**1. Introduction**

Shoulder pain is a common problem with an estimated prevalence of 4–26%. It has been estimated that 20% of the general population will suffer shoulder pain throughout their life with a prevalence that can reach up to 50% [1]. This entity is responsible for approximately 16% of all musculoskeletal conditions only behind patients with low back pain.

Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons

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 locations [3].

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

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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

Upper region Supraspinatus Abduction Posterior region Infraspinatus, teres minor External rotation Anterior region Subescapularis Internal rotation

**Muscle tendon Movements**

Bicipital Elbow flexion-supinatium

Sensory innervation of the shoulder joint is complex and involves contributions of the axillary, suprascapular, subscapular, musculocutaneous, and lateral pectoral nerves. Of these, the axillary and suprascapular nerves are considered the most important. However, variations

It is important to have an exhaustive knowledge of the brachial plexus (**Figure 1**), since before considering a regional technique it is necessary to know well the innervation of the shoulder. The brachial plexus is formed by the anterior or ventral branches of the last four cervical spinal nerves: C5–C8 and the first thoracic: T1. These spinal nerves join together to form the primary trunks: upper (C5–C6), middle (C7), and lower (C8–T1). Just below the clavicle, the six divisions of the trunks will be formed, since each trunk is divided into anterior and posterior branches. From this moment, they are called secondary trunks or cords, which descend to the armpit. The axilla are denominated according to their relation with the axillary artery: anteroexternal (formed by the union of the upper and middle trunks), anterointernal (formed by the anterior branch of the inferior trunk), and posterior, formed by the posterior divisions of the primary trunks. Finally, each secondary trunk will give origin to the different terminal nerves: the posterior cord originates the axillary and radial nerves, the medial cord the ulnar nerve, and the lateral cord will give rise to the musculocutaneous

so-called rotator cuff.

action of the deltoid [7].

**Table 1.** Muscles and function.

**3. Innervation of the joint**

nerve.

and communications between the nerves are common.

"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 activities.

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