CURBS are defined as an enlargement or bowing on the planter aspect (back) of the hock and upper cannon.

They create a convex profile, best appreciated from the side, on the back of the calcaneus, central and distal tarsal bones and the upper metacarpal bones. Curbs are sometimes differentiated into two categories, false and true curbs. False curbs are a conformational deformity of the bones of the hock and upper cannon. They are generally present from a young age or are a result of injuries.

False curbs and the conformational defects they consist of predispose the affected individuals to developing true curbs and distal hock joint injuries. True curbs are soft tissue swellings and were historically thought to be a result of injury and inflammation of the long plantar ligament of the tarsus (hock). With the advent of ultrasound examination, it has become apparent that this is not a single condition but a common clinical presentation of a collection of soft tissue injuries in this region at the back of the hock.

As previously discussed, horses may be susceptible to the formation of curbs due to conformational defects of their hocks. Sickle hocks in particular are seen as a risk factor for the development of curbs as an acute injury during exercise. These conformational abnormalities alter the weight-bearing forces within the limb during exercise, creating increased stress and therefore injury at points of weakness.

The type of work the horse undertakes is also a risk factor; jumping, racing or pulling loads is considered to increase the risk of curb formation. Researchers in America reviewed the outcome of ultrasound examinations of horses with curbs that had been seen at the New Bolton Center, Pennsylvania and the Randall Veterinary Hospital, Ohio, in recent years. In all, 110 horses were included in the study. Curbs were most commonly seen in racehorses, while non-racing sport horses of various disciplines comprised the remainder of the cases, including hunters, eventers and show-jumpers.

We at Mark Johnston Racing find the degree of lameness varies in horses that present with acute curbs. Some can show marked signs of lameness, while others can be sound and just present with acute inflammation, pain and filling on the back of the hock.

In the American study, horses were more likely to be lame if the damage involved the plantar ligament, superficial digital flexor (SDF) tendon or deep digital flexor (DDF) tendon. Some horses had minor damage to the SDF tendon without being lame.

The most common injury, present in 40 horses (36%), involved only the subcutaneous fibrous tissue without any sign of damage to the SDF tendon, DDF tendon or plantar ligament. In six of those cases, there was a haematoma in the subcutaneous tissue. Thirty-two horses (29%) had both subcutaneous swelling and superficial digital flexor (SDF) tendonitis.

The researchers found that SDF tendonitis only occurred in the presence of subcutaneous swelling. They suggest that this might indicate that the subcutaneous swelling precedes the tendon damage, so if treatment consisting of rest and anti-inflammatory medication is initiated immediately at the first signs of injury, more severe soft tissue injuries may be avoided. Overall, only 30% of the horses had damage to the plantar ligament.

TREATMENT REGIME

The treatment regime we use here at Mark Johnston Racing is tailored to each individual case depending on the severity of the horse’s curb. The horses are examined at regular intervals by veterinary surgeons and yard managers to monitor their progress and prevent any deterioration in the injury.

On discovery of a curb that is warm, painful and making the horse lame, phenylbutasone treatment is initiated. The horse is placed on the walker until sound. Once sound the horse completes two weeks walking and trotting exercise on phenylbutasone. After this period if the horse is still sound and the curb is settling, it resumes canter exercise on a flat all weather gallop on phenylbutasone for a week before returning to normal canter exercise.

The prognosis for return to exercise after horses have experienced curb injuries is generally good, providing timely and accurate treatment is initiated. Poor conformation, however, may act as a persistent cause of strain on the hock, predisposing the horse to repeat curb injuries along with distal hock joint osteoarthritis and fracture of the central and distal tarsal bones.

As previously stated, horses are often left with a conformational blemish having had a curb and poor hock conformation can increase the risks of developing curbs. It is accepted that racehorses can be successful in spite of curby confirmation, but this defect is a natural weakness and may increase the number of training days lost to lameness.

Here at Mark Johnston Racing our two on-site vets provide for quick diagnosis and accurate treatment of injuries, with the aim of reducing the number of training days lost to lameness.

A graduate of the University of London, Neil Mechie is a veterinary surgeon with Mark Johnston Racing. This article first appeared in the Kingsley Klarion.