This life-threatening injury can necessitate amputation

Analysis by Dr. Karen Shaw Becker

Story at-a-glance -

  • Brachial plexus avulsion describes a serious, traumatic injury to the nerves that feed an animal’s forelimbs. A better term for this condition is brachial plexus injury, since there’s not an avulsion, or “tearing away” of nerves in every instance
  • The most common cause of this type of injury in dogs and cats is being hit by a car. The primary symptom is forelimb weakness that can range from a problem with just one muscle group, to complete paralysis
  • There are three classes of brachial plexus injuries, ranging from damage that is temporary and fully treatable, to an injury so severe it causes paralysis and loss of sensation in one or both front legs
  • Treatment of a brachial plexus injury is typically focused on physical therapy and supportive care. In very severe cases, amputation may be necessary to save the animal’s life

Brachial plexus avulsion is a medical term to describe damage to the nerves that feed a dog's or cat's front legs. Brachial means relating to the arm, or in the case of a four-legged critter, the front leg. A plexus is a network of nerves, and avulsion is defined as the forcible tearing away of a body part by trauma or surgery.

As you might guess, this type of injury is usually serious because it means significant damage has occurred to the nerves running to the front leg or legs. A more appropriate term for this condition is probably brachial plexus injury, since there's not always a "tearing away" or true avulsion in every case.

Three levels of severity

The severity of this type of peripheral nerve injury falls into one of three categories:

  1. The least serious of the three is a Class I neurapraxia, in which the nerve dysfunction is transient and there is little to no structural damage to the nerve. Sensation in the animal's forelimbs is often preserved with neurapraxia, which is good.
  2. A Class II injury is axonotmesis, in which there is structural damage to the nerves that typically affects both movement and sensation in the front limbs. Nerve regeneration is possible with this type of injury because the nerve sheath remains intact.
  3. The most severe category of injury is a Class III neurotmesis, in which both nerve fibers and supportive connective tissue have been severed or torn away. In this situation nerve regrowth isn't possible, and there is complete paralysis and loss of sensation.

Causes and symptoms of a brachial plexus injury

Brachial plexus injuries are almost always the result of a traumatic accident. The most common cause in dogs and cats is being hit by a car. Other causes include a serious fall, or when a pet gets a foot caught in something while trying to jump. Symptoms depend on the severity of the injury. Typically the animal will have forelimb weakness that can range from a problem with just one muscle group, to complete paralysis. There may also be loss of sensation, in which case the dog or cat feels no pain in the affected leg.

Diagnosis

Diagnosing a brachial plexus injury is usually easy based on the patient's symptoms and the known or suspected traumatic event that caused the damage. Your veterinarian or a veterinary neurologist might also perform nerve conduction testing to determine which nerves and muscles are involved, but this test can't be performed for about five to seven days after the injury because it takes that long for abnormalities to be detectable.

A magnetic resonance imaging (MRI) test may also be done to look for internal lesions, injuries to the spinal cord and associated neurological issues, or to rule out other disorders with similar symptoms — especially when there's no clear indication that your pet has suffered a traumatic injury.

Treatment options

Treatment for a brachial plexus injury is focused on physical therapy with a certified animal rehabilitator, which may include electrostimulation of the affected limb, and general supportive care. If the dog or cat has maintained sensation in the affected limb and is in pain or is experiencing some discomfort, appropriate pain management should also be instituted. Anti-inflammatories are also often prescribed, and electroacupuncture can be beneficial for patients with this type of injury as well.

Sometimes carpal fusion or the use of brace can help prevent knuckling when the animal tries to put weight on the affected leg. Since carpal fusion is permanent, I would recommend starting with a brace first if your pet is knuckling on one or both front legs.

Unfortunately, in worst-case scenarios of brachial plexus avulsion, amputation may be necessary, and is almost always performed in cases where the injury is life-threatening. Short of that, it should only be considered if there is no improvement after several months of intensive physical therapy, if the animal is self-mutilating or there is trauma to the limb from dragging.

The good news is that most pets adjust quite well to life on three legs, so if, God forbid, your pet must have an amputation, know that it's not life-ending in most situations. In animals that maintain sensation in the affected limb, the prognosis is better than for pets with lack of deep pain perception. Since nerves regrow at a rate of only 1 to 4 millimeters a day, it's important to remember that it can take weeks to months for full recovery from a brachial plexus injury.

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