What is Axonotmesis?
Peripheral nerve injuries, also known as PNIs, aren’t very common but they can have serious health consequences. Interestingly, cases of patients being unhappy due to these injuries often result in legal actions following usual procedures like spine, ankle or foot surgery, and joint replacement surgeries. These injuries can be caused by either trauma or other non-traumatic circumstances and can sometimes be the unintended result of medical treatment or surgery. Because the best results in treatment come from early intervention, it’s extremely important to quickly identify these injuries.
Sometimes these nerve injuries can be moderate – more severe than a minor insult, which results in neurapraxia – but less severe than complete nerve transection which is known as neurotmesis. In these moderate cases, we use the term “axonotmesis”. These terms help medical practitioners gauge the level of nerve damage, which helps them figure out the most effective treatment plan and predict the likely patient recovery outcomes.
To understand the different levels of nerve injury, let’s take a look at the structure of a peripheral nerve. From the outermost part to the deepest, a peripherical nerve contains several layers: the epineurium, the epifascicular epineurium (which is found between the fascicles), the perineurium (which covers the individual fascicles), and the endoneurium, which surrounds the axons that are coated in a myelin sheath and Schwann cells.
In the medical world, nerve injuries were classified by Sunderland and Dellon, based on Seddon’s work. They defined six grades of nerve injuries.
- Grade 1, called neurapraxia, where there might be damage to the outer lining of the nerve fiber.
- Grades 2, 3, and 4 are termed axonotmesis.
- Grade 2 – the outermost layer of nerve fibers remains undamaged, but the axons are harmed.
- Grade 3 – the layer around individual fascicles remains intact, but axons and the layer around them are damaged.
- Grade 4 – the outermost layer of the nerve remains healthy, but the axons and the layers covering them are damaged.
- Grade 5, also known as neurotmesis, involves complete nerve transection.
- Grade 6 indicates a mixture of various nerve injuries. This stage is reportedly the most common type of nerve injury seen in medical practice.
What Causes Axonotmesis?
Peripheral nerve injuries (PNIs) can be sorted into two categories, based on the condition of the skin surrounding the injury. “Closed” injuries involve the nerve but leave the skin intact. “Open” injuries, on the other hand, produce damage both to the nerve and the skin around it. Sharp cuts or messy contusion-type injuries can result in open injuries. A clean cut like that from a scalpel slicing the nerve, or a messy contusion injury, like a shrapnel wound involving the nerve, are examples. Ragged injuries can trigger more inflammation, disrupt nerve fibers, displace them, and potentially introduce foreign bodies into the injury.
Closed injuries happen due to strain or bruising and can be caused by joint dislocation or some sort of crushing effect. Missile injuries, or injuries caused by bullets or other projectiles, are considered a kind of closed nerve injury, marked by concussion-like force, heat damage, or nerve severance.
In general, neurapraxia, which is a type of temporary nerve malfunction, typically follows compression or entrapment injuries. Axonotmesis, a more severe nerve injury, often results from crushing or stretching. Neurotmesis, the most severe nerve injury, usually occurs after a sharp wound, pulling, avulsion (or tearing away), or toxic damage to a nerve.
Typical injuries that affect certain nerves might include a seat belt injury affecting the upper brachial plexus nerve, a stab wound in the neck affecting the spinal accessory nerve, or a dislocated knee or broken fibula affecting the peroneal nerve.
Less common in the general population are non-impact nerve injuries. These can be caused by uninterrupted pressure, unpredictable bleeding, blood vessel damage, tumor mass or invasion. For healthy people, they can often alleviate compression-related damage by simply changing positions.
Also, injuries caused during medical procedures, called iatrogenic injuries, can happen. Such injuries can come from pressure due to swelling at the injury site, wrong positioning during surgery, effects of radiation therapy, or using a tourniquet. Some surgeries, like varicose vein procedure, carpal tunnel release, or hernia repair, come with a higher risk of such injuries. For example, the accessory nerve is particularly at risk during a lymph node biopsy, and the median nerve is susceptible during carpal tunnel repair.
Risk Factors and Frequency for Axonotmesis
Peripheral nerve injuries (PNI) following injuries to the arms or legs happens in about 1.64 to 3.4% of cases. In the arms, the nerves most often affected are the radial, ulnar, and median nerves. For the lower body or legs, it’s usually the sciatic, peroneal, and tibial/femoral nerves. Certain nerves in the trunk of the body, such as the ilioinguinal, genitofemoral, and spinal accessory nerves, can also be involved. These types of injuries often happen due to crushing injuries.
One study found that upper body nerve injuries occurred at an average rate of about 43.8 cases per 1 million people every year. This number has been decreasing over the years. However, the cost related to these cases grew by 9.6% between the years 2001 to 2013. Most patients were white men who came to the hospital through the emergency department due to a digital laceration injury (a cut on a finger or toe). The average age of these patients was 38.1, and most of them were sent home after their hospital visit.
Another study found that lower body nerve injuries happened at an annual average rate of 13.3 cases per 1 million people. The most common nerve affected in these cases was the sciatic nerve, and the usual injury was a fracture in the lower body. The average age for these patients was 41.6. Most were male and came to the hospital through the emergency room. The cost for these cases also rose, with an annual growth rate of 8.8% from 2001 to 2013.
Finally, people with extreme body weights, males, and those with a history of nerve disease or other health problems that make them more likely to suffer nerve injuries are most likely to have positioning nerve injuries, which are caused by the position of the body.
Signs and Symptoms of Axonotmesis
Diagnosing and treating nerve injuries largely depends on a careful examination by a healthcare provider. This begins with understanding the patient’s medical history and a detailed physical exam. In cases where the nerve injury is due to trauma, the initial focus is on treating life-threatening conditions, if any. Once the patient is stable, a more detailed examination follows.
Regardless of whether nerve injury is due to trauma or not, a complete neurological exam is needed. This includes testing muscle strength, how different groups of muscles are performing, and which areas of the body are affected. The patient’s own concerns about their physical performance are also considered. Health care providers must figure out whether another injury or medical condition might explain the symptoms noticed during the exam.
In non-trauma related nerve injuries, it’s important to consider factors like the patient’s medications, cancer risk, bleeding disorders, physical activity, and substance use. Advanced imaging and electrophysiological tests can help provide a more accurate diagnosis. Regular assessments are crucial as patients’ conditions can change over time.
Testing for Axonotmesis
When checking for nerve injuries, doctors will start with a detailed history and a physical examination, which will focus especially, on any damage to the body’s automatic functions, muscles, and skin sensations.
If the injury is visible and severe, doctors might need to immediately open up the wounded area to see how much damage there is and decide whether surgery is needed. If it’s a less severe injury that might heal on its own, the doctor will monitor the patient weekly to see if they’re regaining function. If there’s no improvement after several months, then surgery might be necessary.
Various technologies can help evaluate nerve injuries when surgery isn’t urgently required, when the injury isn’t visible, or if surgery has been done, and the recovery process needs monitoring. One such technology is electrodiagnostic studies; however, they might not show the full extent of the injury until about 2-3 weeks after it has occurred.
Nerve conduction studies are beneficial because they can find the location, severity, and how the nerve damage is progressing by studying motor and sensory conduction. The readings from these studies usually remain normal or only slightly decreased until around 11 days after the injury for sensory nerves and seven days after the injury for motor nerves. However, if nerve function doesn’t return after 12 days, it might indicate a specific type of nerve injury called neuropraxia.
An electromyogram (EMG) can be helpful about 2-3 weeks after the injury to identify whether the muscle or nerves are causing weakness. When the doctors observe the muscle response during this procedure, they can also determine the timing, location, nature, and severity of the injury.
Other types of tests that can be used within the surgery to ascertain the integrity of sensory or motor nerves include somatosensory evoked potential (SSEP) and motor evoked potential (MEP) tests.
Additional tools to evaluate nerve injury include ultrasound, magnetic resonance imaging (MRI) scans, CT scans, and other radiology tests. These can provide additional information about the injury and assist in the diagnostic process.
Treatment Options for Axonotmesis
In cases where someone has suffered a nerve injury, it’s important to understand that even with the best care, full recovery may not always be possible.
Keeping active is key in these cases, as it helps the affected nerves to adapt and change. This activity also helps to prevent stiffness and can reduce neuropathic pain, which is pain caused by damage to the nerves.
Depending on the type of nerve injury a person has, regular check-ups might be needed to monitor the recovery process. If there’s no improvement after three to six months, surgery might be considered.
Surgery is used to prevent irreversible damage to the nerves. The type of surgical treatment largely depends on the kind of injury the nerve has sustained. In some cases, if monitoring shows that there is still intact signaling to the nerve after the damage, little further surgical intervention may be required.
When the nerve has been cleanly cut, the surgical procedure should ideally take place within three hours of the injury to avoid retraction of the nerve ends and potential tissue damage. This procedure, known as primary repair, involves connecting the two ends of the nerve.
In other cases, when the nerve has been crushed or torn, a different procedure, known as secondary repair, might be needed. This may involve attaching the nerve endings to surrounding tissue to prevent further retraction, and later reconnecting the nerve ends. If the gap is too large to reconnect the nerve ends directly, a graft might be needed.
For some especially complicated cases, when the gap is too big for primary or secondary repair, there might be other options such as attaching a healthy nerve to the damaged one or using grafts and conduits to bridge the gap.
Unfortunately, even with the best treatment, some people will still experience pain and disability. In these cases, a team of different medical specialists is needed to provide the required support, such as physical therapy, pain management treatment, and possibly prosthetics or cosmetic solutions. The full extent of services needed for people with nerve injuries is beyond this simplified explanation.
What else can Axonotmesis be?
Peripheral Nerve Injuries (PNIs) are typically diagnosed using a detailed review of your medical and health history along with a comprehensive examination of your nervous system. This is often assisted by special diagnostic tests and techniques like ultrasound and MRI scans.
Other possible conditions must be taken into consideration when making the diagnosis, especially those that can affect your feeling, autonomic responses (involuntary body functions), and physical movements. Without a known event that could explain a localized PNI, more in-depth tools and tests are used to identify what’s causing your symptoms.
Other factors like muscle diseases, problems with the body’s main control system or central nervous system, irregular levels of electrolytes in the blood, limited blood supply to an organ, diseases where the body attacks its own cells, exposure to harmful substances, and infections are all evaluated. By using specialized tests, doctors can tell the difference between things like muscle injuries and inflammation of the nerves, which can help guide their treatment decisions.
Certain tests used in the weeks after an injury can help determine the severity of nerve damage. For example, they can distinguish between `axonotmesis` (disruption of the nerve’s axon) and `neurotmesis` (complete severing of the nerve). By combining these tests with regular check-ups to observe natural recovery and documented injury information, it is possible to differentiate between `neurapraxia` (a mild type of nerve injury) and more serious injury types.
What to expect with Axonotmesis
The recovery chance for axonotmesis, a type of nerve injury, depends on the individual’s health condition, and the extent of their injury. In the best situations, the damaged nerve can regenerate in a timely manner through branching or by lengthening the remaining part of the damaged nerve.
Limited injury to the nerve axons and the structural parts within the nerve increases the likelihood of nerve regeneration. If only the Schwann cells, which are part of the nerve structure, are damaged, recovery usually happens within days to weeks. It’s estimated that 90% of patients experiencing nerve injury due to positioning recover completely within three years. Even in axonotmesis, where the nerve’s axons are damaged, spontaneous regeneration is still possible if the perineurium and epineurium, layers of the nerve, remain undamaged. Injuries located closer to the ends of the nerve generally have a better chance of recovering.
However, nerve regeneration does not always mean the restored function of the nerve. The regenerated axons also need to establish an effective communication with the end organ, the part of the body the nerve supplies. Therefore, early treatment of the damaged nerve is recommended to prevent scarring and losing the viability of the end organ due to neglect.
Nerve-connected tissues like muscles and sensorial structures remain viable for a certain period after nerve injury; muscles for up to 1 year and sensorial structures like Merkel, Pacinian, and Meissner’s corpuscles for 2-3 years. Given that a damaged peripheral nerve grows about 1-2 mm/day, it is wise to take early action, especially within the first 3-6 months if no signs of natural recovery are noticeable. Regaining connection with the end organ within limited time is crucial.
Several factors affect the chances of successful recovery. These include the patient’s general health, the mechanics and severity of the injury, the gap in the nerve, the type and location of the injury along the nerve, associated injuries, the time till surgery, the type of surgery, and the patient’s age.
Possible Complications When Diagnosed with Axonotmesis
When nerves are damaged, they often try to heal themselves. But without a specific pathway, this healing attempt can lead to abnormal nerve growth, forming a painful mass called a neuroma. Implanting any foreign material, be it stitches or tissue grafts, can trigger an immune response. This can lead to scarring, pain, and even hinder nerve regeneration.
While tissue transplants from another person are rarely used, if they are, the patient is at risk of having to take drugs to suppress their immune system, which can have their own risks. Similarly, the use of the patient’s own tissues (known as autografts) can potentially raise health issues from damaging the area where the tissues are collected.
Worsening of nerve function is commonly seen within days after a nerve injury. However, if there is a sudden decline or a relapse in nerve function improvement, other factors that may not be related to a trauma, like clotted blood (pseudoaneurysm and hematoma), could be the cause and need to be explored.
Preventing Axonotmesis
The common occurrence of nerve injuries from physical trauma underlines the need for spreading awareness about patient safety and the use of protective gear. If patients notice any unusual sensations, movement disorders, or body system functions, they should not hesitate to seek medical attention.
To avoid accidentally causing nerve injuries, healthcare providers need thoroughly understand the body’s structure where they might insert needles, apply bandages, use orthotic devices or tourniquets, or carry out procedures. Before such interventions, patients should be clearly informed about any potential risks of unintentional tissue damage, including to nerves.
Healthcare providers should be very careful when positioning patients and undertaking procedures. Detailed records about techniques used to prevent nerve damage are strongly encouraged. Nevertheless, such precautions are not a guaranteed protection against legal action in the event of unintended outcomes.
