|Patients with acute trauma are easily identifiable by the emergency of the event, as in the case of crush injury or laceration. But, repeated mechanical injuries resulting from external forces, as when using a tool in a certain manner or maintaining a body part in a certain position for long periods, may cause sub acute or chronic dysfunct of nerves. The affected person or worker is likely to overlook or ignore the problem until the impaired function affects productivity and safety.
Common Causes Of Occupational Nerve Injuries
The peripheral nerves are susceptible to such injury because they do not have the barrier of protection that the skull or the spinal cord or the blood stream provides to the other nerves.
- Focal contusion
- Stretching/traction injury
- Electric injury
Diagnosis of individual nerve dysfunction can be done with an assessment of the history of loss of specific motor and sensory function and with standard neurological examination. Nerve conduction test and electromyography study help in differentiating between lesser and higher grades of injury. If the nerve injury is a result of trauma, X-rays, CT scan or MRI scan may be needed to assess the associated injury to bones, cartilage, muscles, tendons and ligaments.
Injury to peripheral nerves can manifest in a variety of trauma. The loss of specific motor and sensory functions manifests as weakness, numbness, tingling sensation and so on.
Certain anatomic sites or areas of the body are at greater risk for compression or entrapment than others. For example, the ulnar nerve may become entrapped in the hand or at the elbow, the median nerve at the wrist or in the forearm and the radial nerve in the upper arm. Frequent sites of entrapment in lower limb include the sciatic nerve in the glutei region and peroneal nerve at the fibular head.
Degree Of Damage
The classification of the degree of injury helps in the assessment of the prognosis and the determination of treatment-strategy.
- Low degree nerve injury or neuropraxia: A case in which the nerve remains intact but signal ability is damaged.
- Second degree nerve injury or axonotmesis: A case in which the axon is damaged but the surrounding tissue remains intact.
- Last degree nerve injury or neurotmesis: A case in which both the axon and connective tissues are damaged.
Treatment & Prognosis
In lower degree of damage, nerves can heal spontaneously, which may take upto two years and there is a good chance that the patient may not need surgical repair.
If a nerve injury fails to heal properly or when a section of the nerve is cut completely or damaged severely, the patient will need nerve repair/implant or nerve transfer. In nerve transplant, a piece of nerve from any other part of the body is used for repair of the damaged nerve. In nerve transfer, another working nerve is used to make an injured nerve work. If nerve repair is not possible at all, tendon transfer can be done to improve the functions in that particular part of the body.
The expected rate of recovery for nerve repair is 1 mm/day after an initial period of three weeks.
There will be associated muscle fibre atrophy during the first eight weeks, causing temporary weakness in patients (almost 70 per cent of them) during recovery from motor nerve injuries.
The outcome of treatment also depends on the location and territory served by the injured nerve and on whether there is any overlap in its function with the neighbouring nerves that are not injured. Nerve injuries that occur at the spinal cord or close to the spinal cord have a poor prognosis.
Restoring Functions In Muscles Affected By Nerve Injury
- Braces or Splints: These devices help in holding the affected limb, hand, fingers or foot in proper position to improve muscle function and in immobilization and protection of repaired structures.
- Electrical stimulation: It can activate the muscle served by an injured nerve while the nerve regrows or regenerates.
- Physical and occupational therapy:It involves specific movements and exercises to keep the affected muscles and joints active. It can prevent stiffness and help to restore function and promote healing. Occupational therapy may help the individual regain independence in activities of daily living and may assist in the selection and use of appropriate adaptive equipment.
The extent of injury, associated disability and type of work will dictate the type of work restriction and rehabilitation that is necessary. Changes in design of the work stations, modifications in the design of hand operated tools, or adaptations in work procedures may prevent further damage and facilitate recovery.