The bone structure of the shoulder is formed by several bones: (1) The humerus, (4) the scapula whose joint area (glenoid) is the one that articulates with the head of the humerus, (2) the acromion or spine of the scapula that continues with (3) the clavicle through the acromioclavicular joint. All this articulation is integrated into the thorax through the scapulothoracic joint. See figures 1 and 2.
Most of the specific problems of the shoulder develop in the glenohumeral joint and / or in the acromioclavicular joint (AC). In addition there are other problems in the scapulothoracic joint and in the sternoclavicular joint, but the latter are more infrequent. Since all these structures are close to the cervical spine of the neck, there is also radiated pain of cervical origin.
a) Glenohumeral joint:
This joint is the biggest joint in the shoulder. Several layers are necessary to try to achieve maximum mobility between the glenoid and the humeral head. This allows a greater range of mobility and, on the other hand, the necessary stability. The deeper layer is formed by a cartilaginous ring called glenoid labrum, to increase the diameter of the joint cavity. From this ring emerge the anterior glenohumeral ligaments, as well as the long portion of the biceps (PLB).
The PLB leaves the superior glenoid labrum and runs along the bicipital groove, which is delimited by the greater tuberosity and the lower tuberosity, towards the arm. The layer above these is the rotator cuff (Figure 3). This is composed of several tendons (whose muscles originate in the scapula) that are inserted into the head of the humerus and that are: the subscapularis in the anterior part, the supraspinatus in the upper part and infraspinatus and the teres minor in the posterior part. They allow the centering of the humeral head during its movement and prevent the pathological displacement of the humerus upwards. In the same way they collaborate in the control of the anteroposterior translation. These tendons wrap around the humeral head.
La capa más exterior la forman los músculos grandes y superficiales que ejercen la fuerza necesaria sobre el húmero para separarlo del cuerpo. El trabajo principal lo realizan los músculo Deltoides, el pectoral mayor y el dorsal ancho que va hacia la espalda.
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