Sternalis Muscle- Anatomical Variation to Anterior Thorax

Introduction: During a routine cadaver dissection, an accessory muscle was found bilaterally and superficial to the pectoralis major. The sternalis muscle is an anatomical variation not commonly seen throughout the population. Its function, although unknown, is widely debated. Innervation variations were found in studies based on proximal/distal muscle attachments. Most were found to be innervated by either external or internal thoracic nerves (55%), while others were found to be innervated by intercostal nerves (43%). In a 532 cadaver study, it was found that this muscle was present in 11% of Asians, 8% in African Americans, and 2% in Caucasian individuals. More women (8.7%) than men (6.4%) were also found with this attachment.

Objectives: The primary aim of this study is to provide further awareness to healthcare professionals of this anatomical variation as it can interfere with surgical procedures in addition to interfering with the accuracy of mammograms performed, which can increase the risk of breast cancer misdiagnosis.

Methods: This study consists of a systematic literature review of sternalis muscle attachment findings, including its function, neurovascular variations, prevalence in the population, and embryologic origins.

Results: The sternalis muscle was observed to attach proximally at the sternal notch and distally to the 10th and 11th rib .

Conclusion: Due to the results, we postulate that the sternalis muscle is involved in flexion of the thorax and/or respiration although the extent of these functions is unclear. Research surrounding the sternalis muscle is still ongoing and further studies are needed to make conclusive statements regarding its function and embryological origins.