SHINS NA TRAINER ISSUE 32b_Jerkins feature.qxd 17/04/2014 22:16 Page 2
BUCKED SHINS
TREATING SORE SHINS
Can current research make a breakthrough? Last November, Cleburne, a leading fancy in the Breeders’ Cup Juvenile, was scratched in the build-up to the race due to having “bucked shins.” From the turn of the year, consignors have been preparing their horses on both sides of the Atlantic Ocean for the rigorous and demanding process of two-year-old Thoroughbred sales and have, no doubt, been battling the phenomenon of bucked shins.
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WORDS: THOMAS O’KEEFFE PHOTOS: PATRICIA McQUEEN, THOMAS O’KEEFFE
ULTIPLE studies have been performed over the past 30 years to better understand and help prevent the condition. As recently as 2013, the Equine Veterinary Journal published a paper reviewing the incidence of bucked shins and the efficacy of a commonly used preventative technique, “periosteal scraping.” Bucked or sore shins are part of the disease complex known as dorsal metacarpal disease and they have been affecting young racehorses for generations. In North America, a 2002 veterinary report stated that over 70% of horses in training suffer from bucked shins and due to this condition the financial losses for North America alone were estimated to be $10,000,000 in lost training and racing days! Furthermore, it has been demonstrated that 12% of those horses that suffer from bucked shins subsequently develop radiographic evidence of stress fractures of their cannon bone up to one year after the initial injury. Bucked shins is a condition seen throughout the world and has been treated over time in a variety of methods, from surgical management to traditional empirical therapies. Management of sore shins is a controversial subject, with many
trainers and veterinarians differing on the optimal treatment strategy. This article aims to discuss briefly why this condition occurs, the current research undertaken on the bone’s adaptive response to exercise, and the different approaches to managing this condition.
Development of bucked shins Bucked shins usually occur in two-year-old Thoroughbred horses in training or in older horses that have not reached race speed previously or have had a long layoff. They can occur bilaterally and in North America are seen to usually occur sequentially, with the left leg being affected first as a consequence of the anticlockwise direction in which horses are trained and raced. The disease is diagnosed on physical examination, where palpation of the front of the cannon bone reveals heat and pain. Affected horses are uncomfortable, but the presence of overt lameness is variable. Diagnosis can be confirmed radiographically by the presence of periosteal new bone formation over the front of the cannon bone, although this finding is not always initially apparent. Originally, it was thought that bucked shins resulted from concussive damage to the periosteum (the membrane that covers the
outer surface bones), with subperiosteal hematoma formation, microfractures, and inflammation leading to clinical signs. Current research has demonstrated that bucked shins may be the result of high-strain cyclic fatigue, caused by excessive compression on a bone that has not adequately remodeled to withstand such stress. Bone that is stressed immediately seeks to form a new layer of bone at the point of stress. This rapidly formed woven bone is more porous and weaker than the more slowly laiddown lamellar bone. In the process of this rapid bone formation, the periosteum becomes lifted and inflamed, ultimately leading to the clinical signs characteristic of bucked shins. The shin is a barometer of what is going on in the rest of the skeleton, and when sore the shin indicates the skeleton needs more time to adapt, a caution that unheeded can lead to more serious injuries, such as stress fractures of other long bones like the tibia or humerus.
Racehorse training and bucked shins As described above, bucked shins are a result of the mismatching of exercise with the modeling and remodeling of the cannon bone necessary for the bone to withstand the rigors of training and racing. Horses are not born with the right bone
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