What is Accessory Nerve Injury?
The cranial nerves are made up of twelve pairings that branch out beyond the skull to various body structures. One such nerve is Cranial Nerve XI, also known as the accessory nerve. The structure of this nerve is a bit complex. It’s formed from the combination of two to four short strands, which create the cranial roots of the nerve. Then, between two and nine more strands join from the spinal root to complete the nerve. Interestingly, the cranial roots of the accessory nerve could be viewed as part of another nerve, the vagus nerve, when you analyze their functions. Both of these nerve roots start from the same areas within the brain and supply movement control to throat muscles.
The accessory nerve doesn’t just stay in the brain. It travels downwards, with its cranial and spinal parts merging to form what’s known as the spinal accessory nerve. This nerve comes together within the base of the skull and then exits through an opening near the vagus nerve. It then travels downward next to a major vein, passing behind several muscles and structures in the neck before arriving at a region known as the posterior neck triangle. From there, it heads towards two key muscles, the sternocleidomastoid and the trapezius. It’s also worth noting that the pathway of the accessory nerve provides functionality to neck structures. However, due to its length and position, it can be prone to injury, which can occur from blunt trauma, accidental harm, or, most frequently, complications from medical procedures.
What Causes Accessory Nerve Injury?
The accessory nerve can often get injured due to medical interventions like tumor removal or cosmetic surgeries involving the neck, or when biopsies are taken from the lymph nodes in the back of the neck. This is because the neck may be put under stress during these types of surgeries. Other causes that can damage the accessory nerve include stab or gunshot wounds, blunt force, sudden movements of the neck, or a particular type of joint dislocation that affects the part of the neck called the sternocleidomastoid muscle (SCM).
Sometimes, the nerve or its openings can be damaged due to neurological issues that lead to a condition known as CN XI palsy. This can happen, for example, when there’s a tumor near the opening through which the nerve passes. This can lead to syndromes that affect a group of nerves in the head, including the accessory nerve.
Diseases that affect the spinal cord, nerves in the arm, or motor neurons can also lead to injury of the accessory nerve. Some research suggests that unexplained inflammation in the network of nerves in the arm could affect the accessory nerve and this might even be triggered by surgeries.
Procedures like the removal of benign growths in the neck, surgeries of the salivary gland and arteries, or when a needle is inserted into a vein can potentially result in injury to the accessory nerve.
Sports injuries such as a hockey stick blow, a tight knot against the neck in wrestling, attempting hanging, or a “whiplash” injury can also cause accessory nerve damage. Interestingly, a spontaneous, unexplained accessory nerve injury has also been reported.
Risk Factors and Frequency for Accessory Nerve Injury
The accessory nerve can get injured commonly due to specific medical procedures, such as surgeries in the back and sides of the neck. It’s been found that the risk of this injury is the highest when undergoing radical neck dissections, with almost 46.7% of cases resulting in injury. Selective neck dissections and modified neck dissections have slightly lower injury rates at 42.5% and 25%, respectively. Some studies suggest, preserving other structures like nerves, muscles, and veins during these procedures can help to reduce the risk of dysfunction.
Aside from surgeries, accessory nerve injuries can also occur after lymph node biopsies in the back of the neck. This generally results in injury rates of about 3 to 8%. In some severe cases, nearly 60-80% of radical neck dissections could lead to significant dysfunction of the upper extremity. In a thorough review of past cases, about 1.68% showed clinical signs of accessory nerve injury after modified radical neck dissection.
If the dissection includes cervical zones 2 through 4 and 5, about 30% of cases could result in accessory nerve injury. However, if zone 5 is left untouched and only zones 2 through 4 are dissected, the chances of injury significantly decrease.
Signs and Symptoms of Accessory Nerve Injury
Diagnosing an injury to the spinal accessory nerve, which is involved in controlling certain shoulder movements, involves a detailed physical examination and tests to assess nerve and muscle function. The primary signs of an injury to this nerve are shoulder pain and weakness. This pain can radiate to the upper back, neck, and sometimes the arm on the affected side, often becoming worse when unsupported weight is placed on the injured shoulder. Efforts made by other muscles to compensate for the nerve injury, such as the muscle groups known as the rhomboids and levator scapulae, can exacerbate the pain and weakness on the injured side. This combination of pain and decreased strength can limit the ability to move the affected shoulder in a full range of motion.
This pain, which can extend to the upper back and neck or sometimes to the arm on the affected side, can interfere with routine daily activities like placing dishes on overhead shelves and participating in sports or other physical activities. Pain around the shoulder and neck can be measured using a visual analog scale, which goes up to 10 points. The average score observed in spinal accessory nerve related shoulder conditions is around 7, with a typical range between 6 and 9.
The most commonly observed physical sign of this injury is clear asymmetry when looking at the shoulder and upper back, including a diminished capacity to hold the shoulder in an outward movement, a drooping shoulder, and outward winging of the affected shoulder blade. Over time, a limited active range of motion can lead to a decrease in passive range of motion too, resulting in a condition known as “frozen shoulder.” Other possible signs include muscle wastage of the trapezius (depending on how long the injury has occurred) and internal rotation of the humeral head (the top part of the upper arm bone). Additional possible complications might include enlargement or dislocation of the sternoclavicular joint, the joint at the base of the neck, due to abnormal stress following the loss of support from the trapezius muscle.
The restrictions commonly seen in the range of shoulder movement are:
- Active outward movement – 30° to 140°
- Active forward movement – 50° to 180°
Testing for Accessory Nerve Injury
Diagnosing an injury to the accessory nerve can be tricky. An example of this is the trapezius muscle, which receives signals from two nerves. Even if the accessory nerve is injured, some movement may remain because of this double supply, making it harder to identify the injury. The trapezius muscle issues can also cause varied symptoms such as feelings of numbness on the opposite side, muscle pain, and nerve root inflammation, adding to the diagnostic complexity. The presentation of these symptoms can vary based on the extent of nerve injury, how much other tissue is affected, and individual pain tolerances.
Ultrasound, especially high-resolution versions, is a helpful tool in diagnosing accessory nerve injury. It not only helps distinguish the nerve but also allows visualization of the surrounding structures. Ultrasound might find changes in muscles, like shrinkage. Importantly, it aids to accurately target areas for injections or medication administration, reducing potential further damage. However, ultrasounds won’t always show the actual nerve cut.
Tests, such as electromyography (EMG) and nerve conduction studies, aren’t always required for diagnosis, but they can be useful for detailing and quantifying the extent of the damage. In a nerve injury, these tests might show lengthened response times and give clues to nerve damage or repair based on the time of the study. These tools help to design a physical therapy routine to lower possible complications after surgery. They can also be used during surgery to find and preserve the accessory nerve.
The trapezius muscle is mainly responsible for lifting the shoulder, while the deltoid, supraspinatus, and infraspinatus muscles also contribute to this motion. Therefore, injury to certain spinal nerves can sometimes be overlooked because other muscles might compensate for the loss of movement.
Shoulder function is often evaluated by using several methods such as goniometry – to measure the range of motions like bending and lifting around the shoulder joint, and manual muscle strength tests. There are also certain questionnaires that aim to assess the quality of a person’s life, with a focus on evaluating shoulder movement and strength. These include the University of Washington quality-of-life scale, the neck dissection impairment index, and the shoulder disability questionnaire (SDQ).
During surgery, diagnosis often depends largely on the surgeon’s intuition. Any movement of the shoulder caused by surgical actions should be carefully examined. Postoperative checks on motor function and a thorough exploration of the area during surgery can ensure there aren’t any overlooked injuries.
Treatment Options for Accessory Nerve Injury
When it comes to treating an injury to the accessory nerve, how severe the injury is and what causes it are important factors in determining the treatment approach. Some conditions might require surgery such as reattaching disconnected parts of the nerve or nerve grafting. In less severe cases, treatment methods could include using nonsteroidal anti-inflammatory drugs (NSAIDs), nerve stimulation, regional nerve blocking, or physical therapy. Treatment should start immediately for serious incidents like wounds from sharp objects or caused by medical procedures.
For medical treatments, some indicators that it might be the right choice include improved shoulder function seen in regular check-ups, improved electrical activity on the nerve test (EMG), mild symptoms including pain and slightly impaired shoulder function.
Short-term methods to alleviate shoulder pain and improve function might include taking NSAIDs, blocking the affected regional nerve with local anesthetics (this does need frequent repeat injections), or applying nerve stimulation on the skin. However, these options are not practical for the long haul.
Physical and occupational therapies are valuable for significantly improving function. Rehab work aims to gradually increase the range of movement. Keeping the shoulder in its correct position is extremely important during rehab as it reduces stress on the shoulder blade and shoulder area. Elevation of the shoulder blade can help minimize problems with the trapezius muscle (a large muscle at the back of the neck and upper spine).
Patients should be advised to avoid carrying heavy items on the affected side and try to keep their affected hand in the pocket of their pants for relief. An arm sling could help with pain, but could also limit the function of the arm.
Devices that help align body parts (orthoses) have been used in rehab as well. In one study, orthoses were associated with less pain and improved function.
Physical therapy is an essential part of treatment. It aims to maintain passive movement in the shoulder. This could help avoid shoulder joint stiffness due to a misaligned shoulder or inflammation within the joint. Physical therapy is also important for patients who refuse or are not suitable for surgical treatment.
On the other hand, surgical treatment should be considered only when the nerve is not apparently injured or cut, and if regular check-ups after the initial injury show no spontaneous recovery in the trapezius muscle function and ongoing neurological deficits are confirmed.
There are several surgical options, such as Nerve-weakening surgery, Primary nerve anastomosis (attaching two parts of a nerve together), Cable graft (types of graft include a piece of nerve from the patient’s own body, a biosynthetic nerve guide, or a tube made to guide nerve growth), or Eden-Lange muscle transfer.
Quick reconstruction is suggested when there is an obvious full cut of the accessory nerve. If the patient is suffering from a trapezius muscle weakness, with or without prior neck surgery, how long since the symptoms first appeared needs to be established. The Eden-Lange muscle transfer is a good surgical option if the patient has had spontaneous trapezius weakness or they have been experiencing symptoms for longer than 20 months.
What else can Accessory Nerve Injury be?
If the long thoracic nerve gets hurt, it can cause weakness or paralysis of the serratus anterior muscle. This can be identified by a condition where the shoulder blade sticks out like a wing, especially when the arm is lifted forward or pushed against a wall. This is different from an accessory nerve injury, where the shoulder blade wings out when the arm is lifted to the side.
An injury to the rotator cuff, the group of muscles and tendons that stabilize the shoulder, can look similar, except the shoulder blade wouldn’t jut out like a wing.
In diseases like arthritis or shoulder girdle pain syndrome, there is no muscle wasting or winging of the shoulder blade.
Whiplash, an injury from a severe jerk to the neck, can cause neck pain, stiffness, and limited neck movement as a result of muscle spasms and pain.
What to expect with Accessory Nerve Injury
The functioning of the spinal accessory nerve (SAN), following any kind of damage, can be influenced by several factors. These include the type of injury, whether or not radiation therapy was given, the time between injury and treatment, blood supply, and the length of any grafting performed.
In one study, recovery time varied between 4 to 10 months amongst patients who either had a primary nerve repair or nerve graft. Importantly, early referral, which allows a more accurate diagnosis and prompt treatment, greatly improves the outlook. Early surgical intervention has been shown to result in better recovery of function. Conversely, delayed diagnosis and treatment can lead to less effective results.
In a different study, it was revealed that neck cancer patients who had nerve-sparing neck dissections had better recovery of function than those who had dissections involving nerve removal. There was also a link observed between lower quality of life scores and reduced shoulder movement. Interestingly, those who had no neck dissections demonstrated the best level of function.
Possible Complications When Diagnosed with Accessory Nerve Injury
If a person injures their SAN (spinal accessory nerve), they might experience neck pain, uneven height of the shoulders, difficulty shrugging, or neck weakness. There might also be complications due to the treatment they receive. One of these complications could be the creation of a neuroma, which is a nerve tumor, or fibrotic overgrowth. This is when fibrous tissue grows over the graft site, potentially preventing new nerve fibers from growing and leading to the graft’s failure. This issue is more likely to happen if the patient had radiation therapy after surgery, or if the graft used was long and lacking blood vessels. Another possible problem is related to the procedure of obtaining the nerve graft that is to be used. This can cause complications at the site where the graft was taken from.
Common Complications:
- Neck pain
- Asymmetrical shoulders
- Inability to shrug the shoulder
- Neck weakness
- Formation of a neuroma or fibrotic ingrowth over the graft
- Graft failure
- Morbidity at the graft donor site
Preventing Accessory Nerve Injury
If a patient has surgery to repair a nerve, they must be properly informed about how to take care of the wound and how to limit their movement. Physiotherapy is important and if required, the patient should be encouraged to continue with it. After surgery, the patient should go for a check-up once a week for about six weeks, and after that, once a month. The patient should also report any changes in their overall health, whether they feel better or worse, if they feel any pain, or if their shoulder function improves or worsens.
