The anatomy and variation of the coracoid attachment of the subclavius muscle in humans

Abstract

The functions of the subclavius muscle (SM) are described as stabilization of the sternoclavicular joint (SCJ) and resisting elevation of the lateral end of the clavicle. During systematic cadaveric dissections, we observed additional fibrous structures, previously described as variants of the anatomy, extending from the SM and inserting into the coracoid process (CP). Due to the high incidence of these structures in our dissections, we hypothesized that the attachment at the CP is more common than appreciated and that, as a corollary, the function of the SM was (or has been) more complex than simply depressing the clavicle and generating stability at the SCJ. For our investigation, fifty-two upper extremities of 26 human cadavers were dissected. The SM was demonstrated from costal to clavicular attachment. We documented additional fibrous structures apparently derived from the SM inserting into the CP. Measurements of the length of the SM, the length of its attachment, and the length of the clavicle were taken in situ, with the specimens supine and the upper extremity in the anatomical position. Variations in the anatomy of the SM and its coracoidal attachment were recorded, and potential correlations were investigated.For documentation purposes photographs and video sequences of passive motion of the shoulder girdle of the specimens were taken. In 49 of the 52 specimens we found additional fibrous structures passing from the SM to the CP. We differentiated three types: (1) a strong cord-like structure; (2) a small or thin cord-like structure or structures; and (3) a planar twisted sheet-like structure. The SM and its extension to the CP appears to contribute to a 'functional scapular suspension system' together with the other muscles enveloped by the clavipectoral fascia (pectoralis minor, coracobrachialis and the short head of the biceps brachii). This system assists in the control of the position of the scapula in relation to the thorax, particularly in elevated positions of the upper extremity. We speculate that the differentiation of the fibrous structure depends on the functional demands of the individual.

La Rotación Axial de la Clavícula que Plantea la Maniobra de Mulligan ¿Produce una reducción de la presión en el espacio subacromial? Un estudio ex vivo exploratorio

“…A partir de los datos exploratorios obtenidos, se desprende que la función del músculo subclavio podría tener algún rol importante en la mantención del espacio subacromial. El músculo subclavio tiene su origen en la cara superior del primer cartílago costal y primera costilla, insertándose en la parte media de la cara inferior de la clavícula (Crepaz-Eger et al, 2022). Dada la forma de "s" itálica de la clavícula y el lugar de la inserción distal del subclavio, se hace presumible la acción de rotación axial anterior que podría ejercer este músculo sobre la clavícula.…”

Skapulafrakturen

“…Die subakromiale Fläche zum Caput humeri (subakromiales Nebengelenk) und das skapulothorakale Nebengelenk werden als "unechte Gelenke" bezeichnet. 18 Muskeln, die von 11 verschiedenen Nerven innerviert werden, setzen an der Skapula an oder haben ihren Ursprung an der Skapula und ziehen von dort zum Humerus [10,11]. Dieses komplexe System erlaubt die außergewöhnliche Beweglichkeit der Schulter.…”