WITH the sales season in full swing, a set of X-rays of a horse involves usually a standard set of 36 views of the fetlocks, knees, hocks and stifles.

A huge number of abnormalities can be found on X-rays, such as sagittal ridge Osteochondritis Dissecans (OCD) defects in the front fetlocks; fragments off the back of the pastern bone; bone cysts in the ulnar carpal bone; and ‘spurring’ in the hock joints.

But, as highlighted by Rossdales veterinary surgeon Thomas O’Keeffe recently, many scientific studies, including a 2009 study following more than 2,000 horses in Australia, have shown these abnormalities to have no impact on future racing. Despite there being no evidence that these supposed ‘faults’ have an impact on future performance, many veterinary surgeons will ‘fail’ these horses when vetting them.

As a result, consignors are becoming as conscious about producing a horse with a clean set of X-rays as they are about producing a physical specimen that will be able to run fast. This is more prevalent than ever in America where the scrutiny of X-rays is at its greatest. At the Keeneland September Sale, it is universally accepted that all yearlings on the premier days will have a complete set of 36 X-rays.

Compare this with a Fairyhouse Sale I attended, where few horses were offered with X-rays. In America these ‘faults’ identified on X-ray have such an impact on the selling price that a huge proportion of horses will have surgery as foals or yearlings before the sale to try to rectify such issues. But as there is no evidence to confirm that these ‘faults’ have any impact on performance, it can be argued that this surgery is largely cosmetic, simply performed in order to produce clean X-rays.

It was suggested to us recently that one American stud farm had decided to minimise the amount of time its yearlings spent outdoors in order to reduce the amount of abnormalities they acquired and so hopefully produce horses with ‘passable’ X-rays. The negative impact this must have on the development of these horses in this crucial stage of their life must be marked.

FRACTURED SESAMOIDS

With regards to the Mark Johnston Racing policy at the sales in relation to X-rays, there is only one abnormality that is an automatic fail, and that is a fractured sesamoid. The proximal sesamoid bones are a pair of bones at the back of the fetlock; they are encased within the elastic suspensory ligament and the non-elastic distal sesamoidean ligaments, collectively forming the suspensory apparatus. This system functions as an energy-storing device and minimises hyperextension of the fetlock during the stance phase of the stride.

Fractures of the sesamoid are a relatively common occurrence in foals. Uncontrolled galloping in the field can fatigue the suspensory apparatus, causing fetlock extension to become maximal so that the tensile forces exerted exceed the tolerance of the sesamoid bones, leading to a fracture. The reason that we have no tolerance for fractures of the sesamoid is that, unlike other X-ray findings, there is no chance that these will heal or improve.

Non-union or malunion across a sesamoid fracture site has been attributed to sparse blood supply to the bone.

It has been hypothesised that the fracture itself may disrupt the blood supply to the bone, or that constant motion at the fracture line during weight-bearing results in poor fracture healing. The suspensory apparatus and distal sesamoidean ligaments apply traction to the sesamoids in opposite directions, hindering the stability required for effective fracture repair. In addition, the proximal sesamoid bones lack a periosteal covering, which has been implicated in poor fracture healing.

This does not mean to say that these horses have a hopeless prognosis for racing. There are a number of methods of trying to address fractured sesamoids. For example, small fragments may be surgically removed or, if the fracture segments are considered too large for removal, a lag screw can be used to fixate the fragments and, on occasions, be combined with a bone graft.

But the fact that these horses presented at the sales with fractured sesamoids will not heal, means that we are not prepared to buy them at any price. Fractured sesamoids are relatively easy to identify on X-ray, but at sales where X-rays are not readily available, it is vital to be able to identify those horses you suspect may have a fractured sesamoid, simply by manual palpation.

With every single horse that we view at the sales, we will run our hands down the front legs of the yearling and over the back of the fetlock, looking for indicators of injury to the sesamoid bones, such as heat and swelling. If we are suspicious about a particular sesamoid we will request X-rays from the vendor. If they cannot be produced, then that horse will not be purchased.

Manual palpation is not an exact science, for many horses with sesamoid injuries will not be clearly identifiable. But having developed the skill over time, one finds there is a clear correlation between issues identified on the horse and issues identified on X-ray.

In a climate where more and more importance is being placed on the quality of a horse’s X-rays, we will not give undue weight to findings for which there is no evidence that they negatively affect performance, and we will continue to concentrate on the quality of the racehorse.

Charlie Johnston is a veterinary surgeon with Mark Johnston Racing and is the son of trainer Mark Johnston