A Proposed Safe Electromyographic Needle Insertion Technique for the Flexor Pollicis Longus Muscle Using Arterial Pulse Palpation: Preliminary Study with Ultrasonography

Electromyographic needle access to the flexor pollicis longus (FPL) is challenging because of the risk of injuries to the superficial radial nerve (SRN) or radial artery (RA), which run close to the FPL. This study aimed to investigate the safe electromyographic needle insertion point of the FPL using a newly proposed RA pulse palpation method. Fifty forearms of 25 healthy individuals were studied. At the junction of the middle and distal third of the forearm, an RA pulse was palpated, and 5 mm lateral to the pulse was determined as the preliminary needle insertion point. The distance from the vertical virtual needle pathway to the RA and SRN was measured using ultrasonography. In ultrasonography, the distances from the needle pathway to the RA and the SRN were 3.4 ± 0.8 (range, 2.1–6.0) and 5.9 ± 1.8 (range, 2.4–9.4) mm, respectively. The depth of the FPL muscle was 8.4 ± 1.7 mm. Electromyographic needle insertion into the FPL can be safely performed using the RA palpation method. The needle insertion point is 5 mm lateral to the RA pulse at the level between the middle and distal third of the forearm.