of Nerve Injuries
of Nerve Injury
block of nerve
disruption of axon with little disruption of connective tissue
disruption of axon and connective tissue
Nerve injury can be
classified into three types:
- Neuropraxia - physiologic block of nerve
conduction within an axon
without any anatomical interruption.
Many infants with birth brachial plexus injury have neuropraxia and recover spontaneously
because neuropraxia tends to disappear within 4-6 weeks.
- Axonotmesis - anatomical interruption of
the axon with no or only partial interruption of the connective
This type of nerve injury requires regrowth of the axon to the target muscle, which
takes a considerable amount of time. This regrowth can be inhibited by scar formation.
Whether patients with axonotmesis will require surgical treatment depends on the
number of disrupted axons and the extent of scar formation at the site of nerve injury.
When an axon is disrupted,
there is a 2-4 week delay before the axon starts to regenerate. Axons grow in adults
at about 1 inch per month, which means many months will be required for the axon
to grow down to the muscles in the arms. In infants, however, the axon may regenerate
more rapidly, and the distance to be covered is much less. When a muscle loses its
the nerve receptors
will disappear over a period of 12 to 18 months. This affects the timing of neurosurgical
intervention, because a repair done too late will not have receptors in the muscles
for the growing nerves.
- Neurotmesis - complete anatomical disruption
of the both the axon and all of the surrounding connective tissue (rupture of the
Birth brachial plexus injury is sometimes associated with neurotmesis. This is the
most severe type of nerve injury and has no chance of spontaneous recovery. Early
surgical treatment is necessary.