$SPLIT PASTER The injury that gets worse before it gets better Fractures are relatively common injuries in thoroughbred racehorses. This relates to the high athletic demands of racing and training, and the cumulative stresses imposed on the musculoskeletal system by the repetitive nature of race training. Fractures are relatively common injuries in In a recent scientific report published in Equine Veterinary Journal, equine orthopaedic surgeons from Newmarket Equine Hospital (NEH) detailed the healing process and warned that radiographs taken at the time of the initial injury may not be revealing the full extent of the damage that is present. What is a “split pastern?” A “split pastern” is one of the most commonly encountered fractures – a longitudinal fracture of the proximal phalanx (long pastern bone) that extends from the metacarpophalangeal or metatarsophalangeal (fetlock) joint towards the proximal interphalangeal (pastern) joint. This is the most common long bone fracture of thoroughbreds in race training, accounting for 15% of all fracture cases. Fractures of the pastern occur more commonly in training than when racing. Two-year-olds are most often affected, and forelimbs are injured with much greater frequency than hindlimbs. The term ‘fracture configuration’ refers to the path of the fracture through the bone, and there is remarkable consistency in the location and direction in pastern fractures. At the fetlock joint, the bottom of the cannon bone has a ridge that runs from front to back along the centre line of the bone. Opposing this in the top surface of the long pastern bone is a groove – the sagittal groove – that accommodates this ridge. Most commonly, fractures start in the sagittal groove and then course distally (towards the hoof). Fractures can be complete – extending to emerge either at the cortex of the bone or into the pastern joint, or incomplete – with the fracture ending somewhere in the central portion of the bone. Incomplete fractures are more common than complete. The Newmarket Equine Hospital study In all previous reports of fractures of the proximal phalanx, only descriptions of fracture configuration from radiographs obtained at the time of initial injury were available. In cases treated at NEH, vets had observed that pastern fractures often appeared radiologically more complex, and extensive, on follow-up radiographs obtained between during the first two months following initial njury. This concern had not previously been investigated, and it prompted the Newmarket group to embark on a more detailed objective study to document the true configuration of fractures, and investigate how, and over what time period, fractures healed. As cases are usually treated by screw repair, this was set as an entry criteria to identify cases for the fracture-healing part of the study. Radiographs were examined from 121 cases of fracture seen over a five-year period at NEH. Radiographs from the time of initial injury, and then throughout the horses’ recovery from injury whilst the fracture was healing, were examined. The configuration of fracture was determined from the radiographs taken at the time of injury, and then any changes observed in length or complexity of the fracture during the horses recovery were documented. Finally, the way the fracture healed and the time taken was recorded. Progression of the fracture The majority of horses in the study were two- and three-year-olds training or racing on the flat. Consistent with previous observations, long incomplete fractures running parallel with the long axis of the bone were the most common configuration, with complete and comminuted (multi-piece) fractures making up a much smaller proportion of the case population. The study confirmed the surgeons’ suspicions, and a novel conclusion was that in the first two months following injury, in many cases, the fracture was longer or more complex than seen on the initial radiographs. Fractures were on average 15 mm longer, with some cases being over 30 mm longer than initial X-rays suggested. One possible explanation for this was that fractures become longer when the horses recovered from general anaesthesia – a high- risk period for the horse undergoing fracture repair. However,radiographs obtained within the first week after surgery showed injury during anaesthesia was not the culprit. Instead, the change in fracture configuration was a result of the normal process of fracture healing. Damaged, non-viable bone along the fracture line has be removed by the body before healing can occur – resulting in the true configuration of the fracture becoming more apparent on X-rays taken two-to-seven weeks after the injury was sustained. Completion of the healing process After this first seven-week bone removal phase, radiographs showed that the fractures went on to heal progressively, with the majority of them having healed by 100 days following injury. When following cases through during healing, however, it was observed that the bone nearest the fetlock joint surface was slowest to heal. In some horses, delayed healing in this location can require further surgery to obtain complete healing. Advice for the future This study provided some important information for equine surgeons managing split pastern cases in future. There is often repair. However,radiographs obtained within the first week after surgery showed injury during anaesthesia was not the culprit. Instead, the change in fracture configuration quite marked disparity in the degree of comfort of the horse following repair of fractures of the proximal phalanx, a feature that could be explained by the fracture being more complex than suspected on radiographs obtained at the time of initial injury. The second important conclusion from the Newmarket Equine Hospital study is that serial X-rays should be obtained routinely during the period two-to-seven weeks following injury to allow better guidance as to how the horse should be managed during recovery from injury. Thirdly, knowledge of the normal timeframe for fracture healing to occur gained from this study allows more confident identification of cases where healing is delayed which in turn will allow more timely veterinary intervention if problems arise.$

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THIS ARTICLE FIRST APPEARED IN - EUROPEAN TRAINER MAGAZINE ISSUE 45

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