ANATOMICAL VARIATION OF THE LATISSIMUS DORSI AXILLARY ARCH

Purpose: To report an additional anterior attachment of the left latissimus dorsi muscle found in a male cadaver during gross anatomy laboratory dissection of the upper extremity. Methods: During standard dissection of the upper extremity at the UNT Health Science Center Anatomy Cadaver laboratory, we noticed an additional attachment for latissimus dorsi in the left axilla of a male cadaver acquired through the UNT HSC Wiled Body Program. The muscle was thoroughly dissected, described, and photographed for presentation of this case study. Results: The donor possessed the regular attachments for the latissiums dorsi muscle bilaterally. We also observed a group of muscle fibers on the left that appear to have separated from latissimus dorsi to create an anomalous arch of muscular tissue through the axilla. This group of muscle fibers measured 15 cm by 4 cm and attached to latissimus dorsi on the anterior, medial aspect of its humeral insertion. The belly of the anomalous muscle crosses over the brachial plexus and the short head of the biceps brachii muscle and attaches to the long head of the biceps brachii muscle. This muscular arch through the axilla is unusual in that it has no bony attachments, making it more likely that this slip of muscle is a developmental anomaly of latissimus dorsi. Conclusions: Latissimus dorsi is a powerful adductor, extensor, and medial rotator of the arm. Due to the position of the extra attachment of the latissimus dorsi on the left side in this case, we hypothesize that during the donor's lifetime the degree of abduction achieved by the left side may have been greatly constrained compared to the right by the extra muscle's unique attachment closer to the more superior ventral aspect of the body. The more anterior insertion may have also restricted extension to a certain extent, but medial rotation and adduction may have been strengthened. In addition, because of the close proximity of the muscle's belly to the brachial plexus, and especially the median and ulnar nerves, we suspect that when this portion of the latissimus dorsi was activated, the donor may have experienced paresthesia of his anterior hand and/or motor deficits involving the intrinsic hand muscles, thenar muscles and anterior forearm muscles.