Electromyography of the infrahyoid muscles - part 1: normal findings]

BACKGROUND: The infrahyoid muscles (IHM) are very useful as a neurovascular myofascial flap in plastic reconstructive surgery of the upper aerodigestive tract, especially for restoration of the muscular component in larger tongue defects. As a base for further postoperative investigations on the function of transferred IHM this first part of the study describes the physiological function and the electromyographical features of the IHM. METHODS: In 17 patients with cancer of the upper aerodigestive tract the sternohyoid and sternothyroid muscles and in additionally eight patients the upper part of the omohyoid muscle were studied electromyographically. Muscular activity was recorded at various movements and maximal voluntary innervation. In ten healthy volunteers the motor unit potentials (MUP) during light voluntary innervation of these muscles were studied. RESULTS: In both muscles we found the steadist and strongest muscular activity at isometric head bending and yaw opening, in the omohyoid muscle also at head rotation. At swallowing and breathing in (2/3) of the cases muscular activity could be recorded. Amplitudes and electromyographic charge pattern in comparison were diminished. Phonation und tongue movements showed no noticable muscular activity. Analysis of the MUP in 10 healthy volunteers showed a mean amplitude of 274 +/- 59 microV and a mean duration of 8.5 +/- 0.6 ms. CONCLUSIONS: The presented study demonstrates that EMG of the IHM are recorded best while head bending, yaw opening and head rotation. Since there is no interchange of nerve fibres between the hypoglossal nerve and the cervical ansa it should be possible to differentiate between original tongue muscles and transferred muscles in electromyographic studies of myofascial flaps after tongue reconstruction.