Suspensory ligament injuries can limit the future athletic ability of sport horses, so we explain all you need to know about how to identify and treat them

Suspensory ligament injuries can limit the future athletic ability of sport horses, so Horse & Hound explains all you need to know about how to identify and treat them…

Ligaments attach bones to each other and act as supports. The suspensory ligament in the horse is a strong, broad, fibrous anatomical structure that attaches to the back of the cannon bone just below the knee — the origin of the ligament.

About two-thirds of the way down the cannon bone, the ligament divides into two branches which attach to the inside and outside sesamoid bones, on the back of the fetlock.

In the upper third of the cannon region, the suspensory ligament lies between the large “heads” of the splint bones. This means it is impossible to feel the ligament, or apply pressure directly to it, so diagnosis of damage is difficult.

Suspensory ligament in a horse's leg

Sprain of the suspensory ligament (suspensory desmitis) is usually restricted to one of three areas:

  • injury to the upper third of the ligament (called high, or proximal, suspensory desmitis) is common in horses in all disciplines
  • injury to the middle third, or body, of the ligament is easiest to diagnose, but least frequent. National Hunt racehorses and point-to-pointers are most likely to suffer this injury
  • damage to the inside or outside branch of the suspensory ligament is also common, particularly in horses which jump

A ligament sprain causes heat, swelling and pain. When the middle third, or body, of the suspensory ligament is sprained the signs are easy to detect as there is often obvious swelling. It usually occurs on both the inside and outside of the leg, contrasting with swelling associated with a tendon strain, which happens to the back of the leg.

Heat is easily felt. The horse will also resent palpation of the injured part of the ligament, the edges of which may be rounded and poorly defined. The ligament may feel softer than normal.

There is usually some lameness, the degree of which often reflects the severity of the injury. However, lack of lameness does not mean there is no significant injury. With a severe injury, the whole area may be swollen so it can be difficult to assess which part of the ligament is primarily involved.

Cold therapy and bandaging will usually reduce the swelling, making a definitive diagnosis easier. Alternatively a vet can determine which part is involved and assess the extent of the damage using an ultrasound scanner.

An injury to the inside or outside branch of the ligament will cause swelling on one side of the fetlock. Do not confuse this with a swelling due to direct trauma, such as getting cast.

Lameness associated with a branch injury can be mild to moderate, but may improve within days. Again, scanning will confirm the extent and severity of the injury and determine whether there is concurrent damage to either the sesamoid bone or the splint bone on the same side. X-rays may also be needed.

Damage at the top of the suspensory ligament invariably causes lameness — varying from mild to severe — which, if the horse rests, can improve rapidly. The lameness tends to be worst when the horse moves in circles with the affected limb on the outside. Slight localised heat may appear when the lameness is acute, while in subtle cases thermography can detect this. The vein which runs down the inside of the cannon region may be enlarged.

In many cases there is nothing abnormal to feel and the vet will have to use a nerve block to eliminate the lower limb as a source of pain and also determine that the pain is coming from just below the back of the knee.

Scanning is essential, too. Sometimes an obvious black hole in the ligament shows up on the scan; sometimes the changes are more subtle. The ligament may be slightly enlarged, with a tiny disruption of its fibre pattern.

The vet’s aims are to eliminate any predisposing causes such as poor foot balance or inappropriate shoes, to reduce inflammation by the use of cold therapy, laser treatment or therapeutic ultrasound and to encourage good quality repair of the damaged fibres.

Small lesions at the top of the suspensory ligament often resolve with around three months’ box rest, combined with a controlled exercise programme. Scanning can be used to monitor the healing.

Larger injuries in the body or branch may need surgery to remove any blood clots. Prolonged rest combined with an ascending exercise programme is an essential part of any treatment regime.

Prognosis depends on many factors including:

  • the site of the injury
  • its severity
  • the duration of the injury
  • the future athletic expectations for the horse

Most horses are able to return to some level of work. With appropriate early treatment most horses with a sprain around the origin of the ligament make a complete recovery; however, the chance of repeat damage to injuries on the body of the ligament is quite high if the horse returns to its former workload. The prognosis for branch injuries is between the other two.

Some factors may predispose the horse to suspensory ligament injuries or their recurrence.

  • conformation can play a role. A horse with a crooked lower limb will overload one side of the fetlock and predispose it to a branch injury
  • poor foot balance is commonly seen in horses which injure the origin of the ligament. If the shoes are too short and offer little support to the back of the heel region, this can cause overload of the ligament
  • fast work: there is also no doubt that suspensory ligament injuries are an occupational hazard for some horses, particularly those which jump at speed
  • a previous suspensory injury also places a horse at increased risk of repeat injury since, particularly with body and branch injuries, the repair tissue is never as strong as before

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