**2. Anatomy and biomechanics of the shoulder**

The shoulder or shoulder girdle is the anatomical structure with greater mobility of the body, in turn is the most complex structure. The shoulder complex allows an arch of maximum mobility due to the multitude of structures involved in its stabilization: joints, ligaments, and muscles.

The articular complex of the shoulder is an enarthrosis, which confers an ample capacity of movement in the three axes and planes of the space, and this is due to the simultaneous and synchronous functioning of three joints: glenohumeral, acromioclavicular, and sternum-clavicular, in two sliding planes: scapulothoracic and subacromial deltoid. These joints intervene differently in the shoulder movements: in the first 90° of the abduction, the glenohumeral participates, between the 30 and the 135° the scalpulator is added, and from the 90° the acromioclavicular and the sternoclavicular are mobilized.

The glenohumeral joint consists of the head of the humerus and the glenoid cavity, has a large lax capsule, and is lined with a synovium, in which two muscles–tendinous systems of stabilization and fixation are joined. The humeral articular surface closes an ellipse, while the glenoid cavity offers a practically flat articular surface. The consequence of such mobility is the great instability of this joint, the joint being more frequently dislocated.

To compensate this instability, there are passive and active stabilizers. Within the passives is the joint capsule with anterior and posterior reinforcements that become independent in the upper and lower ligaments and the labrum. The labrum is a structure that surrounds the margin of the glenoid cavity conferring a greater congruence with respect to the humeral head. Among the active stabilizers, the most important elements are the components of the so-called rotator cuff.

The rotator cuff consists of the subscapularis muscle anteriorly, the supraspinatus and the long portion of the biceps above, and the infraespinatus and teres minor behind. Each of these muscles has its own rotating function (**Table 1**), but its joint action is the one that coapts the head of the humerus against the glenoid cavity and allows the elevation of the limb by the action of the deltoid [7].


**Table 1.** Muscles and function.

The painful shoulder is the third most frequent reason for consultation of osteoarticular pathology, after low back pain and neck pain. Between 70 and 85% of the consultations are due to pathology of the rotator cuff [2]. In recent years, these conditions are increasing being a reason for increasing consultation in specialized services in the locomotor system. Although the rotator cuff and subacromial structures make up the majority of the presentations of painful pathology of the shoulder, we cannot forget other less frequent but not less important pain

"Painful shoulder syndrome" is a frequent and debilitating disease of diverse etiologies and complex diagnosis, being more common in the female population, and especially after the 5th decade of life [4], in an age range between 45 and 65 years, although it can manifest itself in other age groups [5]. The prevalence increases with age, some professions, and certain sports

Although most chronic shoulder problems can be treated conservatively with activity modification, oral medications, physical therapy, and possible injections of corticosteroids, there are cases where surgical intervention is required. Patients with continuous instability or disabling pain not responding to initial conservative measures may require prior surgical referral. Surgical or specialty referral should also be considered when the diagnosis is unknown [6]. Post-operative pain after shoulder surgery is severe in many patients. For many years, interscalene brachial plexus block has been the gold standard for controlling this pain. However, this is a blockage of the proximal brachial plexus, and therefore, is associated with extensive

The shoulder or shoulder girdle is the anatomical structure with greater mobility of the body, in turn is the most complex structure. The shoulder complex allows an arch of maximum mobility due to the multitude of structures involved in its stabilization: joints, ligaments, and

The articular complex of the shoulder is an enarthrosis, which confers an ample capacity of movement in the three axes and planes of the space, and this is due to the simultaneous and synchronous functioning of three joints: glenohumeral, acromioclavicular, and sternum-clavicular, in two sliding planes: scapulothoracic and subacromial deltoid. These joints intervene differently in the shoulder movements: in the first 90° of the abduction, the glenohumeral participates, between the 30 and the 135° the scalpulator is added, and from the 90° the acromioclavicular and

The glenohumeral joint consists of the head of the humerus and the glenoid cavity, has a large lax capsule, and is lined with a synovium, in which two muscles–tendinous systems of stabilization and fixation are joined. The humeral articular surface closes an ellipse, while the glenoid cavity offers a practically flat articular surface. The consequence of such mobility is

the great instability of this joint, the joint being more frequently dislocated.

nerve block, resulting in significant side effects and possible complications.

**2. Anatomy and biomechanics of the shoulder**

locations [3].

156 Advances in Shoulder Surgery

activities.

muscles.

the sternoclavicular are mobilized.
