Degenerative suspensory ligament desmitis (DSLD) is a progressive and devastating lameness that's gaining attention.
In this condition, there is failure of normal healing, with the ligament in involved legs becoming progressively thicker and more spongy. Once thought to be a problem only of the suspensories, recent research has discovered this is actually a bodywide problem.
What Is It?
In the simplest sense, DSLD is a failure of tendons and ligaments to maintain, remodel and repair themselves in a normal fashion. Over time, the normal rope-like structure of these tissues becomes distorted by accumulation of a large amount of proteoglycans, molecules of proteins linked to sugars. The blood supply to the tendons and ligaments progressively shrinks. The exactly cause for this failure and accumulation of proteoglycans has not yet been determined. However, DSLD has been proven to be a systemic disease, meaning it's a body-wide problem.
Onset is often in early adulthood. The earliest symptoms are often vague and nonspecific, such as unexplained stumbling and vague lameness that may shift from leg to leg (see our table for symptoms of ligament/tendon injury vs. DSLD).
Stiffness, especially when rising, is common. It's not unusual for a DSLD horse to have a long history of lameness and neurological exams and to be misdiagnosed in these early stages. The horse may have asymptomatic periods interspersed with times when symptoms are again obvious. As the disease progresses, changes in the fetlocks become obvious. It may strike the front legs first or the hind legs, may be worse in one leg but always involves more than one.
The first change is often swelling, followed by obvious thickening of the suspensory, usually in the suspensory branches. The joint pouches of the fetlock joint may be enlarged. Heat may be obvious. Palpation of the suspensories elicits a pain response and ankle flexion tests are positive, often extremely so and disproportionate to the amount of lameness the horse may be showing.
At this stage, there's still a pattern of "flares" of symptoms alternating with relatively good periods but over time the suspensories become progressively enlarged, painful and develop a mushy consistency on palpation when the leg is held up but may feel abnormally tight when it is bearing weight.
Conformation changes occur, with the fetlocks either dropping down and the horse becoming coon footed, or the opposite may occur, with the fetlocks becoming very upright. When a hind leg is involved, the whole limb may become post legged. Eventually, the condition progresses to the point that the horse is constantly in pain, may even go down and refuse to rise. Euthanasia is often the only option for these horses.
The gait changes with DSLD. Common abnormalities include toe first landing, development of a "rope walking" like gait, traveling extremely wide behind when the hinds are involved, and hopping like a rabbit at the canter when the hinds are involved. These gait changes sometimes lead to a misdiagnosis of neurological disease. To relieve the strain on their ankles, DSLD horses often dig holes to stand in toe first. When the hind legs are involved, they may sit on fence lines or rocks to rest their legs and may be observed dog sitting.
In the early stages, behavior changes, especially reluctance to work, are common. DSLD horses often have episodes that look like colic/abdominal pain but nothing is found to explain it on examination. Areas other than the fetlocks, such as the back, patellar ligaments of the stifle, and hip joints are commonly painful.