CONDYLAR fractures refer to fractures of the lower part of the cannon bone. The medial and lateral condyles are rounded prominences of the lower cannon bone which articulate with the long pastern bone forming the fetlock joint.

They are the most common fracture seen in the long bones of racehorses. Condylar fractures are twice as likely to occur in forelimbs and four times more likely to occur in the lateral condyle compared with the medial condyle.

Condylar fractures occur generally as a result of repetitive strain on the bone. During high-speed exercise, large loads are transmitted through the bone and this repeated high-speed loading results in the formation of micro-fractures within the bone. In normal circumstances these micro-fractures are repaired naturally by the processes of bone remodelling and modelling.

With repeated loading of the cannon bone during training, the balance in this process can shift towards micro-fracture formation. These micro-fractures accumulate and result in the bone failure and ultimately a condylar fracture. Typically a horse with a condylar fracture will present acutely lame after cantering or galloping. The fetlock joint will be distended and there may be generalised filling around the joint. There will be marked resentment to flexion of the joint.

The first consideration in these cases is carefully transporting the horse from the gallops to a facility for X-rays to be taken without any further displacement of the fracture. Analgesia is given immediately and a large support bandage is applied to the leg.

A diagnosis of a condylar fracture is not difficult as they are generally easily identifiable on X-ray. When viewing a condylar fracture on X-ray, there are a few important points to note.

Is the fracture complete or incomplete? Fractures which exit through any aspect of the bone are described as a complete fracture; those which do not exit are described as incomplete. When a fracture is complete there is no longer a bridge to hold the two fragments of bone together and the fracture may become displaced.

Is the fracture medial or lateral? Medial condylar fractures are more high-risk as they can spiral up the cannon bone resulting in a catastrophic fracture.

Once a diagnosis has made and the extent of the fracture is know then a suitable support bandage is applied again and the horse is referred to a surgical facility for repair.

Horses are generally placed under general anaesthetic and the fracture is repaired using lag screws. This involves inserting screws across the fracture. These screws gain purchase in the bone and compress the fracture. In displaced fractures, the joint surface is often disrupted, so along with repairing the fracture, a camera is inserted into the fetlock joint allowing the surgeon to visualise the joint surface. This is particularly useful in reconstruction of displaced fractures, since accurate alignment of the joint surface improves the chances of healing and minimises arthritis.

STRESS FRACTURES

Identifying horses with complete or displaced condylar fractures as described above is generally straightforward. However, horses with short incomplete condylar fractures or those with stress fractures in the condyle present more of a diagnostic challenge for veterinary surgeons.

Typically these horses will present with recurrent lameness after cantering exercise. There may be some filling in the fetlock joint and some resentment to flexion of the joint but quite often there will be no localised signs of lameness.

Investigation of the lameness with nerve blocks will localise the source of lameness to the fetlock joint. These cases can be quite difficult to manage as there are often no abnormalities detectable on initial X-rays and the horse can often come sound very quickly.

In a horse where we have a suspicion of a condylar stress fracture, they are box-rested initially until they are sound at led trot. Once they are sound, they begin walker exercise and we increase their exercise incrementally continuing to X-ray the fetlock joint weekly.

It can take two to four weeks for a stress fracture to become visible on X-ray. Once a diagnosis has been made, we then make a decision on the best treatment option for that case.

Traditionally these stress fractures were treated conservatively. This consisted of a programme of walk/trotting exercise whilst continuing to X-ray the horse every two weeks until the fracture was no longer visible on X-ray.

With advances in surgical techniques, a single screw can now be inserted across these fractures with the horse standing. Providing the fracture is incomplete and there is no displacement of the fracture then it is possible to repair in the sedated standing patient.

This surgical treatment ultimately can end up being less costly and more effective than conservative treatment as the fracture heals faster with more reliable bone-healing and the horse can return to training and racing more quickly.

Additionally there is minimal risk of the horse re-fracturing in this region in the future.

As with all veterinary treatments and procedures at MJR, the cost of diagnosis and any subsequent surgical treatment at Newmarket Equine Hospital is covered in the daily training rate.

John Martin from Stradbally, Co Laois, graduated from University College Dublin and is in practice at Mark Johnston Racing. This article first appeared in the Kingsley Klarion, published by Mark Johnston Racing.