A surgical approach to acute flaccid myelitis | Overview
In May 2017, a 5-year-old female fell off her bicycle with no immediate signs of injury. A day later, she began complaining of shoulder pain on her left side, where she’d fallen. X-rays taken at an ER near her home in North Carolina were normal. Clinicians diagnosed the patient with a possible sprain and sent her home in a sling.
Over the next few months, the patient’s pain persisted despite multiple follow-up appointments with a local orthopedist. With no prognosis, her arm grew weaker and she lost mobility in her left hand. The orthopedist splinted her fingers, attributing this second injury to the fall. A week later, the patient had no movement in her left arm. She went to physical therapy, and after months on a waiting list, saw a pediatric neurologist. The MRI came back normal, but at a follow-up appointment, when the patient’s mother asked if her daughter would ever be able to move her arm again, the neurologist told her it was unlikely.
A second opinion
Five months after the initial fall, the patient’s parents contacted Boston Children’s Hospital for a second opinion. The patient was seen by orthopedic surgeons Andrea Bauer, MD, and Peter Waters, MD, of the hospital’s Brachial Plexus Program and Hand and Orthopedic Upper Extremity Program.
Bauer and Waters immediately ruled out the bike fall as the cause of the patient’s atrophy. They suspected a virus was at the root of the patient’s pain and paralysis. The patient was given an EMG and MRI of the cervical spine and brachial plexus. Edema exclusive to the brachial plexus indicated acute flaccid myelitis of the brachial plexus, which often manifests in the unilateral upper limb.
This rare but increasingly common polio-like illness, often preceded by a viral infection, affects the nervous system in the area of the spinal cord, causing muscles and reflexes to weaken and become paralyzed. In November 2018, one month after the patient’s initial visit at Boston Children’s, the CDC reported a rise of acute flaccid myelitis among children, the third spike since 2014, and the formation of a new task force by the CDC to study the condition and its cause.
Since acute flaccid myelitis is a patchy paralysis, Bauer hoped it would be possible to improve the patient’s condition through a nerve transfer — moving a working nerve within the brachial plexus to replace another nerve that no longer functions. Nerve transfers were initially developed as a treatment for traumatic brachial plexus injuries and are now increasingly common in treating peripheral nerve injuries throughout the body. Using similar principles as tendon transfers, this method of restoring nerve function by relocating nerves with a less important role to cover for severely damaged, more crucial nerves can now be successful on nearly any nerves that can reach each other.
The main questions surrounding nerve transfer are accurately selecting which nerves to use and timing the procedure for optimal results. Because experts believe there is some amount of natural recovery of the nerves, Bauer had the patient undergo a repeat EMG. The results confirmed that the patient’s axillary nerve was not recovering, troubling because there are very limited options for restoring deltoid function in long-standing axillary nerve palsy. So after waiting for a plateau but not long enough to risk deterioration of the motor endplates , she and Waters planned for a radial to axillary nerve.
Once they targeted the anterior branch of the axillary nerve to maximize restoration of shoulder abduction, the patient was anesthetized and placed in a semi-lateral position with her affected arm over her body. Although Bauer and Waters often use the anterior approach for this transfer, for this case, the traditional posterior approach was used as only a single nerve transfer was required. The interval between the posterior border of the deltoid and the anterior border of the triceps was developed. The axillary nerve was identified in the quadrilateral space, and the radial nerve branches to the triceps were identified just distal to the teres major tendon. A nerve stimulator was used to confirm the identity of the anterior branch of the axillary nerve as well as the branch of the radial nerve to the long head of the triceps. The remainder of the radial nerve was stimulated as well to ensure that there would be adequate innervation of the triceps after the transfer.
Once the proper nerves were selected, the anterior branch of the axillary nerve and the motor nerve to the long head of the triceps branch of the radial nerves were sharply transected. Bauer and Waters ensured the nerves were long enough, without underlying tension, and the nerve ends were directly repaired using fibrin glue — sutures would be used only if there was concern for tension or orientation of the transfer. Post-operative protocol entailed immobilization with a slight abduction using a padded sling that would protect the neurorrhaphy site from excessive tension for three weeks.
Posterior approach of the partial radial to axillary nerve transfer. The incision is made at the border between the deltoid and the triceps. The arrows illustrate the donor nerve (triceps branch of the radial nerve, up arrow) and recipient nerve (anterior branch of the axillary nerve, down arrow).
The importance of timing
One of the keys to success of this particular case was that patient saw clinicians who recognized acute flaccid myelitis within the necessary time frame, before irreversible changes to the motor endplate had occurred, enabling the nerve transfer to be successful. From a provider standpoint, it was important to look beyond the bike fall.
As for the patient, six months after surgery she has full use of her left arm. Her hand has continued to recover well on its own, and the transferred nerve has successfully reinnervated the deltoid muscle, allowing her excellent strength in lifting her arm overhead. She can lift her arm above her head and is riding her bike again. Meanwhile, Dr. Bauer, Dr. Waters, and their colleagues in the Hand and Orthodedic Upper and Extremity Program and Department of Neurology at Boston Children’s continue to raise awareness of acute flaccid myelitis, which many providers still don’t know exists.