Available online 7 April 2024, 152264

Author links open overlay panel, , , , , , ABSTRACTBackground

The pectoralis minor muscle is located in the anterior thoracic wall. Typically, is constituted by a single belly originating from the 3rd to the 5th rib and inserted into the coracoid process near the origins of the biceps brachii shorth head and of the coracobrachialis muscle. The current study, on human fetuses, aims to detect all morphological muscle variants and to create a new classification system.

Material and Methods

Classical dissection of the thoracic wall and the upper limb was bilaterally performed on 25 (13 male and 12 female) human formalin-fixed fetuses aged 18-38 weeks of gestation. The spontaneously aborted fetuses were donated after parental consent to the Medical University anatomy program. The pectoralis minor muscle’s morphology, the number of the muscle’s bellies, their origins, and insertions, as well as the morphometric details of each belly of the pectoralis minor, were assessed.

Results

The pectoralis minor was bilaterally found in all fetuses (50 cases). Three types of muscle were identified based on the number of muscle bellies. In type, I (typical anatomy), were classified the cases with a single belly (in 66%). This type was divided into two subtypes (Ia and Ib). In the subtype Ia, the single belly had a typical course, and in Ib, a proximal attachment was characterized by two small bellies connecting together and creating one muscular mass. In type II, two bellies (24%), and in type III, three bellies (10%) were identified.

Conclusions

Pectoralis minor is morphologically variable in the number of its bellies, its course, its origins, its insertions, and the location of its proximal attachments. The most common type (typical anatomy) was the type I represented by one belly. Other identified variants in the number of bellies by the present study may be hypothetically a result of prematurely terminated embryogenesis.

Section snippetsINTRODUCTION

The pectoralis minor muscle (Pm) is one of the accessory inspiratory muscles, located in the anterior thoracic wall. Typically, has a single belly originating from the 3rd to the 5th rib (by aponeurotic slips), close to their costal cartilages, and inserted onto the anterior half of the medial border and the upper surface of the coracoid process (CP) of the scapula, adjacent to the origins of the short head of the biceps brachii and the coracobrachialis muscle. The Pm is innervated by the

MATERIALS AND METHODS

Twenty-five (13 male and 12 female) spontaneously aborted human fetuses (25 left and 25 right) aged 18-38 weeks of gestation at death and fixed in 10% formalin solution were examined. The fetuses were donated after parental consent to the Medical University anatomy program. Their ages were determined based on craniosacral and head measurements. The dissection started with the removal of the skin and superficial fascia from the thoracic wall and abdomen, the shoulder area, and the anterior and

RESULTS

The Pm was bilaterally found in all fetuses (50 sides). Three morphological types (I, II, and III) were differentiated based on the number of muscle bellies. All cases were innervated by the lateral and medial pectoral nerves and supplied by the axillary artery branches.

Type I with one muscle belly, identified in 66% of the cases. The type I was subdivided into two subtypes (Ia and Ib). The subtype Ia (in 58%) was characterized by a belly originating from the 3rd to 5th, or the 2nd to 5th or

Statistical analysis

Statista 13 software [TIBCO Software Inc. (2017). Statistica. http://statistica.io.] was used for calculations. To compare nominal data between groups, the Chi2 test was employed. As the continuous data in the subgroups did not demonstrate a normal distribution, they were compared using nonparametric tests. Morphometric parameters between groups were compared using the Kruskal-Wallis test by ranks with a dedicated post hoc test. A p-value of less than 0.05 was considered significant and

DISCUSSION

The present study showed that the Pm is morphologically variable in the number of muscle bellies, in its course of insertion, and location of proximal attachments. In the literature, there are also descriptions of the Pm variants. The exact reason of the occurrence of these variants is not known, but disturbed embryological development, or generic, or phylogenetic factors are considered the possible causes (Schwarz and Hirtler, 2019).

In the first developmental stage (5-week embryo), the Pm and

CONCLUSIONS

Pm is morphologically variable not only in the number of muscle bellies, but also in the course of its insertions, or the location of its proximal attachments. The most common type among fetuses was type I represented by a single belly. Other variations in the number of bellies observed in the present study may be hypothetically a result of prematurely terminated embryogenesis.

Ethical approval and consent to participate

The study protocol was accepted by the Bioethics Committee of the Medical University of Lodz (resolution RNN/137/20/KE). The cadavers were the property of the Department of Anatomical Dissection and Donation, Medical University of Lodz. Informed consent was obtained from all participants before they died.

Consent to publish

Not applicable.

Funding

The authors have no financial or personal relationship with any third party whose interests could be positively or negatively influenced by the article’s content. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

CRediT authorship contribution statement

Lukasz Olewnik: Writing – review & editing, Supervision. Maria Piagkou: Writing – review & editing. George Triantafyllou: Writing – review & editing. Nicol Zielinska: Writing – original draft, Visualization, Validation, Supervision, Project administration, Methodology, Funding acquisition, Data curation, Conceptualization. Janusz Moryś: Writing – review & editing. Krzysztof Koptas: Writing – review & editing. Friedrich Paulsen: Writing – review & editing.

Declaration of Competing Interest

The authors declare that they have no competing interests.

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