In Sunderland's classification of nerve injuries, Grade IV injury is characterized by:

• A Loss of axonal continuity with intact endoneurium — axonotmesis
• B Disruption of axon and endoneurium, but perineurium intact
• C Complete transection of the entire nerve trunk
• D Disruption of axon, endoneurium, and perineurium, with intact epineurium ✓

Explanation

Sunderland expanded Seddon's classification into 5 grades: Grade I = neuropraxia (conduction block, no structural loss); Grade II = axonotmesis with intact endoneurium (Seddon's axonotmesis); Grade III = axon and endoneurium disrupted, perineurium intact; Grade IV = axon, endoneurium, and perineurium all disrupted, only epineurium intact; Grade V = complete nerve trunk transection (neurotmesis). Grade IV injuries have poor prognosis for spontaneous recovery due to loss of fascicular architecture; surgical exploration and fascicular repair are usually required.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

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