Nerve Injuries

Nerves are cable-like structures that send information between the central nervous system (spinal cord and brain) and the target organs (internal organs, skin, muscles, joints, etc). A nerve if formed of bundles of axons surrounded by layers of connective tissue. Nerves are responsible for reflexes, sensation and muscle contractions. Pain, tingling, numbness and muscle weakness are tell-tale signs of nerve pathology.

The most common nerve injuries are:

• Stretch-related injuries: these are encountered when traction forces exceed the nerve’s capacity to stretch eg. Erb’s Palsy is an injury to the brachial plexus during childbirth
• Lacerations: these are caused by knifes, glass and other sharp implements
• Compression injuries: these can either be caused by external forces, as in the “Saturday Night Palsy” or “Honeymooners Palsy”  which is a radial nerve compression generally preceded by arm pain to a degree that only excessive alcohol or love would drive a person to keep the arm in such an uncomfortable position; or internal forces eg. carpal tunnel syndrome and sciatica and it’s associated neurological symptoms. The latter is often referred to as a nerve entrapment or “trapped nerve”.

Seddon was the first to classify nerve injuries in 1943. His classification is probably the simplest and is still used today:

• Mild injuries (Neurapraxia): temporary loss of conduction at injury site leading to sensory or motor problems; no damage to axon or surrounding sheath and connective tissue; full recovery within days or weeks.
• Moderate injuries (Axonotmesis): temporary loss of conduction below the site of injury leading to sensory or motor problems; complete disruption of axon and surrounding myelin sheath below the level of injury but connective tissue encapsulations are preserved; because the tunnels formed by connective tissue are preserved, the sprouting axon shoots are able to eventually reconnect to the target organs; the process can take some time as nerves regenerate at a speed of about 1mm/day (0.5-9mm/day).
• Severe injuries (Neurotmesis): temporary or permanent loss of conduction below the site of injury leading to severe sensory, motor and autonomic problems; partial or complete disruption of the entire nerve, including the connective tissue encapsulations; because of the discontinuity in the connective tissue tunnels and the formation of scar tissue, recovery without surgery is unlikely; also, after about a year of denervation, the sprouting axons are no longer able to connect to receptor sites on target organs such as muscle, sensory receptors may survive for many years.

In summary, and this may be obvious, nerve injuries that leave the connective tissue tunnels intact have a greater likelihood of leading to full recovery. Although it may take several months or even up to a year for this to happen. This type of injury usually results from compression injuries or mild stretch-related injuries. Severe stretch-related injuries and lacerations are more serious because they usually damage the connective tissue tunnels. This requires surgery and often leads to incomplete recovery.

Next week we’ll see how acupuncture can promote the regeneration of nerve injuries.