The Japanese Experience with Tendonitis in Racehorses

Evaluation of race performance after tendon injuries in race horses with special respect to lesion related parameters

The study aimed to assess the race performance after injury of the palmar metacarpal tendon region in Thoroughbred and Arabian racehorses. A special scoring system was established to evaluate the performance of the horses for each race after the injury, objectively in this study. Thus, individual total race earnings, the rates of ranking among the top four in at least two and three races and the number of participated races after injury were also analysed. The performance scores after injury were found to be lower in tendinitis cases compared to peritendinitis cases (P=0.0004). It was found that the success rate was lower in cases with tendon lesions than in cases without lesions in terms of race performance after injury (P=0.006). Injuries causing tendon thickening and also tendon echogenicity alterations had negative effects on race performances after injury (P=0.01 and P=0.04, respectively). Also individual total race earnings were lower in cases with tendon thickening compared to those without thickening (P=0.02). According to the results of this study, it is recommended to take prophylactic measures for tendinitis in cases with tendon thickening and echogenicity changes detected by ultrasound in the early stages of tendinitis to be able to display a good race performance after injury.

Relationship between the ultrasonographic findings of suspected superficial digital flexor tendon injury and the prevalence of subsequent severe superficial digital flexor tendon injuries in Thoroughbred horses: a retrospective study

The onset of severe injury to the superficial digital flexor tendon (SDFT) is extremely difficult to predict from slight changes in ultrasonographic findings in cases with no apparent clinical signs. This study investigated the relationship between an increased cross-sectional area (CSA) or edema in the subcutaneous tissue around the tendon and the subsequent onset of severe SDFT injury in Thoroughbred racehorses. Horses were classified into three groups based on ultrasound diagnosis (USD) findings: Group A included cases with enlarged tendons; Group B included cases with tendons of normal size but with prominent edema in the peritendinous tissue; and Group C (control group) included cases with no abnormal USD findings. The incidence of subsequent severe tendon injury was significantly higher in the horses in Groups A (25.7%, 28/101) and B (28.3%, 65/212) than in those in Group C (4.9%, 2/41). There were no significant differences in the median period and the median number of races from the first examination to the subsequent tendon injury between Groups A (140 days, 1 race) and B (120 days, 1 race). The results of this study revealed that horses with increased CSA and peritendinous edema are likely to suffer a subsequent severe tendon injury. Also, these two USD findings, i.e., increased CSA and peritendinous edema, indicate the risk of onset of severe SDFT injury.

Changes in Temperature of the Equine Skin Surface Under Boots after Exercise

Equine distal limbs have evolved to have long tendons coupled with strong, tendinous muscles positioned proximally on the leg, thus enabling the horse to achieve highly efficient locomotion. The tradeoff is, that the tendons are left unprotected and prone to injuries, therefore they are often protected by various boots and bandages, which may insulate the limbs and cause hyperthermia in the underlying tendons. The actual mechanism for the degeneration of tendons is currently unknown, but damaging temperature increases due to hysteresis in hardworking horses has been suggested as a possible cause. This study compared the skin temperature of the palmar/ plantar metacarpal/metatarsal regions of the limbs after exercise with various types of boots and bandages - primarily tendon boots, leather boots and fleece bandages. Several horses were measured before and after the completion of a standard exercise test. The boots or bandages were removed immediately after the exercise and the temperature was measured at 3 separate places with A Testo 850i infrared thermometer. The differences in temperature increases between the various kinds of boots were compared. The results showed a significantly higher average temperature increase in horses wearing boots or bandages compared to the bare limb. The fleece bandages seemed to accumulate the highest amount of heat, followed by the tendon boots.

Ultrasonographic scoring system for superficial digital flexor tendon injuries in horses: intra- and inter-rater variability

Superficial digital flexor tendon (SDFT) tendinopathy is an important musculoskeletal problem in horses. The study objective was to validate an ultrasonographic scoring system for SDFT injuries. Ultrasonographic images from 14 Thoroughbred racehorses with SDFT lesions (seven core; seven diffuse) and two controls were blindly assessed by five clinicians on two occasions. Ultrasonographic parameters evaluated were: type and extent of the injury, location, echogenicity, cross-sectional area and longitudinal fibre pattern of the maximal injury zone (MIZ). Inter-rater variability and intra-rater reliability were assessed using Kendall's coefficient of concordance (KC) and Lin's concordance correlation coefficient (LC), respectively. Type of injury (core vs. diffuse) had perfect inter/intra-rater agreement. Cases with core lesions had very strong inter-rater agreement (KC ≥0.74, P<0.001) and intra-rater reliability (LC ≥0.73) for all parameters apart from echogenicity. Cases with diffuse lesions had strong inter-rater agreement (KC ≥0.62) for all parameters, but weak agreement for echogenicity (KC=0.22); intra-rater reliability was excellent for MIZ location and fibre pattern (LC ≥0.82), and moderate (LC ≥0.58) for cross-sectional area and number of zones affected. This scoring system was reliable and repeatable for all parameters, except for echogenicity. A validated scoring system will facilitate reliable recording of SDFT injuries and inter-study meta-analyses.

ELASTOGRAPHIC EVALUATION OF NATURALLY OCCURING TENDON AND LIGAMENT INJURIES OF THE EQUINE DISTAL LIMB

Compression elastography is an ultrasonographic technique that estimates tissue strain and may have utility in diagnosing and monitoring soft tissue injuries in the equine athlete. Recently, elastography has been proven to be a feasible and repeatable imaging modality for evaluating normal tendons and ligaments of the equine distal forelimb. The purposes of this prospective study were to investigate the ability of elastography to detect spontaneously occurring lesions of equine tendons and ligaments diagnosed with magnetic resonance imaging (MRI) and gray-scale ultrasound (US) and to characterize the differences in the elastographic appearance of acute vs. chronic injuries. Fifty seven horses with a total of 65 lesions were evaluated. Images were assessed quantitatively and qualitatively. Acute lesions were found to be significantly softer (P < 0.0001) than chronic lesions (P < 0.0001) and the stiffness of lesions increased with progression of healing (P = 0.0138). A negative correlation between lesion hypoechogenicity and softness was appreciated with more hypoechoic lesions appearing softer (P = 0.0087) and more hyperechoic regions harder (P = 0.0002). A similar finding occurred with increased signal intensity on short tau inversion recovery (STIR) and proton density (PD) MRI sequences correlating with increased softness on elastography (P = 0.0164). Using US and MRI as references, commonly encountered soft tissue injuries of the equine distal limb could be detected with elastography. However, elastography was limited for detecting small, proximal injuries of the hindlimb proximal suspensory ligament. Elastographic evaluation of equine tendons and ligaments may allow better characterization of lesion chronicity and severity, and sequential examinations may optimize lesion management, rehabilitation, and return to training.

Focal experimental injury leads to widespread gene expression and histologic changes in equine flexor tendons

It is not known how extensively a localised flexor tendon injury affects the entire tendon. This study examined the extent of and relationship between histopathologic and gene expression changes in equine superficial digital flexor tendon after a surgical injury. One forelimb tendon was hemi-transected in six horses, and in three other horses, one tendon underwent a sham operation. After euthanasia at six weeks, transected and control (sham and non-operated contralateral) tendons were regionally sampled (medial and lateral halves each divided into six 3 cm regions) for histologic (scoring and immunohistochemistry) and gene expression (real time PCR) analysis of extracellular matrix changes. The histopathology score was significantly higher in transected tendons compared to control tendons in all regions except for the most distal (P ≤ 0.03) with no differences between overstressed (medial) and stress-deprived (lateral) tendon halves. Proteoglycan scores were increased by transection in all but the most proximal region (P < 0.02), with increased immunostaining for aggrecan, biglycan and versican. After correcting for location within the tendon, gene expression for aggrecan, versican, biglycan, lumican, collagen types I, II and III, MMP14 and TIMP1 was increased in transected tendons compared with control tendons (P < 0.02) and decreased for ADAMTS4, MMP3 and TIMP3 (P < 0.001). Aggrecan, biglycan, fibromodulin, and collagen types I and III expression positively correlated with all histopathology scores (P < 0.001), whereas lumican, ADAMTS4 and MMP14 expression positively correlated only with collagen fiber malalignment (P < 0.001). In summary, histologic and associated gene expression changes were significant and widespread six weeks after injury to the equine SDFT, suggesting rapid and active development of tendinopathy throughout the entire length of the tendon. These extensive changes distant to the focal injury may contribute to poor functional outcomes and re-injury in clinical cases. Our data suggest that successful treatments of focal injuries will need to address pathology in the entire tendon, and that better methods to monitor the development and resolution of tendinopathy are required.

Tenascin-C Expression in Equine Tendon-derived Cells During Proliferation and Migration

In vitro cell studies might be a useful tool for studying tendon pathology, but no suitable in vitro models exist for tendon disorders. The purpose of this study was to confirm whether cell scratch culture using tendon-derived fibroblasts can provide a suitable in vitro tendon disorder model. Extracellular matrix components were examined immunohistochemically in tendon tissue, and then their related gene expression levels were analyzed by conventional reverse transcription polymerase chain reaction (RT-PCR) and/or quantitative real-time RT-PCR in tissues and cells. Collagen type I (Col I), collagen type III (Col III), tenascin-C (TN-C) and cartilage oligomeric matrix protein (COMP) were detected in tendon tissue sections, and RT-PCR confirmed their expression in tendon tissue and cells. Cells that had been cultured from explanted tendon tissue maintained the characteristics of in vivo tendon cells. The combination of TN-C and COMP might be a useful marker of tendon cells because they display more tendon-specific expression than Col I and III. In particular, the significant increase of TN-C mRNA expression in the scratch wound assay, at 12 hr after scratching, concomitant with the regeneration of the cell sheet, indicates its crucial role in tendon cell proliferation and migration. Thus, TN-C appears to be a key factor in tendon wound healing. In vitro cell scratch assays using tendon cells appear to mimic the repair of tendon tissue after injury.

The pathogenesis of tendon microdamage in athletes: the horse as a natural model for basic cellular research

The equine superficial digital flexor tendon (SDFT) is a frequently injured structure that is functionally and clinically equivalent to the human Achilles tendon (AT). Both act as critical energy-storage systems during high-speed locomotion and can accumulate exercise- and age-related microdamage that predisposes to rupture during normal activity. Significant advances in understanding of the biology and pathology of exercise-induced tendon injury have occurred through comparative studies of equine digital tendons with varying functions and injury susceptibilities. Due to the limitations of in-vivo work, determination of the mechanisms by which tendon cells contribute to and/or actively participate in the pathogenesis of microdamage requires detailed cell culture modelling. The phenotypes induced must ultimately be mapped back to the tendon tissue environment. The biology of tendon cells and their matrix, and the pathological changes occurring in the context of early injury in both horses and people are reviewed, with a particular focus on the use of various tendon cell and tissue culture systems to model these events.

Comparative study of the properties of tendinocytes derived from three different sites in the equine superficial digital flexor tendon

This aim of this study was to determine the characteristic differences in tendinocytes derived from three sites of the equine superficial digital flexor tendon (SDFT)-proximally the myotendinous junction (MTJ), mid-metacarpal (mM) and osteotendinous junction (OTJ)-in morphology, proliferation, and ability for synthesis of collagen and matrix metalloproteinases (MMPs). Little difference was observed in cell proliferation. Addition of tumor necrosis factor (TNF) alpha to the culture medium resulted in increased collagen synthesis by tendinocytes from all three sites. The amount of collagen synthesized by tendinocytes derived from the mM and OTJ was much larger than that synthesized by untreated tendinocytes. A collagen zymogram revealed that proMMP-13 synthesis was increased towards the distal site. However, TNFalpha treatment resulted in a significant decrease in the amount of proMMP-13 synthesized by tendinocytes from all three sites. On the other hand, a gelatin zymogram showed that the synthesis level of proMMP-9 tended to decrease towards the distal site, but there was little difference between synthesis levels of proMMP-9 before and after TNFalpha treatment. These results indicated that tendinocytes in the same tendon have different characteristics and that these characterisities would reflect the function of tendinocytes in vivo. Also, the isolated tendinocytes provided much information on the characteristics and properties of tendons for the ECM turnover system and on the responsiveness of tendinocytes to complex inflammatory responses in a tendinopathy condition.

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.

The pathobiology of exercise-induced superficial digital flexor tendon injury in Thoroughbred racehorses

Despite the high incidence of superficial digital flexor tendon (SDFT) injury in racehorses, the pathobiology of the condition is not clearly defined. The SDFT improves locomotor efficiency by storing elastic energy, but as a result it has low mechanical safety margins. As with the Achilles tendon in humans, rupture during athletic activity often follows accumulation of exercise and age-induced degenerative change that is not repaired by tenocytes. There is limited understanding of tenocyte biology and pathology, including responses to high mechanical strains and core temperatures during exercise. Unfortunately, much of the current information on SDFT pathology is derived from studies of collagenase-induced injury, which is a controversial model. Following rupture the overlapping phases of reactive inflammation, proliferation, remodelling and maturation do not necessarily reconstitute normal structure and function, resulting in long-term persistence of scar tissue and high re-injury rates. Tissue engineering approaches are likely to be applicable to SDFT lesions, but will require significant advances in cell biology research.

Effect of heat on synthesis of gelatinases and pro-inflammatory cytokines in equine tendinocytes

The aim of this study was to clarify whether matrix metalloproteinases (MMP-2 and -9: gelatinases) and pro-inflammatory cytokines [tumor necrosis factor (TNF) alpha and interleukin (IL)-1beta] are induced by heat in tendon tissue in vitro and to test the hypothesis that heat exposure causes tendinocytes to synthesize pro-inflammatory cytokines and that synthesis of these cytokines, in turn, leads to up-regulation of synthesis of gelatinases. Isolated tendinocytes from equine superficial digital flexor tendons were cultured and all experiments were performed on cells passaged 3 or 4 times. In the cells exposed to heat (37 to 45 degrees C, 0 to 60 min), the survival rate decreased sharply in a temperature- and time-dependent manner, especially at 42 and 45 degrees C. Cells exposed at 40 degrees C, however, showed little change in survival rate and morphology. Gelatin zymograms revealed that proMMP-2 and -9 were the only two MMPs remaining in the supernatant of the cultured tendinocytes, including that of untreated cells. Addition of TNFalpha and IL-1beta to the culture medium of tendinocytes accelerated proMMP-9 synthesis considerably. Heating the tendinocytes (40 degrees C) led to a three-fold increase in proMMP-9 synthesis in a short time. Only TNFalpha was detected in tendinocytes after heat exposure for 30 and 60 min. In contrast, IL-1beta was under the detectable level in ELISA. Cooling of heat-exposed cells from 40 degrees C to 37 degrees C considerably down-regulated cellular proMMP-9 synthesis. Furthermore, proMMP-9 level was greatly reduced in cells treated at lower temperatures, 20 degrees C and 5 degrees C. These findings support our hypothesis that hyperthermia in the horse tendon induces tendinocytes to synthesize pro-inflammatory cytokines and that the synthesis of these cytokines results in the up-regulation of gelatinases.

Downregulation of decorin and transforming growth factor-beta1 by decorin gene suppression in tendinocytes

Scars formed after tendonitis result in altered tissue mechanical properties after injury. The interaction of collagen molecules with decorin affects collagen fibrogenesis, and scar tissue is fragile as a consequence of a large amount of decorin in the scar. We hypothesized that scar formation could be prevented by controlling decorin expression in tendinocytes. As a preliminary experiment, we treated tendinocytes with decorin antisense oligodeoxynucleotides (ODNs). Tendinocytes were isolated from Achilles tendons of New Zealand white rabbits and treated with ODN. When tendinocytes were transfected with decorin sense ODN, there was no alteration, whereas decorin antisense ODN-treated tendinocytes showed suppression of transforming growth factor (TGF)-beta1 production. Decorin and TGF-beta1-production of tendinocytes is regulated by decorin gene suppression. The results showed that the antisense approach is an attractive therapeutic strategy not only for preventing decorin deposition in scar tissue, which decreases collagen fibril diameter, but also for controlling TGF-beta1 production, which leads to organ fibrosis.

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.