Safe Approach for Flexor Digitorum Profundus I and II Using the Palmaris Longus Tendon

To investigate a safe and accurate approach to achieve needle insertion for electromyography (EMG) of the flexor digitorum profundus (FDP) I and II muscles by identifying the anatomic relationship between the palmaris longus (PL) tendon, FDP muscle, and neurovascular bundle using ultrasonography.

Descriptive study SETTING: Department of physical medicine and rehabilitation.

Healthy individuals (age, 20-70y) without any diseases (N=29; 15 men, 14 women; 58 forearms).

Ultrasonography.

The FDP I and II muscles were transversely scanned on the volar aspect of the forearm at the junction of the middle and distal third between the medial epicondyle and ulnar styloid process. The distances and angles from the medial border of the PL tendon to FDP I, FDP II, and median nerve were measured.

The probability of damage to the neurovascular structures and the accuracy of entering the FDP I and II muscles were calculated for 3 imaginary needle insertion angles (61.7°, 100.6°, and 90°). When the needle was inserted at an angle of 61.7°, it reached FDP I with an accuracy of 91.4%. Upon needle insertions at 90° and 100.6°, the needle reached FDP II with accuracies of 90% and 89.6%, respectively. In all 3 cases (61.7°, 90°, and 100.6°), there was no chance of penetrating the blood vessels or nerves.

EMG of FDP I and II can be performed precisely and safely with the anterior approach at the distal one-third between the medial epicondyle and ulnar styloid process using the PL tendon.