Neurophysiological investigation of posterior interosseous nerve entrapment causing lateral elbow pain

Entrapment of the posterior interosseous nerve has been distinguished as one cause of 'lateral elbow' pain. However, this diagnosis has been confirmed by routine neurophysiological techniques in rather few cases. In order to investigate if a more elaborate neurophysiological technique would lend further support to the entrapment diagnosis, a study was undertaken including determination of the nerve conduction during active contraction of the supinator muscle and a quantified analysis of EMG. Motor conduction velocity of the deep radial nerve at rest did not differ from normal contol subjects. On active resisted supination patients showed a higher frequency of conduction time prolongation at low and moderate contraction strengths. Motor unit analysis showed a significant increase of amplitude, duration, and number of phases among EDC motor units in patients as compared with controls. The study supports the possibility of an entrapment aetiology in cases with lateral elbow pain in combination with local tenderness of the posterior interosseous nerve where it passes through the supinator muscle.