A novel technique for recording from the serratus anterior.
OBJECTIVE
To design an electrodiagnostic technique by which to accurately record the serratus anterior compound muscle action potential (CMAP).


METHODS
Observational study.


METHODS
Academic electromyography laboratory.


METHODS
Fifteen healthy volunteers.


METHODS
The long thoracic nerve was stimulated by using a standard bipolar surface electrode in the axilla, just anterior to the midaxillary line. The serratus anterior CMAP was recorded by using a self-adhesive, 8.0 x 0.5 cm, ring electrode as the E1 placed across the serratus anterior interdigitations starting at the nipple level. A self-adhesive, motor (1 x 1 cm) electrode was used as E2 and placed over the seventh rib. A standard self-adhesive ground electrode was placed over the inferior region of the latissimus dorsi.


METHODS
Distal motor latency (DML), and CMAP amplitude and duration.


RESULTS
After removing 2 outliers, the results are reported as the mean +/- 1.96 standard deviations. Right long thoracic DML was 2.2+/-1.0ms and the left was 2.3+/-0.9ms, with a side-to-side mean difference of 0.3+/-0.4ms. The right serratus CMAP amplitude was 3.8+/-3.9mV and the left was 3.9+/-3.7mV, with a side-to-side mean difference of 0.6+/-1.2mV. Statistical analysis did not reveal a significant side-to-side difference for DML or CMAP amplitude. Both sides were combined to form a single set of trials for DML and CMAP amplitude. The mean DML became 2.2+/-0.7ms, and the CMAP amplitude was 3.5+/-1.9mV. The CMAP duration was 14.5+/-4.3ms on the right and 14.5+/-4.1ms on the left. A significant, positive correlation existed between height and DML ( P <.02). The 95% confidence intervals for DML and CMAP amplitudes were 2.1 to 2.5ms and 1.5 to 3.1mV, respectively.


CONCLUSIONS
Our latency, side-to-side comparisons and amplitude data were consistent with other motor nerve conduction findings in the literature. Stimulating the long thoracic nerve in the axilla will provide a reliable technique to aid in the diagnosis and treatment of long thoracic neuropathy.
Depalma
Michael J
MJ
Department of Physical Medicine and Rehabilitation, Ohio State University, Columbus, OH 43120, USA.
Pease
William S
WS
Johnson
Ernest W
EW
Kadyan
Vivek
V
D000200:Action Potentials / Q000502:physiology*; D000328:Adult; D004558:Electric Stimulation; D004576:Electromyography / Q000379:methods*; D005260:Female; D006801:Humans; D007366:Intercostal Muscles / Q000502:physiology*; D008297:Male; D009431:Neural Conduction / Q000502:physiology; D011930:Reaction Time / Q000502:physiology; D012016:Reference Values; D013900:Thoracic Nerves / Q000502:physiology*