Racing performance after arthroscopic removal of apical sesamoid fracture fragments in Thoroughbred horses age < 2 years: 151 cases (1989--2002)

REASONS FOR PERFORMING STUDY: Studies on arthroscopic removal of apical proximal sesamoid fracture fragments in Thoroughbred (TB) horses age > or = 2 years have reported a high success rate. However, there are no reports documenting the racing prognosis of TB horses that undergo such surgery as weanlings or yearlings. OBJECTIVES: To describe the incidence of apical proximal sesamoid fractures in immature TB horses, age < 2 years and determine probability and quality of racing performance after arthroscopic removal of such fractures in 151 TB weanlings and yearlings. METHODS: The medical records of TB horses age < 2 years that underwent arthroscopic surgery for removal of apical proximal sesamoid fracture fragments were reviewed. Follow-up information was obtained from race records. Student's t tests were used to compare performance variables of operated racehorses to that of their maternal siblings. RESULTS: Ninety-two percent (139/151) of fractures occurred in the hindlimbs and 8% (11/151) in the forelimbs (fracture of both fore- and hindlimb, n = 1). Horses with forelimb fractures had a greatly reduced probability of racing (55%) compared to those with hindlimb fractures (86%). Overall, 84% of the horses raced post operatively and had performance records similar to that of their maternal siblings, 78% (787/1006) of which raced. CONCLUSIONS: Arthroscopic removal of apical proximal sesamoid fracture fragments in TB weanlings and yearlings carries an excellent prognosis for racing in horses with hindlimb fractures and a reduced prognosis in those with forelimb fractures. Medial fractures of the forelimb carry the worst prognosis. POTENTIAL RELEVANCE: The determination of prognosis increases knowledge on apical sesamoid bone fractures and potential for arthroscopic restoration of the ability to race; and enables the value of yearlings for subsequent sale to be established.     

Radiographic changes in Thoroughbred yearlings. Part 2: Associations with racing performance

REASONS FOR PERFORMING STUDY: Although the radiographic examination of yearlings has become commonplace at some large Thoroughbred sales, there are few data to support the decisions facing veterinarians who are asked to evaluate future racing potential. OBJECTIVES: To identify radiographic changes in the fetlocks, proximal sesamoid bones, carpi, tarsi, stifles and fore feet of Thoroughbred yearlings associated with future racing performance during ages 2 and 3 years. METHODS: Radiographs from routine pre- and post sale examinations of 1162 yearlings were used to identify individual radiographic changes in sale yearlings. Starting a race, the percent of starts placed, money earned and earnings per start were used to assess racing performanceand examined for associations with the radiographic changes observed. RESULTS: Overall 946 (81%) yearlings started at least one race during ages 2 or 3 years. Fourteen of 24 (58%) yearlings with moderate or extreme palmar supracondylar lysis of the third metacarpus, 8 of 14 (57%) of those with enthesophyte formation on the proximal sesamoid bones and 19 of 30 (63%) of those with dorsal medial intercarpal joint disease started a race. The odds of starting a race when age 2 or 3 years were 3 times lower for yearlings with these changes (P < 0.01) compared with yearlings that did not have these changes. Twenty-five of 36 (69%) yearlings with proximal dorsal fragmentation of the first phalanx in the hind fetlock started a race and these yearlings were also less likely (OR = 0.51, P = 0.07) to start a race. Yearlings with enthesophyte formation on hind proximal sesamoid bones placed in a smaller percentage of starts (16%, P = 0.01) earned less money (987 US dollars, P = 0.02) and had lower earnings per start (252 US dollars, P = 0.03) compared to starters without this change. CONCLUSIONS: Although many of the changes observed on radiographs of sale yearlings do not appear to influence future racing performance, some are associated with reduced performance. POTENTIAL RELEVANCE: The results of this study are best applied in parallel with the clinical impressions of veterinarians experienced in examining radiographs of sale yearlings. Some findings support those established in the literature as incidental findings and others suggest new areas for concern not previously reported as a problem in Thoroughbred sale yearlings.     

Association between findings on palmarodorsal radiographic images and detection of a fracture in the proximal sesamoid bones of forelimbs obtained from cadavers of racing Thoroughbreds

OBJECTIVE: To determine the distribution for limbs and bones in horses with fractures of the proximal sesamoid bones and relationships with findings on palmarodorsal radiographic images. SAMPLE POPULATION: Proximal sesamoid bones obtained from both forelimbs of cadavers of 328 racing Thoroughbreds. PROCEDURE: Osteophytes; large vascular channels; and fracture location, orientation, configuration, and margin distinctness were categorized by use of high-detail contact palmarodorsal radiographs. Distributions of findings were determined. Relationships between radiographic findings and fracture characteristics were examined by use of chi2 and logistic regression techniques. RESULTS: Fractures were detected in 136 (41.5%) horses. Biaxial fractures were evident in 109 (80%) horses with a fracture. Osteophytes and large vascular channels were evident in 266 (81%) and 325 (99%) horses, respectively. Medial bones typically had complete transverse or split transverse simple fractures, indistinct fracture margins, > 1 vascular channel that was > 1 mm in width, and osteophytes in abaxial wing and basilar middle or basilar abaxial locations. Lateral bones typically had an oblique fracture and distinct fracture margins. Odds of proximal sesamoid bone fracture were approximately 2 to 5 times higher in bones without radiographic evidence of osteophytes or large vascular channels, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Biaxial fractures of proximal sesamoid bones were common in cadavers of racing Thoroughbreds. Differences between medial and lateral bones for characteristics associated with fracture may relate to differences in fracture pathogeneses for these bones. Osteophytes and vascular channels were common findings; however, fractures were less likely to occur in bones with these features.     

Radiographic changes in Thoroughbred yearlings. Part 1: Prevalence at the time of the yearling sales

REASONS FOR PERFORMING STUDY: Radiography in presale examinations of TB yearlings has become standard practice in recent years. OBJECTIVES: To describe the prevalence and distribution of radiographic changes in the fetlocks, carpi, tarsi, stifles and fore feet of Thoroughbred yearlings in central Kentucky when these joints were examined as part of routine pre- and post sale evaluations. METHODS: Horses subjected to radiographs included the fore (n = 1127) and hind (n = 1102) fetlocks, carpi (n = 1130), tarsi (n = 1101), stifles (n = 660) and fore feet (n = 300). Radiographic changes were categorised by location and type of change present (e.g. lucency, fragment) for each series. RESULTS: In the fore fetlocks 1.6% had fragmentation of the proximal dorsal first phalanx and 0.5% fragmentation of the proximal palmar aspect. In the hind fetlocks 5.9% had fragmentation at the plantar aspect and 3.3% fragmentation dorsally. Lucencies, fragments or loose bodies were detected at the dorsal aspect of the distal third metacarpus in 2.8% and, at the same location on the third metatarsus, 3.2%. Most yearlings (98%) had vascular channels in the proximal sesamoid bones and irregular vascular channels (> 2 mm wide or with nonparallel sides) were more common (79%) than regular vascular channels (56%). The intermediate ridge of the distal tibia was the most common location for fragmentation in the tarsus (4.4%). CONCLUSIONS: While some radiographic changes, e.g. vascular channels in proximal sesamoid bones, are very common in Thoroughbred yearlings, others, e.g. fragmentation or subchondral lucency within joints are quite rare usually affecting less than 5% of the population. POTENTIAL RELEVANCE: Veterinarians should expect to find radiographic changes in Thoroughbreds presented for examination prior to the yearling sales. The rarity of some changes thought to affect soundness or racing performance will make further invesigation of these conditions in horses without clinical signs more difficult.     

Racing performance after arthroscopic removal of apical sesamoid fracture fragments in Thoroughbred horses age > or = 2 years: 84 cases (1989-2002)

REASONS FOR PERFORMING STUDY: Studies have shown that surgical removal of apical fracture fragments in Standardbred racehorses carries the best prognosis for return to racing performance, but there are no reports involving mature Thoroughbred (TB) racehorses. OBJECTIVES: To describe the incidence of apical proximal sesamoid fractures in TB racehorses and determine probability and quality of racing performance after arthroscopic removal of such fractures in TB racehorses age > or = 2 years. METHODS: Medical records and pre- and post operative race records of TB racehorses age > or = 2 years that underwent arthroscopic surgery for removal of apical proximal sesamoid fracture fragments were reviewed. RESULTS: Sixty-four percent of fractures occurred in the hindlimbs and 36% in the forelimbs. Horses with forelimb fractures had a reduced probability of return to racing (67%) compared to those with hindlimb fractures (83%), but the majority (77%) of treated horses recovered to return to race post operatively. Horses with medial forelimb fractures raced at only a 47% rate; those with suspensory desmitis at 63%. Unlike Standardbreds, there was no difference in probability of racing post operatively between horses that had, and had not, raced preoperatively. CONCLUSIONS: Data show that arthroscopic removal of apical proximal sesamoid fracture fragments is successful at restoring ability to race in skeletally mature TB horses without evidence of severe suspensory ligament damage. Prognosis for return to racing is excellent (83%) in horses with hindlimb fractures and good (67%) in those with forelimb fractures. Medial fractures of the forelimb have the worst prognosis. POTENTIAL RELEVANCE: The determination of prognosis for differing sites in TB racehorses should increase knowledge of apical proximal sesamoid bone fractures and improve communication from veterinarian to owner, and trainer, on the potential for arthroscopic restoration of the ability to race.     

Risk factors for proximal sesamoid bone fractures associated with exercise history and horseshoe characteristics in Thoroughbred racehorses

OBJECTIVE: To assess individual and combined associations of high-speed exercise and horseshoe characteristics with risk of forelimb proximal sesamoid bone fractures and proximal sesamoid bone midbody fractures in Thoroughbred racehorses. ANIMALS: 269 deceased Thoroughbred racehorses. PROCEDURES: A case-control study design was used to compare 121 horses with a fracture of at least 1 of 4 forelimb proximal sesamoid bones (75 horses had a midbody fracture) and 148 horses without a forelimb proximal sesamoid bone fracture. Univariable and multivariable logistic regression analyses were used to evaluate potential risk factors for association with proximal sesamoid bone fracture. RESULTS: Compared with horses that died without proximal sesamoid bone fractures, horses that died with proximal sesamoid bone fractures were more likely to be sexually intact males, spend more time in active trainingand racing, complete more events, train and race longer since their last layup, have higher exercise intensities during the 12 months prior to death, and have greater cumulative distances for their career. Horses with proximal sesamoid bone midbody fractures were more likely to be sexually intact males, train and race longer since their last layup, and have higher exercise intensities during the 12 months prior to death. CONCLUSIONS AND CLINICAL RELEVANCE: Limitingexercise intensity and the continuous time spent in activity duringa horse's career may decrease the frequency of forelimb proximal sesamoid bone fractures in Thoroughbred horses.     

Prevalence and distribution of radiographically evident lesions on repository films in the hock and stifle joints of yearling Thoroughbred horses in New Zealand

AIM: To characterise the prevalence and distribution of radiographic changes in the hocks and stifles of Thoroughbred yearling colts and fillies in New Zealand and compare them with other populations of young horses. METHODS: Repository radiographs taken in New Zealand for the 2003-2006 Thoroughbred national yearling sales were evaluated by two individual readers. The distribution of radiographic changes was classified as left side only, right side only, or bilateral. Lesions were categorised by type, location, and sex of the yearling. Complete sets of hock and stifle radiographs of 1,505 yearlings were evaluated. RESULTS: Osteophytes or enthesophytes were seen radiographically in the distal tarsal joints of 460/1,505 (31%) horses. Osteochondrosis was seen in the tibiotarsal joint of 66/1,505 (4%) horses, and in the femoropatellar joint of 40/1,505 (3%) horses. Radiographic lucency in the distal or axial aspect of the medial femoral condyle was seen in 247/1,505 (16%) horses, and lucencies consistent with subchondral cyst-like lesions were seen in 26/1,505 (2%) horses. No significant difference was seen in the proportion of colts and fillies with radiographic changes in the hock or stifle. The prevalence of osteochondrosis and subchondral cyst-like lesions in the stifles of the yearlings examined were similar to those reported in Thoroughbred yearling sale horses in the United States of America (USA). The prevalence of changes in the distal tarsal joints was similar to those reported in Standardbred and Thoroughbred yearlings from Scandinavia and the USA. CONCLUSIONS: There was no significant difference in the prevalence of osteochondrosis in the hock and stifle, lucencies in the distal medial femoral condyle, or radiographic changes in the distal tarsal joints between colts and fillies. CLINICAL RELEVANCE: Establishment of the normal prevalence and distribution of radiographic changes in the hocks and stifles of Thoroughbred yearlings in New Zealand will allow comparison with populations of young horses in other countries. Knowledge of the normal prevalence will assist veterinarians to identify abnormally high or low prevalences on individual farms, to further investigate the pathogenesis of the lesions.     

Frequency of and risk factors for epistaxis associated with exercise-induced pulmonary hemorrhage in horses: 251,609 race starts (1992-1997)

OBJECTIVE: To determine the frequency of epistaxis during or after racing among racehorses and identify factors associated with development of epistaxis. DESIGN: Retrospective study. SAMPLE POPULATION: 247,564 Thoroughbred and 4,045 Anglo-Arab race starts. PROCEDURE: Race start information (breed, age, sex, racing distance, and race type) was obtained for Thoroughbred and Anglo-Arab horses racing in Japan Racing Association-sanctioned races between 1992 and 1997. All horses that raced were examined by a veterinarian within 30 minutes of the conclusion of the race; any horse that had blood at the nostrils was examined with an endoscope. If blood was observed in the trachea, epistaxis related to exercise-induced pulmonary hemorrhage (EIPH) was diagnosed. RESULTS: Epistaxis related to EIPH was identified following 369 race starts (0.15%). Frequency of EIPH-related epistaxis was significantly associated with race type, age, distance, and sex. Epistaxis was more common following steeplechase races than following flat races, in older horses than in horses that were 2 years old, following races < or =1,600 m long than following races between 1,601 and 2,000 m long, and in females than in sexually intact males. For horses that had an episode of epistaxis, the recurrence rate was 4.64%. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that frequency of EIPH-related epistaxis in racehorses is associated with the horse's age and sex, the type of race, and the distance raced. The higher frequency in shorter races suggests that higher intensity exercise of shorter duration may increase the probability of EIPH.     

Catastrophic biaxial proximal sesamoid bone fractures in UK Thoroughbred races (1999–2004): Horse characteristics and racing history

Reason for performing study: Catastrophic biaxial proximal sesamoid bone fractures (PSBF) have not yet been described in detail in the UK racing population. Objectives: To determine the incidence and relative risk (RR) of PSBF in different types of racing in the UK; and to describe horse‐level characteristics and racing histories of horses sustaining these injuries. Methods: Distal limbs were collected from all racehorses suffering catastrophic fractures during racing at all 59 racecourses in the UK, in a prospective study from February 1999 to December 2004. Post mortem investigation identified the anatomical location and type of fracture. Horse, racing history, race and racecourse details were obtained. Characteristics of the horses that sustained PSBF were described. The incidence and RR of PSBF in the different types of racing in the UK were calculated. Results: Thirty‐one horses suffered PSBF during the study period. The incidence of PSBF in all types of race was 0.63 per 10,000 starts (31/494,744). The incidence was highest in flat races on all weather surfaces (1.63 per 10,000 starts: 12/73,467; RR = 4.4 when compared to turf flat racing). Affected horses had an average age of 5.6 years and had started a mean of 28 races at the time of fracture. Conclusion and potential relevance: There is a strong association between type of racing surface and PSBF. Horses competing in flat races on all weather surfaces have an increased risk of PSBF. These fractures appear to happen in experienced horses with several starts, with few fractures occurring within the first season of racing. Further research should focus on identification of underlying pathology of these fractures. Epidemiological studies aimed at the identification of risk factors for PSBF in the UK racing population would require a large number of cases acquired over many years given the relatively low incidence of PSBF.     

Prevalence of radiographic changes in yearling and 2-year-old Quarter Horses intended for cutting

Reasons for performing study: There have been many studies that document radiographic findings in young Thoroughbred and Standardbred horses. No such studies have been performed in Quarter Horses. Objective: To describe the prevalence of radiographic changes in the stifles, tarsi, carpi and fetlocks of young Quarter Horses intended for cutting. Methods: Radiographs of yearling and 2‐year‐old Quarter Horses were obtained from a radiograph repository and a private farm. The carpi, tarsi, fetlocks and stifles were evaluated and radiographic changes categorised by type and location. The frequency of changes was calculated and comparisons were made between the 2 age groups. Results: Of 458 included horses, 408 (89.1%) had radiographic changes, most of which were in the tarsi (304, 69.4%) followed by the stifles (202, 44.5%), hind fetlocks (155 of 355, 43.7%), fore fetlocks (131 of 361, 36.3%) and carpi (27 of 342, 7.9%). Of the horses with stifle changes, 188 (93.1%) were in the medial femoral condyle (MFC). There was a significant difference between the age groups for changes on the distal intermediate ridge of the tibia (DIRT), hindlimb middle phalanx (P2) osteophytes and proximal tibial osteophytes. Conclusions: There is a high prevalence of radiographic changes in presale survey radiographs, especially in the stifles and tarsi, of young Quarter Horses intended for cutting. Potential relevance: Veterinarians examining presale radiographs at cutting horse sales should expect a high prevalence of radiographic changes in this population of horses. Work to determine the clinical relevance of these radiographic changes is currently ongoing.     

Arthroscopic removal of fracture fragments involving a portion of the base of the proximal sesamoid bone in horses: 26 cases (1984-1997)

OBJECTIVE: To determine the outcome of horses with basal fractures of the proximal sesamoid bone from which a fracture fragment involving a portion of the base of the bone was removed arthroscopically and to determine whether fragment size was associated with outcome. DESIGN: Retrospective study. ANIMALS: 26 horses. PROCEDURE: Dorsopalmar and axial-abaxial lengths of the fracture fragment were measured on the dorsopalmar and mediolateral radiographic views, respectively, and percentage of the base of the sesamoid bone involved was estimated. Fractures were classified as grade 1 (< or = 25% of the base involved) or grade 2 (> 25% but < 100% of the base involved). Outcome was classified as successful if the horse started at least 2 races or unsuccessful if the horse started only 1 race or failed to return to racing. RESULTS: There were 24 racehorses and 2 nonracehorses. Twelve (50%) of the racehorses returned to racing and started at least 2 races. Eight of 14 horses with grade-1 fractures and 4 of 10 horses with grade-2 fractures had a successful outcome. Ten of 16 horses without associated articular disease had successful outcomes, compared with 2 of 8 horses with associated articular disease. However, fragment size and presence of associated articular disease were not significantly associated with outcome. CONCLUSIONS AND CLINICAL RELEVANCE: Horses with basal fractures of the proximal sesamoid bone from which a fracture fragment involving a portion of the base of the bone is removed arthroscopically have a fair prognosis for return to racing.     

Race-start characteristics and risk of catastrophic musculoskeletal injury in Thoroughbred racehorses

OBJECTIVE: To identify race-start characteristics associated with catastrophic musculoskeletal (MS) injury in Thoroughbred racehorses at 2 racetracks in Florida during 1995 through 1998. DESIGN: Matched case-control study. ANIMALS: 97 Thoroughbreds (case horses) that incurred a catastrophic MS injury during racing and 388 Thoroughbreds (control horses) randomly selected from noninjured participants and matched on the basis of racetrack and year. PROCEDURE: Incidence of MS injury was calculated for all race meets at 2 racetracks in Florida from 1995 through 1998. Race-start characteristics were compared among case and control horses, using conditional logistic regression. RESULTS: Overall incidence of MS injury was 1.2/1,000 race starts (97/79,416 starts). Incidence of injury was significantly higher for turf races (2.3/1,000 starts) than for dirt races (0.9/1,000 starts). Sex, number of days since last race, and racing surface were associated with risk of injury; geldings, > or = 33 days since the last race, and turf racing surface were associated with a higher risk of injury. CONCLUSIONS AND CLINICAL RELEVANCE: Incidence of injury among Thoroughbreds in Florida was associated with sex, number of days since last race, and racing surface. Days since last race may have been an indicator of previous health and lameness problems. Racing surface may have been a risk factor for MS injury because turf races tended to be more competitive than dirt races. Horses running in turf races were more likely to participate in races with a large field, handicap races, long races, and races with high purses.     

A study on the pathogenesis of equine sesamoiditis: the effects of experimental occlusion of the sesamoidean artery

In this study the potential role of circulatory disturbances in the pathogenesis of sesamoiditis was investigated by studying the clinical and histological effects of experimental occlusion of the sesamoidean artery, which is the main nutrient artery of the proximal sesamoid bone (PSB). For this purpose, five adult Dutch Warmblood horses were used in which the sesamoidean artery was occluded with polyvinyl alcohol foam particles. Bone labelling was carried out with oxytetracycline and calcein. All animal were checked clinically three times a week and radiographically at days 14, 21, 28 and 35. At day 35 the animals were killed and the fetlock was dissected and macroscopically evaluated. The PSBs were isolated and radiographed and the soft tissues adjacent to the abaxial side of the PSBs were histologically examined [routine histology and for the neuropeptides substance P (SP) and calcitonin gene-related peptide (CGRP)]. The PSBs were divided into bony slices which were radiographed and evaluated histologically (routine, SP, CGRP, fluorescence). All horses showed a slight lameness that gradually diminished. Radiographically enlarged vascular channels were seen in only one horse. Histological data showed that on average 60% (range 37-89%) of the total area had been deprived of vascularization. In two horses an increase in the extent of the arterial network from the basal side of the PSB was seen. Only in the horse with the greatest extent of occlusion were bone necrosis and a reactively increased uptake of fluorochromes adjacent to the occluded arteries found. Bone density did not change. The distribution of neuropeptides in the surrounding soft tissues was not affected by the occlusion. From this study, it can be concluded that a large part of the arterial supply to the PSB can be interrupted without provoking histological and/or radiographic changes that are consistent with clinical sesamoiditis. Therefore, it seems very improbable that circulatory disturbances are a primary aetiopathogenic factor in the disease.     

Racing and sales performance after unilateral or bilateral single transphyseal screw insertion for varus angular limb deformities of the carpus in 53 thoroughbreds

Objective: To evaluate the racing and sales performance of Thoroughbred horses with varus angular limb deformities of the carpus treated by unilateral or bilateral single transphyseal screw (STS) placement. Study Design: Case series. Animals: Thoroughbred horses (n=53). Methods: Medical records (January 1, 2005–December 31, 2006) of yearling Thoroughbreds treated for carpal angular limb deformity by transphyseal screw insertion in the distal aspect of the radius were reviewed. Retrieved data were sex, surgery, and screw removal dates, surgical site, appearance, limb(s) affected, type of angular limb deformity, and degree of angular deviation measured by a goniometer. Racing and sales data were collected for analysis from an online racing site for all treated horses and their maternal siblings. Results: No significant differences were identified between treated horses and their maternal siblings in yearling sale price, 2‐year‐olds in training sale price, percent starters, percent winners, and starts, earnings, and earnings/start made during the 2‐ and 3‐year old years. Conclusions: No deleterious effects on sales or racing performance were identified after use of STS in the distal aspect of the radius of Thoroughbreds for the treatment of varus angular limb deformities of the carpus.     

BIPARTITE PROXIMAL SESAMOID BONES IN YOUNG THOROUGHBRED HORSES

Twelve foals with unusual sesamoid development were found in a population of 107 Thoroughbred foals (60 males, 47 females) over a three year period. Radiographic examination was done at 14 days of age and at 42 day intervals thereafter. The routine administration was of a dorsopalmar view of the proximal sesamoid bones in the left forelimb. Changes of the proximal sesamoid bones were found in 11% of the foals between 14 and 56 days of age. The change was a radiolucent line at the junction of the middle and proximal third of the sesamoid bone. Of those which were observed with sesamoid bone changes, 8 had a normal radiographic appearance at 60 days. In most foals at least 2 or 3 sesamoid bones of the forelegs were affected. In some only 1 sesamoid bone was affected. The changes did not correlate with a clinical joint disorder. However, females seemed to be affected more than males. This condition may be similar to bipartite sesamoid bones described by others and probably a manifestation of secondary ossification centers.     

Osteomyelitis of the axial border of the proximal sesamoid bones in seven horses

Destructive lesions of the axial region of the proximal sesamoid bones were identified by radiography in eight fetlocks and seven lame adult horses. Lameness ranged from 2 to 5 (mean 4; scale 1 to 5) at the time of examination, with a duration of 10 days to two years (mean 5.6 months). Destructive lesions involved both proximal sesamoid bones when examined radiographically and were situated primarily at the level of the mid-body and apical region of the axial borders. Some lesions were cystic, whereas others eroded the axial border more diffusely. Scintigraphy revealed markedly increased activity within the proximal sesamoid bones of the clinically lame limb of four of the five horses examined. In four horses, post mortem computed tomography revealed axial border bone destruction and cavitary lesions within cancellous bone of affected proximal sesamoid bones. Lesions seen by computed tomography were larger than those identified on radiographic examination. Cavitary lesions not seen radiographically were identified in the proximal sesamoid bones of two clinically unaffected fetlocks examined for comparison in two of the seven horses. Evidence of acute, subacute or chronic/reparative osteomyelitis of the axial region of the proximal sesamoid bones was seen in the 10 fetlocks identified as abnormal from radiography or computed tomography. Also, three horses had septic synovitis of the flexor sheath of the clinically affected limb; of these, two had septic arthritis of the fetlock joint.     

Scintigraphic evaluation of metacarpophalangeal and metatarsophalangeal joints in clinically sound horses.

The purpose of this study was to describe the pattern of radiopharmaceutical uptake in the metacarpophalangeal (MCP) and metatarsophalangeal (MTP) (fetlock) joints in clinically sound horses. Scintigraphic images from 29 clinically normal horses were evaluated. All the images were assessed subjectively. The lateral views were assessed quantitatively using vertical line profiles through the center of the joint, and mean ratios of radiopharmaceutical uptake were calculated from regions of interest around the third metacarpal or metatarsal bones, and the proximal phalanx and proximal sesamoid bones. From the vertical line profiles, in the majority of forelimbs (65%) the peak activity of radiopharmaceutical distribution was at the proximal region of the proximal phalanx, with a significantly lower activity within the condyles of the third metacarpal bone. However, in 84% of hindlimbs there was a broader profile peak incorporating the condyles of the third metatarsal bone and the proximal aspect of the proximal phalanx, indicating a more generalized even uptake of radiopharmaceutical across the MTP joint. When the regions of interest were compared between front and hindlimbs, there was no significant difference between proximal phalanx and proximal sesamoid bones, but the distal condyles of the third metacarpal bone of the forelimb had significantly lower radiopharmaceutical activity than hindlimbs (P < 0.04). In lateral images, the mean forelimb ratios tended to be higher in the left MCP joint compared with the right (P = 0.069). In hindlimbs, the mean ratios tended to be higher in the right MTP joint than the left (P = 0.052). There was no significant effect of age.     

Association between race history and risk of superficial digital flexor tendon injury in Thoroughbred racehorses

OBJECTIVE: To determine whether race history, including the number of races and total race distance, was associated with risk of superficial digital flexor tendon (SDFT) injury in Thoroughbred racehorses in Japan. DESIGN: Matched case-control study. ANIMALS: 515 Thoroughbred racehorses (case horses) that sustained an SDFT injury during training or racing in Japan during 2002 and 951 horses (control horses) without SDFT injury that were matched with case horses on the basis of age and month of the latest race. PROCEDURE: Variables related to race history were compared between case and control horses by means of conditional logistic regression. RESULTS: The odds of SDFT injury increased as mean race distance and mean body weight at race time increased. Compared with females that had never competed in steeplechase races, males regardless of steeplechase race history and females that had competed in steeplechase races had higher odds of SDFT injury. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that longer mean distance per race, heavier mean body weight at race time, steeplechase experience, and sex (male) increased the risk of SDFT injury in Thoroughbred racehorses.     

Risk of fatal distal limb fractures among Thoroughbreds involved in the five types of racing in the United Kingdom

The risk of fatal distal limb fractures in thoroughbreds racing in the UK was calculated and shown to vary considerably between the different types of race. Flat turf racing was associated with the lowest risk (0.4 per 1000 starts) and national hunt flat racing was associated with the highest risk (2.2 per 1000 starts). The types of fracture were classified by detailed radiographic and postmortem examinations of all the cases recorded over two years, and the distribution of the different types of fracture in the five main types of racing was examined. Overall, lateral condylar fractures of the third metacarpus were the most common, and they were also the most common in national hunt-type races (hurdle, steeplechase and national hunt flat races). In all-weather flat racing biaxial proximal sesamoid fractures were most common, and in turf flat racing fractures of the first phalanx were most common. The risk of fractures of more than one bone was greater in national hunt-type races.