Suspensory Ligament Injuries

The suspensory ligament runs from the cannon bone, branches in two, and connects to the rear of the fetlock joint. When the horse lifts its leg, the ligament pushes the fetlock joint up and forward. At rest, the ligament supports the fetlock joint from descending too far. Injury to the suspensory ligament results in loss of the ability to maintain the fetlock joint in its usual, normal position.

Suspensory ligament desmitis can occur in aged horses as a result of the aging process, but more commonly it occurs in performance horses as a result of sudden overextension of the limb during weight bearing. Ligamentous injuries can be career and occasionally life threatening.

Causes of suspensory desmitis involves overextension of the fetlock joint during weight bearing, which in turn causes tearing of the collagen fibers that comprise the ligament. Like tendon injuries, damage can occur from a single insult or from repetitive overloading during the weight-bearing phase of the stride.

Predisposing factors to injury include muscle weakness and fatigue during competitions that lead to hyperextension of the fetlock joint and overstretching of the tendons and ligaments. Inadequate training and conditioning may also predispose to injury. Tendons and ligaments become stronger with the help of appropriate conditioning exercises.

Suspensory injury can occur in all breeds and genders but occurs most frequently in horses used for competitive sports. Injury most commonly occurs in the forelimbs of horses. However, in racing Standardbreds injury occurs with equal frequency in forelimbs and hindlimbs.

Anatomically the suspensory ligament is divided into three regions: the origin at the top of the cannon bone, the body, and the branches (medial and lateral). Long term outcome varies with the anatomical location.

What to Watch For

• Swelling and pain at the site of the injury
• Obvious, acute lameness
• Dropping of the fetlock during weight bearing
• Inflammation of the proximal sesamoid bones (sesamoiditis)

Diagnosis

Physical examination findings consistent with suspensory desmitis include heat, swelling, enlargement of the ligament and a painful response to ligament palpation. Lameness evaluation with the use of diagnostic anesthetic injections may be necessary to confirm that subtle ligamentous change or previously healed injuries are the source of the horse's current lameness. During the examination, the horse will be evaluated at the gait in which it appears unsound. Sequential anesthetic nerve and joint injections will be performed to rule in or rule out the ligament as the source of the horse's lameness. Additional tests include:

• Ultrasound evaluation of the suspensory ligament is the best method for your veterinarian to confirm the presence of an injury, determine its severity, to monitor healing, and to determine a prognosis for soundness.
• Radiographs are recommended to diagnose proximal suspensory ligament avulsions, splint bone fractures, and sesamoiditis.
• Nuclear scintigraphy is very sensitive in diagnosing horses that have high suspensory ligament avulsion injuries. In many of these horses the ultrasound examination will not be diagnostic. Nuclear scintigraphy is also helpful to determine if a chronic or subtle suspensory injury is currently active. There will be an increase in isotope activity in active injury.

Treatment

Initial therapy is directed at reducing the inflammation present in an acute injury. Rest, cold therapy (water, ice pack), bandaging, and the use of systemic anti-inflammatory medications is recommended. Cold therapy should be applied frequently throughout the day but the duration of application limited to less than 20 minutes at a time. Additional tests include:

Stall rest is important until the horse is able to walk soundly. Once he is walking soundly, you can start controlled hand-walking exercise. Increase in intensity and duration of exercise will be directed by the progression of healing seen in sequential ultrasound evaluations.

In horses with severe lesions of the suspensory, a splint or half limb cast may be used initially to prevent further damage to the ligament during early healing.

Typical healing times for high suspensory lesions range from 3 to 9 months, with hindlimb lesions requiring more time than forelimb lesions. Suspensory desmitis of the body or branches can require more protracted healing times than those for high suspensory lesions. Controlled exercise treatment plans and return to exercise will be dictated by the results of sequential ultrasound evaluations.

Home Care and Prevention

• It is often difficult to determine if the swelling is associated with the tendons or with the suspensory ligament. Horses that develop swelling of the distal limb should have the limb hosed with cold water or have a cold water bandage or an ice pack applied for 10 to 15 minute intervals several times a day to reduce the inflammation. This will help to minimize ongoing damage.
• The limb should be kept in a stable bandage when not being treated with cold therapy. Avoid the use of topical medications that generate heat. The goal is to minimize inflammation, not to create it.
• All handwalking and turnout is forbidden until a veterinary consult can be obtained.
• If your horse develops an acute lameness in conjunction with the swelling, consult your veterinarian immediately. It is necessary to treat some suspensory injuries on an emergency basis.
• It is important that you adhere to your veterinarian's treatment plan. Failure to do so often leads to protracted healing and unsatisfactory long-term results. Even under the best of circumstances suspensory injuries carry a guarded prognosis for long-term future soundness. Reinjury is common.
• Prevention is not always possible in competitive horses. The chances of injury can be reduced by making sure horses are physically trained prior to participating in strenuous events.
• Other sites of unsoundness (lameness associated with arthritis of a joint) should be addressed. Failure to do so results in the horse bearing more weight on the other sound limbs. The sound limbs because they are bearing more of the horse's weight are more prone to excessive strain due to overloading.
• Make a habit of observing and palpating the horse's limbs on a routine basis. This will allow you to learn what is normal for your horse and to identify subtle changes when they occur.
• A veterinary consult is recommended for all horses that develop swelling in the region of the suspensory tendons or within the digital flexor tendon sheath, regardless of the duration of the swelling or the degree of the animal's soundness.