A. Nagy

A veterinary review of endurance riding as an international competitive sport

The popularity of competitive endurance riding is growing worldwide and this has led to considerable changes in the discipline (e.g., fitter and faster horses and different types of injuries), which create challenges to all involved in the sport, including veterinarians. During endurance competitions, horses are closely monitored by veterinarians throughout the ride, with the aim of removing from the competition animals whose welfare appears to be endangered. This close monitoring provides veterinarians with an insight into problems during competitions. However, there is a relatively small amount of clinically relevant, evidence-based data published on endurance horses, and this article reviews the evolution of the discipline, the published information on epidemiological data on endurance rides, the problems veterinarians face at competitions, and highlights those areas where research is warranted.

CLINICAL AND DIAGNOSTIC IMAGING FINDINGS IN HORSES WITH SUBCHONDRAL BONE TRAUMA OF THE SAGITTAL GROOVE OF THE PROXIMAL PHALANX

Eight sports horses with unilateral (4) or bilateral (3) forelimb or unilateral hindlimb (1) lameness had subtle radiologic abnormalities of the subchondral bone of the sagittal groove of the proximal phalanx associated with moderate or intense increased radiopharmaceutical uptake. High-field or low-field magnetic resonance (MR) imaging confirmed the presence of a fissure fracture or subchondral and trabecular bone trauma. Seven of eight lesions were located approximately midway between the dorsal and palmar cortices of the proximal phalanx; the eighth was sited more dorsally. Two horses underwent follow-up MR imaging and abnormal signal intensity persisted, with little change.

Diffusion of contrast medium after four different techniques for analgesia of the proximal metacarpal region: an in vivo and in vitro study

REASONS FOR PERFORMING STUDY There is limited information on potential diffusion of local anaesthetic solution after various diagnostic analgesic techniques of the proximal metacarpal region. OBJECTIVE To document potential distribution of local anaesthetic solution following 4 techniques used for diagnostic analgesia of the proximal metacarpal region. METHODS Radiodense contrast medium was injected around the lateral palmar or medial and lateral palmar metacarpal nerves in 8 mature horses, using 4 different techniques. Radiographs were obtained 0, 10 and 20 min after injection and were analysed subjectively. A mixture of radiodense contrast medium and methylene blue was injected into 4 cadaver limbs; the location of the contrast medium and dye was determined by radiography and dissection. RESULTS Following perineural injection of the palmar metacarpal nerves, most of the contrast medium was distributed in an elongated pattern axial to the second and fourth metacarpal bones. The carpometacarpal joint was inadvertently penetrated in 4/8 limbs after injections of the palmar metacarpal nerves from medial and lateral approaches, and in 1/8 limbs when both injections were performed from the lateral approach. Following perineural injection of the lateral palmar nerve using a lateral approach, the contrast medium was diffusely distributed in all but one limb, in which the carpal sheath was inadvertently penetrated. In 5/8 limbs, following perineural injection of the lateral palmar nerve using a medial approach, the contrast medium diffused proximally to the distal third of the antebrachium. CONCLUSIONS AND POTENTIAL RELEVANCE Inadvertent penetration of the carpometacarpal joint is common after perineural injection of the palmar metacarpal nerves, but less so if both palmar metacarpal nerves are injected using a lateral approach. Following injection of the lateral palmar nerve using a medial approach, the entire palmar aspect of the carpus may be desensitised.

Radiographic, scintigraphic and magnetic resonance imaging findings in the palmar processes of the distal phalanx

REASON FOR PERFORMING STUDY Increased radiopharmaceutical uptake (IRU) in the palmar processes of the distal phalanx is recognised but its clinical significance has not been established. OBJECTIVES To investigate the relationship between radiographic, scintigraphic and MRI findings in the palmar processes of the distal phalanx. HYPOTHESES Increased radiopharmaceutical uptake in the palmar processes of the distal phalanx is associated with MRI abnormalities; IRU and MRI abnormalities are over-represented in lame limbs. METHODS Clinical data, radiographic, scintigraphic and MRI findings of 258 horses with unilateral or bilateral foot pain were recorded. Scintigraphic images were assessed subjectively and using region of interest and profile analysis, and intensity of IRU graded. Alteration in signal intensity in T1 and T2 weighted and short tau inversion recovery (STIR) MR images was documented, and MRI abnormalities graded. Relationships between scintigraphic, MRI, radiographic and clinical findings were assessed. RESULTS Focal IRU was over-represented in palmar processes with most MRI abnormalities. There was a significant correlation between IRU and MRI grades and IRU was over-represented in palmar processes with MRI Grades 2 and 3. Both IRU and MRI abnormalities occurred most frequently in the medial palmar process. MRI abnormalities were generally over-represented in lame limbs. The most common MRI abnormality was mild diffuse decreased signal intensity in T1 and T2 weighted images, which was associated with mild generalised IRU. CONCLUSIONS There was considerable variation in the radiographic, scintigraphic and MRI appearance of palmar processes of the distal phalanx. Focal IRU in a palmar process was seen in association with MRI abnormalities and lameness or as an incidental finding. Magnetic resonance imaging abnormalities occurred more frequently in lame limbs, either contributing to lameness or as a consequence of lameness. POTENTIAL RELEVANCE Further investigation is needed to establish the clinical significance of MRI abnormalities in the palmar processes of the distal phalanx and their relationship with lesions in adjacent structures.

Magnetic resonance imaging findings in the carpus and proximal metacarpal region of 50 lame horses

REASONS FOR PERFORMING STUDY There is limited information on magnetic resonance imaging (MRI) findings in the carpus and proximal metacarpal region of lame horses. OBJECTIVES To document MRI findings in horses with lameness localised to the carpus and/or proximal metacarpal region. METHODS Clinical records of horses that underwent MRI of the carpus and/or proximal metacarpal region at the Animal Health Trust between January 2003 and September 2010 were reviewed. Magnetic resonance images of all horses and available radiographs, ultrasonographic and scintigraphic images were assessed. When possible, MRI findings were related to the results of other diagnostic imaging techniques. RESULTS Seventy-two MR studies of 58 lame limbs in 50 horses from a broad range of work disciplines and ages were reviewed. The most commonly detected primary abnormality was decreased signal intensity in T1- and T2-weighted images in the medial aspect of the carpal bones and/or the proximomedial aspect of the metacarpal bones (n = 29). Nine horses had syndesmopathy between the second and third metacarpal bones. In 6 horses the primary abnormalities were identified in the palmar cortex of the third metacarpal bone (McIII). Significant abnormalities of the suspensory ligament (SL) with associated lesions in the adjacent palmar cortex of the McIII were seen in 4 limbs. Ligament and associated osseous abnormalities between the second and third carpal bones and second and third metacarpal bones were detected in 4 limbs. CONCLUSIONS AND POTENTIAL RELEVANCE Magnetic resonance imaging enabled diagnosis of a variety of lesions not detected by conventional imaging in horses from a wide range of work disciplines. The distribution of injury types differed considerably from previous studies.

Descriptive epidemiology and risk factors for eliminations from Fédération Equestre Internationale endurance rides due to lameness and metabolic reasons (2008–2011)

REASONS FOR PERFORMING THE STUDY There is limited information on international endurance rides and on risk factors for eliminations. OBJECTIVES To describe and compare the frequency of occurrence of elimination due to lameness and metabolic reasons from Fédération Equestre Internationale (FEI) endurance rides (≥100 km) during 2008-2011 in all countries and to assess risk factors for elimination due to lameness and metabolic reasons. STUDY DESIGN Retrospective unmatched case-control study. METHODS Data collected from the FEI website included the following: the country where the ride was held; the year; the result for each horse-rider combination; the number of entries in each class; whether the class was restricted to young riders; and the winning speed. Descriptive data were summarised, and univariable and multivariable logistic regression analyses were performed to assess risk factors for eliminations due to lameness and metabolic reasons. RESULTS Between 2008 and 2011, there were 30,741 horse starts at FEI endurance rides of 100-160 km distance in 47 countries. Of all started horses, 30% were eliminated for lameness. Eliminations for metabolic reasons were recorded for 8.7% of all started horses. There was a large range of winning speeds amongst countries (10.2-29.5 km/h). Multivariable analysis revealed that the risk of elimination due to lameness was significantly associated with the country where the ride was held, the year, the distance of the ride and the number of entries. Elimination for metabolic reasons was significantly associated with the country where the ride was held, the year and the number of entries. CONCLUSIONS Differences existed among elimination rates at FEI endurance rides in different countries (2008-2011). Lameness was the most common reason for elimination globally. POTENTIAL RELEVANCE These results provide objective global data on endurance riding that can replace anecdotal information, which has been the base of opinions, decisions and regulations. The Summary is available in Chinese - see Supporting information.

Horse-, rider-, venue- and environment-related risk factors for elimination from Fédération Equestre Internationale endurance rides due to lameness and metabolic reasons

REASONS FOR PERFORMING THE STUDY There is limited information on risk factors for elimination from endurance rides. OBJECTIVES To assess risk factors for elimination for lameness and metabolic reasons from Fédération Equestre Internationale (FEI) endurance rides of 80-160 km distance. STUDY DESIGN Unmatched case-control. METHODS Venue-, horse- and rider-related data were collected from the FEI website. Data on weather conditions and terrain were collected at the venue. Univariable and multivariable logistic regression analyses were used to assess risk factors for elimination for lameness and metabolic reasons, respectively. RESULTS Multivariable logistic regression on 1435 horse starts revealed that the venue was significantly associated with elimination for lameness (P = 0.013). The horses previous experience at a greater distance than the current ride (odds ratio [OR] = 0.82, 95% confidence interval [CI] 0.71-0.95, P = 0.008) and > 90 days elapsed since the last FEI ride (OR = 0.78, 95% CI 0.62-0.99, P = 0.044) significantly reduced the risk of elimination for lameness. In the multivariable model for elimination for metabolic reasons, the venue (P = 0.011), increasing number of started horses (OR = 1.008, 95% CI 1.00-1.01, P = 0.001) and deep sand or soil on the track (OR = 1.98, 95% CI 1.17-3.35, P = 0.001) significantly increased the risk of elimination for metabolic reasons. CONCLUSIONS Reducing the frequency of racing may contribute to decreased risk of elimination for lameness. Competing in deep sand or soil may contribute to exhaustion, leading to elimination for metabolic reasons. Eliminations are likely to be the end result of a complex process, and not every aspect was or can be measured. Further studies with a larger number of horse starts and assessment of variables that could not be measured in this study may identify additional risk factors that can be modified.

Scintigraphic examination of the cartilages of the foot.

REASONS FOR PERFORMING STUDY Radiographic examination of the cartilages of the foot is well documented; however, there is limited information about their scintigraphic assessment. OBJECTIVES To evaluate the scintigraphic appearance of the cartilages of the foot using subjective and quantitative image analysis and to correlate radiographic and scintigraphic findings. HYPOTHESES An ossified cartilage would have similar radiopharmaceutical uptake (RU) to the ipsilateral aspect of the distal phalanx; RU would extend throughout the length of the ossified cartilage; a separate centre of ossification (SCO) would be identified on a scintigraphic image; and fracture or trauma to an ossified cartilage would manifest as increased RU (IRU). METHODS Front feet (n = 223) of horses (n = 186) that had dorsopalmar radiographic views and dorsal scintigraphic images were included in the study. The cartilages of the foot were graded radiographically and scintigraphically. Quantitative evaluation of the scintigraphic images was carried out using region of interest (ROI) analysis. For statistical analysis RU ratios were used. Correlations between a radiographically detected SCO and focal RU and between IRU and radiographic abnormalities were assessed. RESULTS There was a good correlation and an excellent agreement between radiographic and scintigraphic grades. ROI analysis showed a proximal to distal increase in RU ratios within each cartilage of the foot. A radiographically identified SCO could be detected scintigraphically in 12/17 feet (70.6%). Thirty-eight feet had IRU in the region of a cartilage, 25 of which (65.8%) had corresponding radiographic abnormalities. Fracture of an ossified cartilage was associated with IRU in all horses. CONCLUSIONS AND POTENTIAL RELEVANCE Scintigraphy may give information about the potential clinical significance of ossification of the cartilages of the foot and associated lesions, therefore prompting further investigation by use of a uniaxial ipsilateral palmar nerve block and imaging, using either magnetic resonance imaging and/or computed tomography.

Magnetic resonance anatomy of the carpus of the horse described from images acquired from low-field and high-field magnets.

Cadaver carpi of 30 mature horses with no history of carpal or proximal metacarpal pain were examined using low-field (0.27 T) and high-field (1.5 T) magnetic resonance imaging (MRI). Normal MRI anatomy in transverse, sagittal, and dorsal plane images was determined by comparison with anatomical specimens and standard texts. Subchondral bone and cortical bone thickness measurements were obtained from standardised sites. There was variable subchondral bone thickness in the radius and carpal bones; subchondral bone thickness was consistently larger at dorsal compared with palmar sites in the proximal row of carpal bones. The endosteal surface of the subchondral bone was smooth. The shape of the ulnar carpal bone was variable and one or more small osseous fragments were identified palmar to the bone in 5/30 limbs. There was no evidence to suggest that these were pathological fractures or avulsions of the lateral palmar intercarpal ligament. The amount of muscle tissue in the superficial and deep digital flexor tendons in the proximal aspect of the carpus varied, but none was present at the level of the middle carpal joint and distally. Several structures could be evaluated that cannot be imaged using radiography, ultrasonography, or arthroscopy, including the transverse intercarpal ligaments, the radiocarpal ligament, the short palmar carpal ligaments, and the carpometacarpal ligaments. Anatomical variations not previously described were identified, including the layers of the medial aspect of the carpal fascia. Knowledge of the variation in MRI appearance of the carpus of nonlame horses is helpful for interpretation of MR images of lame horses.

Magnetic resonance imaging and histological findings in the proximal aspect of the suspensory ligament of forelimbs in nonlame horses

REASONS FOR PERFORMING STUDY Detailed magnetic resonance imaging (MRI) and histological appearances of the proximal aspect of the suspensory ligament (PSL) in the forelimb of nonlame horses have not been previously documented. OBJECTIVES 1) to describe detailed anatomy of the PSL, 2) describe high- and low-field MRI and histological appearances of the PSL and surrounding structures in the forelimb of horses with no carpal or proximal metacarpal pain, 3) assess the relationship between age, breed, gender, height, bodyweight and MRI findings and 4) describe the histological appearance of the PSL and compare this with MRI findings. METHODS High- and low-field MR images of the PSL and related structures from 30 cadaver limbs of nonlame horses were analysed subjectively and objectively. Univariable and multivariable linear regression analyses were used to assess the association of age, breed, gender, height and bodyweight with MRI findings. Histological and MRI findings of the PSL of 9 limbs were compared subjectively. RESULTS The collagenous tissue of the PSL had low to intermediate signal intensity depending on the pulse sequence. There was a large variation among horses in the amount, shape and signal intensity of the muscle and adipose tissue within the PSL. Comparison of MR images with histological slides revealed that the high signal intensity areas corresponded to adipose tissue and intermediate signal intensity areas to muscle tissue. The medial lobe of the PSL had a smaller cross sectional area (CSA) than the lateral lobe; there was a positive association between CSA of the PSL and both horse height and bodyweight (P<0.001). CONCLUSIONS AND POTENTIAL RELEVANCE The large variability in the MRI appearance of the PSL in nonlame horses should be borne in mind when interpreting MR images of lame horses.