Describing the sternalis muscle: a new variant and an amended classification.

PURPOSE: With emphasis on the clinical setting, knowledge of anatomical variation decreases misdiagnoses and surgical complications. We report a previously undocumented variant of sternalis muscle and recommend an augmented classification scheme.

METHODS: Dissection of the anterior thoracic wall on an 83-year-old female cadaver revealed bilateral sternalis muscles. The Snosek et al. classification system was referenced to describe the variant types.

RESULTS: The right sternalis muscle has a single belly and can be classified using the Snosek et al. classification system as a simple type, right single. The left sternalis muscle presented with three muscle bellies, each having a unique pattern of superior attachments (heads). This variation is previously undocumented and requires a more detailed classification.

CONCLUSIONS: We propose the addition of a new subtype of sternalis classification, as well as a modification to the Snosek et al. (Clin Anat 27:866-884, 2014) classification scheme, to include classification of different muscle bellies when multiple are present.