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The double-crush hypothesis(DCH)proposes that a proximal lesion along an axon predisposes it to injury at a more distal site along its course through impaired axoplasmic flow.Although this hypothesis has been accepted,it has anatomic and pathophysiologic restrictions that limit its application as an explanation for coexisting cervical root lesions(CRLs) and carpal tunnel syndrome(CTS)or ulnar neuropathy at the elbow(UN-E).We retrospectively surveyed all electrodiagnostic(EDX)reports of coexisting CTS or UN-E and CRL for anatomic correlation,if any,between the proximal root lesion and the distal entrapment neuropathy.In the period between January 1982 and August 1995 there were 12,736 limbs with CTS or UN-E.In 435 of these limbs(3.4%),there was a coexisting CRL but only 98(0.8%)had an association that was anatomically appropriate.Moreover,only 69(0.5%)of the 98 cases demonstrated axon loss at the distal lesion site on EDX examination.Therefore,cumulatively,only 69 of our 12,736 cases of CTS and UN-E satisfied the pathophysiologic and one of the anatomic requirements of the DCH.Our data thus suggest that a CRL can seldom serve as the proximal lesion with these entrapment neuropathies in the DCH. |
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