Anat Cell Biol.  2022 Dec;55(4):406-413. 10.5115/acb.22.076.

Variant pectoralis minor muscle: a case study with clinical relevance

• Motwani R
• Kaliappan A
• Chandrupatla M

• KMID: 2537459
• DOI: http://doi.org/10.5115/acb.22.076

Abstract

The pectoralis minor (PMn) muscle originates from the third, fourth, and fifth ribs near the costochondral junctionusually and gets inserted on the medial margin and upper surface of the coracoid process of the scapula. To look at the morphological insertion patterns and sites of attachment of the PMn muscle in the donated cadavers. Over all 19 limbs were included in the study (9 right and 10 left). Out of 19 limbs, 10 belonged to female and 9 belonged to male cadavers. The cadavers were meticulously dissected to determine the morphological insertion types and location of the attachment of the muscle. Unusual pattern of insertion was observed in 6 limbs (31.6%) out of total 19 limbs included in the study. The variations we observed does not fall completely in the classification by Le Double, hence variations we observed can be considered as new and rare variant which to our knowledge is not reported in literature. We propose this new variant to be type 4 of Le Double classification. The potential of ectopic PMn tendon should be taken into consideration and tested out, especially in patients with shoulder discomfort and stiffening who have ruled out the more frequent diseases. For proper surgical planning, a preoperative magnetic resonance imaging or USG examination of the shoulder joint is required considering the prevalence of variation in the insertion pattern of PMn muscle. Preoperative identification of any abnormal PMn insertion can help to reduce the risk of iatrogenic tendon injury and post-operative problems.

Keyword

Pectoralis minor; Variation; Origin; Insertion; Aponeurosis

Figure

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  Fig. 1 Showing dissected pectoral region, with the variation in the origin of pectoralis minor (PMn) muscle bilaterally. Right pectoralis minor (RPMn) and left pectoralis minor (LPMn) muscles taking origin from second to fifth ribs near their costochondral junction. MS, manubrium sternum (red asterisk, sternal angle); LBB, left biceps brachi; LCB, left coracobrachialis; RBB, right biceps brachi; RCB, right coracobrachialis; CC, costal cartilage; LSCM, left sternocleidomastoid muscle.

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  Fig. 2 Showing variant form of insertion of pectoralis minor (PMn) muscle in cadaver-1. Dual insertion of PMn in right side (A) and in left side (B), in the form of medial tendon (Ten) and lateral aponeurosis (Apo). MCN, musculocutaneous nerve; MPN, medial pectoral nerve; SHBB, short head of biceps brachii; CB, coracobrachialis; CP, coracoid process.

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  Fig. 3 Showing variant form of insertion of pectoralis minor (PMn) muscle in cadaver-2. (A) Right PMn is with two tendons, superficial tendon (SpT) and deep tendon (DpT). DpT is inserted on the coracoid process (red asterisk) along with coracobrachialis (CB) and short head of biceps brachii (SHBB). SpT got merged with the capsule of the shoulder joint and inserted at upper part of greater tubercle along with supraspinatus muscle. (B) Left PMn muscle (cut) inserted as a single tendon gets merged with the capsule of the shoulder joint and was inserted at upper part of greater tubercle. Cap, capsule of shoulder joint; Cla, clavicle; HH, humeral head; LHBB, long head of biceps brachii.

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  Fig. 4 Showing variant form of insertion of pectoralis minor (PMn) muscle in cadaver-1. (A) Right PMn where tendon (Ten) part is crossing the coracoid process (red asterisk). (B) Left side PMn Ten crossing the coracoid process (red asterisk) and entering deep to coracoacromial ligament (CAL). SHBB, short head of biceps brachii; CB, coracobrachialis; AA, axillary artery; Cla, clavicle; HH, humeral head; Apo, aponeurosis; AP, acromion process.

Reference

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