Anatomy
- Formed from spinal nerves
- 31 pairs of spinal nerves
- Peripheral nerves are mixed nerves – carry motor, sensory and autonomous innervation to the limbs
- An individual nerve fibre is enclosed in a collagen connective tissue called an endoneurium
- A bundle of these nerve fibres are bound together by fibrous tissue (perineurium) to form a fasciculus
- A number of fasciculi are bound together by a fibrous tissue sheath called an epineurium
Etiology
- Fractures and dislocations – most common cause
- Direct injury – cuts, lacerations
- Infections – leprosy
- Mechanical injury – compression, traction, friction
- Frostbite, thermal injury
- Toxic agents – tetracycline injection can cause radial nerve palsy
- Radiation for cancer treatment
Classification – Seddon’s Classification
- Classified injuries into 3 types
Neurapraxia
- Physiological disruption of conduction in the nerve fibre
- No structural change
- No Wallerian degeneration
- Complete recovery occurs within a few weeks
Axonotmesis
- Axons are damaged but the internal architecture of the nerve is preserved
- Wallerian degeneration occurs
- Recovery may be spontaneous but can take several months
Neurotmesis
- Structure of the nerve is damaged by cutting or scarring of a segment
- Wallerian degeneration occurs
- Spontaneous recovery is not possible; nerve repair is required
Diagnosis
Attitude and deformity
- Wrist drop – wrist remains in palmar flexion due to weakness of dorsiflexors (radial nerve palsy)
- Foot drop – foot remains in plantar flexion due to weakness of dorsiflexors (common peroneal nerve palsy)
- Claw hand – hyperextension at the MCP joint and flexion at the PIP and DIP joints, due to paralysis of the lumbricals (ulnar nerve palsy)
- Ape thumb – thumb is in the same plane as the wrist (median nerve palsy)
- Waiter’s tip – arm hangs by the side of the body with elbow extended and arm fully pronated (brachial plexus palsy – specially C5-C6)
Muscle wasting
- Thenar eminence – median nerve
- Hypothenar eminence – ulnar nerve
- Hollowing between metacarpals – ulnar nerve
- Thigh wasting – femoral nerve
- Calf wasting – sciatic nerve
Skin
- Becomes dry – there is lack of sweating due to involvement of sympathetic nerves
- Pallor, cyanosis
- Shiny, atrophic nails
- Ulcers
Sensory examination – changes in sensations of touch, pain, temperature and vibration
Reflexes – decreased/absent reflexes
Motor examination of muscles
Nerve conduction studies
- Electromyography – assesses function at the neuromuscular junction
- Nerve conduction velocity – assesses large myelinated fibres
Treatment
- Observation with EMG
- Direct muscular neurotisation – for irreparable nerve ending at risk of forming neuroma
- Surgical repair
- Nerve grafting
- Nerve transfer