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.     

Risk factors for race-associated sudden death in Thoroughbred racehorses in the UK (2000-2007)

Reasons for performing study: Sudden death adversely affects racehorse welfare, jockey safety and the public perception of horseracing. Objective: To describe the risk of racing‐associated sudden death in Thoroughbred racehorses in the UK from 2000 to 2007, to identify whether there were risk factors uniquely associated with sudden death and to improve the understanding of the pathogenesis of racing‐associated sudden death by identification of risk factors for such cases. Methods: A sudden death was defined as an acute collapse and death, in an apparently healthy Thoroughbred racehorse, during or immediately after racing, in the absence of clinical data indicative of a catastrophic orthopaedic injury. The retrospective study included 201 case race starts and 705,712 control race starts. Univariable and multivariable logistic regression were used to identify risk factors for sudden death at any one start. Results: In the multivariable model, age, distance, race type, season and number of starts in the 60 days prior to the race were associated with sudden death. Conclusions: The risk factors identified in this study are not uniquely associated with sudden death and have been also been identified in studies using all causes of fatality as the outcome. These data suggest that a generic approach to reduce fatal musculoskeletal injury and sudden death may be possible. Potential relevance: The identification of risk factors allows speculation on the underlying mechanisms of sudden death in racing. This may stimulate hypothesis‐led investigations into the pathogenesis of exercise‐related arrhythmias, exercise‐induced pulmonary haemorrhage and blood vessel rupture. See also correspondence by Cook     

Management and assessment of prognosis after gastrocnemius disruption in Thoroughbred foals: 28 cases (1993–2007)

Reasons for performing study: Few studies have evaluated the athletic prognosis of foals affected by gastrocnemius disruption. Objective: To examine the diagnosis and management of gastrocnemius disruption in Thoroughbred (TB) foals, determine short‐term survival rate and assess future racing performance. The hypothesis was that Thoroughbred foals with gastrocnemius disruption are able to perform as racehorses comparably to their age matched maternal siblings. Methods: The medical records of foals diagnosed with gastrocnemius muscle disruption were reviewed. Information on training and racing was acquired from published works and race records. Paired t tests were utilised to compare performance variables of affected racehorses to their maternal siblings in starts, earnings and earnings/start for their 2‐ and 3‐year‐old racing seasons. Fisher's exact tests were employed to determine the association between sex, limb affected, age on admission, degree of caudal reciprocal apparatus dysfunction, concurrent disease, antibiotic therapy, complications, abscess formation and likelihood of entering training or starting a race. Results: Sample size was too small to detect significant differences in performance variables between affected horses and controls. Of 28 foals, 17 (61%) presented with concomitant illness; foals without concurrent disease were more likely to achieve race training or start a race (P = 0.04); 23 (82%) were short‐term survivors defined as survival to discharge. Of these 23 survivors, 7 were aged <2 years at the time of the study. Eighty‐one percent (13/16) of the survivors that were of racing age were in training or had started a race. Conclusions: In this population, 82% of TB foals affected with gastrocnemius disruption were able to achieve training or start a race. Foals presenting for gastrocnemius disruption have a high prevalence of concurrent disease processes. Potential relevance: The assessment of athletic prognosis and treatment complications provides useful information to clinicians treating gastrocnemius muscle disruption in foals and making recommendations to clientele.     

Palmar or plantar process fractures of the distal phalanx in riding horses: 22 cases (1994–2003)

No case series exists in the literature describing palmar/plantar process fractures (PPFs) of the distal phalanx in a nonracehorse population. We aim to describe the distribution of these injuries, together with their clinical, radiographic and scintigraphic features. In a retrospective case study, horses were selected based on radiographic evidence of a PPF. Data were collected relating to clinical and lameness examination, radiography, scintigraphy, management and follow‐up information. Oblique and flexed oblique radiographic views of the distal phalanx are the most sensitive in detecting PPFs of the distal phalanx and this study concluded that fractures of palmar or plantar process are likely to be missed in horses showing mild lameness if oblique radiographic views of the palmar process are not included.     

Musculoskeletal injuries in Thoroughbred racehorses: A study of three large training yards in Newmarket, UK (2005–2007)

Musculoskeletal injury is the most common cause of lost training days in the young Thoroughbred horse in flat race training. To date, there has been little investigation of the regional patterns of injury frequently observed by clinicians in racehorse practice. The present study was conducted to determine incidence of musculoskeletal injuries in Thoroughbreds in training in Newmarket, United Kingdom. Veterinary records for all horses resident in three large (>100 horse) training yards were assessed for occurrence of significant musculoskeletal injury.A total of 248 injuries were recorded in 217 individual horses, from a total population of 616 individual horses; fractures of the tibia (20.7%) and proximal phalanx (14.5%) were the most common. Overall injury rates were similar between yards (23–26%/year), with seasonal patterns noted for some injury types. Incidence of certain injuries (P1, metacarpal/metatarsal condylar, pelvic fractures, and superficial digital flexor tendonitis) varied between yards. The majority of carpal, P1 fracture and SDF tendonitis cases were right-sided.     

Frequency distributions of 174 fractures of the distal condyles of the third metacarpal and metatarsal bones in 167 Thoroughbred racehorses (1999–2009)

Reasons for performing study: Although fractures of the metacarpal and metatarsal condyles are the most common long‐bone fractures of Thoroughbred horses in training, limited data on variations in morphology and incidence have been published. Additionally, grouped analyses of previous studies from the UK and USA would permit comparison between study groups and the creation of a substantial pool of international data. Methods: Retrospective analysis of case records of horses with fractures of the distal condyles of third metacarpal/metatarsal bones seen over the last 10 years at Newmarket Equine Hospital. The current series was compared with a prior series from the UK; pooled analyses of these, and series from the USA were also compared. Results: One hundred and seventy‐four fractures were identified in 167 racehorses. The current series contained a significantly lower proportion of medial condylar fractures than in a similar population 17 years earlier. Fractures that originated more abaxially tended to be shorter, and a significant proportion of lateral condylar fractures arose outside of the condylar groove. There was also some apparent seasonality of fractures of the lateral condyles in 2‐year‐old horses, but not so in older horses or those with medial condylar fractures. Conclusions and potential relevance: A substantial portion (approximately 50%) of fractures in the present series cannot be explained by unifying theories of aetiopathogenesis, which suggest that fractures usually arise within the condylar groove, as a focus of cumulative fatigue and failure of adaptation of bone. A separate aetiopathogenesis may be responsible for a proportion of condylar fractures encountered in racehorses, and further work is required to elucidate this. Changes in the number of medial condylar fractures encountered may reflect the introduction of artificial racing and training surfaces, and also may reflect changes in the age demographic of horses racing in the UK since the introduction of year‐round ‘all‐weather’ racing.     

Racing performance after combined prosthetic laryngoplasty and ipsilateral ventriculocordectomy or partial arytenoidectomy: 135 Thoroughbred racehorses competing at less than 2400 m (1997–2007)

Reasons for performing study: The success of combined prosthetic laryngoplasty with ipsilateral ventriculocordectomy (LPVC) has not been compared to that of partial arytenoidectomy (PA) in a clinical population. Hypotheses: In Thoroughbred (TB) racehorses: 1) earnings after LPVC are unaffected by the severity of recurrent laryngeal neuropathy (RLN) (laryngeal grade III vs. grade IV); 2) LPVC and PA yield similar results in the treatment of grade III RLN; 3) performance outcome following PA is independent of diagnosis (RLN vs. unilateral arytenoid chondritis [UAC]); and 4) neither LPVC nor PA returns horses to the level of performance of controls. Methods: Medical and racing records of 135 TB racehorses undergoing LPVC or PA for the treatment of grade III or IV RLN or UAC were reviewed. Racing records of age and sex matched controls were also reviewed. Results: After LPVC, horses with grade III RLN performed better compared to those with grade IV RLN. Furthermore, horses treated for grade III RLN by LPVC showed post operative earnings comparable to controls. Rate of return to racing were similar for PA and LPVC, although LPVC resulted in higher post operative earnings. Performance after PA was similar regardless of diagnosis (UAC or RLN). Finally, neither LPVC when performed for grade IV RLN, nor PA performed for either diagnosis restored post operative earnings to control levels. Conclusions: Thoroughbred racehorses treated by LPVC for grade III RLN show significantly better post operative earnings compared to horses treated for grade IV disease. In grade III RLN, LPVC returns earning potential to control levels. PA and LPVC lead to similar success in terms of rate of return to racing, but PA leads to inferior earnings after surgery. Potential relevance: Laryngoplasty should be recommended for all TB racehorses with grade III RLN to maximise return to racing at a high level. This contradicts the common approach of waiting for complete paralysis.     

Tendonitis of branches of the superficial digital flexor tendon in Standardbred racehorses: 15 cases

This case report describes the clinical and ultrasonographic findings and performance outcome of distal tendonitis of the superficial digital flexor tendon (SDFT) in Standardbred racehorses. Cases with distal tendonitis of the SDFT in isolation (not associated with a metacarpal lesion) were reviewed retrospectively. The clinical and ultrasonographic findings and performance outcome were reviewed. The injury was located on the left forelimb in 67% (10/15) of horses and on the right forelimb in 33% (5/15). None of the horses were affected bilaterally. The lateral branch was involved in 80% of the cases (12/15) and medial branch in 20% (3/15). None of the horses were affected biaxially. Mean time between injury and first start ± s.d. was 302 ± 142 days. Returning to racing was observed in 93% of the horses (14/15), with a reinjury rate of 22% (2/9). For horses which raced after the injury, the number of starts, shows and wins was not significantly different before and after injury, regardless of the location of the lesion. Tendonitis of branches of the SDFT in isolation carries a good prognosis in Standardbred racehorses. A higher return to racing and a lower reinjury rate may be expected compared to lesions in the metacarpal region.     

Stress fractures of the tibia and humerus in Thoroughbred racehorses: 99 cases (1992-2000)

OBJECTIVE: To determine clinical characteristics of and outcome in Thoroughbred racehorses with tibial or humeral stress fractures. DESIGN: Retrospective study. ANIMALS: 99 Thoroughbreds with tibial or humeral stress fractures. PROCEDURE: Information obtained from the medical records included history, signalment, and clinical, radiographic, and scintigraphic findings. Outcome was determined by interviewing trainers, performing follow-up examinations, and analyzing race records. RESULTS: Seventy-four tibial stress fractures were identified in 61 Thoroughbreds, and 48 humeral stress fractures were identified in 39 Thoroughbreds (1 horse was included in both groups). Tibial stress fractures occurred most commonly in 2-year-old or unraced horses. Fractures were located in 1 of 3 sites in the tibia (most commonly, the caudolateral cortex of the mid-diaphysis) and 1 of 4 sites in the humerus (most commonly, the caudodistal cortex). Forty-four of 58 (76%) tibial stress fractures and 18 of 32 (56%) humeral stress fractures were identified radiographically. Humeral stress fractures involving the caudodistal cortex were not detected radiographically. Treatment consisted of rest and exercise restriction, and 49 of 61 (80%) horses with tibial stress fractures and 30 of 39 (77%) horses with humeral stress fractures returned to racing. Humeral stress fractures recurred in 6 horses. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that in Thoroughbred racehorses, tibial stress fractures occurred most commonly in unraced 2 year olds, whereas humeral fractures occurred most commonly in older horses that had raced previously. The prognosis for racing following treatment was good.     

Surgical excision of large melanocytic tumours in grey horses: 38 cases (2001–2013)

Melanocytic tumours are common in grey horses. Large tumours can obstruct the rectum, or prepuce, inhibit food intake and impinge upon the upper airway. Surgical excision is locally curative, but is controversial for large or confluent tumours. Limited information on outcome following surgical excision of large melanomas is available. The objective of this study was to report outcome following surgical excision of large (≥4 cm) melanocytic tumours in horses. Our hypothesis was that surgical excision of large (≥4 cm) single and coalescing melanomas would be locally curative. Medical records were reviewed and cases that underwent excision of a single or coalescing melanoma, with at least one lesion ≥4 cm in diameter, included. Follow‐up information was obtained a minimum of 12 months post‐surgery from owners and referring veterinarians via telephone interviews, questionnaire, or direct examination. A total of 48 cases were identified; 38 horses with follow‐up were included in the study. Tumours involved the parotid, perianal or mid‐cervical regions, ventral tail base, prepuce, penis, ear, or thoracic inlet. There were no cases of tumour regrowth following excision. Post‐operative complications occurred in five cases and were easily resolved in all but one. Continued or new growth of distant melanocytic tumours occurred in 50% of cases. Results suggest that excision of large melanocytic tumours in horses is a viable treatment option that is locally curative with minimal complications.     

Return to use and performance following exploratory celiotomy for colic in horses: 195 cases (2003–2010)

Reasons for performing study: There are few objective data on return to use and performance in horses following colic surgery. Objective: To investigate return to functional use of horses following colic surgery and factors associated with a negative outcome. Methods: The North Carolina State University Equine Colic Database was reviewed for horses that underwent exploratory celiotomy for colic (2003–2010). Horses were excluded from the study if they survived <6 months, had no intended use preoperatively, or if further data were not available at attempted follow‐up. Information retrieved included history, background, use, and selected pre‐, intra‐, and post operative factors. Telephone interviews were used to obtain follow‐up data. Logistic regression was used to investigate associations between clinical data and outcome, reported as odds ratios with a 95% confidence interval and corresponding P value. Results: Of patients surviving to 6 months, 133/195 (68%) were performing their intended use and 85/156 (54%) were at or above preoperative performance. At one year, 145/190 (76%) horses were performing their intended use and 101/153 (66%) were at or above preoperative performance. Animals were significantly less likely to return to use/performance if they had a previous celiotomy, stall rest for an orthopaedic condition, a nonstrangulating lesion type, incisional hernia, diarrhoea or laminitis. Conclusions: The overall prognosis for return to use and performance following colic surgery is fair to good. Multiple pre‐ and post operative factors may affect the likelihood of return to use and performance. Potential relevance: Targeted owner education regarding preoperative lameness, post operative rehabilitation and treatment for complications, such as incisional hernioplasty, may help inform owners about their horse's potential for return to use and performance following colic surgery.