Bone scans in horses

In theory, nuclear scintigraphy (bone scanning) sounds like the ideal imaging modality to localize problem areas in horses’ bodies. Veterinarians inject a radioisotope into the horse, which gets deposited in areas where bone is changing rapidly, as often occurs at healing injury sites. Then, they use special gamma cameras to acquire images that show these rapidly changing areas. Easy, right?

Not so fast. Recent research suggests that bone scans in horses aren’t always accurate in diagnosing causes of lameness and poor performance in sport horses when used alone.

However, said Sue Dyson, MA, VetMB, PhD, DEO, FRCVS, head of Clinical Orthopaedics Animal Health Trust Centre for Equine Studies, in Newmarket, U.K., bone scans in horses used alongside other imaging modalities and diagnostic procedures can provide clinically useful information.

“Its value in diagnosing specific lesions or injuries in combination with other imaging modalities, clinical examination, and the results of diagnostic analgesia has been documented for several anatomic sites in horses, especially in racehorses,” she said.

But researchers hadn’t verified its validity as a diagnostic screening test in lame or poorly performing sport horses. So, Dyson and colleagues reviewed 690 bone scans performed at the Centre for Equine Studies from March 2008 to December 2014. Of those, they included sport horses with a definitive lameness or poor performance diagnosis (480 horses). They did not include racehorses in this study.

“We hypothesised that skeletal scintigraphy would not be verified as a useful diagnostic test when used as an indiscriminate screening examination in sports horses presented for lameness or poor performance,” Dyson said.

The researchers believed the radiopharmaceutical uptake for lesions contributing to lameness or poor performance would vary in different parts of the body, and the data confirmed their hypothesis.

“The agreement between increased radiopharmaceutical uptake and final diagnosis was less than chance,” Dyson said. “There was a high proportion of false-negative and false-incidental results.”

In other words, the researchers found no greater correlation between problematic areas found on bone scans and the diagnosed lameness cause than would be expected through pure chance.

The team did observe bone scan results closely linked with lameness causes in two anatomic regions: the front feet and forelimb’s proximal (upper) structures (elbow, shoulder, and scapula). They confirmed it had limited usefulness in assessing lameness associated with hock and sacroiliac pain.

The researchers concluded that isolated or indiscriminate bone scans in horses are unlikely to lead to a full—and correct—diagnosis.

“The high potential for missed diagnoses renders skeletal scintigraphy unreliable as a diagnostic screening tool for sports or pleasure horses with lameness or poor performance,” Dyson said.

The study, “Evaluation of the diagnostic accuracy of skeletal scintigraphy in lame and poorly performing sports horses,” was published in Veterinary Radiology & Ultrasound.