Suspensory ligament injuries in horses can affect the animal’s future athletic ability. In order to understand why and how injuries occur, it is helpful to be familiar with the structures involved.
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 or hock — 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 here is difficult.
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, called body desmitis.
- damage to the inside or outside branch of the suspensory ligament is also common, particularly in horses which jump, called branch desmitis.
Signs of suspensory desmitis
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 that can be seen on both the inside and outside of the injured leg.
Heat is easily felt on close examination of the limb. 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. Once the injured soft tissue structure has been identified, your vet can assess the extent of the damage using an ultrasound scanner, however this is often easier for body or branch lesions than clearly imaging proximal suspensory lesions by ultrasound.
An injury to the inside or outside branch of the ligament will cause swelling on one side of the fetlock. Take care not to 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 also damage to either the sesamoid bone or the splint bone on the same side. X-rays may also be useful, particularly to check for splint bone fractures or sesamoid bone damage, which can be associated with a suspensory ligament branch injury.
Damage at the proximal part or 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 and sometimes the vein that runs down the inside of the cannon region may be enlarged.
In many cases there is nothing abnormal to feel and the vet may 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.
Imaging the damaged area is key. 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 just a tiny disruption of its fibre pattern. X-ray changes may be apparent in a few cases. Research has shown that high field MRI is considered the gold standard for diagnosis, but is rarely performed as a general anaesthetic is required and the equipment is only available in a few specialist centres, instead fastidious and thorough ultrasonographic imaging is required.
Treatment of a suspensory injury
The vet will seek to eliminate any predisposing causes such as poor foot balance or inappropriate shoes; reduce inflammation by the use of cold therapy, laser treatment or therapeutic ultrasound; and to encourage good quality repair of the damaged fibres. Scanning can be used to monitor the healing.
The exact type of treatment will vary depending on the area of damage,
Shockwave therapy has been successfully used for cases of proximal suspensory desmitis (PSD) and some suspensory body lesions.
Use of injectable therapies such as PRP (platelet rich plasma) or stem cells may be used in suitable cases. They may not help to alleviate the pain causing the lameness.
Surgery in the form a neurectomy to relieve the pain, together with cutting specific soft tissues (fasciotomy) has been used successfully in both hind and front legs for proximal suspensory lesions. Some suspensory ligament branch injuries will also require surgery, if there is damage within the fetlock joint. In one report this helped 13/18 horses to recover.
Prognosis after suspensory ligament injuries
This 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.
For proximal suspensory lesions the overall prognosis for return to exercise is better in the forelimbs (about 80% resolve), whereas hindlimbs can be more problematic with less than 20% recovering, however shockwave therapy and surgery improve the chances of an injured horse returning to work.
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 guarded because of the high incidence of reoccurrence and the slow unpredictable rate of healing.
Which horses are most at risk?
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
- dressage horses are at risk from damage to the hindlimb origin as a result of repetitive overloading during training for collected work and tissue degeneration.
- suspensory ligament injuries are an occupational hazard for horses that do regular fast work and jump at speed
- a previous suspensory injury places a horse at increased risk of repeat injury since, particularly with body and branch injuries, the repaired tissue is never as strong as before
https://onlinelibrary.wiley.com/doi/abs/10.1111/eve.13187 – An investigation into the occurrence of, and risk factors for, concurrent suspensory ligament injuries in horses with hindlimb proximal suspensory desmopathy – October 2019