Morphology and Morphometry of the Pectoralis Minor Muscle: A Cadaveric Cross-sectional Study

Abstract

Introduction: Shoulder pain is a common clinical presentation and can be attributed to an anatomically anomalous insertion of the Pectoralis Minor (PMn) muscle tendon into the glenohumeral joint capsule. Therefore, understanding these anomalous patterns is crucial for clinicians in diagnosing and treating patients to prevent misdiagnosis and iatrogenic injury. Aim: To analyse the morphological patterns in the origin and insertion of the PMn muscle and to assess the morphometric dimensions of the muscle. Materials and Methods: This observational cross-sectional study was conducted on 60 upper limbs from 30 embalmed cadavers of both sexes. The specimens were obtained from the Department of Anatomy, ESIC Medical College and Hospital, Hyderabad, Telangana, India, between November 2018 and January 2023. The PMn muscles were thoroughly examined, and the various patterns in the origin and insertion were recorded. The length of the muscle was measured from the sternocostal junction of the inferior aspect of the fourth rib to the medial border of the coracoid process. The width of the muscle was measured at the midclavicular line and at the insertion. The frequency and percentage of each pattern were recorded and statistically analysed. Results: The present study found that the origin of PMn Type-2 was predominantly observed, with an incidence of 86.6%. Type-1 was observed in 6.7% of the upper limbs, while Type-3 was observed in 6.7% as well. Regarding the insertion of the PMn, Type-1 was predominantly observed, with an incidence of 76.7%. Type-2 was observed in 20% of the upper limbs, and Type-3 in 3.3%. The average length of the muscle was 14.01 cm, while the average width at the midclavicular line and at the insertion were 6.16 cm and 1.69 cm, respectively. Conclusion: A high incidence of Type-2 patterns in the origin, and Type-1 was predominant in the insertion of the pectoralis minor muscle. Knowledge of the morphometric measurements of the PMn muscle would be valuable for surgeons performing surgeries in the shoulder and pectoral region.