Proximal suspensory desmopathy in horses - DVM
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Proximal suspensory desmopathy in horses
An overview of the causes, diagnostic approach and treatment options for this common condition in performance horses.


DVM360 MAGAZINE


Clinical signs and diagnosis

The clinical signs associated with hind limb PSL desmopathy can vary from extremely mild to moderate lameness. Horses may show classic, unilateral low-grade lameness and be unable to perform certain specific athletic movements (i.e., uneven or poorly performed canter pirouettes in the dressage ring, uneven stops or resistance and twisting when backing up in western events, uneven jumping and landing over fences and so on) or may exhibit very subtle performance problems that are only "felt" by upper-level riders as a resistance or hesitancy in specific movements. Even more subtle signs, such as altered head carriage, bolting or other behavioral changes, have been caused by PSL desmopathy.

Diagnosis of this particular injury can be difficult because of the number of structures present in the area of the PSL. Clinicians must try to rule out the distal limb and the hock joint and capsule as sources for the hind limb pain and lameness. Thermography can often confirm increased heat in the area of the PSL but cannot differentiate between ligamentous inflammation and neuritis at that location.

Proximal suspensory desmopathy cases often show no swelling or palpable tenderness. Regional anesthesia can be helpful in this diagnostic process, but closely associated structures in this area other than the PSL may also be affected so nerve blocks are not considered completely diagnostic. Ultrasound evaluation is the field diagnostic modality of choice, and abnormalities of an affected PSL include changes in size (bigger), shape (uneven), echogenicity (small- to large-core lesions) and fiber pattern (disrupted fiber development). But even ultrasound leaves something to be desired and can underrepresent the amount of damage to the PSL.

Robert Cole, DVM, DACVR, an assistant professor of radiology at Auburn University's College of Veterinary Medicine, cautions that a complete workup of a case of suspected PSL desmopathy should also include radiography. Primary bone pathology, distal intertarsal joint issues, avulsions and numerous other bony causes of lameness can mimic PSL desmopathy and should be properly investigated.

Cole also adds that magnetic resonance imaging (MRI) is rapidly becoming the gold-standard diagnostic tool for cases of PSL desmopathy, as it allows surgeons to know if the ligament is the primary issue or if nerve compression is the major cause of lameness. "Neurectomy is not a procedure done casually, and MRI really lets the surgeon be sure that it's the correct procedure for the condition," says Cole.

Treatment and outcomes

Initial cases of proximal suspensory desmopathy are treated routinely utilizing cold therapy, compression and rest. These injuries are monitored over the following eight weeks before any attempts at surgery are made.

"Case selection is extremely important for success when using a fasciotomy–neurectomy treatment approach for PSL desmopathy," explains Reid Hansen, DVM, DACVS, DACVECC, professor of equine surgery and lameness at Auburn University's College of Veterinary Medicine.

Some surgeons, such as John Peroni, DVM, MS, DACVS, an associate professor of large animal surgery at the University of Georgia's College of Veterinary Medicine, believe there are no contraindications for a fasciotomy at almost any point in the suspensory ligament injury timeline. "Relieving pressure can only help the underlying ligament heal, so performing this procedure—even in acute desmitis cases—is quite acceptable," states Peroni.

The neurectomy part of the procedure, however, is saved for a time much later in the disease process. Horses are given four to eight weeks of rest and then reevaluated. If significant healing is occurring, as evidenced by ultrasonographic changes in the thickness and character of the suspensory ligament, then the horse is given additional healing time along with appropriate slow rehabilitation.

Nathaniel White, DVM, MS, DACVS, a professor emeritus of equine surgery at the Marion DuPont Scott Equine Medical Center at Virginia-Maryland Regional College of Veterinary Medicine at Virginia Technical Institute, teaches that rest is the most common and often most effective treatment for proximal suspensory desmopathy.

"The greatest success with no relapses," says White, "includes absolute stall rest for four weeks prior to initiating controlled and gradual increase in walking concurrent with stall rest." Horses that do not respond to this initial healing phase are then candidates for fasciotomy and ligament splitting.

Excellent results are being reported for this approach to these performance injuries. White summarizes, "To date, 95 percent of horses with rear limb proximal suspensory desmitis, which did not heal with rest or rest and shock wave therapy, healed and returned to normal work after suspensory desmoplasty."

Horses that respond to time and treatment and eventually have well-healed suspensory ligaments, as shown with sequential ultrasound evaluations or preferably MRI, but that are still painful and lame are candidates for neurectomy. These athletes have strong enough ligaments to handle a return to work, and neurectomy can be beneficial in eliminating neuritis of the lateral plantar nerve and the associated lameness.

Horses that do not respond after longer periods of rest are labeled as chronic, and their thickened, fibrotic, hypoechoic suspensory ligaments are not likely to change. These horses are poorer candidates for a fasciotomy-neurectomy procedure. Once these horses undergo a neurectomy they are more likely to load the suspensory ligament, and there is no remaining pain response to keep them from excessive activity. A number of horses that have had neurectomies without well-healed ligaments have suffered catastrophic breakdowns of the hind limb suspensory apparatus following a return to exercise.

Fasciotomy and neurectomy of the proximal suspensory ligament and associated nerve is a procedure that offers hope to affected horses, but the selection of candidates must be done carefully. MRI should be utilized if at all possible to identify those horses best suited to these surgeries, and strict postoperative care and rehabilitation are required to achieve a positive outcome.

Dr. Kenneth Marcella is an equine practitioner in Canton, Ga.

Reference

1. Toth F, Schumacher J, Schramme M, et al. Compressive damage to the deep branch of the lateral plantar nerve associated with lameness caused by proximal suspensory desmitis. Vet Surg 2008;37:328-335.


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