Lesions involving the musculoskeletal system of racehorses are some of the most common causes of financial loss in the racehorse industry worldwide.1 These lesions can involve soft tissue and bony structures and often result in days lost from training or catastrophic career-ending injuries. Many of the injuries develop without a specific traumatic event, yet are highly consistent in their morphology and frequently develop at the same locations within a bone.2 In addition, preexisting stress fractures are associated with the development of complete bone fractures.3
Stress fractures have been described as damage to the bone that results from repetitive loading. Such fractures are commonly associated with microcracks in the bone.4,5 Intense exercise, such as race training and racing, predisposes horses to this condition. Therefore, stress fractures are common in Thoroughbred racehorses; however, all horses that undergo repetitive activities are susceptible.4 In Thoroughbred racehorses, tibias are the bones most susceptible to stress fractures.6
Nuclear scintigraphy is a highly sensitive method for identifying regions of bone in which remodeling activity is increased, compared with activity in apparently normal bone. This imaging modality is the method of choice for diagnosing stress fractures in athletic horses.7 Currently, most diagnoses of tibial stress fractures via image analyses are performed subjectively. Subjective grading systems for tibial stress fractures have been proposed in equine and human medicine.8,9 A correlation between scintigraphic grades of tibial stress fractures and intervals between fracture and recovery in human athletes has been reported.9 A repeatable and objective method of measuring the severity of a stress fracture may facilitate choice of treatment regimen and may aid in determining the period of recovery required before returning to race training. Quantitative evaluations of various skeletal regions in horses have been reported.10–13 The purposes of the study reported here were to establish a quantitative method of interpreting tibial scintigrams in Thoroughbred racehorses with tibial stress fractures that may facilitate diagnosis of stress fractures and to provide prognostic information regarding future performance of affected horses.
Magnetic resonance imaging
Region of interest
Bloodstock Research Information Services Inc, Lexington, Ky.
Omega 500, Technicare, Cleveland, Ohio.
Mirage 2000-AP, Seganicorp, Columbia, Md.
Nuclear Mac, version 5.2.1, Scientific Imaging, Littleton, Colo.
Nuclear Mac, version 9.7, Scientific Imaging, Littleton, Colo.
Intercooled Stata, version 8.0 for Windows, StataCorp, College Station, Tex.
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