Editor's Note: This article is part of TheHorse.com's ongoing coverage of topics presented at the British Equine Veterinary Association's 51st annual Congress, held Sept. 12-15 in Birmingham, U.K.
Incomplete, or hairline, fractures of the cannon bone can occur in horses due to acute trauma as well as repetitive loading (known as stress-related bone injury).
Although most of the research on these injuries has involved racehorses, sport horses and general-purpose riding horses are not exempt. Thus, Rhiannon Morgan, BVSc, MRCVS, who is currently completing her PhD at the University of Liverpool's Institute of Aging and Chronic Disease, conducted a study comparing sport horse cannon bone fractures to those of racehorses. She presented her findings at the British Equine Veterinary Association's 51st annual Congress, held Sept. 12-15 in Birmingham, UK.
In her retrospective study, Morgan evaluated the medical records of horses examined by Sue Dyson, MA, VetMB, PhD, DEO, FRCVS, head of Clinical Orthopaedics at the Animal Health Trust, in Newmarket, England, from 1985 to 2010. She included in the study horses with pain localized to proximopalmar (upper back) region of the cannon bone and radiographic (X ray) evidence of an incomplete fracture or changes indicating potential fracture. From these she identified 55 horses--15 racehorses aged 2 to 10 years and 40 sport horses aged 3 to 14 years. The sport horses included 13 Thoroughbreds, eight Warmbloods, four Thoroughbred crosses, and 15 other breeds.
Upon reviewing the sport horses' clinical signs, Morgan determined:
- 11 (28%) were lame at the walk;
- 37 (92.5%) had unilateral (only on one limb) forelimb lameness at the trot; and
- 3 (7.5%) had bilateral (in both limbs) forelimb lameness.
These findings were all similar to what is seen in racehorses, she said. Also similar between sport and racehorses was degree of lameness (moderate, or 4 on a 0-8 scale); lameness on a straight line vs. a circle; and lameness on hard vs. soft surfaces. However, only 65% of lame limbs in the sport horses revealed radiologic abnormalities, compared to 94% in racehorses, she relayed.
Horses received a variety of treatments including "correction of foot imbalance and a minimum of three months stall rest with ascending amounts of controlled walking exercise," Morgan explained.
In 46 horses (both sport and racehorse) for which long-term follow-up was available, Morgan noted 98% returned to full athletic function, resuming work two and a quarter to nine months after diagnosis.
From this large study comparing different breeds and disciplines, Morgan determined that horses with these injuries exhibit a wide range of radiological abnormalities. Based on this finding, she suggested that owners and veterinarians perform scintigraphy (bone scan) on sport horses whose pathology is not radiologically evident.
Overall, Morgan concluded that "incomplete fractures and stress-related bone injury are not restricted by breed, discipline, or age."
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.