University of Pennsylvania School of Veterinary Medicine | 382 West Street Road Kennett Square, PA 19348 | Phone: 610.444.5800
Grayson Jockey Club Research Foundation Bucked Shin Project
There is growing evidence from previous studies conducted at the New Bolton Center (University of Pennsylvania) that training programs have much to do with contributing to the onset of Bucked Shins. It is hypothesized that failure to adequately expose the horse to racing or similar stress conditions prior to racing, denies the horse the chance to build bone structure compatible to performing under these conditions, and hence puts the bone at risk for failure. The purpose of the present study is to continue to evaluate the efficacy of a modified training program.
Dr. Ray Boston and Dr David Nunamaker (VMD).
Anatomy of the horse leg
The diagnosis of bucked shins is not usually provided by the trainer or owner of the horse. It is usually indicated by a history of acute tenderness or soreness of the left or both Metacarpal III (MC III) bones following high speed workouts or after a race, immediately after or up to a day later. Physical examination will reveal pain on the dorsal or dorsomedial aspect of the third Metacarpal, this may also be accompanied by swelling and tenderness which would indicate new bone proliferation in the affected area.
Previously, veterinarians have been taught that bucked shins were the result of microfractures on the dorsal surface of MC III, thought to be due to fatigue injuries that occur during high speed work. Subsequent investigations have suggested a different understanding of the etiology of bucked shins which lead to the formation of the hypothesis that high strain cyclic fatigue causes reduced bone stiffness which in turn leads to the bone increasing its inertial properties in compensation first using lamellar bone and later using fiber type bone. Fiber bone forms much faster than lamellar bone, so if the bone stiffness decreases quickly enough for the bone to change from lamellar formation to periosteal/fiber formation, bucked shines can result.