What is Accessory Nerve Injury?
The cranial nerves are twelve sets of nerves that travel from your brain to different parts of your body such as the head, face and neck. One of these is the 11th cranial nerve, also called the accessory nerve (see Image: The Accessory Nerve). This nerve is composed of several short strands, which unite to form a larger strand. It actually branches off from two other nerves, the vagus nerve and the structure that gives rise to the vagus nerve (the nucleus ambiguus and dorsal nucleus of the vagus nerve), and goes to the muscles in the throat, providing them with the signals they need to move (see Image: Muscles of the Head, Face, and Neck).
As the accessory nerve stretches away from the brain, it joins with another set of nerves coming from the spinal cord to form the spinal accessory nerve. After leaving the brain, this nerve actually exits the skull through a hole near the ear, close to the vagus nerve. It then travels downwards alongside a major vein in the neck, looping behind several facial structures and muscles before finally entering an area known as the posterior cervical triangle (see Image: Superficial Neck Anatomy). From there, the accessory nerve couples with the nerves connecting to the muscles on the side and back of the neck (the sternocleidomastoid and trapezius muscles).
Throughout its complex journey, the accessory nerve plays a crucial role in helping the structures in the back of the neck function. Yet, because of its long path and its position close to the surface of the skin, this nerve can be easily damaged. This damage can happen from blunt force, accidental causes, or, most commonly, as a side effect of medical procedures (iatrogenic reasons).
What Causes Accessory Nerve Injury?
The accessory nerve can get injured in a number of ways, but the most common is during medical procedures like neck surgeries. These can include operations like lymph node biopsies in the back part of your neck, removal of a tumor, procedures on the carotid or jugular veins in your neck, various types of neck dissection, or cosmetic procedures like a facelift. The strain placed on the neck during these procedures can lead to injury.
There are also other ways the accessory nerve can get injured. It can be from severe injuries like knife or gunshot wounds, or even from something as simple as sudden pressure or movements to the neck. Dislocating the acromioclavicular joint – the one that connects the collarbone to the shoulder – can strain the muscles in the neck and lead to accessory nerve injury.
Sometimes, the nerve can be affected by neurological conditions. For instance, if a tumor forms in the opening through which the nerve passes, it can lead to cranial nerve palsies – conditions marked by the weakening or paralysis of the cranial nerves. Some examples of these are the Collet-Sicard syndrome, which affects cranial nerves IX, X, XI, and XII, and Vernet syndrome, which impacts cranial nerves IX, X, and XI.
There are also certain conditions that can lead to injuries of the accessory nerve. They include Syringomyelia, brachial neuritis, poliomyelitis, and motor neuron disease. Other possibilities include traction palsies to the brachial plexus and thoracic outlet. A study suggested that a condition known as idiopathic brachial plexitis, which often affects the brachial plexus, can also impact the accessory nerve, sometimes following surgery.
Enjoying sports is a fun way to stay fit, but certain sports injuries can also lead to damage of the accessory nerve. For instance, getting hit with a hockey stick, a wrestling match injury, or whiplash, which is a neck injury due to forceful, rapid back-and-forth movement of the neck, similar to the cracking of a whip, can cause harm to the accessory nerve. In rare cases, the accessory nerve can also get injured all on its own, without an obvious cause.
Risk Factors and Frequency for Accessory Nerve Injury
Accessory nerve injuries mainly happen due to surgeries in the back and side of the neck. This risk led to research into different types of neck surgery – radical, selective, and modified. A study found that radical neck surgeries had the highest risk of accessory nerve injury at 46.7% compared to selective neck surgeries at 42.5% and 25% in modified neck surgeries.
- Accessory nerve injury is often an unintended consequence of surgeries on the back and side of the neck.
- The risk of this injury led to studying various types of neck surgeries: radical, selective, and modified.
- A study shows that radical neck surgeries had the highest risk of accessory nerve injury at 46.7%, followed by selective neck surgeries (42.5%) and modified neck surgeries (25%).
Preserving other structures like nerves, muscles, and veins during the surgery can result in less dysfunction than if only the nerve is saved. Injuries to the cranial nerve XI are rare, but they are considered in investigating the causes of accessory nerve injuries.
Accessory nerve injuries are often seen after lymph node biopsies in the back of the neck. These procedures can cause injury in 3% to 8% of cases. Up to 60% to 80% of severe upper extremity dysfunction has been associated with radical neck dissections. Accessory nerve injury was seen in 1.68% of cases in a large review of modified radical neck dissections.
Clinically diagnosed accessory nerve injuries have been observed in 30% of selective neck surgeries that include cervical zones 2 through 4 and 5. However, the risk significantly reduces when cervical zone 5 is left untouched during dissection.
Signs and Symptoms of Accessory Nerve Injury
When diagnosing an injury to the Spinal Accessory Nerve (SAN), doctors typically carry out a thorough physical check-up and follow this up with tests that help study the nerves and muscles involved. Often, the main symptoms of SAN injury include pain and weakness, particularly in the shoulder area. The pain can spread to the upper back, neck, and the same side arm. This discomfort aggravates when weight is placed on the affected shoulder that lacks support. Unintentionally, the surrounding muscles, like rhomboids and levator scapulae, may strain themselves to compensate for the nerve injury, leading to increased pain and a drop in strength on the injured side. This combination of pain and reduced strength can limit the movement in the affected shoulder.
The pain may extend to the upper back and neck, and in some rare cases to the arm on the same side. This pain can be due to several factors, including possible straining of the involved muscles leading to stretching of the brachial plexus. The accompanying deformity can interfere with daily activities like putting dishes on overhead shelves and performing physical tasks that put weight on the shoulders.
The intensity of pain around the shoulder joint and neck area can be measured using a visual analog scale (VAS) of 10 points. On average, patients with SAN-related shoulder syndrome tend to score around 7 (with the range from 6 to 9).
The most common physical sign is an obvious unevenness noted in the shoulder and upper back during inspection. A patient would typically exhibit reduced ability to lift the shoulder sideways, drooping of the shoulder, and scapular winging on the same side (condition where the shoulder blade sticks out). Over time, a limited active range of motion can deteriorate into restricting the passive range of motion, giving rise to a condition called adhesive capsulitis. Some of the other possible observations include atrophy (waste away) of the trapezius muscle (depending on injury duration) and internal rotation of the humeral head. Enlargement or displacement of the sternoclavicular joint may also happen due to abnormal strain on the inner part of the clavicle as a result of the missing support from the trapezius muscle.
Movement restrictions noted in muscle movement (ROM) include:
- Active abduction (sideways lift): 30 to 140 degrees
- Active forward flexion: 50 to 180 degrees
Testing for Accessory Nerve Injury
Diagnosing an accessory nerve injury can be tricky due to several reasons. For example, the trapezius muscle, which helps move and stabilize the shoulder, is controlled by two different nerves. If only one of these nerves is damaged, some movement will still be possible, making it hard to diagnose the injury just from a patient’s symptoms.
Some symptoms such as pain, numbness on the opposite side, myofascial pain syndromes (a type of muscle pain disorder), and radiculitis (irritation of the spinal nerves) can vary widely in different patients. This diversity makes it harder still for doctors to diagnose nerve injury. The range of symptoms can result from differences in the extent of nerve injury, damage to surrounding tissues and individual variations in pain tolerance.
Using high-resolution ultrasonography (a type of ultrasound) can help to confirm whether the accessory nerve is the one that’s been injured, and to see the structures around it. The ultrasound can show if muscles have started to waste away (atrophy) but it cannot show if the nerve has been completely cut off.
In some cases, electromyography (EMG) and nerve conduction studies are not always needed for the diagnosis, but can help determine the level of nerve damage. These tests are actually the most sensitive for assessing decreased nerve conduction. Results from these tests can show extended response times in nerve conduction studies and indications of loss or restoration of nerve function on EMG, depending on when the test is performed.
EMG studies have established that the trapezius mainly lifts the shoulder and helps raise the arm via its upper part. However, this function also involves the involvement of other muscles; the deltoid, supraspinatus, and infraspinatus muscles. Therefore, a spinal nerve injury affecting only one nerve may be missed by doctors because the other muscles might compensate for lost movement.
These electrodiagnostic tests are useful for planning physical therapy to reduce any complications after surgery. Also, during surgery, these tests can help identify and preserve the accessory nerve.
The appropriate site for nerve conduction studies for the spinal accessory nerve was noticed by Kim et al to be the midpoint between the acromion and the C7 spinous process (bone protrusions on the back of the neck), particularly for the upper part of the trapezius while for the middle trapezius, the site is in between the middle and the outer one third of the line from the root of the shoulder blade spine to the spine of the vertebra.
Clinical assessments for shoulder function include goniometry to measure the range of motion in the shoulder joint, and manual measurements of muscle strength in elevation, flexion, and abduction.
There are also disease-specific surveys like the University of Washington’s quality-of-life scale, the neck dissection impairment index, and the shoulder disability questionnaire (SDQ) to help assess the quality of life related to shoulder movements and strength.
During surgery, diagnosis also relies heavily on the surgeon’s experience and judgement. Any unexpected shoulder movements during cautery or surgical dissection should be carefully observed. Checking motor function post-operation is also crucial. And the surgeon must thoroughly explore the area during surgery to make sure no other injuries have inadvertently occurred.
Treatment Options for Accessory Nerve Injury
The treatment of a spine accessory nerve (SAN) injury will depend on how severe the injury is and what caused it. The treatment may be surgical, such as reconnecting the nerves or grafting nerve tissue, or it may be non-surgical and involve things like anti-inflammatory drugs, nerve stimulation, local or regional nerve blocks, and physical therapy. For severe injuries, like those caused by a penetration or medical mistake, treatment is needed right away.
In cases where there is improvement in shoulder function over time, or if there are only mild symptoms like pain or some dysfunction, medication may be used as a form of treatment. Some treatment options for short-term relief of shoulder pain include anti-inflammatory drugs, regional nerve blocks using painkillers, and transcutaneous nerve stimulation. These treatments are usually not feasible for long-term use.
Physical therapy and occupational therapy can have significant benefits in terms of improving function. The goal of rehabilitation is to promote a wide range of motion and to avoid the development of shoulder dysfunction. Keeping the shoulder aligned is very important for successful rehabilitation, as it reduces any strain on the scapula and shoulder region. Some tips for patients include not carrying heavy weights on the affected side, hooking the thumb or placing the affected hand in the pants pocket for relief, or using an arm sling for comfort.
Orthotic devices, which are used to support or correct the function of a limb or the torso, have been found to be somewhat effective in aiding rehabilitation. While they have shown some improvement in pain and function, they do not seem to significantly improve the amount of motion in the shoulder.
Physical therapy, particularly exercises aimed at strengthening the shoulder blade, can help keep shoulder function and reduce pain. Testing the electrical activity in the muscles and nerves can help track the progress of the patient. However, early surgical treatment often leads to the best outcomes.
Surgical intervention is typically considered when other treatments aren’t working, and the patient has troubling symptoms like severe pain or dysfunction. Surgical treatments may include freeing up a nerve that is trapped, reconnecting the ends of an injured nerve, or grafting nerve tissue. In some cases, a procedure known as an Eden-Lange muscle transfer might be recommended for patients with muscle weakness or paralysis that’s been present for more than 20 months.
What else can Accessory Nerve Injury be?
When trying to diagnose an accessory nerve injury, doctors may have to rule out various other conditions that could cause similar symptoms. These could include:
- Injuries to the long thoracic nerve, which can result in the weakening or paralysis of the serratus anterior muscle and cause the shoulder blade to stick out (a condition known as winging). This is especially noticeable when lifting your arm or pressing it against a wall. However, this type of injury is different from accessory nerve injury, where the shoulder blade wings out when you move your arm sideways.
- Rotator cuff injuries, which can have similar symptoms when lifting your arm behind your head. However, these injuries do not result in winging of the shoulder blade.
- Shoulder girdle arthritis and syndromes that cause shoulder pain do not lead to muscle shrinkage and winging of the shoulder blade.
- Whiplash injuries could cause neck pain, a stiff neck, and limited neck movement due to muscle tension and pain.
What to expect with Accessory Nerve Injury
Several factors can affect the recovery of the spinal accessory nerve (SAN, a nerve in your neck) after it’s been damaged. These include the type of neck surgery undergone, the severity of the injury, whether radiation therapy was used, the length of time between the injury and the repair, the blood supply to the area, and the length of the graft (transplanted tissue).
In a study, it was found that recovery time varied between 4 to 10 months for patients. Half of these patients had a primary nerve repair (directly fixing the nerve), and the other half received a nerve graft (transplanting a new section of nerve). But it was seen that an early referral to a specialist—leading to a faster diagnosis and appropriate treatment—was one of the most important factors in having a good recovery.
In other words, the earlier the treatment, the better the chance of getting functionality back. If the diagnosis and treatment are delayed, the treatment may not work as well, and the results may be less predictable.
In patients with neck cancer, a study reported that patients who had surgery that spared the nerve had better leftover function than those who had surgery where the nerve was removed. Connections were also found between having lower scores on Quality of Life (QOL) measures and having reduced shoulder movement. Those who did not have neck surgery showed the best level of function.
Possible Complications When Diagnosed with Accessory Nerve Injury
If a patient injures their spinal accessory nerve (SAN), they might show symptoms like neck pain, uneven shoulders, inability to lift their shoulders, or weakness surrounding the neck area. They might also face complications from the treatment itself.
Treatment complications can include the generation of a neuroma, or a bumpy nerve tissue, or fibrous growth over the grafted nerve. These complications can interfere with new nerve growth from the proximal axon, leading to the failure of the graft. These complications are more frequent in patients who received postoperative radiotherapy or in cases where a long, unvascularized graft was employed.
Another potential complication is the side effect from the harvesting of the autologous nerve graft, which is the nerve graft taken from the patient’s body. This can lead to problems at the site from where the graft was taken or the donor site.
Common Symptoms and Complications:
- Neck pain
- Asymmetrical shoulders
- Inability to shrug the shoulder
- Weakness in the neck area
- Formation of a neuroma or fibrotic ingrowth on the nerve graft
- Graft failure
- Morbidity of the donor site from nerve graft harvesting
Preventing Accessory Nerve Injury
If a patient has surgery to repair a nerve, it’s crucial for them to know how to limit their movement and take care of the surgical wound during the recovery. It’s also important for them to know that physical therapy can play a huge role in helping them regain full function if it’s required as part of their treatment. Patients should be aware that they will have to come back for check-ups once a week for about 6 weeks after the surgery, and then once a month after that. They should be encouraged to let their doctor know about any changes they observe in terms of recovery progress, comfort level, and the functioning of their shoulder.