stringhalt in horses

The underlying causes of stringhalt remain poorly understood. A whole horse perspective can offer insight into better understanding and addressing this mysterious condition.

“Stringhalt” is a motor disease of the rear limbs in horses. Affected horses rapidly jerk one or both hind limbs in full flexion up toward the abdomen. For the horse owner who has never seen this condition before, it can be quite startling. Soundness is a concern because the spastic movements make riding difficult; in fact, stringhalt can end a performance horse’s career if it cannot be corrected.

Types of stringhalt

There are two forms of stringhalt – the Australian form and the Classic form. The Australian form is a bit of a misnomer; while the toxic plant that causes it (Hypochaeris radiata, a form of flat weed also known as false dandelion) is commonly found in Australia, it can also be found in other parts of the world, including the United States. (False dandelion has also been reported in New Zealand and South America.)  Positive identification of the toxic plants, along with removing the horse from exposure to said plants, usually leads to a disappearance of clinical signs, given time.

The second, more common Classical form of stringhalt has no known underlying cause. The condition is believed to be due to a degeneration of nerves to the lateral digital extensor (LDE) tendon.  However, the question remains whether the nerve degeneration starts locally at the lumbar spinal cord, or further forward in either the head or the neck.

Muscle malfunctions

Presumed deterioration of the nerves to the LDE results in spastic movements of the rear limb(s), resulting in stringhalt. Unfortunately, while it’s known that the LDE muscles are involved in stringhalt, the exact mechanism of spasticity is not known, and the current best “treatment” is to surgically transect (cut) these muscles. Future “treatment” possibilities include injection of “Botox” (botulinum toxin) into the affected neuromuscular unit, offering the same kind of result as transecting the muscle.

Before one considers transecting the LDE of the affected limb(s), it helps to understand the function of the muscle. Despite its name, the LDE is actually involved in the flexion of the hock joint. The LDE works in conjunction with a number of other muscles that together make up the reciprocal apparatus in the hind limb – when the hock flexes, the stifle automatically flexes too. In a horse with stringhalt, the entire leg is forced ballistically toward the abdomen due to this interrelationship between the rear leg muscles.

A secondary function of the LDE is to help laterally stabilize the hock joint. Transection of the LDE can result in lateral instability in the horse’s hind limb. This resultant instability can lead to breakdown of the hock joint, especially if both limbs are affected and both are surgically treated.

The sciatic nerve

Though uncommon, some cases of stringhalt have been caused by medical intervention. Rarely, local or epidural anesthesia can result in interference with nerve signals to the LDE, such that the horse develops a case of stringhalt. Regardless of whether it is an idiosyncratic reaction to anesthetic, or direct contact of anesthetic with a nerve root, the result is the same – spastic movement of the affected rear limb. This unfortunate side effect of epidural anesthesia can give some insight into a potential mechanism behind stringhalt, and therefore, how it may be treated.

In an epidural, the sciatic nerve, along with many others, is blocked. The sciatic nerve is made of components from the last three lumbar and first three sacral nerve segments. Each of these nerve branches leaves the spinal canal at their respective vertebral segments – lower lumbar and sacral vertebral  – then they join together to form the sciatic nerve. Therefore, dysfunction at any of these spinal cord levels can impact the sciatic nerve, which in turn branches into other nerves that connect to the LDE. For this reason, a well-performed chiropractic adjustment with concentrated focus placed on the sacrum and lower lumbar segments may benefit stringhalt horses tremendously. (Acupuncture and massage can also help.)

Neck issues and stringhalt

Another insight into stringhalt includes research indicating  that horses with cervical arthrosis (essentially arthritis in the neck) are more likely to have stringhalt. Normal nervous system function includes inhibiting information sent to the limbs from higher up the spinal cord. This inhibition dampens the spastic movement associated with stringhalt. Recall the  examination in which a doctor taps on the human subject’s knee (the patellar tendon) with a reflex hammer – the normal response is a small “kick” from  the lower leg. This response is dampened in a well-functioning nervous system. In subjects with deficient descending inhibition, the patellar reflex will be quite pronounced, almost ballistic. Thus, we have another possible way to explain stringhalt – interference with descending, inhibitory information from the cervical spine region.

Nutritional considerations

The positive response some horses have to adjunctive nutritional treatment suggests another potential cause of the condition: Many horses with stringhalt show some degree of improvement when supplemented with B vitamins and vitamin E, which can help stabilize nerve membranes. A healthy cecum and diet of fresh grass should normally result in plentiful B vitamin production for the normal healthy horse. Vitamin E is plentiful in seeds, and flax seed-based supplements may be quite beneficial. The implication for the stringhalt horse that improves when fed vitamin supplements and fresh pasture is that diet can be related to nerve function; vitamins and minerals (balanced appropriately) are crucial to a properly functioning nervous system.

A holistic approach

The horse with stringhalt will benefit from a natural diet and bodywork. Taken as a whole, input to the nervous system affects the entire body, including the brain. By providing the best nutrition (fresh grass, wholesome B vitamins and vitamin E), and balancing the body with chiropractic, acupuncture and massage, the brain will work at its best and thus help the body work at its best. As discussed above, a natural, fresh grass diet contains nerve-supportive biologicals – these will be anti-inflammatory and protect the nerves.

Chiropractic, acupuncture and massage can help the horse with stringhalt in a number of ways:

  1. Restoring/maintaining balance and motion at the hock joint will help the LDE function more appropriately and assist with balance in those horses with transected LDEs.
  2. Innervation to the LDE comes from the tibial nerve branch of the sciatic nerve. The sciatic nerve travels through the lumbar and sacral vertebrae from the spinal cord. Therefore, chiropractic adjustment of the lower lumbar vertebrae and sacrum may be most beneficial. (Anecdotally, some practitioners have seen the best improvement by focusing on the affected horse’s sacrum.)
  3. The third way occurs at the neck level. As discussed in this article, there may be a correlation between cervical arthrosis and stringhalt. Restoring motion at the neck may be crucial for helping the stringhalt horse by supporting optimal nerve function that allows for dampening signals to reach the hock/LDE and reduce spastic movements. Chiropractic, acupuncture and massage are all excellent modalities to restore motion in the cervical spine (once it is determined there are no other concurrent cervical conditions).

While stringhalt does not have one clear cause or explanation, nor one clear-cut treatment, there is hope for the affected horse through excellent food/nutrition and body balancing care – be it chiropractic, acupuncture, massage or another movement restoring modality.

Dr. Cathy Alinovi is a retired holistic veterinarian, animal lover, frequent media guest and nationally celebrated author. She is quickly gaining national recognition for her integrative approach to animal health. After graduating from veterinary school, she realized conventional medicine did not meet enough of her patients’ needs, and became certified in Animal Chiropractic, Veterinary Acupuncture and other alternative modalities. While in practice, Dr. Cathy treated 80% of what walked in the door — not with expensive prescriptions, but with adequate nutrition. Now retired from private practice, she spends her time writing and helping pet owners feed their animals the best food for best health.