Nerves are carriers of messages to and from the brain to the rest of the body and vice versa. Nerve injuries refer to the damage caused to the nerves' outer layer alone or the entire thickness of the nerve.
How do the nerves get injured?
Nerves are highly delicate, and any form of pressure or cutting or stretching can cause damage to them. Nerve injuries mean no signal to and from the brain can happen between the injured area, and hence the muscles do not function properly.
The damage to the nerves depends upon the type of injury. In case of a nerve injury due to a knife or glass, the site of the trauma due to the transaction, will be precise. A blunt trauma/ injury will cause widespread, long segment injury especially when accompanied by an avulsion component.
Usually, peripheral nerves are affected, that is nerves of the upper and lower limbs. Patients experience various signs and symptoms depending upon the nerve that is injured, type, and extent of the injury. However, a few of the symptoms are -
Loss of sensation/Numbness – The patient will experience numbness if the nerves that transmit sensation are injured
Loss of sensation/Weakness - The patient will experience immobility if the nerves that help in movement i.e. in the transmission of motor signals are injured
Pain – The patient will experience pain associated with nerve injury at the injury site and along the nerve’s course.
Combined paralysis: where there is loss of both motor and sensory function. Sometimes if the entire plexus of nerves is injured, then the entire limb becomes paralysed with not even a flicker of movement.
This is commonly seen in the upper limb which is supplied by the brachial plexus. Brachial plexus injuries leave the patient with a lame upper limb and need active intervention to restore function.
It is possible to experience intermittent or constant pain depending upon the extent of the injury. In addition, the patient can display reduced muscle size, skin colour changes, and changes in the sweat discharge in select areas.
Presentation of Nerve Injuries based on time elapsed since injury
Timing of presentation
- Acute condition refers to nerve injuries that are presented immediately for treatment
- Subacute condition refers to nerve injuries presented between the 1st day and six weeks after the injury.
- Chronic condition refers to nerve injuries presented six weeks after the injury.
In-depth investigation and evaluation of Nerve Injuries
Electromyography (EMG) and Nerve Conduction Studies help to ascertain the extent of nerve injury. These tests measure the electrical activity of the nerves and muscles. It is possible to measure the reaction of the muscles when they receive the nerve signals.
The EMG test focuses on the electric signals of the muscles when in rest mode and when in use. A nerve conduction test (NCV) measures the speed of the body’s electrical signal travelling through the nerves and whether that speed is slow or fast.
These tests help to detect issues in the muscles, nerves, and both together. These tests can be done singly or together, which most treating doctors prefer. These tests are also known as electrodiagnostic studies or ENMG.
Management of Nerve Injuries
Primary repair of nerve injuries
A four-step commonly used nerve repair procedure involves -
- Preparation – The necrotic or unhealthy tissue is removed while two normal-looking ends are kept ready. If required, the joint above the nerve injury is flexed to allow tension-free repair. If there is a gap between the nerve ends then a piece of nerve from elsewhere, called, a nerve graft is taken to bridge the gap.
- Approximation – The open nerve ends are brought nearly together in perfect apposition for the best outcomes.
- Alignment – The plastic surgeon must ensure proper blood vessels and proper rotational alignment.
Maintenance – The sutures in the epineural layer are crucial in nerve repair. Their placement prevents the nerve ends from malrotation. If required, individual fascicular groups are also sutured. This type of primary nerve repair is done for larger nerves where the sensory and motor fibres can be distinguished and separated.
- The repair is reinforced using fibrin glue.
Nerve Graft repair is performed to repair the gap between the transected nerve's stumps without exerting excess tension. The autogenous donor grafts are taken from the patient after prior consent. These grafts are placed strategically between the nerve stumps in the injured area. Also, the area from where the graft has been grafted does not cause major trauma to the area or the patient.
This surgery involves redirecting a nerve branch from a neighbouring nerve with a distal end of the injured nerve. The plastic surgeon prefers to use a functioning branch located close to the injured or the non-functional nerve as the healing and regeneration process of the nerve is accelerated with better outcomes, especially in the injured area due to the shorter distance of regeneration.
It is the preferred treatment option in late in injuries where the time for regeneration if too long will not be of any use as by then the affected muscle will shrink and become non-functional. Nerve transfers involve good anatomical knowledge and surgical skill.
In patients presenting very late, where nerve transfers are futile due to target muscle degeneration, tendons of functioning muscles can be transferred to tendons of affected muscles to bring about their movements. Muscles chosen for transfer are such that primary and fundamental function of the hand of foot is not affected.
Functioning muscle transfers
Where there is widespread muscle mass loss or brachial plexus injury, the entire muscle-tendon complex is replaced from muscle-tendon taken elsewhere in the body along with its nerve and blood supply. This is called a free functioning muscle transfer- FFMT.
This is done for:
- facial nerve paralysis to restore a smile
- brachial plexus injuries to bring about elbow bending and fingers bending to form a fist
- Volkmanns ischemic contracture where the entire muscle mass of the forearm may be lost due to compartment syndrome.
- FFMT is a highly specialized reconstructive hand surgery requiring microsurgical skill.
This is yet another very important last pillar for a successful nerve repair or reconstruction. Patients have to be vigilant about post-surgery strengthening exercises and joint movements to restore strength and range of movements.