Optimal Radial Motor Nerve Conduction Study Using Ultrasound in Healthy Adults

Abstract

ObjectiveTo obtain reference values, to suggest optimal recording and stimulation site for radial motor nerve conduction study (RmNCS), and to analyze the correlation among RmNCS parameters, demographics and ultrasonography (US) findings.MethodsA total of 55 volunteers participated in this study. We hypothesized that ‘lateral edge of spiral groove (A)’ was the optimal stimulation site, and the ‘largest cross-sectional area (CSA) of extensor indicis proprius (EIP) muscle (B)’ was the optimal recording site. The surface distance between ‘A’ and the lateral epicondyle of the humerus divided by upper arm length, was named the spiral groove ratio. The surface distance between ‘B’ and the ulnar styloid process divided by forearm length, was named the EIP ratio. Using US, we identified these sites, and further conducted RmNCS.ResultsData was collected from 100 arms of the 55 volunteers. Mean amplitude and latency were 5.7±1.1 mV and 5.7±0.5 ms, respectively, at the spiral groove, and velocity between elbow and spiral groove was 73.7±7.0 m/s. RmNCS parameters correlated significantly with height, weight, arm length, and CSA of the EIP muscle. Spiral groove ratio and EIP ratio were 0.338±0.03 and 0.201±0.03, respectively; both values were almost the same, regardless of age, sex and handedness.ConclusionWe established a reference value and standardized method of RmNCS using US. Optimal RmNCS can be conducted by placing the recording electrode 20% (about one-fifth) of forearm length from the ulnar styloid process, and stimulating at 34% (about one-third) of the humeral length from the lateral epicondyle.

Ultrasonographic Analysis of Optimal Needle Placement for Extensor Indicis

“…The needle can be placed in the extensor digiti minimi or extensor carpi ulnaris after superficial insertion or the pronator quadratus after deep insertion [ 13 , 16 ]. Third, because the EI is not clearly separated from other muscles that are innervated by the radial nerve, it is difficult to distinguish the EI from other muscles [ 17 ]. Due to the characteristics of the EI, a muscle contraction is often induced to identify the location of the muscle and insert the needle exactly.…”

Optimal recording electrode placement for radial motor nerve conduction study using extensor indicis muscle: Cadaver and electrophysiological studies

“…The active recording sites were determined based on textbooks of radial motor nerve conduction study using the extensor indicis muscle and the results of our cadaver study: two fingerbreadths proximal to the USP (Method 1) (approximately 3 cm proximal to the USP) 4,9 ; the distal 1/4 point of the forearm length (Method 2) based on the results of our cadaveric study; and the most prominent site during activation of the extensor indicis, which is frequently used in clinical practice (approximately 1 cm to 1.5 cm proximal to the recording electrode site of Method 2) (Method 3) 9 . Reference recording electrodes were located at two sites: the USP (A), as recommended by textbooks and a previous study 1,4,8,9 ; or the tendon of the extensor indicis muscle at the level of the USP (B), according to the belly‐tendon method 4 . The onset latency and baseline‐to‐peak amplitude of the compound muscle action potentials (CMAPs) were measured.…”

“…In studies using the extensor indicis muscle, the recommended location of the E1 electrode is two fingerbreadths or 2 to 4 cm proximal to the ulnar styloid process (USP) 4,9 . In contrast, a recent study using ultrasonography recommended placing the E1 electrode over a point in the distal 20% of the forearm 1 …”

“…Issues that have been raised regarding uncommon motor nerve conduction studies include recording electrode sites, stimulation sites, and types of recording electrodes 1 . Among them, questions regarding the recording electrode sites can encompass the choice of muscle, and the location of active and reference recording electrodes over the selected muscle.…”

Ultrasound guidance may have advantages over landmark‐based guidance for some nerve conduction studies

“…High‐resolution ultrasonography (US) is regarded as an effective tool in assessing the peripheral nerves of the limbs 4‐9 . Several studies have demonstrated the utility of US‐guided NCSs in more accurately applying stimulation or placing recording electrodes, particularly with regard to the lower limb nerves 10‐12 . While this focus has been on the lower limbs, upper limb nerve injuries are common, and certain nerves are at a higher risk for injury due to their anatomic locations 13 .…”