Peripheral nerve injury: classification, timing and repair

1. A Sunderland second-degree injury is expected to recover fully because the endoneurial tubes remain intact to guide regenerating axons back to their targets.

True

Sunderland's 1951 classification expanded Seddon's three types into five degrees by the connective-tissue layer disrupted. In a second-degree injury (Seddon's axonotmesis) the axon is interrupted and Wallerian degeneration follows, but the endoneurium is preserved, so each regenerating axon is channelled down its own tube to its original end organ and recovery is complete, though slow, at roughly 1–3 mm per day. Third-degree injuries add endoneurial disruption and recover incompletely; fourth-degree injuries disrupt the perineurium and usually need surgery; fifth-degree injuries are complete transections.

• Grinsell D, Keating CP. Peripheral nerve reconstruction after injury: a review of clinical and experimental therapies. Biomed Res Int. 2014;2014:698256. PMID 25276813
• Sunderland S. A classification of peripheral nerve injuries producing loss of function. Brain. 1951;74(4):491-516. PMID 14895767
• Menorca RM, Fussell TS, Elfar JC. Nerve physiology: mechanisms of injury and recovery. Hand Clin. 2013;29(3):317-30. PMID 23895713

2. An advancing Tinel sign after nerve repair confirms that useful functional recovery will follow.

False

A distally progressing Tinel sign shows that regenerating sensory axon sprouts are advancing along the distal stump, and its pace, roughly a millimetre a day, is used to monitor the regeneration front. It does not guarantee that axons will reach and reinnervate appropriate end organs, nor that motor or discriminative sensory function will return; misdirection, intraneural scarring and end-organ degeneration can all prevent useful recovery despite an advancing sign. Tinel's 1915 description was of a marker of regeneration, and Hoffmann described the sign independently in the same year.

• Davis EN, Chung KC. The Tinel sign: a historical perspective. Plast Reconstr Surg. 2004;114(2):494-9. PMID 15277821
• Tinel J. "Tingling" signs with peripheral nerve injuries. 1915. J Hand Surg Br. 2005;30(1):87-9. PMID 15620500

3. Fibrillation potentials on needle electromyography typically appear one to four weeks after an axonal injury, and later for more proximal lesions, rather than in the first 48 hours.

True

Fibrillation potentials are the spontaneous discharges of denervated muscle fibres and appear only once Wallerian degeneration has reached the motor end plates, which takes longer the more proximal the lesion. The accepted guideline of one to four weeks rests largely on animal data, and reviews quote three to six weeks for proximal injuries. Needle electromyography in the first days therefore cannot distinguish neurapraxia from axonotmesis, whereas nerve conduction studies in the first week can already demonstrate conduction block across a neurapraxic segment with preserved distal conduction.

• Willmott AD, White C, Dukelow SP. Fibrillation potential onset in peripheral nerve injury. Muscle Nerve. 2012;46(3):332-40. PMID 22907222
• Campbell WW. Evaluation and management of peripheral nerve injury. Clin Neurophysiol. 2008;119(9):1951-65. PMID 18482862

4. After microsurgical repair, ulnar nerve injuries have a better chance of satisfactory motor recovery than median nerve injuries.

False

In an individual-patient-data meta-analysis of 623 median and ulnar nerve repairs, the odds of satisfactory motor recovery (Medical Research Council grade 4 or 5) were 71% lower for ulnar than for median nerve injuries. Age (under 16 versus over 40 years, odds ratio 4.3), a proximal level and delay to repair (odds ratio 0.94 per month) were the other independent predictors, and only about half of all repairs achieved satisfactory motor recovery. The ulnar nerve supplies most intrinsic hand muscles, which require precise motor reinnervation over long distances, which is one reason distal nerve transfers such as anterior interosseous to deep motor ulnar are used for high ulnar injuries.

• Ruijs AC, Jaquet JB, Kalmijn S, Giele H, Hovius SE. Median and ulnar nerve injuries: a meta-analysis of predictors of motor and sensory recovery after modern microsurgical nerve repair. Plast Reconstr Surg. 2005;116(2):484-94; discussion 495-6. PMID 16079678

5. Hollow nerve conduits give outcomes equivalent to autograft for nerve gaps greater than 3 cm.

False

Hollow conduits contain no Schwann cells or basal lamina, and Schwann-cell migration into a conduit is insufficient beyond about 2 cm, so their clinical use is confined to short gaps in small sensory nerves; no conduit has demonstrated outcomes equivalent to autograft for gaps over 3 cm. A 2023 meta-analysis of gap repairs found meaningful-recovery rates of 81.6% for autograft and 87.1% for processed allograft against 62.2% for conduits even in short sensory gaps. Cabled sensory-nerve autograft remains the standard for long gaps, proximal injuries and motor or mixed nerves.

• Grinsell D, Keating CP. Peripheral nerve reconstruction after injury: a review of clinical and experimental therapies. Biomed Res Int. 2014;2014:698256. PMID 25276813
• Lans J, Eberlin KR, Evans PJ, Mercer D, Greenberg JA, Styron JF. A Systematic Review and Meta-Analysis of Nerve Gap Repair: Comparative Effectiveness of Allografts, Autografts, and Conduits. Plast Reconstr Surg. 2023;151(5):814e-827e. PMID 36728885
• Rbia N, Shin AY. The Role of Nerve Graft Substitutes in Motor and Mixed Motor/Sensory Peripheral Nerve Injuries. J Hand Surg Am. 2017;42(5):367-377. PMID 28473159