Bilateral Anatomical Variation of the Upper Serratus Anterior: A Cadaveric Dissection

Anatomical variation can have clinical implications in terms of pathology, musculature surgical considerations, and biomechanical function. While many anatomical variations have been reported, it is critical to continue to expand the record when deviations are found. According to most sources, the upper serratus anterior originates at the first and second ribs and inserts at the superior angle of the scapula. Some variations in attachments of the upper serratus anterior have been described, especially regarding variations in origin at the first few ribs. (Smith, et al., 2003). However, the literature does not describe the insertion of the serratus anterior muscle as extending along the superior border of the scapula. PURPOSE To report a bilateral anatomical variation of the upper serratus anterior discovered during routine dissection on a female specimen. METHODS While under the supervision of the anatomist at Texas Woman’s University Dallas, Doctor of Physical Therapy students dissected an 82‐year‐old Caucasian female. The students employed techniques described in Grant’s Dissector (Detton, 2017), to expose the shoulder and neck regions of the specimen. Blunt dissection techniques were utilized to expose the area further once they discovered the anatomical variation of the upper serratus anterior. Students measured the length of the upper serratus anterior that inserted on the superior border. RESULTS The cadaver with the serratus anterior variation, had the muscle attached to 56% of the superior border of her scapula. Comparatively, 3 other female cadavers of similar ages had significantly less attachment to the superior border‐‐an average of 27%, with a range from 16.7% to 32.6%. DISCUSSION Based on widely accepted descriptions of the serratus anterior attaching to the superior angle, without extending extensively onto the superior border of the scapula, and in comparison to other available cadavers, this subject had a serratus anterior with a significantly larger attachment to the superior border of the scapula. The specific actions of the upper serratus anterior include stabilizing the scapula during humeral elevation, and in upward rotation and abduction of the scapula. Therefore, this variation may have functional and clinical implications for the scapulothoracic and shoulder regions. CONCLUSIONS It appears that variations in the upper serratus anterior may not only include its rib attachments but also its scapular attachment. This may affect function including limitations in scapular rotation and shoulder elevation. Therefore, further investigation into anomalies and function of the upper serratus anterior is warranted. SA Anatomical Variation: Serratus anterior attaching to the superior angle, without extending extensively onto the superior border of the scapula. Figure 1