Ann Rehabil Med.  2018 Jun;42(3):473-476. 10.5535/arm.2018.42.3.473.

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

• Im JY
• Park HB
• Lee SJ
• Lim SG
• Kim KH
• Kim D
• Rhyu IJ
• Park BK
• Kim DH

• KMID: 2417840
• DOI: http://doi.org/10.5535/arm.2018.42.3.473

Abstract

OBJECTIVE
To identify the center of extensor indicis (EI) muscle through cadaver dissection and compare the accuracy of different techniques for needle electromyography (EMG) electrode insertion.
METHODS
Eighteen upper limbs of 10 adult cadavers were dissected. The center of trigonal EI muscle was defined as the point where the three medians of the triangle intersect. Three different needle electrode insertion techniques were introduced: M1, 2.5 cm above the lower border of ulnar styloid process (USP), lateral aspect of the ulna; M2, 2 finger breadths (FB) proximal to USP, lateral aspect of the ulna; and M3, distal fourth of the forearm, lateral aspect of the ulna. The distance from USP to the center (X) parallel to the line between radial head to USP, and from medial border of ulna to the center (Y) were measured. The distances between 3 different points (M1- M3) and the center were measured (marked as D1, D2, and D3, respectively).
RESULTS
The median value of X was 48.3 mm and that of Y was 7.2 mm. The median values of D1, D2 and D3 were 23.3 mm, 13.3 mm and 9.0 mm, respectively.
CONCLUSION
The center of EI muscle is located approximately 4.8 cm proximal to USP level and 7.2 mm lateral to the medial border of the ulna. Among the three methods, the technique placing the needle electrode at distal fourth of the forearm and lateral to the radial side of the ulna bone (M3) is the most accurate and closest to the center of the EI muscle.

Keyword

Electrodiagnosis; Electromyography; Cadaver; Needles; Extensor indicis

MeSH Terms

Adult
Cadaver*
Electrodes
Electrodiagnosis
Electromyography*
Fingers
Forearm
Head
Humans
Needles*
Ulna
Upper Extremity

Figure

• 

  Fig. 1. Schematic diagram of center (C) of extensor indicis (EI) muscle (left forearm pronated with dorsal view). (A) The triangle formed by three points (O1, O2, and MT) in EI muscle. (B) The center of EI (C) was defined as the centroid of the triangle. O1, distal origin of EI muscle; O2, proximal origin of EI muscle; MT, musculotendinous junction of EI; USP, the lower border of ulnar styloid process.

• 

  Fig. 2. Parameters measured in the cadaver (left forearm pronated with dorsal view). A, angle between ulna and the line connecting the proximal origin of extensor indicis (EI) muscle and C; MT, musculotendinous junction of EI muscle; M1, 2.5 cm above the lower border of USP lateral aspect of the ulnar bone; M2, 2 finger breadths proximal to USP, lateral aspect of the ulna; M3, distal fourth of the forearm, lateral aspect of the ulna; O1, distal origin of EI muscle; O2, proximal origin of EI muscle; C, center of EI muscle; USP, tip of ulnar styloid process; C_X, distance between USP and C; C_Y, distance from medial border of ulnar bone to C.

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