Stringhalt

Stringhalt is a gait abnormality of horses that is characterized by exaggerated upward flexion of the hindlimb occurring with every stride at the walk. The gait abnormality usually lessens at the trot and is not evident at the canter. It can occur unilaterally or bilaterally.

Any degree of hyperflexion—from mild, spasmodic lifting and grounding of the foot to extreme cases in which the foot is drawn sharply up until it touches the belly and is then struck violently on the ground—is possible with stringhalt. Severe cases include atrophy of the lateral thigh muscles.

The etiology of stringhalt is unknown; however, lesions of peripheral neuropathy have been identified in the sciatic, peroneal, and tibial nerves in affected horses. Severe forms of stringhalt have been attributed to lathyrism (sweet pea poisoning) in the US and possibly to flatweed intoxication in Australia.

Australian stringhalt and lathyrism in horses can be progressive, and the gait abnormality can become so severe that euthanasia is warranted. Mild stringhalt can be intermittent. Stringhalt signs are most obvious when the horse is sharply turned or backed. In some cases, the condition is apparent only in the first few steps when the horse moves. The signs are often less intense or even absent during warmer weather.

Although regarded as unsoundness, stringhalt might not materially hinder the horse’s ability to work, except in cases so severe that the constant concussion gives rise to secondary complications. However, the condition might make the horse unsuitable for some equestrian disciplines (eg, dressage).

Diagnosis of stringhalt is based on clinical signs and can be confirmed by electromyography. If the diagnosis is in doubt, the horse should be observed as it is backed out of a stall after hard work for 1–2 days.

When intoxication is suspected as the cause of stringhalt, moving the horse to another paddock might be all that is required. Many horses with intoxication-induced stringhalt apparently recover spontaneously. In chronic cases, myotenectomy of the lateral digital extensor musculotendinous junction has given the best results. Improvement might not be evident until 2–3 weeks after surgery, and not all affected horses respond.

Stringhalt-like signs ('false stringhalt') can occasionally occur as a result of temporary irritation to the lower pastern area or even a painful lesion in the foot.