What Is Stringhalt?

Q: My 29-year-old Quarter Horse gelding has been diagnosed with a condition that my veterinarian called "stringhalt." He indicated that this condition is rare in this breed and in this location of the United States (northwestern Pennsylvania). What causes this condition? What is the treatment and prognosis?                Missy

A: Stringhalt is an abnormal gait that involves exaggerated flexion of one or both hock joints, resulting in a rapid elevation of the hind limb. The abnormality might be subtle--such as minor upward jerking of the hind leg, or so severe that the canon bone and fetlock are pulled violently against the horse's belly. Some severely affected horses have difficulty moving forward because of the over-flexion at every step. Signs could be exaggerated in nervous or agitated horses, or when they are backed. There is no breed or age predilection. Other syndromes that can cause somewhat similar gait abnormalities include shivers, fibrotic myopathy, intermittent upward fixation of the patella, and peripheral neuropathy (nerve degeneration) due to equine protozoal myelitis (EPM).

Most cases of stringhalt are associated with nerve degeneration. The specific cause this degeneration is unclear, but it might be caused by ingestion of certain plants such as vetch and sweet peas, which contain compounds that damage peripheral nerves. Australian stringhalt commonly involves groups of horses and is thought to be caused by ingestion of flatweed (Hypochoeris radica). Trauma to the dorsal hock or dorsal metatarsal regions can also cause the abnormality by damaging nerves or causing adhesions to tendons.

Some cases of stringhalt may resolve without treatment, often requiring months. Affected horses should be removed from pasture and the pasture should be inspected for toxic plants known to cause stringhalt. Sedative medications may reduce anxiety and improve the condition. A surgical procedure, which involves removing a section of one of the tendons crossing the outer portion of the hock, will bring about improvement in some cases. The prognosis for recovery from stringhalt is guarded to fair; some horses never recover from the condition regardless of treatment.

By Atwood Asbury, DVM, Professor Emeritus, University of Florida; and A.J. Kaneps, DVM; Beverly, Mass.

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