MYOLINE concentric EMG needle

The concentric needle is the basic tool of detection EMG. A hollow cannula carries an insulated central wire; the recording surface is the cross-section of that wire, of the order of a few hundredths of a square millimetre. That smallness is what allows a motor unit potential to be isolated from the noise of the whole muscle.

Choosing the size is not a preference, it follows from anatomy. A first dorsal interosseous is sampled with a short, fine needle; a gluteus medius or tibialis posterior demands length, otherwise the tip stays in subcutaneous tissue and records nothing usable.

The MYOLINE colour code carries that information. White for 20 x 0.35 mm, violet for 25 x 0.30 mm, red for 30 x 0.35 mm, orange for 30 x 0.45 mm, grey for 40 x 0.35 mm, black for 40 x 0.45 mm, green for 50 x 0.35 mm, yellow for 50 x 0.45 mm, blue for 60 x 0.50 mm, brown for 75 x 0.60 mm. Operators quote the colour before the dimension, and it is the colour to trust when reaching for the box.

Diameter plays on two opposing things. Finer is less painful and less traumatic; thicker is stiffer, so easier to steer into a deep muscle. Between 0.35 and 0.45 mm, the difference is felt at insertion.

They connect to a separately referenced lead, in 100 or 200 cm. The needle is sterile and single use: it is not resterilised, and a blunt needle distorts recruitment as much as it hurts.