Peripheral Nerve Lesions

Functional point of view

Purely sensory nerves (e.g. anterior femoral cutaneus n., sural n. etc.)

Purely motor nerves (e.g. deep branch of radial nerve at the forearm, deep branch

of ulnar nerve at the hand)

Mixed nerves (motor, sensory and sympathetic fibers). Majority of peripheral nerves (median, radial, ulnar, sciatic nerves)

axon

myelinendoneurium

perineurium

interfascicular epineurium

Connective tissuesof nerve trunks

The fascicle is the smallest nervous structure which can be sutured and anastomosed.

An axon (single nerve fiber) or its endoneurium cannot be sutured

Anatomy

epineurium

healthy nerve, myelin stain

Epineurectomy (Resection of epineurium)

• Numerous interfascicular anastomoses.

• Constantly changing fascicular pattern during the course of nerve.

• Towards the periphery, the number of these anastomoses decrease.

Interfascicularanastomoses

Clinical examination

Motor deficit

• In the beginning: atrophy and paresis (reversible).

• If denervated for long (18 months): Degenerate (irreversible) Muscle fibers replaced by connective and fat tissue.

• Repair a severed motor nerve as early as possible.

• Sensory nerves: longer denervation periods supportable.

Peripheral Nerve Vascularisation

Two vascular systems:1. Extrinsic: epineural perifascicular2. Intrinsic: intrafascicular

Numerous vascular anastomoses within and between the two systems.

The risk of an ischaemic nerve lesion is very low during peripheral nerve surgery

Within 8 days after nerve grafting, new vessels grow into the Nerve grafts from the surrounding tissue.

Classification of nerve lesions (Seddon 1943)

Neurapraxia:

• Axonal conduction impaired. • But intact structure of axon and endoneurium.

Axonotmesis:• Degeneration of endoneurial tube (axon and endoneurium).• Nerve conduction slowed

or abolished.• Perineurium and endoneurium

intact.Examples: Nerve entrapment syndromes (carpal tunnel syndrome)Radial nerve compression after fracture of humerus

Neurotmesis:• Total nerve transection

Degeneration ad Regeneration

Axonotmesis and Neurotmesis :

• Degeneration of the axons distal to the lesion.

• Only empty endoneurial tubes survive: Wallerian Degeneration.

Following Axonotmesis: Regenerating axons find their proper endoneurial tubes.

Following Neurotmesis: Regenerating axons do not or do rarely find back into their original endoneurial tubes.

Sciatic nerve neuroma 36 year afterleg amputation at thigh level

Neuroma

Normal (regular structure ofmyelinated nerve fibers)

Regeneration(so.called mini-fascicles)

Muscle Denervation

Degeneration

Atrophy: • Reversible • Decreased diameter of muscle fibers.

Degeneration: • Irreversible• Muscle replaced by fat and connective tissue

A muscle denervated for 18 monthswill degenerate .

The diagnosis of a peripheral nerve lesiondepends primarily on

a precise history and

an exact clinical examination

Additional technical examinations : often superfluous.

Traumatic nerve lesions

Open Injury

Sharp nerve transection

No loss of nerve substance. If possible Primary (immediate) nerve repair.

Traumatic nerve lesions

Open injury

Nerve laceration

Nerve ends rugged and contused.Some loss of nerve substance.Usually, repaired by using a nerve graft

Traumatic nerve lesions

Indirect lesions

Usually, a stretch-contusion injury. Example: radial nerve paresis after fracture of humerus.

Frequently, the lesion extends over long distance.

Recovery difficult.

Traumatic nerve lesions

Ischaemic lesion

Interruption of the arterial flow secondary to a Volkmann‘s ischaemic contracture

Median nerve, forearm

Avulsion of cervical roots

A forceful traction on the arm can lead to an avulsion of cervical roots from the spinal cord.

Frequently seen in motorcycle accident

Surgery

Sharp nerve transectionby piece of glass

Immediate (primary)nerve suture

Surgery

• Lacerations and contusions are repaired 2 – 3 weeks after injury by an early secondary repair.

• If the nerve cannot be repaired end-to-end without tension, an interfascicular graft interposed between the nerve stumps.

• 2 – 3 weeks after surgery, the nerve suture is stable.

• The region of surgery should be immobilised for 3 weeks.

• Physiotherapy.

Radial n. Radial n.callus

Removal of callus, external neurolysis and epineurectomy of radial nerve.

Fracture of the humerus

No neurological deficitimmediately after the injury

Some weeks later: progressiveradial nerve paresis

Surgical strategy

Open Injury with sharp nerve transection (glass, knife) and immediate neurologic deficit.

Examination: clinical only, nothing else Differential diagnosis: none Treatment: surgical.Primary (immediate) nerve repair orEarly secondary nerve repair after 2 – 3 weeks

Surgical strategy

Open Injury with nerve laceration and immediate neurologic deficit.

Examination: clinical only, nothing else Differential diagnosis: none

Treatment: surgical Early secondary nerve repair after 2 – 3 weeks,

or whenever possible

Surgical strategy

Closed lesion and immediate neurologic deficit. • Frequently, the nerve recovers spontaneously. • Regular clinical examinations (every month)

• If there is no spontaneous functional improvement after 4 months: surgery.

Surgical strategy

Closed lesion, initially no neurologic deficit, but later progressive neurologic deficit:

• Operation early after start of deficit.

Iatrogenic nerve lesion: Judgement is often difficult (lack of precise information about original surgery).

• If there is no spontaneous improvement after 4 months: surgical exploration.

Nerve Regeneration

• A muscle which has been without innervation for 18 months has practically no chance to recover.

• Period of denervation: period between injury and the arrival of regenerating axons at the surface of the muscle fibers.

• After re-establishment of the motor endplates the muscleitself must recover, too. This needs several months.

• The axons regenerate at 1 mm / day (3 cm /month)

• In case of a lesion 60 cm proximal to the target muscle:

Muscle degenerated at the arrival of regenerating axons – even if nerve repaired immediately after the trauma.

• It makes no sense to repair an ulnar nerve lesion at the brachial plexus level.

• Intrinsic muscles of the hand degenerated at the arrival of regenerating axons. The distance between site of injury and target muscles is > 60 cm).

•

Nerve Regeneration

• Discrepancy between the nerve regeneration seen by electromyography and the functional (useful) recovery or improvement.

• After surgery, EMG proof of arrival of axons at the most distal muscles in 95 % of cases.

• However, on clinical examination : muscle power either good or moderate in 61 % only.

Nerve RegenerationPrognostic factors for the result of nerve repair

(suture or grafting)Factors outside the our influence• Nerve injured (motor, sensory, mixed)• Level of lesion (proximal – distal)• Accompanying lesion (fractures etc.)• Age of patient

Factors which we can influence• Delay between injury and surgery• Surgical technique