Mateusz Gładysz FESSH prep

FESSH prep Compressive neuropathies Pathophysiology — compression and traction

Pathophysiology of peripheral nerve compression and traction injury

Last reviewed v1.0

FESSH-008Compressive neuropathies●●● advanced

Pathophysiology of peripheral nerve compression and traction injury.

  1. 1.Peripheral nerve compression is a combination of mechanical compression and ischaemic injury, leading to nerve dysfunction.

  2. 2.Posterior interosseous nerve syndrome at the radial tunnel typically presents with finger and thumb extension weakness without sensory loss because the superficial branch of the radial nerve has already separated proximally.

  3. 3.With continued compression, intraneural fibrosis can develop, further limiting recovery potential.

  4. 4.Nerve conduction studies in early radial nerve compression always show conduction block.

  5. 5.In experimental models, modest stretch of a peripheral nerve impairs intraneural blood flow and conduction, with measurable amplitude reduction occurring at strains as low as 6%.

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Question ID
FESSH-008
First published
Last reviewed
Version
v1.0
Answer key and explanations — open after answering

  1. 1. Peripheral nerve compression is a combination of mechanical compression and ischaemic injury, leading to nerve dysfunction.

    True

    Rydevik, Lundborg and Bagge's intravital microscopy study of the rabbit tibial nerve showed venular flow impairment at 20–30 mm Hg of applied pressure, arteriolar and intrafascicular capillary flow impairment at 40–50 mm Hg, and complete cessation at 60–80 mm Hg, establishing that mechanical compression and microvascular ischaemia are both central to compression neuropathy. Mackinnon's experimental rat model and 2002 review extend this to chronic compression, demonstrating fibrosis of the epineurium and perineurium that perpetuates ischaemia and impairs nerve gliding.

    • Rydevik B, Lundborg G, Bagge U. Effects of graded compression on intraneural blood flow. An in vivo study on rabbit tibial nerve. J Hand Surg Am. 1981;6(1):3-12. PMID 7204915
    • Mackinnon SE, Dellon AL, Hudson AR, Hunter DA. Chronic nerve compression — an experimental model in the rat. Ann Plast Surg. 1984;13(2):112-120. PMID 6476732

  2. 2. Posterior interosseous nerve syndrome at the radial tunnel typically presents with finger and thumb extension weakness without sensory loss because the superficial branch of the radial nerve has already separated proximally.

    True

    At the level of the radial tunnel the radial nerve has divided into the superficial (sensory) branch and the deep branch (continuing as the posterior interosseous nerve, PIN); compression of the PIN therefore produces a pure motor deficit — finger and thumb extension weakness — without sensory loss, in contradistinction to radial tunnel syndrome which is a pain syndrome without motor or sensory deficit.

    • Roles NC, Maudsley RH. Radial tunnel syndrome: resistant tennis elbow as a nerve entrapment. J Bone Joint Surg Br. 1972;54(3):499-508. PMID 4340924

  3. 3. With continued compression, intraneural fibrosis can develop, further limiting recovery potential.

    True

    Mackinnon and colleagues' chronic-compression rat model demonstrated alterations in the blood-nerve barrier followed by histological changes in the large myelinated fibres at the periphery of the fascicles and at the nodes of Ranvier; in Mackinnon's 2002 review, chronic compression produces thickening of the external epineurium and perineurium with connective-tissue deposition that impairs intraneural blood flow and nerve gliding, perpetuating dysfunction.

    • Mackinnon SE, Dellon AL, Hudson AR, Hunter DA. Chronic nerve compression — an experimental model in the rat. Ann Plast Surg. 1984;13(2):112-120. PMID 6476732
    • Mackinnon SE. Pathophysiology of nerve compression. Hand Clin. 2002;18(2):231-241. PMID 12371026

  4. 4. Nerve conduction studies in early radial nerve compression always show conduction block.

    False

    In Wall and colleagues' rabbit tibial nerve model, 6% strain produced a 70% reduction in action potential amplitude at one hour with full recovery, whereas only 12% strain produced complete conduction block; in clinical compression neuropathies (including radial tunnel syndrome), nerve conduction studies are frequently normal or only subtly abnormal in early disease, and Mackinnon notes that some patients with significant symptoms have normal electrodiagnostic studies because pathology resides in the connective-tissue container rather than the axons.

    • Mackinnon SE. Pathophysiology of nerve compression. Hand Clin. 2002;18(2):231-241. PMID 12371026
    • Wall EJ, Massie JB, Kwan MK, Rydevik BL, Myers RR, Garfin SR. Experimental stretch neuropathy. Changes in nerve conduction under tension. J Bone Joint Surg Br. 1992;74(1):126-129. PMID 1732240

  5. 5. In experimental models, modest stretch of a peripheral nerve impairs intraneural blood flow and conduction, with measurable amplitude reduction occurring at strains as low as 6%.

    True

    Wall and colleagues stretched rabbit tibial nerves at 0%, 6% and 12% of length: at 6% strain the action potential amplitude fell by 70% at one hour with full recovery; at 12% strain conduction was completely blocked at one hour with minimal recovery. Lundborg and Rydevik's rabbit tibial nerve work demonstrated impairment of intraneural circulation at approximately 8% elongation, and Ogata and Naito reported complete arrest of intraneural blood flow at a mean of 15.7% stretching of the rabbit sciatic nerve.

    • Wall EJ, Massie JB, Kwan MK, Rydevik BL, Myers RR, Garfin SR. Experimental stretch neuropathy. Changes in nerve conduction under tension. J Bone Joint Surg Br. 1992;74(1):126-129. PMID 1732240
    • Lundborg G, Rydevik B. Effects of stretching the tibial nerve of the rabbit. A preliminary study of the intraneural circulation and the barrier function of the perineurium. J Bone Joint Surg Br. 1973;55(2):390-401. PMID 4707307
    • Ogata K, Naito M. Blood flow of peripheral nerve effects of dissection, stretching and compression. J Hand Surg Br. 1986;11(1):10-14. PMID 3958526