Our peripheral nervous system is an extensive network of nerves that integrates diverse body parts with our brain and spinal cord. Peripheral nerves are composed of different motor, sensory, and autonomic neurons. They communicate with distant target organs by bringing sensory information to the brain and giving neural signals to the muscles or organs.
When the nerves get injured
Peripheral nerve fibres are very delicate and, hence more susceptible to damage. Peripheral nerve injury (PNI) is a neurological condition that can cause long-term functional and physiological disabilities. It affects more than a million people worldwide and reduces the quality of life for the affected. A medical, surgical or traumatic injury can damage these nerves. People suffering from peripheral nerve injuries face a broad range of symptoms depending on the injury’s severity and the nerve involved.
What causes PNI?
Primarily, nerve injury results from direct physical forces applied to it. For example, a sudden stretch of a limb, a deep cut in the tissue (laceration), or compression can damage the peripheral nerves. Sometimes, reduced blood supply (vascular ischemic damage) can also damage the peripheral nerves.
Peripheral nerve injury hampers daily activities for the individual. There is a partial or complete loss of sensory and motor function in the affected part of the body due to poor nerve recovery. For example, there could be numbness, lack of sensations, and impaired muscle movement in the affected region. It is followed by muscle atrophy (loss of muscle mass), chronic pain, profound weakness or paralysis, leading to severe disability and a diminished quality of life in a person with nerve injury.
Types of peripheral nerve injuries
Each peripheral nerve extends into multiple axons, which act like a wire to conduct the electrical impulse across neurons. Three layers of connective tissue — epineurium, perineurium and endoneurium – envelop them. Further, the nerve cells are covered by an insulating myelin sheath, increasing nerve impulse conduction.
Depending on the extent of damage to the axons, the peripheral nerve injuries are classified as:
- Neuropraxia – when the myelin sheath of axons is damaged.
- Axonotmesis – when the damage to the nerve is partial.
- Neurotmesis – when the nerve gets severed completely.
PNIs take a long time to repair as the peripheral nerves have a slow regrowth rate – around 1-3 mm per day. However, the process can be speeded up with external intervention like surgery. Also, other factors, such as loss of extensive nerve tissue and prolonged loss of nerve supply to the affected organs, enhance the possibility of reduction in that organ’s size (atrophy).
The diagnosis of peripheral nerve injuries is based on history and clinical examination with good knowledge of the anatomy of the specific body regions. Needle electromyography (EMG) and nerve conduction studies are essential for diagnosing nerve injuries. In addition, magnetic resonance imaging (MRI) may show early damage to the peripheral nerve and surrounding tissues in severe cases.
Managing the condition
Depending on the degree of injury and nerve damage, surgical and nonsurgical methods are employed to treat PNI.
- When the damage to the nerve is less than a centimetre long, Neurorrhaphy or suturing the injured nerve ends is employed.
- The gold standard procedure of Autograft helps bridge significant nerve gaps of more than 3 cm and in critical nerve injuries. In this technique, a graft from the person’s body parts or another nerve is transplanted into the injured site.
- In the nerve guide conduit method, engineered tissue structures are used to bridge the ends of the injured nerve to help in nerve regeneration.
- Nerve growth factors are molecules released naturally in the injury process and directly enhance nerve regeneration. They are used in combination with nerve guide conduits for nerve regeneration.
- Mesenchymal stem cells promote nerve regeneration by signalling cell-to-cell contact, cell differentiation into tissue-specific cell types and release of neurotrophic factors.
- Peripheral nerve injury leads to sensory and motor function loss in the body.
- It is managed through various surgical and nonsurgical procedures encouraging nerve regeneration.