The brachial plexus is the equivalent of an electrical junction box supplying the wiring to the front limbs.
There is a separate brachial plexus for each leg, located in each armpit (the axilla). An avulsion means a “pulling apart.” In this scenario, it is equivalent to unplugging an electrical device from the mains.
A case that springs immediately to mind is that of Bruce, a 6-month-old Labrador. He was riding in the passenger seat of an open-top convertible when something caught his attention and he jumped out.
Unfortunately, poor Bruce was dragged a short distance by his left foreleg. Miraculously, his injuries were minor — except for the brachial plexus avulsion to his left front leg.
It is not uncommon for a dog or cat to have numbness in the front leg as a result of doing the splits on laminate flooring. This stretches the plexus and causes inflammation and decreased sensation in the nerves, but this usually returns once the swelling has gone down.
However, a complete avulsion, as in Bruce’s case, means the nerves are torn and the damage is permanent.
A brachial plexus avulsion means loss of nerve supply and, therefore, loss of sensation. Typically, this condition is not painful, and the dog or cat does not mind the leg being manipulated as he feels nothing.
When standing, the affected leg looks longer than the other side because the shoulder is dropped and the wrist flexed. The dog frequently stands with the paw flipped over so the top surface contacts the ground. This can lead to abrasions and scuffs on the back of the paw. Apply a light protective dressing prevent it.
Just over half the cases also show a neurological abnormality to the eye on the side known as Horner’s syndrome. This presents as a smaller pupil and a droopy eyelid when compared to the normal side.
Brachial plexus avulsion is always associated with a trauma that physically stretches the nerve plexus in the armpit. This commonly happens as a result of a traffic collision or slipping on a smooth floor.
A dog or cat with a numb front leg needs to be checked for other injuries, such as broken bones, especially to the upper arm (humerus), which can have a similar appearance. Radiographs quickly show if fractures are present or not.
However, broken bones do not usually interfere with nerve reflexes, and a detailed neurological exam will show if the patient has full feeling in his paw and lower limb. If he does not have full sensation, then electrodiagnostic tests can prove if the nerves are working or not.
Also, an MRI scan creates a 3-D picture of the plexus and shows if the nerves are torn beyond repair.
There is no specific effective treatment or repair other than to wait and see if nerve function returns. This may take as long as 6 months to occur.
As a general rule, if there is no improvement at all a month after the accident, then it is unlikely the limb will fully recover. If this happens, amputation is the best option.
Although this sounds scary, there is a saying that dogs and cats have “3 legs and a spare,” and do fantastically well after an amputation.
While waiting to see if the nerves recover, keep the muscles conditioned with physiotherapy exercises. The back of the paw gets scuffed from being dragged on the ground, and a soft bandage or thick sock helps prevent skin damage.
In Bruce’s case, there was no improvement after 6 months, and the numb leg was getting in his way. His human decided to amputate, and, happily, Bruce never looked back.
He leads a full life, including siring a litter of puppies. As his human remarked, he was so used to seeing Bruce charging around on 3 legs it came as a shock to see he had sired puppies with 4 legs!
Keep animals under control near the road.
- “Brachial plexus injuries and dysfunctions.” Steinberg (1988). Vet Clin North Am, 18: 565–580.
This pet health content was written by a veterinarian, Dr. Pippa Elliott, BVMS, MRCVS. It was last reviewed Jan. 2, 2016.