Bone scanning: diagnosis of orthopaedic conditions in the horse

Tony Kaye BVSc MRCVS, St David’s Equine Practice

Bone scanning (Bone-Phase Gamma Scintigraphy) is a specialised diagnostic technique used in the diagnosis of lameness, back pain and other orthopaedic conditions in horses. The technique uses a short acting radioisotope (Technecium 99^m) attached to a bone seeking molecule that is injected and taken up by all active bone cells. The pattern of radioactivity that results is then read by a gamma camera and sophisticated computer software is used to generate images of the regions of the skeleton under investigation.

The amount of radioactive isotope taken up by bone depends on how active the bone is. Areas of bone which are more active than others will take up more isotope and appear brighter or “hotter” on the resulting scan picture. Bone in areas of bone disease tends to be more active than in other areas and these areas will be highlighted as bright “hot spots” on the scan picture and so can be identified for further investigation. Bone scanning is a sensitive method of identifying certain bone diseases such as fractures, arthritis and bone infection. The technique can be highly sensitive in comparison to X-rays and therefore can sometimes be used to detect early bone disease before X-ray changes appear.

Scintigraphy does not replace other diagnostic techniques such as x-rays, ultrasound and nerve and joint blocks but should be used in conjunction with them. However, it provides information that cannot be gathered in other ways and can help to answer many lameness questions that we previously could not answer with other techniques alone.

Bone scanning can be particularly useful in the diagnosis of the following conditions:

It is highly sensitive for the diagnosis of stress fractures or incomplete fractures (which can be difficult to see on X-ray pictures).

Bony disorders of the back, pelvis or sacro-iliac joint (some of which can be difficult or impossible to diagnose by X-ray or ultrasound scanning).

Horses with lameness originating from several sites or in more than one limb.

Obscure or intermittent lameness.

Tooth root abscesses and sinus disease.

Bone scanning is a common and safe clinical procedure and is routinely carried out on humans at the hospital. The dose of radiation administered is very small and has no effect on the well-being of the horse. Two hours after injection, all of the radioisotope not attached to bone will have been removed from the body in urine and only that attached to bone is left. The radioisotope attached to bone is also rapidly eliminated and is virtually undetectable after 36-48 hours.

St David’s Equine Practice near Exeter was one of the first equine veterinary clinics in the UK to use scintigraphy in horses in 1986. When our purpose built clinic opened near Exeter in 2005, we installed a new updated bone scanning facility with state of the art computer software. This remains one of only a few such units in the country and the only one in the South West, south of Langford (Bristol University).

For more information on Scintigraphy, or our other equine veterinary services, please contact our equine team at St David’s Equine Practice on 01392 876622 (option 2). St David’s Equine Practice also provides the equine veterinary services for Molecare Veterinary Services in the South Molton, Newton Abbot and Cullompton areas.