Stringhalt

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Stringhalt is a sudden flexion of one or both hind legs in the horse, most easily seen while the horse is walking or trotting. It is most evident when the horse is backing up slowly, turning on the affected leg, or suddenly frightened. It can involve one or both hind legs of the horse. It is a spasmodic contraction of the lateral extensor tendons of the hind legs.

Contents

An example of bilateral stringhalt in a horse: the hocks are spasmodically and rapidly flexed with the feet held high before quick placement back on the ground. The condition is more evident during turning and backing.

There are four forms of stringhalt: [1] [2]

Treatment varies.

Australian stringhalt

Australian stringhalt was described and differentiated from classical stringhalt in 1884. [3] Australian stringhalt is differentiated from classical stringhalt by the severity, occurrence of outbreaks, distinct seasonal pattern and the ability of affected horses to recover spontaneously. [4] This condition is characterised by the sudden exaggerated flexion of either one or both hocks. This form of stringhalt most commonly occurs in the summer and autumn while horses are out on pasture. Epidemics of Australian stringhalt are usually witnessed during drought or abnormally dry conditions.

Affected areas in the horse

The long digital extensor muscle (usually in the hind limb) is the muscle that appears to be the most affected by this condition. [3] The most severe muscle lesions have been found within the long and lateral digital extensors and lateral deep digital flexor. The location of neuromuscular lesions in Australian stringhalt may be explained by the susceptibility of longer, larger myelinated nerve fibres to injury. [4] Regenerating nerve fibres with disproportionately thin myelin sheaths are more common in the proximal parts of affected nerves in horses with Australian stringhalt. Distal axonopathy occurs most severely in the longest nerve in the horse. [5] The cause for this distal axonopathy remains unknown. [4]

Treatment

Horses affected with this condition rarely recover without surgical intervention, although there have been some instances where horses have recovered without treatment. The recovery time in affected horses can range from three months to three years. [3] Horses may be affected so severely that euthanasia is necessary. It is unknown how long it takes for clinical signs to develop after the exposure to the cause of the condition. [3]

The majority of horses affected by stringhalt are dependent upon pasture for nutrition. [3] Removal of the horse from its original paddock containing low-quality pasture, weeds and native grasses, along with dietary control, was the most common and successful treatment. Lateral digital extensor tenectomy has also been used as a treatment by veterinarians with a success rate of just over 50%. [3]

Phenytoin has been used in the management of Australian stringhalt. [6] Two weeks after treatment with phenytoin, significant improvement was observed in the gait abnormality of horses affected with Australian stringhalt at the trot and canter, but no significant improvement was observed at the walk or while turning. [6]

Causes

H. radicata is linked to some cases of stringhalt in horses. Hypochaeris radicata plant1 (14632148832).jpg
H. radicata is linked to some cases of stringhalt in horses.

The most common plant species that have been found and identified in pastures where affected horses were located include: flatweed ( Hypochaeris radicata ), sheep's sorrel ( Rumex acetosella ) and couch grass ( Elymus repens ). The type of nerve damage sustained in horses with Australian stringhalt suggests a mould toxin (mycotoxin) or a fungal 'poison' found in the soils may be a cause for this condition. Mycotoxins can directly affect the long myelinated nerves in the hind limbs. [3]

See also

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Human leg Lower extremity or limb of the human body (foot, lower leg, thigh and hip)

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Ankle Region where the foot and the leg meet

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Wrist drop

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Upper limb

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Foot drop Gait abnormality

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Curb is defined in older literature as enlargement secondary to inflammation and thickening of the long plantar ligament in horses. However, with the widespread use of diagnostic ultrasonography in equine medicine, curb has been redefined as a collection of soft tissue injuries of the distal plantar hock region. Curb is a useful descriptive term when describing swelling in this area.

Ulnar claw

An ulnar claw, also known as claw hand, or 'spinster's claw' is a deformity or an abnormal attitude of the hand that develops due to ulnar nerve damage causing paralysis of the lumbricals. A claw hand presents with a hyperextension at the metacarpophalangeal joints and flexion at the proximal and distal interphalangeal joints of the 4th and 5th fingers. The patients with this condition can make a full fist but when they extend their fingers, the hand posture is referred to as claw hand. The ring- and little finger can usually not fully extend at the proximal interphalangeal joint (PIP).

Limbs of the horse

The limbs of the horse are structures made of dozens of bones, joints, muscles, tendons, and ligaments that support the weight of the equine body. They include two apparatuses: the suspensory apparatus, which carries much of the weight, prevents overextension of the joint and absorbs shock, and the stay apparatus, which locks major joints in the limbs, allowing horses to remain standing while relaxed or asleep. The limbs play a major part in the movement of the horse, with the legs performing the functions of absorbing impact, bearing weight, and providing thrust. In general, the majority of the weight is borne by the front legs, while the rear legs provide propulsion. The hooves are also important structures, providing support, traction and shock absorption, and containing structures that provide blood flow through the lower leg. As the horse developed as a cursorial animal, with a primary defense mechanism of running over hard ground, its legs evolved to the long, sturdy, light-weight, one-toed form seen today.

Stay apparatus

The stay apparatus is a group of ligaments, tendons and muscles which "lock" major joints in the limbs of the horse. It is best known as the mechanism by which horses can enter a light sleep while still standing up. It does, however, exist in other large land mammals, where it plays a role in reducing fatigue while standing. The stay apparatus allows animals to relax their muscles and doze without collapsing.

References

  1. James Rooney. "Stringhalt". The Lame Horse. Horseshoes.com. Retrieved 1 July 2007.
  2. Doug Butler. Stringhalt.[ full citation needed ]
  3. 1 2 3 4 5 6 7 Huntington, PJ; Jeffcott, LB; Friend, SC; Luff, AR; Finkelstein, DI; Flynn, RJ (July 1989). "Australian Stringhalt--epidemiological, clinical and neurological investigations". Equine Veterinary Journal . 21 (4): 266–73. doi:10.1111/j.2042-3306.1989.tb02165.x. PMID   2767028.
  4. 1 2 3 Slocombe, RF; Huntington, PJ; Friend, SC; Jeffcott, LB; Luff, AR; Finkelstein, DK (May 1992). "Pathological aspects of Australian Stringhalt". Equine Veterinary Journal . 24 (3): 174–83. doi:10.1111/j.2042-3306.1992.tb02810.x. PMID   1606929.
  5. Cahill, JI; Goulden, BE; Jolly, RD (September 1986). "Stringhalt in horses: a distal axonopathy". Neuropathology and Applied Neurobiology. 12 (5): 459–75. doi:10.1111/j.1365-2990.1986.tb00054.x. PMID   3024050. S2CID   26816155.
  6. 1 2 Huntington, PJ; Seneque, S; Slocombe, RF; Jeffcott, LB; McLean, A; Luff, AR (July 1991). "Use of phenytoin to treat horses with Australian stringhalt". Australian Veterinary Journal . 68 (7): 221–4. doi:10.1111/j.1751-0813.1991.tb03210.x. PMID   1929987.