A novel needle insertion technique for electromyography targeting the flexor digitorum profundus (Digits 2 and 3): A cadaveric validation study

The flexor digitorum profundus (FDP) muscle plays a crucial role in finger flexion and is innervated by the anterior interosseous and ulnar nerves. Electromyographic evaluation of the FDP is essential in diagnosing neuromuscular disorders but carries a risk of neurovascular injury due to the complexity of accurate needle placement. This study aimed to evaluate the anatomical feasibility of a landmark-based needle insertion technique for the index- and middle-finger portions of the FDP in fresh cadaveric specimens by assessing targeting accuracy and the distances from the insertion point to the median nerve and ulnar artery. A cadaveric study was conducted using 21 upper limbs from 11 specimens. Needles were inserted into FDP 1 (digit 2) and FDP 2 (digit 3), using the palmaris longus tendon as a key anatomical landmark. India ink injections were performed at the needle tip to verify correct placement relative to neurovascular structures. The accuracy of placement, distances from the median nerve and ulnar artery, and muscle widths were measured. Anatomical targeting was successful for FDP 1 (digit 2) in 19 of 21 limbs (90.5%) and for FDP 2 (digit 3) in 17 of 21 limbs (81%). The median horizontal distances from the needle insertion point to the median nerve and ulnar artery were 7.0 mm and 9.5 mm, respectively, providing anatomical reference data for needle placement. The median muscle widths were 8.8 mm for FDP 1 and 9.4 mm for FDP 2. These findings support the feasibility of landmark-based needle placement in the FDP, with a high anatomical targeting rate for FDP 1. This anatomical landmark-based technique may provide a useful option for electromyographic evaluation of the FDP, particularly FDP 1, when real-time imaging is unavailable. However, FDP 2 showed lower targeting accuracy. Further clinical studies are needed to evaluate the safety and practicality of this technique in patients.