Single-fibre and macro EMG needle

The single-fibre electrode carries a lateral recording surface of 25 micrometres, a hundred times smaller than that of a concentric. At that scale you no longer record a whole motor unit but one or two isolated muscle fibres.

That is what allows jitter to be measured, the variability of the interval between two fibre potentials belonging to the same motor unit. Jitter is the reference study of neuromuscular transmission, and it often decides a suspicion of myasthenia when repetitive stimulation is negative.

Fibre density is measured with the same electrode: how many fibres of the same motor unit lie within the pickup radius. It rises in reinnervation processes.

The macro needle does the opposite. Its cannula, uninsulated over a long stretch, picks up the full territory of the motor unit, giving a global measure of its size. Single fibre and macro thus bracket the concentric, one by detail, the other by the whole.

Two lengths in single fibre, 25 and 37 mm at 0.45 mm, and a macro in 37 x 0.45 mm. Sterile, single use, in boxes of five: these are specialised studies, not routine consumables.