Classification of unusual insertion of the pectoralis minor muscle
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The pectoralis minor muscle (PMi) generally originates from the third, fourth, and fifth ribs and inserts on the medial and superior margins of the anterior portion of the coracoid process. Variations in the shape and attachment point of the PMi could cause discomfort in the shoulders. The aim of this study was to observe the types of morphological insertion patterns and attachment sites of the PMi.
Seventy-four sides of fresh, embalmed Korean (42 sides; mean age 78 years) and Thai (32 sides; mean age 78 years) cadavers were dissected to analyze the morphological insertion types and attachment sites of the PMi.
Unusual insertion patterns were evident in about 23% of the samples. When the portion of the PMi tendon ran over the coracoid process, the most common attachment site was the glenohumeral joint capsule. We also confirmed the attachment of the PMi to the clavicle. Costal attachments of the PMi that extend from the second rib to the fourth rib were observed frequently as well.
Unusual insertion patterns of the PMi are common. Some authors consider that tendon attachment to the joint capsule can cause shoulder pain. In addition, the PMi tendon could be utilized in acromioclavicular joint reconstruction. Surgeons need to be aware of the possibility of a PMi variant being found during surgery even when this is not visible in magnetic resonance or ultrasound imaging.
KeywordsPectoralis minor muscle Coracoid process Glenohumeral joint capsule Coracohumeral ligament Clavicle Variation
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (No.2018R1A5A7023490).
K-SH: project/project development, manuscript editing. K-WL: project/project development, data collection, analysis, manuscript writing. Y-JC: data collection, providing anatomical opinion. H-JL: data collection, providing anatomical opinion. Y-CG: data collection, providing anatomical opinion, data analysis. H-JK: providing anatomical opinion. TT: providing clinical opinion and practical reference.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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