57 - New Bilateral Variation of the Serratus Anterior Muscle

Poster Board Number: 57
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Odd poster #s – first hour
Even poster #s – second hour

Co-authors:

William Jacobs - Student Physical Therapist, Philadelphia College of Osteopathic Medicine; Rishi Nathan - Student Physical Therapist, Philadelphia College of Osteopathic Medicine; Kole Rogers - Student Physical Therapist, Philadelphia College of Osteopathic Medicine; Philip Fabrizio - Philadelphia College of Osteopathic Medicine

Abstract Body : Introduction and Objective: Serratus Anterior muscle (SA) variations are rare. The SA typically originates from the first through the seventh rib, and inserts on the anterior surface of the medial border of the scapula and the inferior angle of the scapula. The action of the SA is protraction and upward rotation of the scapula. Previous research indicates several unilateral variations, with varying rib attachments. However, there are no reports for bilateral SA variations that are consistent with the current finding. The objective of this research was to observe and describe the variation of the muscle and determine the clinical implications of the variation.


Materials and Methods: Routine and fine dissection techniques were used to reveal the SA of a 60 year old male embalmed cadaver.



Results: A bilateral SA muscle variation was discovered. While the SA muscles demonstrated consistent typical insertions, the origins were not consistent with typical findings. The bilateral variants originated from the anterior surface of all 12 ribs and fused with the fibers of the external oblique muscles, thereby creating an indirect connection to the pelvis. The innervation by the long thoracic nerve was observed bilaterally.



Conclusions: This bilateral variation of the SA muscle presented here, has not previously been seen. The SA muscle had much broader attachments than typical, and connected to the external oblique muscles. These findings may have clinical implications.


Significance: The clinical significance may impact muscle function, range of motion (ROM), and imaging. Considering the attachment of the SA directly to the external obliques, it would be challenging to perform upward rotation and protraction of the scapula without any assistance from the external obliques at the pelvis. To achieve full ROM of protraction and upward rotation of the scapula, contraction of the ipsilateral external oblique could lead to contralateral trunk rotation. During imaging of the abdominal wall components, an extra layer of muscle may be seen, causing confusion of interpretation.