EQUINE VETERINARY EDUCATION / AE / MAY 2015
259
Original Article
Retrospective study on the effect of wither fracture on racing performance in Thoroughbred racehorses in Hong Kong (2003 to 2013)
R. J. T. Y. Graham*, C. M. Riggs and S. M. Rosanowski†
Department of Veterinary Clinical Services, Hong Kong Jockey Club, Sha Tin, Hong Kong; and †Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand. *Corresponding author email:
robyn.jty.graham@
hkjc.org.hk
Keywords: horse; wither fracture; Thoroughbred racehorse; return to racing; prognosis
Summary The training programme for Thoroughbred flat racehorses is intense, with pressure to limit nontraining days. Fracture of the dorsal spinous processes is a traumatic event that affects a horse’s ability to train and race, with little information available regarding short-term treatment and long-term outcomes for elite racing horses. Using a retrospective cohort study of the Hong Kong Jockey Club’s veterinary clinical records, cases of wither fracture were identified radiographically, with clinical features, treatment and subsequent return to training and racing described. The prevalence of wither fracture was 0.152% and in 6 out of 8 cases, the fracture occurred following identified trauma. Clinical signs varied from mild swelling and pain of the affected region to acute, severe forelimb lameness with spinal deformation. Prognosis for recovery was excellent, with all horses returning to a level of racing performance equal to or better than before the injury. The time from injury to return to ridden work was <2.5 months and return to racing was 9 months, with horses that returned to training sooner after injury having more favourable outcomes. The period of rest identified in this study was shorter than previously reported, with the median interval between injury and first gallop <2.5 months and most horses back racing within 6 months.
Introduction
The term ‘withers’ in the horse is used to describe the protuberance in the dorsal aspect of the back, at the base of the neck, formed by the dorsal spinous processes (DSP) of the first 10 thoracic vertebrae (Jeffcott 1979). These processes extend in a dorsocaudal direction from the dorsal arch of each vertebra. Externally the withers are the most dorsal point of the back, with the apex formed by the DSP of T4–T7. The DSP are surrounded by the epiaxial muscles and function as levers through which muscles act to provide support and movement, namely spinal rotation and extension. The DSP are characterised by having separate centres of ossification dorsally, and while these centres calcify at age approximately 12 months they do not fuse to the parent bone (Jeffcott 1979). Fractures of the DSP most commonly occur at or near T6
(Driver and Pilsworth 2009) and are usually associated with direct trauma, such as impact from falling over backwards (Robertson and Samii 2012). Fractures have been reported as secondary complications in animals where the bone has been weakened by some other pathology, such as neoplasia, osteomyelitis and dietary insufficiency (Farrow 2006). The degree of displacement of the fracture fragments and clinical signs vary, depending on the cause and severity of the injury.
Fracture of the withers usually involves concurrent soft tissue injuries, and strain of the longissimus muscles is common (Jeffcott and Haussler 2004). Fractures of the DSP are generally not associated with spinal cord compromise and resultant mortality, in contrast to injuries involving the vertebral body or neural arch (Jeffcott and Whitwell 1976). Most cases of fracture of the DSP of the withers respond
well to conservative treatment, including analgesia and anti-inflammatory therapy. Stall confinement for a minimum of 4 weeks to allow stabilisation of the fractured segment(s) followed by approximately 6 months’ extended conservative management has been recommended (Molnar et al. 2012; Piat et al. 2012). Surgical intervention is rarely necessary, the exceptions being where the bone fragments become sequestered, erode through the skin or interfere with saddle placement (Jeffcott and Haussler 2004; Perkins et al. 2005; Driver and Pilsworth 2009; Robertson and Samii 2012). Subtotal ostectomy of the DSP (Perkins et al. 2005) and internal fixation with plates and screws have also been reported (Robertson and Samii 2012). The prognosis for return to previous levels of ridden work is generally good, with the majority of the cases described in the veterinary literature reporting a satisfactory clinical resolution with no permanent effect on performance (Jeffcott 1999). Residual depression or chronic thickening may remain (Jeffcott 1999), with impingement of the saddle on the withers reportedly common and hence additional padding or modified saddle pads have been recommended (Robertson and Samii 2012). There is little information on short-term management of
and long-termoutlook following DSP injury in the Thoroughbred racehorse. The training programme for racehorses is intense and often economically motivated. There is pressure from owners and trainers to reduce the number of nontraining days, with a rapid return to exercise and the resumption of full work after a horse suffers an injury. The aim of this retrospective study was to describe the prevalence of wither fracture in a population of Thoroughbred racehorses in training, the associated history and clinical signs, the effect of injury on return to racing and the long-term consequence on racing performance.
Materials and methods
A retrospective cohort study of horses was conducted using the veterinary clinical records of racehorses from the Hong Kong Jockey Club to identify horses that had experienced wither fracture. Data on all horses imported into Hong Kong for racing between 1 September 2003 and 31 December 2013
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