Nerve Injuries

NERVE INJURIES

• Effects of nerve injury depend upon degree of damage.

Types of neuronal injury:

1. Based on Seddon’s classification,

Nerve injury type	Injury	Axonal damage	Degeneration	Recovery	Prognosis	Features	Examples
NEUROPRAXIA	Temporary injury. Contusion of peripheral nerve occurs.	No. Axon preserved.	No	Complete recovery	Best	Physiological conduction block without anatomic disruption.	Seen in Crutch palsy, Tourniquet palsy, Saturday night palsy.
AXONOTMESIS	Disrupted axons & myelin. Intact endoneurium	Yes.	Yes.	Spontaneous	Good		Seen in, Closed fracture & Dislocations.
NEUROTMESIS	Complete anatomical section of nerve	Yes	Yes	No possible recovery	Bad		Seen in open wound.

2. Based on Sunderland’s grading of nerve injury:

I	M/C type, due to ischemia, only transient loss of function, no anatomical disruption
II	Prolonged/severe pressure, death of axon locally/ distally
III	Interruption of endoneurial tubes
IV	Fascicles becoming disorganized
V	Complete transection of nerve fibers

PATHOLOGICAL CHANGES AFTER NERVE INJURY:

• These changes were seen only in Axonotmesis & neurotmesis.
• Not seen in neuropraxia – Due to no anatomical disruption.

NERVE DEGENERATION:

Sequential changes occurring,

 Wallerian/Secondary degeneration:

• Secondary degeneration occurring distal to site nerve injury site (within 24hrs).
• Axon degeneration followed by myelin degeneration.
• Axon with its endoneurium initially breaks into small rodlets.
• All debris is cleared by Schwann cells & macrophages, resulting in Ghost tubes formation.
• Intact neurilemma.

Retrograde/primary degeneration:

• Degenerative changes in proximal fragment up to first node of Ranvier.
• Chromatolysis (Breakdown of Nissl granules) – Most Important histological sign of neuronal injury.
• Disappearance of golgi apparatus & neurofibrils.

NERVE REGENERATION:

Distal to injury:

• Rate of axon recovery – 1 mm/day.

Shows “Positive Tinel’s sign” – 

• Patient experiencing tingling sensation when skin over nerve is percussed gently from distal to proximal on nerve recovering – Sign for recovery. 
• Absent in neuropraxia.

“Motor march” – 

• Nearest muscle to injury recovers first followed by other innervated muscles from proximal to distal. 
• Seen only in axonotmesis.

Proximal to injury:

• Reappearance of Nissl granules (within 48hrs), neurofibrils & Golgi apparatus.

Note: No regeneration occurs in CNS, because it has no centrosomes.

Don’t Forget to Solve all the previous Year Question asked on NERVE INJURIES