It’s very common to sustain an acute nerve injury, and these can be caused by a number of different traumas.
Injuries sustained to the nerves outside of the spinal cord and brain (the peripheral nerve) could arise from crush injuries, fractures, stretching, cuts, or blunt force, with the upper limb’s nerves often being the ones that are injured.
When you have a nerve injury, the healing process can vary from several weeks to several months – but the repair and recovery of this injury are highly dependent on the type of injury you’ve sustained and how much damage has been caused.
To better understand one particular nerve injury – axonotmesis – and its symptoms and signs, we’ll take a look at the nerve structure as a whole, how axonotmesis compares to neurotmesis, and how you can recover from this type of injury.
How Are Our Nerves Structured?
Schwann cells and axons make up the peripheral nerve, and these nerves can be myelinated (they come with an outer layer that’s made up of myelin) or they might not have this insulation (they’re unmyelinated).
In myelinated nerves, a sheath is created over each axon by the Schwann cells, but in unmyelinated nerves, a group of axons is covered by a Schwann cell-sheath. These axons that have a Schwann cell-sheath are also covered in a layer that’s known as endoneurium (made up of connective tissue).
A nerve fascicle (aka a nerve bundle) is formed by several of these endoneurial tubes. Each of these bundles of nerve fibers is covered in perineurium (another layer of tissue). A final layer, the epineurium, covers a number of nerve bundles.
Each of these nerves receives its blood supply by the vasa nervorum – a system of blood cells that run through each nerve.
Why is all this important?
Because in axonotmesis, the endoneurium, epineurium, perineurium, and Schwann cells remain intact, but the myelin sheath and axons are damaged.
In layman’s terms, axonotmesis is an injury that occurs in the nervous system, causing severe damage to the axons but without damaging the aforementioned layers. That’s why this type of nerve injury tends to be caused by a more severe contusion or crush compared to other nerve injuries, like neuropraxia.
Axonotmesis injuries can result in sensory, motor, and autonomic paralysis. But if the force that created the nerve damage is removed as quickly as possible, the axon may start to regenerate itself, allowing the patient to make a full recovery from their injuries. Recovery usually takes from a couple of months to several years, depending on the severity of the nerve injury.
Neuropraxia and Neurotmesis vs. Axonotmesis
Physicians often classify nerve injuries using the Seddon and Sunderland classifications. This divides these types of injuries into different degrees, including neuropraxia, axonotmesis, and neurotmesis.
Neurotmesis occurs when the sheath and axons are completely or partially severed (cut) – hence why it’s the severest nerve injury you can suffer from. That said, if the cut is clean, this can provide doctors with the chance to immediately repair it, providing patients with a faster recovery time.
Another common nerve injury is neuropraxia, and this is the least serve form. Despite the nerve fibers being intact (the sheath and axon aren’t cut), it results in nerves transmissions being completely blocked. Neuropraxia is often caused when nerves are stretched in dislocation or fractures, or it may arise when there has been prolonged pressure on a nerve or a blunt injury. Patients suffering from neuropraxia tend to recover spontaneously within a few months, perhaps even after several hours.
The Symptoms of Axonotmesis
The loss of normal function is often what characterizes an acute nerve injury – with this being either sensory or motor depending on the nerve injury sustained.
Muscle function (motor function) is affected by a motor nerve injury, while the senses are impaired as the result of a sensory nerve injury.
When muscle function is lost, you may notice paralysis or weakness (this could occur if you’ve damaged the nerves in your back, for example). Whereas sensory impairment can lead to pain, abnormal sensations (known as paresthesia), or loss of sensations.
Recovering from Axonotmesis
It may take weeks or months to recover from axonotmesis, providing there is no cut to the nerve. If the nerve has been completely severed, recovery may never occur.
For the nerve to repair itself, it needs to go through a degeneration process first – this is known as Wallerian degeneration. After this, the nerve will start to regenerate very slowly, working its way from the proximal end to the distal part of the nerve. The speed at which this happens is 1mm per day.
During this time patients may feel several sensations, including the “motor march” phenomena, which is a sign of nerve regeneration.
Sometimes, there may be abnormal connections within a regenerated nerve, which can result in strange sensations or movements. For example, when a nerve that supplies the muscles is injured, it will only be able to restore its natural functions if the regeneration occurs within 18 months of the injury happening.
However, compared to other nerve injuries, like neurotmesis, the prognosis for recovering from axonotmesis is generally quite positive, especially if the nerve is treated quite quickly after the injury.