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Musculoskeletal injuries in Thoroughbred racehorses: A study of three large training yards in Newmarket, UK (2005–2007)
The Veterinary Journal 187 (2011) 325–329
Contents lists available at ScienceDirect
The Veterinary Journal journal homepage: www.elsevier.com/locate/tvjl
Musculoskeletal injuries in Thoroughbred racehorses: A study of three large training yards in Newmarket, UK (2005–2007) Peter H.L. Ramzan *, Lorraine Palmer Rossdale and Partners, Beaufort Cottage Stables, High Street, Newmarket, Suffolk CB8 8JS, United Kingdom
a r t i c l e
i n f o
Article history: Accepted 22 December 2009
Keywords: Racehorse Thoroughbred Musculoskeletal Injury Incidence
a b s t r a c t 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. Ó 2009 Elsevier Ltd. All rights reserved.
Introduction Epidemiological studies of exercise-related musculoskeletal injuries in Thoroughbred racehorses have been undertaken in several racing jurisdictions (Peloso et al., 1994; Verheyen and Wood, 2004; Parkin et al., 2004; Perkins et al., 2005a; Oikawa and Kusunose, 2005; Cogger et al., 2006; Boden et al., 2006; Wilsher et al., 2006; Dyson et al., 2008). The majority have investigated injuries sustained during racing (Parkin, 2008), although it is known that this accounts for only a small proportion of total injuries in Thoroughbreds in flat race training (Pickersgill et al., 2000; Verheyen and Wood, 2004). It is generally acknowledged that variation in injury patterns exists between training centres and even individual trainers (Bathe, 1994; Verheyen and Wood, 2004; Dyson et al., 2008; Cogger et al., 2008) although specific risk factors that might account for this variation have received little attention to date (Pickersgill et al., 2000; Verheyen et al., 2006a,b). In order to further characterise regional patterns of exercise-related musculoskeletal injuries seen in Thoroughbred racehorse practice, an investigation of three training yards in Newmarket, UK was undertaken.
* Corresponding author. Tel.: +44 1638 663150. E-mail address: [email protected] (P.H.L. Ramzan). 1090-0233/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.tvjl.2009.12.019
Materials and methods Yard selection Three flat racing yards were chosen for the study on the basis of similarity in population of horses in training, approach to veterinary intervention and availability of comprehensive records. Each yard was attended by one of three experienced veterinary surgeons, with some crossover attendance by these individuals as primary treating clinicians during the course of the study period. An intensive level of veterinary care was a feature of the management of each yard, with once or twice-daily routine visits by clinicians throughout the study period. Data collection A retrospective analysis of individual veterinary records for all horses in flat training in the three yards during the period from 1st January 2005 to 31st December 2007 was undertaken. Records were accessed through a computerised database (Rossdale and Partners’ Eclipse Practice Management System v2.3, Systems Support). Veterinary reports, diagnostic images (radiography, ultrasonography, scintigraphy, magnetic resonance imaging) and surgical notes for every recorded episode of lameness were examined. Data were collated on the following injury types: (1) stress fractures (tibia/pelvis/radius/humerus/metacarpus/metatarsus/vertebral column); (2) fractures involving the metacarpophalangeal/metatarsophalangeal joints, carpus, tarsus and proximal sesamoid bones; (3) suspensory branch desmitis, and (4) superficial digital flexor (SDFT) tendonitis. Carpal fractures included displaced or non-displaced osteochondral chip and slab fractures causing acute lameness. To be included as a case, all episodes of eligible injury had to result in clinical signs necessitating veterinary attention, and diagnosis of injury had to be confirmed using one or more of the specified imaging modalities. Injuries incurred during both training and racing were included for analysis. Injuries diagnosed upon a horse’s arrival from another training yard were excluded, as were injuries sustained by horses being trained/raced temporarily outside Newmarket for international race
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P.H.L. Ramzan, L. Palmer / The Veterinary Journal 187 (2011) 325–329
meetings. Multiple injuries in the same horse at different times through the study period were included. Re-injuries at the same site were not included as separate events when considering incidence of injury types. Data analysed included type of injury, date of initial examination, age, sex and limb. Injury categories typically associated with variable clinical signs (such that trainer or veterinary tolerance might differ substantially between yards) were not included for analysis. These included osteochondral chip fractures of the metacarpophalangeal/metatarsophalangeal joints, dorsal metacarpal disease, metacarpal/ metatarsal condylar ‘stress reactions’ (Shepherd and Pilsworth, 1997), primary articular synovitis, ‘juvenile’ superficial digital flexor tendonitis (Reimer, 2002) and proximal metacarpal lameness (Powell et al., 2008). Injuries resulting from trauma, such as kicks or interference wounds, were also excluded.
Results Average number of horses in training per year over the period of study was 106 for Yard 1, 106 for Yard 2 and 120 for Yard 3, as determined from information published in two annual lists of horses in training (Raceform; Thoroughbred Printing and Publishing). Yards 1 and 3 each had a greater proportion of 2 year-olds than 3 and 3+ year-olds, respectively. Yard 2 had an equal proportion of 2- and 3 year-olds. Ratio of male:female horses was 1.63 for Yard 1, 1.24 for Yard 2 and 1.02 for Yard 3. Over the study period the percentage of wins to runners for Yard 1 was 19.6%, Yard 2 15.3% and Yard 3 13.3% (Racing Post Online). A total of 248 injuries sustained in 217 horses met the inclusion criteria; 241 of these episodes were individual injury events (seven were re-injuries). Tibial stress fractures were found to be the most common injury (50/241, 20.7%), followed by fractures of the proximal phalanx (P1) (35/241, 14.5%), carpal fractures (27/241, 11.2%), pelvic stress fractures (26/241, 10.8%) and SDF tendonitis (26/241, 10.8%), and metacarpal/metatarsal condylar fractures (25/241, 10.4%) (Table 1). The hock fractures documented were predominantly (7/9) slab fractures of the third tarsal bone, with 2/9 being central tarsal bone fractures. The majority of stress fractures categorised as ‘Other’ in this study involved the humerus (5/10), with the remainder being injuries of the vertebral column, femur and unspecified stress fractures. Seven horses sustained catastrophic fractures necessitating euthanasia: these involved the proximal phalanx or distal metacarpus/metatarsus (4), pelvis (1), tibia (1) and humerus (1). The majority (43/50, 86.0%) of tibial injuries occurred at the distocaudal predilection site. The majority of P1 (24/35, 68.6%) and condylar (14/25, 56.0%) fractures, and suspensory branch lesions (16/21, 76.2%) were detected in the forelimb. For some injury types a right-sided predilection was observed: P1 (24/35, 68.6%) and carpal (22/27, 81.5%) fractures and SDFT injuries (18/26, 69.2%) occurred predominantly in the right forelimb. While SDFT (24/26, 92.3%) and condylar (18/25, 72%) injuries occurred mostly in males, sex distribution of all other injury types approximated that of the study population.
Twenty-two horses sustained more than one injury type during the study period (contributing 46 injury events). A further seven horses were diagnosed with re-injuries (same limb and site): these comprised short incomplete P1 (2) and carpal (2) fractures, SDF tendonitis (2) and tibial (1) fractures. All of these cases sustained re-injuries in the season following original injury, aside from the single case of tibial stress fracture which re-injured 5 months following original diagnosis. The number of injuries in all three training yards was greatest between the months of March and September, a period closely corresponding to the UK flat racing season. The month with the greatest number of injuries was July. Some injury types (SDFT tendonitis, suspensory branch desmitis, condylar fractures) had a year-round incidence (Fig. 1) with inconsequential seasonal peaks while others (tibial and P1 fractures) had apparent seasonal distribution (Figs. 2 and 3). Average annual injury rates were similar between the three training yards investigated (Yard 1: 23%, Yard 2: 25%, Yard 3: 26%), however incidence of certain injury types was seen to vary considerably between yards (Table 1). P1 fractures were up to three times more prevalent in Yard 2 than the other yards. Yard 2 also contributed fewer cases of SDFT tendonitis and pelvic stress fracture than the other yards. Yard 1 had the lowest incidence of tibial stress fractures, and also a lower incidence of injury in its 2 year-old population relative to Yard 3. The P1 fractures in Yards 2 and 3 were most frequently sustained in the forelimb, while in Yard 1 hindlimb P1 fractures were most common.
Discussion To date, many of the studies of incidence of orthopaedic injuries incurred by Thoroughbred racehorses have been concerned with those sustained on the racetrack (Peloso et al., 1994; Estberg et al., 1996; Hernandez et al., 2001; Parkin et al., 2004; Oikawa and Kusunose, 2005; Boden et al., 2006, 2007). Studies of wastage in the Thoroughbred industry as a whole have been undertaken, although these have generally included data from more than one training centre and have not primarily investigated regional or training yard variations in patterns and incidence of musculoskeletal injury (Verheyen and Wood, 2004; Perkins et al., 2005a,b; Verheyen et al., 2006a; Dyson et al., 2008). It is recognised that the incidence of certain orthopaedic injuries can differ between training centres (Bathe, 1994; Kasashima et al., 2004; Perkins et al., 2005a,b). Factors such as training regimen, training track characteristics (configuration, surface material, gradient, maintenance) and horse type are considered to account for a large part of this variation (Cogger et al., 2006). Additionally, there is support in the literature that patterns of orthopaedic injury
Table 1 The injury categories by total number of counts (excluding re-injuries), and proportion of total injuries (overall and within each yard). Injury type/s with greatest incidence in each yard is underlined.
Tibia Proximal phalanx Carpus Pelvis SDFT Mc3/Mt3 (condylar) Suspensory branch Other Hock Mc3/Mt3 (cannon) Sesamoid
n
Yards 1–3 (%) (n = 241)
Yard 1 (%) (n = 71)
Yard 2 (%) (n = 78)
Yard 3 (%) (n = 92)
50 35 27 26 26 25 22 10 9 9 2
20.7 14.5 11.2 10.8 10.8 10.4 9.1 4.1 3.7 3.7 0.8
11.3 8.5 9.9 15.5 15.5 15.5 8.5 0.0 5.6 7.0 2.8
21.8 25.6 12.8 6.4 2.6 9.0 9.0 2.6 6.4 3.8 0.0
27.2 9.8 10.9 10.9 14.1 7.6 9.8 8.7 0.0 1.1 0.0
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10 Yard 1 Yard 2 Yard 3
Total Number
8
6
4
2
0 Jan
Feb
Mar
Apr
May
June
July
Aug
Sep
Oct
Nov
Dec
Month Fig. 1. Numbers of cases of SDF tendonitis by month for the 3 year study period.
10 Yard 1 Yard 2
Total Num ber
8
Yard 3
6
4
2
0 Jan
Feb
Mar
Apr
May
June
July
Aug
Sep
Oct
Nov
Dec
Month Fig. 2. Numbers of cases of tibial stress fractures by month for the 3 year study period.
10 Yard 1 Yard 2 Yard 3
Total Number
8
6
4
2
0 Jan
Feb
Mar
Apr
May
June
July
Aug
Sep
Oct
Nov
Month Fig. 3. Numbers of cases of P1 fractures by month for the 3 year study period.
Dec
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may vary between yards at the same training centre (Verheyen et al., 2006b; Cogger et al., 2008). The training yards recruited for this study were selected primarily due to similarity in yard population and level of veterinary input. Veterinary records for all three yards were comprehensive, and whereas variation in approaches to low-grade or early-stage lameness existed, for the injuries investigated in this study all had a similar level of veterinary involvement that was likely to have minimised under-reporting. It is possible that the choice of yards with high veterinary input might have led to bias and the results should not necessarily be considered applicable to the wider Newmarket population. The musculoskeletal injuries included in the study were selected on the grounds that they were associated with significant clinical signs or lameness, such that removal from ridden work would be necessary and veterinary examination and/ or imaging sought. Injuries such as dorsal metacarpal disease, condylar ‘stress reactions’, and proximal metacarpal lameness, although undoubtedly the cause of significant morbidity in racehorses, were considered to be too variable in their reporting and management to warrant inclusion. Trainers in Newmarket have the use of a wide range of training tracks within the public grounds maintained by the Jockey Club Estates. Although these vary in length, surface (turf or all-weather) and gradient, all yards in the present study used uphill all-weather tracks for the majority of daily cantering exercise throughout the study period. Choice of track for fast-speed (gallop) work differed between and within yards, due to stage of season, weather and track condition. The training programme in all three yards was geared towards training predominantly 2- and 3 year-old Thoroughbreds (with a small proportion of older horses) for the British flat turf racing season which runs from March to November. Only a small number of horses from each yard were kept in full work through the autumn/winter to compete on the domestic all-weather circuit or at international race meetings. Tibial stress fractures were the most common single type of injury observed in this study population. This differs from the findings of other researchers who have variably documented third metacarpal, pelvic and carpal fractures as being more common in Thoroughbreds than tibial injuries (Bathe, 1994; Pickersgill et al., 2000; Verheyen and Wood, 2004; Cogger et al., 2008). It is possible that the higher incidence of tibial stress fractures (and of hindlimb fractures overall) in the present study was related to the heavy use of uphill training tracks in Newmarket. Three predilection sites for tibial stress fractures are recognised: (1) the proximolateral cortex, (2) mid-diaphysis and (3) distocaudal cortex (Pilsworth and Shepherd, 1997). The majority (43/50, 86.0%) of tibial injuries in the present study occurred at the distal site. This contrasts with the findings of an Australian study that recorded the mid-diaphyseal site to be most prevalent (77%) (O’Sullivan and Lumsden, 2003). Previously it has been stated that the proximolateral site is most commonly affected in the UK (Pilsworth and Shepherd, 1997), although it is likely that the widespread adoption of gamma scintigraphy as a diagnostic aid over the past decade has led to greater recognition of distocaudal injuries, which are frequently radiographically silent. Fractures to P1 were the second most common musculoskeletal injury. The predominant fracture configuration was the incomplete mid-sagittal fracture, with a small number of frontal fractures observed. Seasonal incidence of P1 fractures was more exaggerated than for metacarpal/metatarsal condylar fractures; most injuries occurred between May and July with no injuries occurring between November and March. P1 fractures were more common in the forelimb and appeared to be over-represented in Yard 2. An unexpected finding was that of the predominance of rightsided injuries for some injury types (81.5% of carpal fractures, 69.2% of SDFT injuries and 68.6% of P1 fractures). During the period
of study most daily cantering exercise was on straight tracks, and fast work predominantly on straight or straight/left-handed tracks. In previous studies of racehorse injuries in the UK, left and right limbs were equally represented in both forelimb and hindlimb injuries (Bathe, 1994; Verheyen and Wood, 2004). In the past it has been assumed that the higher prevalence of right-sided carpal injuries noted in studies from the USA reflected the anticlockwise direction of training and racing tracks (Schneider et al., 1988). Track configuration is unlikely to account for the findings of the present study and it is possible that laterality of gait may have been a factor (Williams and Norris, 2007). Overall incidence of musculoskeletal injury was similar in all three yards. Approximately 25% of horses in training in each yard sustained a significant musculoskeletal injury per calendar year. This figure was lower than that reported by other authors (Cogger et al., 2008), probably due primarily to the exclusion of dorsal metacarpal disease (‘sore shins’) from analysis. It must be noted that true quantification of risk (i.e. horse days at risk) was not possible with the available data (Parkin, 2008). While numbers of certain injuries (carpal fractures, suspensory branch desmitis) were similar in all three yards, considerable variation between yards was observed in several injury groups. The most common injuries recorded in Yard 1 were (with equal incidence) pelvic fractures, condylar fractures and SDFT injuries; P1 fractures were most common in Yard 2, and tibial fractures in Yard 3. Yard 2 contributed a much higher number of P1 fractures than the other yards. Yard 1 recorded fewer than half the number of tibial stress fractures than each of the other yards. It is important to note that this study did not attempt to identify risk factors for musculoskeletal injury in the target population, and therefore conclusions cannot be drawn on the underlying reasons for any yard-related injury patterns. Conclusions The present study quantified injuries associated with significant morbidity in three training yards of similar size in a single UK training centre. The incidence of certain injuries appeared to vary between yards and seasonal peaks occurred for some injury categories. Hindlimb stress fractures were the most common injury group. Awareness of the existence of possible local, seasonal and training-yard patterns of exercise-related injury is important for clinicians advising on the diagnosis, management and prevention of such injuries, while further work is required to quantify the risk factors responsible for these variations. Conflict of interest statement None of the authors of this paper has a financial or personal relationship with other people or organisations that could inappropriately influence or bias the content of the paper. Acknowledgements The authors are grateful for the cooperation of Mr. L. Cumani, Bedford House Stables; Mr. E. Dunlop, Gainsborough Stables and Mr. J. Noseda, Shalfleet Stables, Newmarket, UK. References Bathe, A.P., 1994. 245 Fractures in Thoroughbred racehorses: results of a 2-year prospective study in Newmarket. In: Proceedings of the 40th Annual Convention of the American Association of Equine Practitioners, pp. 175–176. Boden, L.A., Anderson, G.A., Charles, J.A., Morgan, K.L., Morton, J.M., Parkin, T.D., Slocombe, R.F., Clarke, A.F., 2006. Risk of fatality and causes of death of Thoroughbred horses associated with racing in Victoria, Australia: 1989–2004. Equine Veterinary Journal 38, 312–318.
P.H.L. Ramzan, L. Palmer / The Veterinary Journal 187 (2011) 325–329 Boden, L.A., Anderson, G.A., Charles, J.A., Morgan, K.L., Morton, J.M., Parkin, T.D., Clarke, A.F., Slocombe, R.F., 2007. Risk factors for Thoroughbred racehorse fatality in flat starts in Victoria, Australia: 1989–2004. Equine Veterinary Journal 39, 430–437. Cogger, N., Perkins, N., Hodgson, D.R., Reid, S.W., Evans, D.L., 2006. Risk factors for musculoskeletal injuries in 2-year-old Thoroughbred racehorses. Preventive Veterinary Medicine 74, 36–43. Cogger, N., Evans, D.L., Hodgson, D.R., Reid, S.W., Perkins, N., 2008. Incidence rate of musculoskeletal injuries and determinants of time to recovery in young Australian Thoroughbred racehorses. Australian Veterinary Journal 86, 473– 480. Dyson, P.K., Jackson, B.F., Pfeiffer, D.U., Price, J.S., 2008. Days lost from training by two- and three-year-old Thoroughbred horses: a survey of seven UK training yards. Equine Veterinary Journal 40, 650–657. Estberg, L., Stover, S.M., Gardner, I.A., Drake, C.M., Johnson, B., Ardans, A., 1996. High-speed exercise history and catastrophic racing fracture in Thoroughbreds. American Journal of Veterinary Research 57, 1549–1555. Hernandez, J., Hawkins, D.L., Scollay, M.C., 2001. Race-start characteristics and risk of catastrophic musculoskeletal injury in Thoroughbred racehorses. Journal of the American Veterinary Medical Association 218, 83–86. Kasashima, Y., Takahashi, T., Smith, R.K., Goodship, A.E., Kuwano, A., Ueno, T., Hirano, S., 2004. Prevalence of superficial digital flexor tendonitis and suspensory desmitis in Japanese Thoroughbred flat racehorses in 1999. Equine Veterinary Journal 36, 346–350. Oikawa, M., Kusunose, R., 2005. Fractures sustained by racehorses in Japan during flat racing with special reference to track condition and racing time. The Veterinary Journal 170, 369–374. O’Sullivan, C.B., Lumsden, J.M., 2003. Stress fractures of the tibia and humerus in Thoroughbred racehorses: 99 cases (1992–2000). Journal of the American Veterinary Medical Association 222, 491–498. Parkin, T.D., 2008. Epidemiology of racetrack injuries in racehorses. Veterinary Clinics: Equine, vol. 24. Elsevier Saunders, pp. 1–19. Parkin, T.D., Clegg, P.D., French, N.P., Proudman, C.J., Riggs, C.M., Singer, E.R., Webbon, P.M., Morgan, K.L., 2004. Race- and course-level risk factors for fatal distal limb fracture in racing Thoroughbreds. Equine Veterinary Journal 36, 521–526. Peloso, J.G., Mundy, G.D., Cohen, N.D., 1994. Prevalence of, and factors associated with musculoskeletal racing injuries of Thoroughbreds. Journal of the American Veterinary Medical Association 204, 620–626.
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Perkins, N.R., Reid, S.W., Morris, R.S., 2005a. Risk factors for musculoskeletal injuries of the lower limbs in Thoroughbred racehorses in New Zealand. New Zealand Veterinary Journal 53, 171–183. Perkins, N.R., Reid, S.W., Morris, R.S., 2005b. Risk factors for injury to the superficial digital flexor tendon and suspensory apparatus in Thoroughbred racehorses in New Zealand. New Zealand Veterinary Journal 53, 184–192. Pickersgill, C.H., Reid, S.W.J, Marr, C.M., 2000. Musculoskeletal injuries and associated epidemiological risk factors among Thoroughbred flat racehorses. In: Proceedings of the 39th British Equine Veterinary Association Congress, pp. 208–209. Pilsworth, R.C., Shepherd, M.C., 1997. Stress fractures. In: Robinson, N.E. (Ed.), Current Therapy in Equine Medicine IV. W.B. Saunders, Philadelphia, pp. 104–112. Powell, S.E., Baldwin, G.I., Ramzan, P.H.L., Shepherd, M.C, Head, M.J., 2008. Standing MRI examination assists the differentiation of proximal metacarpal pain from middle carpal joint pain in the racing Thoroughbred: 25 cases. In: Proceedings of the 47th British Equine Veterinary Association Congress, p. 146. Reimer, J.M., 2002. Enlarged superficial digital flexor tendons in immature Thoroughbred horses: prognosis for racing. In: Proceedings of the 48th Annual Convention of the American Association of Equine Practitioners, pp. 335–336. Schneider, R.K., Bramlage, L.R., Gabel, A.A., Barone, L.M., Kantrowitz, B.M., 1988. Incidence, location and classification of 371 third carpal bone fractures in 313 horses. Equine Veterinary Journal 6, 33–42. Shepherd, M.C., Pilsworth, R.C., 1997. Stress reactions to the plantarolateral condyles of MtIII in UK Thoroughbreds: 26 cases. In: Proceedings of the 43rd Annual Convention of the American Association of Equine Practitioners, pp. 128–131. Verheyen, K.L., Wood, J.L., 2004. Descriptive epidemiology of fractures occurring in British Thoroughbred racehorses in training. Equine Veterinary Journal 36, 167– 173. Verheyen, K.L., Newton, J.R., Price, J.S., Wood, J.L., 2006a. A case-control study of factors associated with pelvic and tibial stress fractures in Thoroughbred racehorses in training in the UK. Preventive Veterinary Medicine 74, 21–35. Verheyen, K., Price, J., Lanyon, L., Wood, J., 2006b. Exercise distance and speed affect the risk of fracture in racehorses. Bone 39, 1322–1330. Williams, D.E., Norris, B.J., 2007. Laterality in stride pattern preferences in racehorses. Animal Behaviour 74, 941–950. Wilsher, S., Allen, W.R., Wood, J.L., 2006. Factors associated with failure of Thoroughbred racehorses to train and race. Equine Veterinary Journal 38, 113–118.
Contents lists available at ScienceDirect
The Veterinary Journal journal homepage: www.elsevier.com/locate/tvjl
Musculoskeletal injuries in Thoroughbred racehorses: A study of three large training yards in Newmarket, UK (2005–2007) Peter H.L. Ramzan *, Lorraine Palmer Rossdale and Partners, Beaufort Cottage Stables, High Street, Newmarket, Suffolk CB8 8JS, United Kingdom
a r t i c l e
i n f o
Article history: Accepted 22 December 2009
Keywords: Racehorse Thoroughbred Musculoskeletal Injury Incidence
a b s t r a c t 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. Ó 2009 Elsevier Ltd. All rights reserved.
Introduction Epidemiological studies of exercise-related musculoskeletal injuries in Thoroughbred racehorses have been undertaken in several racing jurisdictions (Peloso et al., 1994; Verheyen and Wood, 2004; Parkin et al., 2004; Perkins et al., 2005a; Oikawa and Kusunose, 2005; Cogger et al., 2006; Boden et al., 2006; Wilsher et al., 2006; Dyson et al., 2008). The majority have investigated injuries sustained during racing (Parkin, 2008), although it is known that this accounts for only a small proportion of total injuries in Thoroughbreds in flat race training (Pickersgill et al., 2000; Verheyen and Wood, 2004). It is generally acknowledged that variation in injury patterns exists between training centres and even individual trainers (Bathe, 1994; Verheyen and Wood, 2004; Dyson et al., 2008; Cogger et al., 2008) although specific risk factors that might account for this variation have received little attention to date (Pickersgill et al., 2000; Verheyen et al., 2006a,b). In order to further characterise regional patterns of exercise-related musculoskeletal injuries seen in Thoroughbred racehorse practice, an investigation of three training yards in Newmarket, UK was undertaken.
* Corresponding author. Tel.: +44 1638 663150. E-mail address: [email protected] (P.H.L. Ramzan). 1090-0233/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.tvjl.2009.12.019
Materials and methods Yard selection Three flat racing yards were chosen for the study on the basis of similarity in population of horses in training, approach to veterinary intervention and availability of comprehensive records. Each yard was attended by one of three experienced veterinary surgeons, with some crossover attendance by these individuals as primary treating clinicians during the course of the study period. An intensive level of veterinary care was a feature of the management of each yard, with once or twice-daily routine visits by clinicians throughout the study period. Data collection A retrospective analysis of individual veterinary records for all horses in flat training in the three yards during the period from 1st January 2005 to 31st December 2007 was undertaken. Records were accessed through a computerised database (Rossdale and Partners’ Eclipse Practice Management System v2.3, Systems Support). Veterinary reports, diagnostic images (radiography, ultrasonography, scintigraphy, magnetic resonance imaging) and surgical notes for every recorded episode of lameness were examined. Data were collated on the following injury types: (1) stress fractures (tibia/pelvis/radius/humerus/metacarpus/metatarsus/vertebral column); (2) fractures involving the metacarpophalangeal/metatarsophalangeal joints, carpus, tarsus and proximal sesamoid bones; (3) suspensory branch desmitis, and (4) superficial digital flexor (SDFT) tendonitis. Carpal fractures included displaced or non-displaced osteochondral chip and slab fractures causing acute lameness. To be included as a case, all episodes of eligible injury had to result in clinical signs necessitating veterinary attention, and diagnosis of injury had to be confirmed using one or more of the specified imaging modalities. Injuries incurred during both training and racing were included for analysis. Injuries diagnosed upon a horse’s arrival from another training yard were excluded, as were injuries sustained by horses being trained/raced temporarily outside Newmarket for international race
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meetings. Multiple injuries in the same horse at different times through the study period were included. Re-injuries at the same site were not included as separate events when considering incidence of injury types. Data analysed included type of injury, date of initial examination, age, sex and limb. Injury categories typically associated with variable clinical signs (such that trainer or veterinary tolerance might differ substantially between yards) were not included for analysis. These included osteochondral chip fractures of the metacarpophalangeal/metatarsophalangeal joints, dorsal metacarpal disease, metacarpal/ metatarsal condylar ‘stress reactions’ (Shepherd and Pilsworth, 1997), primary articular synovitis, ‘juvenile’ superficial digital flexor tendonitis (Reimer, 2002) and proximal metacarpal lameness (Powell et al., 2008). Injuries resulting from trauma, such as kicks or interference wounds, were also excluded.
Results Average number of horses in training per year over the period of study was 106 for Yard 1, 106 for Yard 2 and 120 for Yard 3, as determined from information published in two annual lists of horses in training (Raceform; Thoroughbred Printing and Publishing). Yards 1 and 3 each had a greater proportion of 2 year-olds than 3 and 3+ year-olds, respectively. Yard 2 had an equal proportion of 2- and 3 year-olds. Ratio of male:female horses was 1.63 for Yard 1, 1.24 for Yard 2 and 1.02 for Yard 3. Over the study period the percentage of wins to runners for Yard 1 was 19.6%, Yard 2 15.3% and Yard 3 13.3% (Racing Post Online). A total of 248 injuries sustained in 217 horses met the inclusion criteria; 241 of these episodes were individual injury events (seven were re-injuries). Tibial stress fractures were found to be the most common injury (50/241, 20.7%), followed by fractures of the proximal phalanx (P1) (35/241, 14.5%), carpal fractures (27/241, 11.2%), pelvic stress fractures (26/241, 10.8%) and SDF tendonitis (26/241, 10.8%), and metacarpal/metatarsal condylar fractures (25/241, 10.4%) (Table 1). The hock fractures documented were predominantly (7/9) slab fractures of the third tarsal bone, with 2/9 being central tarsal bone fractures. The majority of stress fractures categorised as ‘Other’ in this study involved the humerus (5/10), with the remainder being injuries of the vertebral column, femur and unspecified stress fractures. Seven horses sustained catastrophic fractures necessitating euthanasia: these involved the proximal phalanx or distal metacarpus/metatarsus (4), pelvis (1), tibia (1) and humerus (1). The majority (43/50, 86.0%) of tibial injuries occurred at the distocaudal predilection site. The majority of P1 (24/35, 68.6%) and condylar (14/25, 56.0%) fractures, and suspensory branch lesions (16/21, 76.2%) were detected in the forelimb. For some injury types a right-sided predilection was observed: P1 (24/35, 68.6%) and carpal (22/27, 81.5%) fractures and SDFT injuries (18/26, 69.2%) occurred predominantly in the right forelimb. While SDFT (24/26, 92.3%) and condylar (18/25, 72%) injuries occurred mostly in males, sex distribution of all other injury types approximated that of the study population.
Twenty-two horses sustained more than one injury type during the study period (contributing 46 injury events). A further seven horses were diagnosed with re-injuries (same limb and site): these comprised short incomplete P1 (2) and carpal (2) fractures, SDF tendonitis (2) and tibial (1) fractures. All of these cases sustained re-injuries in the season following original injury, aside from the single case of tibial stress fracture which re-injured 5 months following original diagnosis. The number of injuries in all three training yards was greatest between the months of March and September, a period closely corresponding to the UK flat racing season. The month with the greatest number of injuries was July. Some injury types (SDFT tendonitis, suspensory branch desmitis, condylar fractures) had a year-round incidence (Fig. 1) with inconsequential seasonal peaks while others (tibial and P1 fractures) had apparent seasonal distribution (Figs. 2 and 3). Average annual injury rates were similar between the three training yards investigated (Yard 1: 23%, Yard 2: 25%, Yard 3: 26%), however incidence of certain injury types was seen to vary considerably between yards (Table 1). P1 fractures were up to three times more prevalent in Yard 2 than the other yards. Yard 2 also contributed fewer cases of SDFT tendonitis and pelvic stress fracture than the other yards. Yard 1 had the lowest incidence of tibial stress fractures, and also a lower incidence of injury in its 2 year-old population relative to Yard 3. The P1 fractures in Yards 2 and 3 were most frequently sustained in the forelimb, while in Yard 1 hindlimb P1 fractures were most common.
Discussion To date, many of the studies of incidence of orthopaedic injuries incurred by Thoroughbred racehorses have been concerned with those sustained on the racetrack (Peloso et al., 1994; Estberg et al., 1996; Hernandez et al., 2001; Parkin et al., 2004; Oikawa and Kusunose, 2005; Boden et al., 2006, 2007). Studies of wastage in the Thoroughbred industry as a whole have been undertaken, although these have generally included data from more than one training centre and have not primarily investigated regional or training yard variations in patterns and incidence of musculoskeletal injury (Verheyen and Wood, 2004; Perkins et al., 2005a,b; Verheyen et al., 2006a; Dyson et al., 2008). It is recognised that the incidence of certain orthopaedic injuries can differ between training centres (Bathe, 1994; Kasashima et al., 2004; Perkins et al., 2005a,b). Factors such as training regimen, training track characteristics (configuration, surface material, gradient, maintenance) and horse type are considered to account for a large part of this variation (Cogger et al., 2006). Additionally, there is support in the literature that patterns of orthopaedic injury
Table 1 The injury categories by total number of counts (excluding re-injuries), and proportion of total injuries (overall and within each yard). Injury type/s with greatest incidence in each yard is underlined.
Tibia Proximal phalanx Carpus Pelvis SDFT Mc3/Mt3 (condylar) Suspensory branch Other Hock Mc3/Mt3 (cannon) Sesamoid
n
Yards 1–3 (%) (n = 241)
Yard 1 (%) (n = 71)
Yard 2 (%) (n = 78)
Yard 3 (%) (n = 92)
50 35 27 26 26 25 22 10 9 9 2
20.7 14.5 11.2 10.8 10.8 10.4 9.1 4.1 3.7 3.7 0.8
11.3 8.5 9.9 15.5 15.5 15.5 8.5 0.0 5.6 7.0 2.8
21.8 25.6 12.8 6.4 2.6 9.0 9.0 2.6 6.4 3.8 0.0
27.2 9.8 10.9 10.9 14.1 7.6 9.8 8.7 0.0 1.1 0.0
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10 Yard 1 Yard 2 Yard 3
Total Number
8
6
4
2
0 Jan
Feb
Mar
Apr
May
June
July
Aug
Sep
Oct
Nov
Dec
Month Fig. 1. Numbers of cases of SDF tendonitis by month for the 3 year study period.
10 Yard 1 Yard 2
Total Num ber
8
Yard 3
6
4
2
0 Jan
Feb
Mar
Apr
May
June
July
Aug
Sep
Oct
Nov
Dec
Month Fig. 2. Numbers of cases of tibial stress fractures by month for the 3 year study period.
10 Yard 1 Yard 2 Yard 3
Total Number
8
6
4
2
0 Jan
Feb
Mar
Apr
May
June
July
Aug
Sep
Oct
Nov
Month Fig. 3. Numbers of cases of P1 fractures by month for the 3 year study period.
Dec
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may vary between yards at the same training centre (Verheyen et al., 2006b; Cogger et al., 2008). The training yards recruited for this study were selected primarily due to similarity in yard population and level of veterinary input. Veterinary records for all three yards were comprehensive, and whereas variation in approaches to low-grade or early-stage lameness existed, for the injuries investigated in this study all had a similar level of veterinary involvement that was likely to have minimised under-reporting. It is possible that the choice of yards with high veterinary input might have led to bias and the results should not necessarily be considered applicable to the wider Newmarket population. The musculoskeletal injuries included in the study were selected on the grounds that they were associated with significant clinical signs or lameness, such that removal from ridden work would be necessary and veterinary examination and/ or imaging sought. Injuries such as dorsal metacarpal disease, condylar ‘stress reactions’, and proximal metacarpal lameness, although undoubtedly the cause of significant morbidity in racehorses, were considered to be too variable in their reporting and management to warrant inclusion. Trainers in Newmarket have the use of a wide range of training tracks within the public grounds maintained by the Jockey Club Estates. Although these vary in length, surface (turf or all-weather) and gradient, all yards in the present study used uphill all-weather tracks for the majority of daily cantering exercise throughout the study period. Choice of track for fast-speed (gallop) work differed between and within yards, due to stage of season, weather and track condition. The training programme in all three yards was geared towards training predominantly 2- and 3 year-old Thoroughbreds (with a small proportion of older horses) for the British flat turf racing season which runs from March to November. Only a small number of horses from each yard were kept in full work through the autumn/winter to compete on the domestic all-weather circuit or at international race meetings. Tibial stress fractures were the most common single type of injury observed in this study population. This differs from the findings of other researchers who have variably documented third metacarpal, pelvic and carpal fractures as being more common in Thoroughbreds than tibial injuries (Bathe, 1994; Pickersgill et al., 2000; Verheyen and Wood, 2004; Cogger et al., 2008). It is possible that the higher incidence of tibial stress fractures (and of hindlimb fractures overall) in the present study was related to the heavy use of uphill training tracks in Newmarket. Three predilection sites for tibial stress fractures are recognised: (1) the proximolateral cortex, (2) mid-diaphysis and (3) distocaudal cortex (Pilsworth and Shepherd, 1997). The majority (43/50, 86.0%) of tibial injuries in the present study occurred at the distal site. This contrasts with the findings of an Australian study that recorded the mid-diaphyseal site to be most prevalent (77%) (O’Sullivan and Lumsden, 2003). Previously it has been stated that the proximolateral site is most commonly affected in the UK (Pilsworth and Shepherd, 1997), although it is likely that the widespread adoption of gamma scintigraphy as a diagnostic aid over the past decade has led to greater recognition of distocaudal injuries, which are frequently radiographically silent. Fractures to P1 were the second most common musculoskeletal injury. The predominant fracture configuration was the incomplete mid-sagittal fracture, with a small number of frontal fractures observed. Seasonal incidence of P1 fractures was more exaggerated than for metacarpal/metatarsal condylar fractures; most injuries occurred between May and July with no injuries occurring between November and March. P1 fractures were more common in the forelimb and appeared to be over-represented in Yard 2. An unexpected finding was that of the predominance of rightsided injuries for some injury types (81.5% of carpal fractures, 69.2% of SDFT injuries and 68.6% of P1 fractures). During the period
of study most daily cantering exercise was on straight tracks, and fast work predominantly on straight or straight/left-handed tracks. In previous studies of racehorse injuries in the UK, left and right limbs were equally represented in both forelimb and hindlimb injuries (Bathe, 1994; Verheyen and Wood, 2004). In the past it has been assumed that the higher prevalence of right-sided carpal injuries noted in studies from the USA reflected the anticlockwise direction of training and racing tracks (Schneider et al., 1988). Track configuration is unlikely to account for the findings of the present study and it is possible that laterality of gait may have been a factor (Williams and Norris, 2007). Overall incidence of musculoskeletal injury was similar in all three yards. Approximately 25% of horses in training in each yard sustained a significant musculoskeletal injury per calendar year. This figure was lower than that reported by other authors (Cogger et al., 2008), probably due primarily to the exclusion of dorsal metacarpal disease (‘sore shins’) from analysis. It must be noted that true quantification of risk (i.e. horse days at risk) was not possible with the available data (Parkin, 2008). While numbers of certain injuries (carpal fractures, suspensory branch desmitis) were similar in all three yards, considerable variation between yards was observed in several injury groups. The most common injuries recorded in Yard 1 were (with equal incidence) pelvic fractures, condylar fractures and SDFT injuries; P1 fractures were most common in Yard 2, and tibial fractures in Yard 3. Yard 2 contributed a much higher number of P1 fractures than the other yards. Yard 1 recorded fewer than half the number of tibial stress fractures than each of the other yards. It is important to note that this study did not attempt to identify risk factors for musculoskeletal injury in the target population, and therefore conclusions cannot be drawn on the underlying reasons for any yard-related injury patterns. Conclusions The present study quantified injuries associated with significant morbidity in three training yards of similar size in a single UK training centre. The incidence of certain injuries appeared to vary between yards and seasonal peaks occurred for some injury categories. Hindlimb stress fractures were the most common injury group. Awareness of the existence of possible local, seasonal and training-yard patterns of exercise-related injury is important for clinicians advising on the diagnosis, management and prevention of such injuries, while further work is required to quantify the risk factors responsible for these variations. Conflict of interest statement None of the authors of this paper has a financial or personal relationship with other people or organisations that could inappropriately influence or bias the content of the paper. Acknowledgements The authors are grateful for the cooperation of Mr. L. Cumani, Bedford House Stables; Mr. E. Dunlop, Gainsborough Stables and Mr. J. Noseda, Shalfleet Stables, Newmarket, UK. References Bathe, A.P., 1994. 245 Fractures in Thoroughbred racehorses: results of a 2-year prospective study in Newmarket. In: Proceedings of the 40th Annual Convention of the American Association of Equine Practitioners, pp. 175–176. Boden, L.A., Anderson, G.A., Charles, J.A., Morgan, K.L., Morton, J.M., Parkin, T.D., Slocombe, R.F., Clarke, A.F., 2006. Risk of fatality and causes of death of Thoroughbred horses associated with racing in Victoria, Australia: 1989–2004. Equine Veterinary Journal 38, 312–318.
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