Peripheral nerves like those
found in the foot can be injured by many mechanisms--blunt force to the nerve,
chronic low-grade pressure from weight bearing or surrounding tissue swelling,
lacerations, or excessive stretching, for example.
The nerve injury is most commonly
classified in one of two ways.
Sutherland Classification of Nerve Injury
with only local changes to the nerve sheath (myelin).
Incomplete injury to the nerve axons (the functional unit of the nerve).
Nerve itself is still intact.
axonal injury with scar tissue. Nerve itself may be injured, but is still
disruption of axon. Nerve itself may be severely injured, but is still
transection of the nerve.
Seddon's Classification of Nerve Injury
probably the most well-known classification system.
injury to the nerve covering (called the myelin sheath), but
not the nerve, by trauma or compression, which causes blockage of the nerve
signals. Larger nerves covered by greater amounts of myelin are most
susceptible to this injury. Reflexes, muscle function, vibratory and
two-point discrimination are typically lost, while pain, temperature and
autonomic function (sweating and circulatory regulation controlled by
nerves) is typically preserved. Repair may take days to months and
healing is usually perfect as only the sheath need be repaired. This
corresponds to Sutherland's 1st Degree injury.
disruption of the nerve itself, but the surrounding and
supportive nerve myelin sheath is not affected. Causes include long or
severe periods of compression, pulling or loss of blood flow to the
nerve. All nerve types may be affected. Nerve fibre healing
occurs at a rate of 1mm per day from the point of injury. Recovery is
usually good, though the further from the spine the injury occurs, the
better the prognosis. This corresponds to a 2nd or 3rd degree
injury in Sutherland's system.
disruption of both the nerve
fibre and the supportive myelin
sheath. This injury may be seen with severe trauma such as lacerations,
gunshot wounds, open bone fractures, punctures, and exposure to
toxins. Healing is usually poor without surgical repair. This
corresponds to a 4th or 5th degree injury in Sutherland's system.