Electrophysiological analysis of the patients with hourglass-like constriction of radial nerve/posterior interosseous nerve

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Objective To analyze the electrophysiological characteristics of the patients with hourglass-like constriction of radial nerve (RN)/posterior interosseous nerve (PIN) and explore the possible causes. Methods From January 2011 to November 2018, 18 patients with hourglass-like constriction of RN/PIN were treated in our hospital. The electrophysiological results of them were analyzed retrospectively. The extent and degree of lesion involvement were evaluated. Results The course of disease was 3 weeks to 13 months before electrophysiological examination in 18 patients. 14 patients (77.8%) suffered from complete injury and 4 patients (22.1%) suffered from incomplete injury. The coincidence rate between electrophysiological results and intraoperative findings was 94.4%. In addition to the abnormalities directly related to hourglass-like constriction, 88.9% of RN hourglass-like constriction patients and 11.1% of PIN hourglass-like constriction patients were associated with other neurological abnormalities. Among them, 8 patients with RN hourglass-like constriction were complicated with the abnormalities of median nerve (50%), ulnar nerve (50%), musculocutaneous nerve (37.5%), axillary nerve (25%), suprascapular nerve (25%), triceps brachii branch (75%), and the nerves of contralateral upper extremity (25%), contralateral phrenic nerve (12.5%) and the nerves of four extremities (12.5%). The main manifestations were abnormal insertion potential, resting spontaneous fibrillation potential, prolongation of light contraction time limit, simple phase of forced contraction and decrease of amplitude of motor evoked potential in sensory and motor nerve conduction. There was no obvious abnormality in nerve conduction velocity. Conclusion The hourglass-like constriction of RN/PIN is often associated with other neural abnormalities. The higher the location of hourglass-like constriction, the wider the range of involvement. It is different from the electrophysiological characteristics of peripheral nerve entrapment, indicating possible presence of neuralgic amyotrophy. Key words: Electrophysiology; Radial nerve; Posterior interosseous nerve; Hourglass-like constriction