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
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:
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.