Variation in the axillary brachial plexus detected via ultrasonography and nerve stimulation from skin surface

I Introduction

When performing axillary brachial plexus block, we consider anatomical differences to increase success rate¹⁾. Recently, ultrasound-guided axillary blocks have become widespread using both ultrasound and nerve stimulator as a dual guidance method. Previous studies^2–4) have reported anatomical variations in the brachial plexus nerves in the axillary region using both ultrasonography and a needle-type nerve stimulator, i.e., (Stimuplex, B/Brawn, Germany). There are few reports that researched anatomical variation of brachial plexus using both ultrasonography and a pen-type nerve stimulator via skin for volunteers. On the other hand, most of previous references reported either left or right side of brachial plexus anatomically due to orthopedic operations. Therefore, we originally compared the difference between both sides of nerve positions for each case.

II Methods

This study was approved by the institutional review board (#4679) on 3.1.2017 and registered with University hospital Medical Information NetworkCenter (UMIN 000041569). All volunteers were doctors and nurses provided written informed consent. First, they lay in the supine position, and their arms were abducted and rotated externally with a 90 degrees elbow flection based on Winne's methods⁵⁾. We used the ultrasound device and a pen-type nerve stimulator (Stimuplex-Dig, B-Braun, Germany). The radial, median, ulnar, and musculocutaneous nerves were identified at the elbow, forearm, or wrist points using the ultrasound device and asking each subject which finger, muscle and dermatome stimulated by setting minimum current of milliamps (mA). Once each location was detected, we were sliding the probe and following nerves to the proximal side with keeping images continuously and back to axilla.

The probe was placed perpendicular at the intersection of the pectoralis major muscle with the biceps brachii to be placed the axillary artery at the center of the image and stored. The angles measured by protractor were used to create scatter plots, and the distribution of each nerve was analyzed between the left and right sides using the unpaired Student t-test.

III Results

Thirty-six volunteers were recruited and their characteristics were male: female 19:17, age; 37.5±11.9 y/o, height; 166.9±8.5 cm, body weight; 59.1±11.1 kg, and right/left handed; 35:1. The mean and standard deviation value of each nerve angle (left and right) was the following; 174±20° and 173°±16° of the radial nerve, 328°±124° and 326°±136° of the median nerve, 90°±6° and 90°±6° of the ulnar nerve and 246°±2° and 244°±2° of the musculocutaneous nerve and p-value of the difference between left and right are shown in Figure 1, without any significance.

Figure 1

Scatter plotting of each nerve and mean±SD

Top of perpendicular lines were set as zero degree and angles were measured clockwisely.

There was no significant difference between left and right side.

IV Discussion and Conclusions

Our results showed that the distribution of median and musculocutaneous nerves in the axillary region of the brachial plexus were almost similar to those of previously reported^2,3). Only one study⁴⁾ suggested distributions of all four nerves that were almost the same as ours. All previous studies were used pie charts to record axillary brachial plexus nerves. However, the angles of subdividing pie charts varied in each report, such as eight pie chart sectors used to record nerve positions¹⁾, while in others 12 pie chart sectors^2,4). Therefore, we decided to measure the angle of each nerve using original scatter plotting method to describe more precise location and diversity.

Next point of the study was using a pen-type nerve stimulator via skin for volunteers, which could be easier to collect data without scheduled orthopedic surgeries by repeating the procedure because patients with fractures were limited to stimulate due to pain or swelling, but volunteers were not and there was no time limit for the research.

Third point was to compare both left and right sides of each nerve. We first speculated that the difference in the dominant arm causes a difference in muscle mass, resulting in the difference running of the brachial plexus. However, all nerves did not have any difference of location angle. We have to add that there was no previous references to compare left and right side of brachial plexus nerves yet. However, there was one left-hand volunteer, and the absence of a power calculation should be explained as a limitation.

References

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• 2)   Christophe  JL,  Berthier  F,  Boillot  A, et al. Assessment of topographic brachial plexus nerves variations at the axilla using ultrasonography. Br J Anaesth 2009; 103: 606–12.
• 3)   Remerand  F,  Laulan  J,  Couvret  C, et al. Is the musculocutaneous nerve really in the coracobrachialis muscle when performing an axillary block? An ultrasound study. Anesth Analg 2010; 110: 1729–34.
• 4)   Ustuner  E,  Yılmaz  A,  Özgencil  E, et al. Ultrasound anatomy of the brachial plexus nerves in the neurovascular bundle at the axilla in patients undergoing upper-extremity block anesthesia. Skeletal Radiol 2013; 42: 707–13.
• 5)   Winnie  AP. Axillary perivascular technique of brachial plexus block. In: Winnie AP, Hakansson L, eds. Plexus anesthesia. Vol.1, 3^rd ed, Philadelphia, WB Saunders, 1993, pp121–43.