Optimal Placement of Needle Electromyography in Extensor Indicis: A Cadaveric Study

Area of Science:

• Anatomy
• Clinical Electrophysiology

Background:

• Accurate electrode placement is crucial for reliable electromyography (EMG) studies.
• The extensor indicis (EI) muscle is important for hand function, and precise localization is needed for targeted interventions.

Purpose of the Study:

• To anatomically identify the center of the extensor indicis (EI) muscle via cadaver dissection.
• To evaluate and compare the accuracy of three distinct needle electromyography (EMG) electrode insertion techniques.

Main Methods:

• Eighteen upper limbs from ten adult cadavers were dissected to define the EI muscle center.
• Three insertion techniques (M1, M2, M3) were assessed based on their proximity to the identified muscle center.
• Distances from the ulnar styloid process (USP) to the center (X, Y) and from each technique to the center (D1, D2, D3) were measured.

Main Results:

• The EI muscle center was located approximately 48.3 mm proximal to the USP and 7.2 mm lateral to the ulna's medial border.
• The median distances from the insertion points to the muscle center were D1=23.3 mm, D2=13.3 mm, and D3=9.0 mm.

Conclusions:

• The extensor indicis muscle center is consistently located relative to the ulnar styloid process and ulna.
• The M3 technique, involving needle insertion in the distal fourth of the forearm, lateral to the ulna, demonstrated the highest accuracy for EI muscle EMG.