Femoral Nerve Paralysis in Horses

Femoral Nerve Paralysis (Crural Paralysis) in Horses is the paralysis of the femoral nerve affects the quadriceps femoris group of muscles. This muscle group is comprised of the rectus femoris muscle, vastus lateralis muscle, vastus medialis muscle, and vastus intermedius muscle.

Etiology

Femoral nerve paralysis may arise from trauma or unknown causes, and may be associated with rhabdomyolysis. Injury to the nerve may occur from overstretching the limb during exertion, kicking, slipping, or while the horse is tied in a recumbent position. It has also been reported as a complication of general anaesthesia.

Clinical Signs

The horse assumes a crouched position with the fetlocks flexed and the toes on the ground and is unable to bear full weight on the affected limb. There is difficulty advancing the limb, but the affected horse can do so because the hock can be sufficiently flexed to pull the limb forward.

After the condition has been present for some time, atrophy of the quadriceps muscles occurs, causing them to lose their normal softness and become more like tendinous structures. If rhabdomyolysis is present, the horse is more painful and less willing to attempt to stand.

Diagnosis

The signs listed above are characteristic and are used for diagnosis. The condition should be differentiated from lateral (true) luxation of the patella, rupture of the quadriceps femoris muscles, avulsion of the tibial crest, and distal luxation of the patella. Any of these conditions could cause a similar syndrome; however, all are rare. Lateral luxation of the patella can be diagnosed by palpation of the displaced patella; rupture of the quadriceps femoris muscle also can be palpated. A radiographic examination can determine avulsion of the tibial crest where the patellar ligaments insert. Electromyography of the quadriceps femoris muscles 5 days after the first signs of femoral nerve paralysis provide a definitive diagnosis.

Treatment

No treatment is known for Femoral Nerve Paralysis in Horses. If the condition is due to injury of the femoral nerve, the animal should be stalled until improvement occurs. If rhabdomyolysis is present, intensive care and support is indicated, and repeated attempts to use the muscles should be discouraged.

Prognosis

The prognosis is guarded to unfavorable.