Plexus lumbosacralis
The lumbosacral plexus is formed by the ventral branches of the lumbar (roughly L4–L6) and sacral (S1–S3) spinal nerves. The lumbar plexus gives rise to the femoral and obturator nerves. The sacral plexus forms the sciatic nerve, the largest peripheral nerve in the horse, which divides into the tibial and common peroneal (fibular) nerves at or above the stifle. The pudendal nerve (roughly S2–S4) innervates the perineum, external genitalia, and urethral sphincter.
Post-anesthetic neuropathy from prolonged recumbency on a hard surface is a recognized risk in equine anesthesia and can affect nerves from this plexus. Sciatic nerve injury produces characteristic gait deficits. Diagnosis is clinical and sometimes supported by electrodiagnostics.
## Overview Femoral nerve paralysis causes loss of quadriceps function. The horse cannot bear weight because the stifle collapses, and marked muscle atrophy develops quickly. It is a lower-motor-neur
## Overview Peroneal (fibular) nerve paralysis affects the nerve that runs over the outside of the stifle. Injury, often from prolonged lateral recumbency on a hard surface, causes knuckling of the f
Stringhalt is a condition characterized by involuntary, exaggerated flexion of one or both hind limbs during movement. The limb is jerked upward toward the belly in a spasmodic manner, most noticeably
## Overview Cauda equina syndrome is a constellation of neurologic signs caused by disease of the nerve roots that form the cauda equina at the end of the spinal cord. Affected horses show varying co
After anesthesia, any abnormal hind-limb function or weakness should be reported promptly. Trauma to the pelvis or hind limb can affect these nerves.
## Overview Femoral nerve paralysis causes loss of quadriceps function. The horse cannot bear weight because the stifle collapses, and marked muscle atrophy develops quickly. It is a lower-motor-neuron injury. ## Causes Trauma or iatrogenic (anesthesia-related) nerve damage. ## Diagnosis Clinical signs and electromyography. ## Treatment Conservative management and nursing care. ## Recovery and Prognosis Variable and often incomplete. ## Prevention Careful handling and anesthetic positioning. Signs include: inability to bear weight; stifle collapses; rapid quadriceps atrophy; reduced patellar reflex
## Overview Peroneal (fibular) nerve paralysis affects the nerve that runs over the outside of the stifle. Injury, often from prolonged lateral recumbency on a hard surface, causes knuckling of the fetlock, dragging of the toe, and inability to flex the hock and extend the digit. A characteristic goose-stepping gait may be seen during recovery. ## Causes Compression during anesthesia or recumbency, or direct trauma. ## Diagnosis Characteristic gait and neurologic examination. The horse cannot extend the digit or flex the hock properly. ## Treatment Supportive care, protection of the dorsum of the fetlock, and time. Most compressive injuries improve over days to weeks. Physical therapy helps. ## Recovery and Prognosis Good for compressive injuries if secondary trauma to the limb is prevented. Complete severance has a poorer outlook. ## Prevention Adequate padding during anesthesia and recumbency. Signs include: knuckling of the fetlock; dorsal hoof dragging; inability to flex the hock and extend the digit; goose-stepping gait during recovery
Stringhalt is a condition characterized by involuntary, exaggerated flexion of one or both hind limbs during movement. The limb is jerked upward toward the belly in a spasmodic manner, most noticeably at the walk. It can be idiopathic, acquired (often linked to toxic plants), or occur after trauma or surgery. ## What it is Stringhalt involves abnormal function of the nerves and muscles that control hind limb flexion, most classically the lateral digital extensor muscle and its tendon. In acquired stringhalt, damage or irritation to this muscle-tendon unit leads to the characteristic hyperflexion. The Australian form is associated with ingestion of the weed *Hypochaeris radicata* (catsear), while other cases may follow trauma, surgery, or occur idiopathically with no clear cause. The condition is usually more obvious at the walk than at faster gaits and often improves when the horse is turned or backed. It can be unilateral or bilateral and ranges from mild to severely debilitating. ## Signs and symptoms - Exaggerated, spasmodic upward flexion of the hind limb during walking (snapping toward the belly) - Worse at walk than trot; often improves at canter - More noticeable when turning, backing, or in cold weather - Can be unilateral or bilateral - In severe cases, the horse may hit the abdomen or chest with the hoof - Australian stringhalt often follows ingestion of toxic weeds and may affect multiple horses in a group ## Causes and risk factors Stringhalt has several forms. The acquired form is often linked to ingestion of toxic plants (especially *Hypochaeris radicata* in Australia and New Zealand). Other cases follow trauma to the hind limb, surgery in the area, or occur idiopathically. There is no strong breed or age predisposition, though it can appear at any age. ## How it is diagnosed Diagnosis is primarily based on the characteristic gait abnormality observed during movement. A thorough neurologic examination helps rule out other causes of abnormal hind limb movement. In some cases, electromyography or ultrasound of the lateral digital extensor muscle and tendon is used. Ruling out other neurologic diseases is important. ## Treatment and management Treatment depends on the type and severity. In mild cases, many horses can continue light work. For more severe or acquired cases linked to toxic plants, removal from the offending pasture is essential. Surgical removal of a section of the lateral digital extensor tendon (myotenectomy) can provide significant improvement in many horses. Medical management with phenytoin or other medications has been tried with variable success. ## When to call the vet Contact your veterinarian if you notice sudden or progressive exaggerated hind limb flexion. While stringhalt itself is not an emergency, it is important to differentiate it from other neurologic conditions that may require urgent attention. ## Prevention For acquired stringhalt, prevention involves avoiding pastures containing known toxic plants such as *Hypochaeris radicata*. Regular pasture management and monitoring horses for early signs after moving to new properties can help reduce risk. ## Frequently asked questions **Is stringhalt painful?** Most horses with stringhalt do not appear to be in pain, though the gait abnormality can affect performance and, in severe cases, cause the horse to hit itself. **Does stringhalt get worse over time?** Idiopathic cases may remain stable or slowly progress. Acquired cases linked to toxic plants can improve once the horse is removed from the source, though some horses retain a degree of abnormality. **Can stringhalt be cured?** Surgical treatment (lateral digital extensor myotenectomy) provides good improvement in many horses, though complete resolution is not guaranteed in all cases. This information is for educational purposes only. Always consult with a licensed veterinarian for diagnosis and treatment of your horse. Signs include: Exaggerated, spasmodic upward flexion of the hind limb during walking (snapping toward the belly); worse at walk than trot, often improves at canter; more noticeable when turning, backing, or in cold weather; can be unilateral or bilateral; in severe cases, the horse may hit the abdomen or chest with the hoof; Australian stringhalt often follows ingestion of toxic weeds and may affect multiple horses in a group
## Overview Cauda equina syndrome is a constellation of neurologic signs caused by disease of the nerve roots that form the cauda equina at the end of the spinal cord. Affected horses show varying combinations of hind-limb weakness, urinary incontinence, fecal retention, and loss of tail tone. Causes include trauma, equine protozoal myeloencephalitis, polyneuritis equi, and space-occupying lesions. ## Causes Trauma to the sacrum, infectious or inflammatory neuritis, protozoal myelitis, and neoplasia can all damage the cauda equina. The specific cause determines treatment and prognosis. ## Diagnosis Neurologic examination demonstrates lower-motor-neuron signs to the tail, anus, bladder, and hind limbs. Rectal examination, cerebrospinal fluid analysis, and advanced imaging help identify the lesion. Testing for Sarcocystis neurona or other infectious agents is often performed. ## Treatment Therapy is directed at the underlying cause when known (antiprotozoal drugs, anti-inflammatories, or surgical decompression). Supportive care includes bladder management, fecal softeners, and prevention of urine scald. ## Recovery and Prognosis Prognosis is guarded and depends on the cause and severity. Some horses with inflammatory disease improve; severe trauma or advanced denervation often leaves permanent deficits. ## Prevention No specific prevention exists beyond minimizing sacral trauma and controlling known infectious risks where possible. Signs include: hindlimb weakness or ataxia; urinary incontinence; fecal retention; reduced tail tone; muscle atrophy of the hindquarters in chronic cases
Post-anesthetic neuropathy from prolonged recumbency on a hard surface is a recognized risk in equine anesthesia and can affect nerves from this plexus. Sciatic nerve injury produces characteristic gait deficits. Diagnosis is clinical and sometimes supported by electrodiagnostics.
After anesthesia, any abnormal hind-limb function or weakness should be reported promptly. Trauma to the pelvis or hind limb can affect these nerves.
See the Lumbosacral Plexus on our interactive 3D horse model. Open 3D Model