In supine surgery, free-running EMG is often not observed, although the patient is observed to move.
Is this possible?
The free-running EMG is related to the spinal nerve, so can the movement of the muscle itself not related to the spinal nerve occur?
Electromyography (EMG), the recording of electrical activity in muscle, should be regarded as an extension of the clinical examination. It can distinguish myopathic from neurogenic muscle wasting and weakness. It can detect abnormalities such as chronic denervation or fasciculations in clinically normal muscle. It can, by determining the distribution of neurogenic abnormalities, differentiate focal nerve, plexus, or radicular pathology; and it can provide supportive evidence of the pathophysiology of peripheral neuropathy, either axonal degeneration or demyelination. EMG is an obligatory investigation in motor neurone disease to demonstrate the widespread denervation and fasciculation required for secure diagnosis.
It is doubtful that you have EMG electrodes overlying all muscles that could possibly cause a movement. In addition, the depth into a muscle EMG activity can be detected is roughly equal to the distance separating a pair of electrodes.
If nerve conduction studies are also being utilised the movement could be caused by contraction of distal muscles not being recorded via the free running EMG.
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