Brachial Plexus Avulsion: A Kitten Sustains Nerve Damage To Her Front Leg
By Rachele Baker, DVM – “Dr. Baker to the treatment room – STAT!” The veterinary nurse’s voice sounded a little panicked over the intercom. “Those are never good words to hear,” I thought to myself as I jumped out of the chair in my office and rushed to the treatment room.
When I got to the treatment room, the veterinary nurse was holding a five-month-old gray tabby kitten named Mia on the exam table. The kitten’s left front leg was grossly swollen. Mia was being boarded at the veterinary hospital where I was working as a relief veterinarian. The kennel attendant had just found Mia with her left front leg stuck underneath her cage door.
There was an area of flattened fur with exposed skin right above Mia’s elbow which I assumed was where the cage door had pressed on her skin. Mia’s entire left front leg and paw was firmly swollen. When I placed Mia on the exam table, her paw knuckled over when she attempted to stand but she was able to move her leg. I pinched Mia’s toes to determine if she retained the ability to perceive pain sensation in that leg. She meowed to let me know that she felt the pinch. However she did not withdraw her leg in response to the pinch (no withdrawal reflex). I noted that Mia’s left pupil was slightly smaller than her right pupil. Mia’s heartrate was extremely rapid, so I knew that she was painful.
I gave Mia a pain injection as well as a long-lasting steroid injection to help to bring down the swelling in her leg. I instructed the veterinary nurses to take x-rays of Mia’s leg so that I could determine if there was any fracture involved. There was no evidence of a fracture on the x-rays.
I called Mia’s parents to let them know what had happened. I assured Mia’s parents that the x-rays showed no fracture. I let them know that I had given Mia a pain injection and a steroid injection to bring down the swelling. I told Mia’s parents that I was concerned that Mia had sustained nerve damage while trying to free her front leg from under the cage door. I explained that the injury I was concerned about was called “brachial plexus avulsion.”
When Mia’s parents came to pick her up and take her home, we discussed brachial plexus avulsion in more detail, and I gave them an article about brachial plexus avulsion to read at home. They said that they knew that Mia was “crazy,” and they were not surprised that she had pushed her leg under the cage door. They were very concerned about Mia’s prognosis for recovery. I explained that it could be months before we would know if Mia was going to regain normal function in her leg.
I sent Mia’s parents home with pain medication for Mia and advised them that it might be necessary to protect Mia’s paw with an infant’s sock if she dragged her paw on the ground when walking. I instructed Mia’s parents in how to perform physical therapy on Mia’s leg. And I recommended that they take Mia to see a local veterinary neurologist for a consultation and further evaluation.
Brachial Plexus Avulsion:
The brachial plexus is a large network of nerves that innervate the front legs. The brachial plexus is formed by nerve roots of the sixth cervical through second thoracic spinal nerves (C6-T2). Extreme abduction of a front leg or trauma to the shoulder region can result in nerve damage or in complete avulsion (tearing away) of the nerve roots that form the brachial plexus. Although the term “brachial plexus avulsion” is commonly used to describe damage to the brachial plexus, there may be injury or damage to the nerves without an actual avulsion.
Clinical signs associated with brachial plexus avulsion depend on which nerve roots are affected. Caudal brachial plexus injury involving damage to the radial nerve causes front leg paresis (weakness) characterized by flexion of the elbow and knuckling of the carpus (wrist). Injury involving the brachial plexus at the level of the first and second thoracic vertebrae (T1, T2) usually results in partial Horner’s Syndrome (constricted pupil) on the side of the injury. Complete Horner’s Syndrome (constricted pupil, drooping of the upper eyelid, sunken eye, and elevated third eyelid) does not usually occur.
There are three classes of brachial plexus avulsion based on the severity of the nerve damage sustained:
A Class I brachial plexus injury is called neuropraxia. Neuropraxia is temporary nerve dysfunction with little to no structural damage to the nerve. With neuropraxia, the clinical signs resolve in a few days to a few weeks.
With a Class II brachial plexus injury, there is structural damage to some or all of the brachial plexus nerves. Nerve regrowth is possible because the nerve sheaths are still intact. Nerves regrow at a rate of 1-4 mm/day, so it may take months for clinical improvement.
A Class III brachial plexus injury is the most severe and occurs when the nerves and supportive connective tissue are completely severed. Nerves cannot regrow because there is no remaining connective tissue to guide their regrowth. Without innervation, the front leg will become completely paralyzed and there will be no pain perception in that leg.
The prognosis for recovery from brachial plexus injury is fair to guarded. Pain perception in the affected leg (nociception) is the most important prognostic indicator. If pain perception is absent, there is a poor prognosis for recovery of function in the affected leg. Recovery can take four months or longer, so pets may be monitored for a number of months before considering amputation of the leg.
Amputation of the affected leg may be indicated if the pet develops non-healing wounds as a result of dragging the paw on the ground when walking or if the pet causes self-mutilation to the leg or paw due to paresthesia (an abnormal sensation such as tingling or itching caused by damage to peripheral nerves).
Treatment of brachial plexus injury involves supportive care and physical therapy. If the pet is dragging his or her paw on the ground, an infant’s sock can be used to protect the paw from injury. The sock may be taped in place if needed. The sock should be changed daily and washed between uses.
Physical therapy should be performed to prevent the muscle contracture that is common with brachial plexus injuries. Physical therapy should be performed at least three times a day and may need to be continued for many months.
How to Perform Passive Range of Motion Physical Therapy After Brachial Plexus Injury:
Passive “Range of Motion” (ROM) physical therapy exercises help to diminish the effects of disuse of a leg after brachial plexus injury. It is generally appropriate to initiate passive ROM physical therapy as soon after the injury as possible.
Physical therapy should be administered in a quiet and comfortable area away from loud noises and other pets. The pet should be placed on his or her side with the affected leg up. When performing passive ROM exercises, the motions should be slow, smooth, and steady.
Passive ROM exercises are begun with the toes. While supporting the pet’s wrist area in one hand and the toes in the other, the toes are gently flexed and extended. Place your fingers or palm on the bottom of the pet’s paw and slowly extend the toes. Then place your fingers or palm on the top of the pet’s paw and slowly flex the toes.
After physical therapy is performed on the toes, ROM exercises are performed on the other joints. Slowly and gently flex and then extend all of the joints in the leg simultaneously.
Passive ROM exercises should be performed three to four times a day with each session consisting of fifteen to twenty repetitions of flexion and extension of the joints or based on the protocol developed by your veterinarian or veterinary physical therapist.