Effects of exercise on biomechanical properties of the superficial digital flexor tendon in foals

Mechanical properties, collagen and glycosaminoglycan content of equine superficial digital flexor tendons are not affected by training

Physical activity can activate extracellular matrix (ECM) protein synthesis and influence the size and mechanical properties of tendon. In this study, we aimed to investigate whether different training histories of horses would influence the synthesis of collagen and other matrix proteins and alter the mechanical properties of tendon. Samples from superficial digital flexor tendon (SDFT) from horses that were either (a) currently race trained (n = 5), (b) previously race trained (n = 5) or (c) untrained (n = 4) were analysed for matrix protein abundance (mass spectrometry), collagen and glycosaminoglycan (GAG) content, ECM gene expression and mechanical properties. It was found that ECM synthesis by tendon fibroblasts in vitro varied depending upon the previous training history. In contrast, fascicle morphology, collagen and GAG content, mechanical properties and ECM gene expression of the tendon did not reveal any significant differences between groups. In conclusion, although we could not identify any direct impact of the physical training history on the mechanical properties or major ECM components of the tendon, it is evident that horse tendon cells are responsive to loading in vivo, and the training background may lead to a modification in the composition of newly synthesised matrix.

Equine tendon mechanical behaviour: Prospects for repair and regeneration applications

Tendons are dense connective tissues that play an important role in the biomechanical function of the musculoskeletal system. The mechanical forces have been implicated in every aspect of tendon biology. Tendon injuries are frequently occurring and their response to treatments is often unsatisfactory. A better understanding of tendon biomechanics and mechanobiology can help develop treatment options to improve clinical outcomes. Recently, tendon tissue engineering has gained more attention as an alternative treatment due to its potential to overcome the limitations of current treatments. This review first provides a summary of tendon mechanical properties, focusing on recent findings of tendon mechanobiological responses. In the next step, we highlight the biomechanical parameters of equine energy-storing and positional tendons. The final section is devoted to how mechanical loading contributes to tenogenic differentiation using bioreactor systems. This study may help develop novel strategies for tendon injury prevention or accelerate and improve tendon healing.

Ultrasound Morphometry and Mean Echogenicity of Digital Flexor Tendons, Suspensory Ligament, and Accessory Ligament of Digital Deep Flexor Tendon in Gaited Horses

The objective of this study was to evaluate and compare the sonographic characteristics of the digital flexor tendons and ligaments of the palmar/plantar of the metacarpal and metatarsal regions in gaited horses, as well as to establish normal reference ultrasound values for Mangalarga Marchador (MM) and Campeiro breeds. Transverse sonographic images were obtained of 50 adult and healthy horses from the MM (n = 25) and Campeiro (n = 25) breeds. The images were taken in six metacarpal/metatarsal zones, and the following measurements were taken: transverse area, circumference, dorsopalmar/plantar length, lateromedial length, and mean echogenicity. Differences were observed between breeds in the fore- and hindlimbs, and, even when not significant, the Campeiro breed tended to have higher values for most variables and structures. Variations between zones and between structures in the same zone followed a similar trend in both breeds for all variables. In addition, the dimensions and variations between zones and structures were different between the fore- and hindlimbs, highlighting the need for specific values for the digital flexor tendons and ligaments of the metatarsal plantar region. In conclusion, the digital flexor tendons, suspensory ligaments, and accessory ligaments of the digital deep flexor tendon are influenced by the breed factor in gaited horses, and they are different between the fore- and hindlimbs.

Mechanical Properties of Animal Tendons: A Review and Comparative Study for the Identification of the Most Suitable Human Tendon Surrogates

The mechanical response of a tendon to load is strictly related to its complex and highly organized hierarchical structure, which ranges from the nano- to macroscale. In a broader context, the mechanical properties of tendons during tensile tests are affected by several distinct factors, due in part to tendon nature (anatomical site, age, training, injury, etc.) but also depending on the experimental setup and settings. This work aimed to present a systematic review of the mechanical properties of tendons reported in the scientific literature by considering different anatomical regions in humans and several animal species (horse, cow, swine, sheep, rabbit, dog, rat, mouse, and foal). This study was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) method. The literature research was conducted via Google Scholar, PubMed, PicoPolito (Politecnico di Torino’s online catalogue), and Science Direct. Sixty studies were selected and analyzed. The structural and mechanical properties described in different animal species were reported and summarized in tables. Only the results from studies reporting the strain rate parameter were considered for the comparison with human tendons, as they were deemed more reliable. Our findings showed similarities between animal and human tendons that should be considered in biomechanical evaluation. An additional analysis of the effects of different strain rates showed the influence of this parameter.

Maternal effect on first-year growth of Hokkaido native foals kept outdoors all year round

In this study, we investigated maternal effects on the growth of Hokkaido native horses kept outdoors throughout the year. We used the data on body weight (BW), height at withers (HW), heart girth (HG), and cannon circumference (CC) of 517 foals during the first year of life to (1) examine the growth patterns by comparing six linear mixed models and (2) analyze the maternal effect on BW, HW, HG, and CC for each month by estimating variance components. The segmented polynomial third-order regression equation was selected as the best model for all the traits. The estimated proportion of variance components for the effects of the dam were 0.25-0.38 for BW, 0.19-0.28 for HW, 0.19-0.34 for HG, and 0.10-0.21 for CC. A higher effect of the dam compared with that of the sire was observed on BW and HG at all months of age and HW at 0-2 months of age. Therefore, the dam contributed to foal growth not only through half of its heredity but also through the maternal effect derived mainly from its milk. These results provide valuable information for the breeding of Hokkaido native foals.

The influence of the metacarpophalangeal joint angle on the transversal area and mean echogenicity of the superficial digital flexor tendon and suspensory ligament in gaited horses

The objective of this study was to assess the influence of the metacarpophalangeal (MCP) joint angle on the transversal area (TA) and mean echogenicity (ME) of the superficial digital flexor tendon (SDFT) and suspensory ligament (SL) in gaited horses. Ultrasound images were obtained from 50 healthy adult horses of the Mangalarga Marchador (MM; n=25) and Campeiro (n=25) breeds. Static and dynamic angles of the MCP joint were measured from photographs and video recordings. Higher ME values were evinced for the SL only in the group with the smaller dynamic angles of the MCP joint in the MM horses, in addition to weak negative correlation between the dynamic angle and ME. Moreover, weak negative correlation was also observed between the static angle and TA of the lateral branch of the SL and between the static angle and the ME of the SDFT. However, the difference observed in the group of MM horses, as well as the weak correlation, was not considered sufficient to support the hypothesis that a smaller angle of the MCP joint (greater extension) is associated with larger TA and ME values for the structures. The results also suggest that the static and dynamic angles of the MCP joint do not influence the TA and ME values of the SDFT and SL in gaited horses.

Postnatal mechanical loading drives adaptation of tissues primarily through modulation of the non-collagenous matrix

Mature connective tissues demonstrate highly specialised properties, remarkably adapted to meet their functional requirements. Tissue adaptation to environmental cues can occur throughout life and poor adaptation commonly results in injury. However, the temporal nature and drivers of functional adaptation remain undefined. Here, we explore functional adaptation and specialisation of mechanically loaded tissues using tendon; a simple aligned biological composite, in which the collagen (fascicle) and surrounding predominantly non-collagenous matrix (interfascicular matrix) can be interrogated independently. Using an equine model of late development, we report the first phase-specific analysis of biomechanical, structural, and compositional changes seen in functional adaptation, demonstrating adaptation occurs postnatally, following mechanical loading, and is almost exclusively localised to the non-collagenous interfascicular matrix. These novel data redefine adaptation in connective tissue, highlighting the fundamental importance of non-collagenous matrix and suggesting that regenerative medicine strategies should change focus from the fibrous to the non-collagenous matrix of tissue.

Evaluation of Return Rates to Races in Racehorses After Tendon Injuries: Lesion-Related Parameters

Metacarpal tendon diseases are important problems that may cause a decrease in performance and even may finish sport life in equine athletes. In this study, it was aimed to evaluate the ratio of return to races and the time of staying away from races and also to detect the prognostic value of ultrasonographic findings in Thoroughbred and Arabian racehorses with metacarpal flexor tendon injury or peritendonitis. Of 120 cases, 84 (70.0%) returned to races. Among these, 82.1% had tendonitis (69/84) and 17.9% peritendonitis (15/84). Among the cases being unable to return to races, 91.7% had tendonitis (33/36), and 8.3% had peritendonitis (3/36). Although not statistically significant (P > .05), tendonitis cases were found to be away from races for longer periods. Tendonitis cases (85.0%, 102/120) stayed away from races for an average of 39.9 months, whereas peritendonitis cases (15.0%, 18/120) stayed away from races for an average of 27.1 months. It was found that the ratio of return to races after injury was higher in cases without tendon thickening (86.7%, 26/30) than in cases with tendon thickening (64.4%, 58/90). The results of this study show that tendon injuries causing tendon thickening have a negative effect on the ratio of return to races (P < .05).

Administration of enrofloxacin during late pregnancy failed to induce lesions in the resulting newborn foals

BACKGROUND

A recent study demonstrated that enrofloxacin and ciprofloxacin cross the equine placenta without causing gross cartilage or tendon lesions in the 9-month fetus; however, long-term effects of in utero fluoroquinolone exposure remain unknown.

OBJECTIVES

To assess effects of fetal exposure to enrofloxacin on the resulting foal's cartilage and tendon strength.

STUDY DESIGN AND METHODS

Healthy mares at 280 days' gestation were allocated into four groups: untreated (n = 5), therapeutic treatment (7.5 mg/kg enrofloxacin, PO × 14 days, n = 6), supratherapeutic treatment (15 mg/kg, PO × 14 days, n = 6) and no mare treatment with treatment of the foals post-partum (n = 2). Mares were allowed to carry pregnancy to term, and foals were maintained on pasture for 5 weeks. After that foals were euthanized, and their articular cartilage and extensor and flexor tendons were examined macroscopically and histologically for lesions. Tendon strength was tested by loading until failure.

RESULTS

Administration of enrofloxacin at recommended doses in late gestation did not result in cartilaginous lesions or clinical lameness in any foal by 5 weeks old. Tensile strength was greater in hind tendons than front tendons, but no difference was found between foals born from treated and control mares. Expectedly, osteochondral changes were present both in foals born from enrofloxacin-treated mares and in negative control foals with no apparent association with fluoroquinolone treatment during pregnancy.

MAIN LIMITATIONS

Only one time point in gestation was evaluated, and mares treated in the study were healthy at time of treatment. Additionally, it is possible that the assessments performed herein were not sensitive enough to detect subtle or functional changes in the articular cartilage. Further studies are needed to determine if enrofloxacin administration during late pregnancy potentiates osteochondral alterations in the first year of life.

CONCLUSIONS

While this study did not assess other stages of gestation or long-term foal outcomes, short-term administration of enrofloxacin to late gestation mares did not result in macroscopic or microscopic lesions in the resulting foals by 5 weeks of age.

Characterization of collagen fibrils after equine suspensory ligament injury: an ultrastructural and biochemical approach

Suspensory ligament (SL) injuries are an important cause of lameness in horses. The mechanical properties of connective tissue in normal and pathological ligaments are mainly related to fibril morphology, as well as collagen content and types. The purpose of this study was to evaluate, using biochemical and ultrastructural approaches, the alterations in collagen fibrils after injury. Eight Warmblood horses with visible signs of injury in only one forelimb SL were selected and specimens were examined by transmission electron microscope (TEM). Collagen types I, III and V were purified by differential salt precipitation after collagen extraction with acetic acid containing pepsin. TEM revealed abnormal organization as well as alterations in the diameter and shape of fibrils after SL injury. The bands corresponding to types I, III and V collagen were assessed by densitometry after sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Densitometric analysis indicated that the proportions of type III and type V collagen were higher (P < 0.001) in damaged tissues compared with normal tissues with a mean increase of 20.9% and 17.3%, respectively. Concurrently, a decrease (P < 0.001) in type I collagen within damaged tissues was recorded with a mean decrease of 15.2%. These alterations could be the hallmark of a decrease in the tissue quality and mechanical properties of the ligament. The findings provide new insight for subsequent research on tissue regeneration that may lead to the development of future treatment strategies for SL injury.

Achilles tendon injuries in elite athletes: lessons in pathophysiology from their equine counterparts

Superficial digital flexor tendon (SDFT) injury in equine athletes is one of the most well-accepted, scientifically supported companion animal models of human disease (i.e., exercise-induced Achilles tendon [AT] injury). The SDFT and AT are functionally and clinically equivalent (and important) energy-storing structures for which no equally appropriate rodent, rabbit, or other analogues exist. Access to equine tissues has facilitated significant advances in knowledge of tendon maturation and aging, determination of specific exercise effects (including early life), and definition of some of the earliest stages of subclinical pathology. Access to human surgical biopsies has provided complementary information on more advanced phases of disease. Importantly, equine SDFT injuries are only a model for acute ruptures in athletes, not the entire spectrum of human tendonopathy (including chronic tendon pain). In both, pathology begins with a potentially prolonged phase of accumulation of (subclinical) microdamage. Recent work has revealed remarkably similar genetic risk factors, including further evidence that tenocyte dysfunction plays an active role. Mice are convenient but not necessarily accurate models for multiple diseases, particularly at the cellular level. Mechanistic studies, including tendon cell responses to combinations of exercise-associated stresses, require a more thorough investigation of cross-species conservation of key stress pathway auditors. Molecular evidence has provided some context for the poor performance of mouse models; equines may provide better systems at this level. The use of horses may be additionally justifiable based on comparable species longevity, lifestyle factors, and selection pressure by similar infectious agents (e.g., herpesviruses) on general cell stress pathway evolution.

The cross-sectional area changes in digital flexor tendons and suspensory ligament in foals by ultrasonographic examination

REASONS FOR PERFORMING STUDY

Flexural deformities are common conditions of growing horses and are suggested to have a relationship with the contraction of musculotendinous units. However, limited studies have documented the changes in each tendon and ligament in the metacarpal region with age.

OBJECTIVES

To investigate the changes in the cross-sectional area (CSA) of each tendon and ligament in the metacarpal region with age by ultrasonographic examination.

STUDY DESIGN

Longitudinal study of foals from Day 1 to age 24 months.

METHODS

The CSA of the superficial digital flexor tendon, deep digital flexor tendon, accessory ligament of the deep digital flexor tendon and suspensory ligament was measured by ultrasonographic examination at monthly intervals from Day 1 to age 24 months in 7 Thoroughbred foals.

RESULTS

Changes in superficial digital flexor CSA in all regions were larger than those of other structures from 10 months to 15 months. The suspensory ligament CSA was significantly larger than those of other structures on Day 1 in both the region of suspensory origin (RSO) and region of suspensory body (RSBO). This condition continued until 2 months in the RSO and until 5 months in the RSBO. The changes in deep digital flexor CSA were larger than those of other structures from 2 to 5 months in both the RSO and RSBO.

CONCLUSIONS

The rate of change in each structure varies with age. Thus, the functional adaptation with age that takes place may differ among structures because the primary function of each structure differs.

Cross sectional area of forelimb metacarpal region flexor tendons in horses of different breeds and age

There are few studies on the effects of age within breeds on cross sectional area (CSA) of flexor tendons in horses. This study was designed to evaluate the relationship between age and the CSA of the superficial flexor tendon (SDFT), the deep digital flexor tendon (DDFT) and its accessory ligament (AL-DDFT) of both forelimbs in horses utilising ultrasound. Ages of the horses ranged from 2 years to aged, and the breeds evaluated were Thoroughbred (TB), Standardbred (SB), Quarterhorse (QH) and German Warmblood Riding horse (WB). CSAs were measured with ultrasound at 4 cm intervals, starting 4 cm from the distal border of the accessory carpal bone down to the metacarpophalangeal joint. The CSA of the SDFT in 3-year-old and older TB, QH and WBs was smaller than in the 2-year-olds (all P<0.001) and did not differ between 3-year-olds and older horses (P≯0.05). In comparison, the CSA of the SDFT in 2-year-old and 3-year-old SBs was smaller than in the horses older than 3 years (P<0.05 among age groups). The 2-year-olds had larger CSA of the DDFTs than the 3-year-olds (P<0.01), and the CSA was also larger in the older horses of all breeds (P<0.01). However, the 3-year-old QH and SBs had smaller CSAs of the DDFT than the horses older than 3 years of age, (P<0.001), but interestingly the CSA was not different in the TB and WBs based on age (P≯0.05). The CSA of the AL-DDFT in the left forelimb was smaller than in the right forelimb (P<0.01) of all horses. The results of this study show that differential effects exist between age and within breeds on the CSA of the SDFT, DDFT and AL-DDFT, indicating that training and management may play a role, in addition to genetics, in the CSA of the metacarpal region flexor tendons of horses. The data on the CSAs of the SDFT, DDFT and AL-DDFT in WB, QH and SBs provides additional physiological references for these breeds to compliment the CSA data previously published for other breeds.

Relationship between tendon stiffness and failure: a metaanalysis

Tendon is a highly specialized, hierarchical tissue designed to transfer forces from muscle to bone; complex viscoelastic and anisotropic behaviors have been extensively characterized for specific subsets of tendons. Reported mechanical data consistently show a pseudoelastic, stress-vs.-strain behavior with a linear slope after an initial toe region. Many studies report a linear, elastic modulus, or Young's modulus (hereafter called elastic modulus) and ultimate stress for their tendon specimens. Individually, these studies are unable to provide a broader, interstudy understanding of tendon mechanical behavior. Herein we present a metaanalysis of pooled mechanical data from a representative sample of tendons from different species. These data include healthy tendons and those altered by injury and healing, genetic modification, allograft preparation, mechanical environment, and age. Fifty studies were selected and analyzed. Despite a wide range of mechanical properties between and within species, elastic modulus and ultimate stress are highly correlated (R(2) = 0.785), suggesting that tendon failure is highly strain-dependent. Furthermore, this relationship was observed to be predictable over controlled ranges of elastic moduli, as would be typical of any individual species. With the knowledge gained through this metaanalysis, noninvasive tools could measure elastic modulus in vivo and reasonably predict ultimate stress (or structural compromise) for diseased or injured tendon.

Cross-sectional area of the tendons of the tarsal region in Standardbred trotter horses

REASONS FOR PERFORMING STUDY

The assessment of a normal range for cross-sectional area (CSA) of tendons in the tarsal region is important in order to use them as reference values in the identification of pathological changes of dimensions.

OBJECTIVES

To provide normal reference values for the CSA of the tendons of the tarsus of Standardbred trotter horses (STH) by means of ultrasonography.

METHODS

Transverse echographic images of the tendons were obtained at different levels proximodistally; these images were digitised and CSA values (mean ± s.d.) were obtained for each structure.

RESULTS

The largest structure corresponded with the lateral digital flexor/caudal tibial tendon complex at Level 1 and the smallest was the medial digital flexor tendon at Level 4. Almost all tendons showed a slight decreasing in their CSA when crossing the tarsus.

CONCLUSIONS

The normal CSA values of tendinous structures in the tarsal region of the STH are reported. These data could be used as anatomical references.

POTENTIAL RELEVANCE

The establishment of reference values could serve as a tool to discriminate between normal and abnormal dimensions of tarsal tendons in STH. Other horse breeds should need their own reference values.

The effect of age and spontaneous exercise on the biomechanical and biochemical properties of chicken superficial digital flexor tendon

The aim of this study was to evaluate if spontaneous (nonforced active) exercise and age (maturation process) alter the biomechanical and biochemical properties of superficial digital flexor tendon. Chickens aged 1, 5, and 8 months were divided into two groups: caged and penned. The caged group was reared in an area of 0.5 m(2) (3 animals/cage), while the penned group was reared in an area of 60 m(2) (3 animals/area). For biochemical analysis, the tendon was divided into tensile and compressive regions for quantification of hydroxyproline and glycosaminoglycan content. Biomechanical properties were analyzed from tensile tests of intact tendons. The biomechanical measurements were taken at maximum load and maximum stress. In both the caged and penned groups, maximum load and energy absorption increased with maturation; however, the elastic modulus, maximum stress, and maximum strain did not increase with maturation. Exercise resulted in a higher load, stress, and elastic modulus in the fifth month. Collagen content increased with age in the penned group and with exercise in the fifth and eighth months. Exercise results in a higher expression of glycosaminoglycans in young tendons compared to mature tendons. Thus, low-intensity mechanical stimuli promote the synthesis and possible rearrangement of molecules in immature tendons, whereas inactivity leads to deleterious effects on the material properties (maximum stress and elastic modulus) during growth and maturation.

Effect of uphill exercise on equine superficial digital flexor tendon forces at trot and canter

REASONS FOR PERFORMING STUDY

One cause of overstrain injury to the superficial digital flexor tendon (SDFT) in horses is the force loaded on the SDFT during repeated running. Therefore, decreasing this force may reduce SDFT injury. It has been reported that strain on the SDFT decreases with a toe-wedge shoe. Uphill courses are used for training of racehorses, and the angle of hoof-sole to the horizon during uphill running is similar to that of the toe-wedge shoe.

OBJECTIVES

To determine the effects of uphill exercise on the force on the SDFT during trotting and cantering.

METHODS

Arthroscopically implantable force probes (AIFP) were implanted into the SDFT of the left or right forelimb of 7 Thoroughbred horses and AIFP output recorded during trotting and cantering on a treadmill inclined at slopes of 0, 3 or 8%, and then 0% again. Superficial digital flexor tendon force was calculated as a relative value, with the amplitude of AIFP output voltage at initial 0% slope equal to 100.

RESULTS

Out of 14 sets of experiments, AIFP data were analysed successfully in 9 at the trot, in 3 at the canter in the trailing forelimb on a slope of 3 and 8%, and in 2 at the canter in the leading forelimb on a slope of 3%. Increasing the incline from 0-8% tended to decrease peak force in the SDFT at the trot, and in the trailing forelimb at the canter. However, force in the SDFT was unchanged in the leading forelimb at the canter on the 3% incline.

CONCLUSIONS

The force in the SDFT trotting or cantering uphill is unchanged or lower than that loaded at the same speed on a flat surface. Because at similar speeds the workload for uphill exercise is greater than on the flat, uphill running increases exercise intensity without increasing force in the SDFT.

POTENTIAL RELEVANCE

Uphill exercise may reduce the risk of SDFT injury as both running speed and SDFT force are decreased on an incline as compared to the flat, even when exercise intensity is the same. Further study is needed to confirm these findings at canter in a larger population of horses.

Ultrasonographic morphometric measurements of digital flexor tendons and ligaments of the palmar metacarpal region in Haflinger horses

The aim of the study was to determine morphometric values of the superficial and deep digital flexor tendon, the inferior check ligament and the suspensory ligament in the palmar metacarpal region of sound Haflinger horses using ultrasonography and to assess the influence of different factors on them. The findings were compared with the literature. A total of 30 sound Haflinger mares aged 4-20 years were used. Transverse ultrasound images were obtained with an 8-10 linear MHz transducer and the cross-sectional area, the circumference and the dorsopalmar and lateromedial width were determined for each structure at six regions of interest (ROI) in both forelimbs. The coefficient of variation was <3%. The structures were compared between each other and the values of each structure at the ROIs. Age, height at the withers, body mass index, diameter of the Os metacarpale III and the circumference of the mid-metacarpal region showed significant influences on some of the parameters. Reference values for the tendons and ligaments in the palmar metacarpal region in sound Haflinger mares were obtained and the influence of different factors was tested. Description of the dimensional relationship between the structures and comparison of the data with the literature provide knowledge required for adequate veterinary care.

Obesity affects collagen fibril diameter and mechanical properties of tendons in Zucker rats

Obesity is currently considered to be a world epidemic and one of the major public health problems in many countries, whose incidence is increasing at alarming rates. Genetically obese Zucker rats are used as a model of obesity and were employed in the present study. Tendons transmit contractile force from muscles to bone, thus permitting articular movement. The objective of our study was to analyze the ultrastructural, biochemical, and biomechanical alterations that occur in the deep digital flexor tendon of obese Zucker rats compared to lean animals. Ultrastructural analysis showed differences in collagen fibril diameter distribution and mass-average diameter between obese and lean animals. Regarding mechanical parameters, there was a significant difference in maximum displacement and strain. Hydroxyproline content was higher in obese animals. In view of the excess weight and peculiar conditions to which the tendon of obese animals is submitted, we concluded that obesity provokes alterations in the composition and organization of tendon extracellular matrix components. These alterations might be related to organizational and structural modifications in the collagen bundles, influencing the mechanical properties of the tendon and the progression to a pathological state.

Influence of early conditioning exercise on the development of gross cartilage defects and swelling behavior of cartilage extracellular matrix in the equine midcarpal joint

OBJECTIVE

To investigate the influence of early conditioning exercise on the development of gross cartilage defects and swelling behavior of cartilage extracellular matrix (ECM) in the midcarpal joint of horses.

ANIMALS

12 Thoroughbreds.

PROCEDURES

6 horses underwent early conditioning exercise from birth to 18 months of age (CONDEX group), and 6 horses were used as control animals (PASTEX group). The horses were euthanized at 18 months of age, and the midcarpal joints were harvested. Gross defects of the cartilage surface were classified and mapped. Opposing surfaces of the third and radial carpal bones were used to quantify swelling behavior of the cartilage ECM.

RESULTS

A wide range of gross defects was detected in the cartilage on the opposing surfaces of the bones of the midcarpal joint; however, there was no significant difference between the CONDEX and PASTEX groups. Similarly, no significant difference in swelling behavior of the cartilage ECM was evident between the CONDEX and PASTEX groups.

CONCLUSIONS AND CLINICAL RELEVANCE

In the study reported here, we did not detect negative influences of early conditioning exercise on the prevalence of gross defects in cartilage of the midcarpal joint or the quality of the cartilage ECM as defined by swelling behavior. These results suggested that early conditioning exercise may be used without negative consequences for the midcarpal joint and the cartilage ECM of the third and radial carpal bones.

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.

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.

Biomechanical and biochemical properties of chicken calcaneal tendon under effect of age and nonforced active exercise

This study investigated if nonforced active exercise alters the biomechanical and biochemical properties of calcaneal tendon during maturation. Chickens at 1, 5, and 8 months old were divided into two groups: caged and penned. Intact tendons were used for biomechanical analysis, but they were divided into tensile and compressive regions for quantification of hydroxyproline and glycosaminoglycans. The exercise increased tendon strength after the fifth month, energy absorption in the eighth month, and ultimate tensile stress in the first month. Age increased tendon strength and energy storage and reduced stiffness but did not alter stress. There was an increase in collagen content in the fifth month. Glycosaminoglycans showed a progressive decline in the tensile region. Thus, some biomechanical and biochemical changes depend on the maturation process itself and also are influenced by spontaneous exercise, showing that mechanical stimulation of low intensity may help to improve the quality of the tendon.

Rehabilitation and Conditioning of Sporting Dogs

Owners and trainers exercise sporting dogs to increase their fitness and optimize their conditioning and performance. Training is designed to in-crease strength, endurance, and agility and is sport-specific. Sporting dogs are susceptible to specific musculoskeletal injuries. The rehabilitation of sporting dogs after these injuries follows specific principles during the acute, subacute, and reconditioning periods.

Mechanical and functional properties of the equine superficial digital flexor tendon

The in vitro and in vivo mechanical properties of the superficial digital flexor tendon have been described. To date the focus has been on single load to failure testing, however refined in vivo methods may prove useful to evaluate the effects of treatment and exercise on tendons. During maximal exercise, the adult superficial digital flexor tendon operates close to its functional limits with a narrow biomechanical safety margin. This combined with exercise and age associated microdamage, and a limited adaptive ability may increase the risk of fatigue failure. Studies evaluating treatment regimens for tendonitis have focused on repair and regeneration and yielded varying results. It would appear that the superficial digital flexor tendon has a limited ability if any to adapt positively to exercise after maturity. In contrast, the foal's superficial digital flexor tendon may have a greater adaptive ability and may respond to an appropriate exercise regimen to produce a more functionally adapted tendon. Recent studies have shown that foals allowed free pasture exercise develop a larger, stronger, more elastic tendon compared to foals that were confined or subjected to a training program. Effects on the non-collagenous matrix appear to be responsible for these differences. In contrast, training or excess exercise may have permanent detrimental effects on the biomechanical and functional properties of the superficial digital flexor tendon in the foal. The implication is that the determination of optimum exercise intensity and timing, and the role of the non-collagenous matrix in tendon physiology in the young horse may hold the key to developing tendons more capable of resisting injury.

Musculoskeletal responses of 2-year-old Thoroughbred horses to early training. 3.In vivoultrasonographic assessment of the cross-sectional area and echogenicity of the superficial digital flexor tendon

AIM

To determine if the superficial digital flexor tendon (SDFT) of young Thoroughbred horses changed in size and echogenicity in association with early race training.

METHODS

Cross-sectional area (CSA) and echogenicity were determined ultrasonographically at five levels of the SDFT of the forelimbs of 2-year-old fillies (n=14), corresponding to 4, 8, 12, 16 and 20 cm distal to the accessory carpal bone (DACB). Measurements were made before and after a 13-week period in which a trained group of seven horses was compared with another group of seven untrained horses.

RESULTS

Level below the accessory carpal bone had a significant effect on CSA and Level 8 was smaller than all other levels except Level 12, while Level 12 was smaller than Levels 4 and 20 but not different from Levels 8 and 16. There was a significant interaction between level and time due to effects observed at Level 8. The CSA at Level 8 measured pre-training was different from that of Levels 4 and 20 in both pre- and post-training groups (p<0.05), but when measured post-training was not different from any other measurement. There was also a significant interaction between treatment group and time. There was no difference between CSA for the untrained and trained groups at the pre-training observation (p=0.9), but post-training the CSA (pooled over all levels) in trained horses was significantly larger than that of the untrained horses both post-training (p=0.019) and pre-training (p=0.034), and was not different from the pre-training CSA recorded in the trained group (p=0.29). Treatment group had no effect on echogenicity (p=0.43), while echogenicity was less at the end of the trial in both trained and untrained horses (p<0.001).

CONCLUSIONS

Early training for racing was associated with an increase in mean CSA of the SDFT. Other factors such as age and maturity may play a role in limiting this increase.

Musculoskeletal responses of 2-year-old Thoroughbred horses to early training. 4. Morphometric, microscopic and biomechanical properties of the digital tendons of the forelimb

AIM

To determine the weight, volume, density and cross-sectional area (CSA) of the digital flexor tendons, common digital extensor tendon (CDET) and suspensory ligament (SL) of the forelimb of young Thoroughbred horses in early training, and to assess the response to a training programme of known parameters of superficial digital flexor tendon (SDFT) tissue at mid-metacarpal level.

METHODS

The tendons of seven 2-year-old Thoroughbred horses in training were inspected, transected into segments of known length, and compared with those from seven untrained horses matched for age, sex and breed. The weight, volume, density and CSA of each segment, and the crimp angle, histological features, and biomechanical ultimate stress and stiffness of tendon samples from the mid-metacarpal region of the SDFT were determined.

RESULTS

There was no macroscopic evidence of swelling or discolouration in any of the tendon segments or cut surfaces. The volumes of SDFT and CDET segments of horses in the trained group were significantly greater than those in the untrained group (p=0.036 and p=0.039, respectively). A greater increase in volume than weight resulted in a lower density in the SDFT but not CDET in trained compared with untrained horses (p=0.038). CSA of these two tendons was significantly greater in the trained group (p=0.002 and 0.036, respectively), the percentage increase being greater in the CDET than the SDFT. The number of tenocytes at four sites in the mid-metacarpal SDFT region was less in trained than untrained horses (p=0.025). There was no histological evidence of inflammation, and no difference in crimp angle between groups. There was no significant between-group difference in stiffness or ultimate stress of tendon strips.

CONCLUSIONS

Volume and CSA of the SDFT and CDET were larger in trained than untrained horses. The SDFT was less dense in the trained group. Because no evidence of tendonitis was detected and training appeared to have no significant effect on crimp angle or biomechanical properties of tendon strips, the size and density changes were presumed to be adaptive and induced by the training.

CLINICAL RELEVANCE

Although evident in this in vitro study, the detection of adaptive from initial pathological increase in size of the SDFT is likely to be difficult in vivo.

Force- and moment-generating capacities of muscles in the distal forelimb of the horse

A detailed musculoskeletal model of the distal equine forelimb was developed to study the influence of musculoskeletal geometry (i.e. muscle paths) and muscle physiology (i.e. force-length properties) on the force- and moment-generating capacities of muscles crossing the carpal and metacarpophalangeal joints. The distal forelimb skeleton was represented as a five degree-of-freedom kinematic linkage comprised of eight bones (humerus, radius and ulna combined, proximal carpus, distal carpus, metacarpus, proximal phalanx, intermediate phalanx and distal phalanx) and seven joints (elbow, radiocarpal, intercarpal, carpometacarpal, metacarpophalangeal (MCP), proximal interphalangeal (pastern) and distal interphalangeal (coffin)). Bone surfaces were reconstructed from computed tomography scans obtained from the left forelimb of a Thoroughbred horse. The model was actuated by nine muscle-tendon units. Each unit was represented as a three-element Hill-type muscle in series with an elastic tendon. Architectural parameters specifying the force-producing properties of each muscle-tendon unit were found by dissecting seven forelimbs from five Thoroughbred horses. Maximum isometric moments were calculated for a wide range of joint angles by fully activating the extensor and flexor muscles crossing the carpus and MCP joint. Peak isometric moments generated by the flexor muscles were an order of magnitude greater than those generated by the extensor muscles at both the carpus and the MCP joint. For each flexor muscle in the model, the shape of the maximum isometric joint moment-angle curve was dominated by the variation in muscle force. By contrast, the moment-angle curves for the muscles that extend the MCP joint were determined mainly by the variation in muscle moment arms. The suspensory and check ligaments contributed more than half of the total support moment developed about the MCP joint in the model. When combined with appropriate in vivo measurements of joint kinematics and ground-reaction forces, the model may be used to determine muscle-tendon and joint-reaction forces generated during gait.