The shoulder girdle is made up of the bones connecting the shoulders to the trunk: it therefore includes the scapula (scapula) and the clavicle. This set of bones serves as an attachment to the upper limb. Thus, the shoulder girdle participates in the movements of the upper limbs by providing them with their mobility.

This structure, which connects the arm to the trunk, has great freedom of movement. It is as “posed” on the thorax, the collarbone being in front, the scapula behind. In fact, correct shoulder coordination requires relative independence of movement between the scapula and the arm. 

«It is thanks to the shoulder girdle that humans are able to perform complex movements, such as climbing, crawling or hanging from trees! ” indicates Futura-Sciences, a reference website devoted to scientific questions.

Indeed, this scapular girdle is made up of bones that connect the shoulders to the trunk. It is thus made up of the scapula (or scapula) and the collarbone.

The etymological origin of the term “scapular“Is the Latin word”scapulaWhich means “shoulder“. With great freedom of movement, the shoulder girdle seems to be “placed” on the thorax. The collarbone is positioned forward and the scapula is posteriorly.

What is the clavicle?

It is a long bone which has two ends as well as two faces: the upper face is smooth, it gives insertion to the trapezius muscle and the deltoid muscle, the lower face is rough and has tubercles.

What is the scapula?

Also called scapula, it has the shape of a triangle which has two faces, an anterior face biconcave in front, and a posterior face subdivided in two by the spine of the scapula.

More precisely, this bony set that forms the scapular girdle is composed, on the one hand, by the clavicle, and on the other hand, on the scapula, by the acromion (name of a part of the bone of the scapula which forms an upper and posterior bony outgrowth) and by the spine of the scapula (a ridge which runs laterally all over the posterior part of this bone).

The function of this shoulder girdle is to serve as an attachment to the upper limb, the arm. It therefore constitutes an important center of mobility located at the level of the shoulder. Thus, correct shoulder coordination requires relative independence of movement between the scapula and the arm.

The muscles of the shoulder girdle have, in fact, a stabilizing activity, a condition of freedom of movement for the arm. In addition, you should know that the clavicle works mainly in compression, that is to say “qu‘toIt transmits the load from the upper limbs to the axial skeleton through its major axis“, Indicates a scientific article published by Jean-Luc Voisin, doctor in human paleontology. 

In addition, it would seem that it is necessary to maintain a relative autonomy between the shoulder girdle and the cervical ones: the mobility of the latter is, in fact, often limited by the tensions of the muscles of the shoulder.

Eventually, the shoulder girdle rotates around a vertical axis at the end of the collarbone. The shoulder therefore turns out to constitute a particular anatomical complex, being made up of several joints which intervene in synergy during the movements of the arm.

Several anomalies or pathologies can affect the shoulder girdle and in particular:

• malposition: in unbalanced positions of the shoulder girdle, it is most frequently high and forward. This is due to excess tension in the pectorals, upper trapezius and / or latissimus dorsi;
• osteoarthritis: this type of pathology is quite rare for the shoulder girdle;
• periarthritis: more frequent, they can be relatively disabling. All the pain localized in this region of the shoulder is also called scapulalgia;
• tendonitis: they can limit certain movements;
• lesions: lesions, relatively frequent, of the articular complex represented by the shoulder girdle involve the fracture of any bone related to the shoulder or the scapula.

The treatment of dysfunction of the shoulder girdle and particularly its lesions is essentially based on adapted exercises, which aim to stabilize and strengthen this belt, thanks to the intervention of a physiotherapy professional.

In addition, with regard to disabling scapulalgia, the management is multiple and includes:

• taking nonsteroidal anti-inflammatory drugs (NSAIDs) and analgesics: these are intended to relieve pain and reduce inflammation;
• cortisone injections that help fight inflammation;
• physiotherapy sessions are necessary in case of decreased range of motion.

If such treatment does not work, surgery may be considered, which will also be followed by rehabilitation of the shoulder.

The diagnosis of a pathology related to the shoulder girdle and in particular a scapulalgia, recommends carrying out:

• a clinical examination: by evaluating the mobility of the shoulder, by mobilizing it in an active and passive way, by describing the areas of pain as well as the intensity of the pain;
• medical imaging examinations if necessary, such as: an x-ray of the shoulder, magnetic resonance imaging (MRI) or even an ultrasound;
• a blood test: it makes it possible in particular to confirm the inflammatory aspect;
• an electromyogram: this examination assesses the functioning of the suprascapular and long thoracic nerves in cases of compression. In fact, an electromyogram allows the analysis of nerve impulses in the motor and sensory nerves as well as in the muscles.

A synthesis concerning the evolution of the morphology of the clavicle within the genus Homo, led by the team of Jean-Luc Voisin, doctor in human paleontology at the Paris Natural History Museum, revealed the architectural and functional consequences of this morphology on the shoulder girdle. 

In the great apes, clavicular peculiarities have made it possible to optimize the pendulum movement, in particular in the gibbon. Thus, the clavicular morphology is characteristic of great apes: their clavicle presents a deflection (that is to say a modification of position) with two curvatures. These species are, moreover, characterized by a high scapula and dorsal in relation to the thorax, allowing both suspended movements and movements on the ground. 

The exit of the head beyond the shoulders

Man is, for his part, characterized by the “cervico-cephalic” emergence, compared to the great apes: thus, again indicates the article of Jean-Luc Voisin, “the neck grows in height causing the head to come out of the shoulders“. And, according to scientist Sakka, this phenomenon has been “associated with a descent of the shoulder girdle along the thorax “. Ultimately, “the descent of the shoulder girdle in humans, compared to that of the great apes, would explain the presence of a single lower curvatureOf the human clavicle in comparison to the existence of both an upper and lower curvature in other primates.

Morphology related to bipedalism

And in the end, it appears that “human clavicular morphology is an adaptation to bipedalism because it allows the mechanical maintenance of the shoulder in an erect position, that is to say with a minimum energy cost“, Adds Jean-Luc Voisin.

In addition, he adds “qu’un such modern human clavicular morphology in superior view appeared rapidly in human history: as soon as bipedalism became predominant and the hand was freed from locomotor constraints«.

The bipedalism, in humans: a big step in the history of its evolution, the consequences of which are, even today, the subject of much scientific research.