in this model. Modern diets low in n-3 PUFAs have been linked with increases in inflammatory disorders, possibly including OA. However, n-3 is also thought to increases bone density, which is a possible contributing factor in OA. Therefore we aim to determine the net influence of n-3 in disease development.

METHOD

OA-prone Dunkin-Hartley (DH) Guinea pigs were compared with OA-resistant Bristol Strain-2s (BS2) each fed a standard or an n-3 diet from 10 to 30 weeks (10/group). We examined cartilage and subchondral bone pathology by histology, and biochemistry, including collagen cross-links, matrix metalloproteinases (MMPs), alkaline phosphatase, glycosaminoglycan (GAG), and denatured type II collagen.

RESULTS

Dietary n-3 reduced disease in OA-prone animals. Most cartilage parameters were modified by n-3 diet towards those seen in the non-pathological BS2 strain - significantly active MMP-2, lysyl-pyridinoline and total collagen cross-links - the only exception being pro MMP-9 which was lower in the BS2, yet increased with n-3. GAG content was higher and denatured type II lower in the n-3 group. Subchondral bone parameters in the DH n-3 group also changed towards those seen in the non-pathological strain, significantly calcium:phosphate ratios and epiphyseal bone density.

CONCLUSION

Dietary n-3 PUFA reduced OA in the prone strain, and most disease markers were modified towards those of the non-OA strain, though not all significantly so. Omega-3 did not increase markers of pathology in either strain.

Mild exercise early in life produces changes in bone size and strength but not density in proximal phalangeal, third metacarpal and third carpal bones of foals

Exercise or lack of it in early life affects chondro-osseous development. Two groups of horses were used to investigate the effects of age and exercise regimen on bone parameters of diaphyseal, metaphyseal, epiphyseal and cuboidal bones of the distal limb of Thoroughbreds. One group had exercised only spontaneously from an early age at pasture (PASTEX group), while the other group of horses were exposed to a 30% greater workload through additional defined exercise (CONDEX). Longitudinal data from peripheral quantitative computed tomography (pQCT) were obtained from eight scan sites of the left forelimb (proximal phalangeal (P(p); 1 site), third metacarpal (Mc3; six sites) and third carpal (C(3); one site) bones) of 32 Thoroughbred foals scanned five times from ∼3 weeks to 17 months of age. The primary outcome measures were bone mineral content (BMC), bone area (BA), and periosteal circumference (Peri C) in diaphyseal bone, with cortical thickness (CortTh), volumetric bone mineral density (BMD(v)) and a bone strength index (SSI) also being analysed. At the P(p) site within the model there was a significant effect (P=0.00-0.025) of conditioning exercise increasing bone parameters, except endosteal circumference (Endo C) and BMD(v). The BMC, BA, and SSI of P(p) were significantly greater in the CONDEX than PASTEX groups at 12 and 17 months (P=0.015-0.042) and CortTh at 17 months (P=0.033). At the M55 site of Mc3 BMC, BA and SSI (P=0.02-0.04), and at the M33 site, SSI (P=0.05) were higher in the CONDEX than PASTEX group. The adaptive responses, consistent with diaphyseal strengthening, were more marked in the diaphysis of P(p) than Mc3. In the Mc3, metaphysis, trabecular BMD(v) was less in the CONDEX than PASTEX group, associated with greater bone mineral accretion in the outer cortical-sub-cortical bone in the CONDEX group. There were no significant between-group differences in any epiphyseal or cuboidal bone parameter. Although the early imposed exercise regimen was not intensive, it had significant effects on diaphyseal bone strength, through change in size but not bone density.

Physical exercise improves properties of bone and its collagen network in growing and maturing mice

This study characterized bone structure, composition, and mechanical properties in growing male mice. The development of the collagen network during maturation was monitored, and the effect of voluntary physical exercise was investigated. We hypothesized that increased bone loading from exercise would increase the amount and improve the properties of the collagen network during growth and maturation. Half of the mice (total n = 168) had access to running wheels, while half were kept sedentary. Weight and running activity were recorded, and groups of mice were killed at 1, 2, 4, and 6 months of age. The collagen network was assessed by biochemical evaluation of collagen content and cross-links and by tensile testing of decalcified bone. Mineralized femur was analyzed with pQCT and three-point-bending and femoral neck-strength tests. After 6 months, the exercising mice had 10% lower body weight than the sedentary group. There was no difference in the amount of collagen or collagen cross-links, while tensile testing had higher breaking force and stiffness of the collagen network in runners after 4 months but not after 6 months. The bone mineral density and cross-sectional area were higher in the running group after 6 months. Runners also showed higher breaking force and stiffness of the diaphysis and the femoral neck at 2 and 6 months. The significant modulation of mechanical properties of the collagen network without any change in collagen content indicates that physical exercise improves properties of the collagen network in maturing bone. The improvement after exercise of the properties of mineralized bone appears to be more pronounced and long-lasting compared to the early improved properties of the collagen network.