**3. Innervation of the joint**

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 and communications between the nerves are common.

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 nerve.

The axillary or circumflex nerve is a branch of the posterior secondary trunk (C5–C6). It forms on the lateral border of the subscapularis muscle, and is directed toward the posterior part of the surgical neck of the humerus. It runs below the shoulder joint about 2–3 mm below the lower capsule. Along with the posterior humeral circumflex artery, the nerve passes through a quadrilateral space forming a small aperture delimited by teres minor, teres major below, long head of medial biceps, and proximal humerus laterally. It provides motor innervation mainly to deltoids with branches to the teres minor, provides sensitive innervation to the lower, lateral, and anterior joint capsule, and innervates the humeral head and upper humeral neck. It has a cutaneous branch, which contributes sensitivity of the skin on the deltoids.

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**1.** They allow a better control of the pain, decreasing the need for opiates, both intra- and

**2.** Decreases the incidence of nausea and vomiting, which increases patient satisfaction and

The reference technique for intraoperative analgesia is brachial plexus block at interscalene level [9]. Multiple approaches have been described: Winnie, Pippa, and Meier are the best known. Until not many years ago, the use of the neurostimulator for the accomplishment of the blockade was the gold standard technique. It was recommended to obtain a good response of the triceps (C5–C6) rather than a response of the biceps (C4–C5), ensuring a better distribu-

With the development of ultrasound techniques and their progressive introduction into anesthesiology services, the use of neurostimulation for nerve localization in analgesic or anesthetic blocks has become obsolete. At the moment, the realization of a blockade that is not

The use of this technology brings a number of advantages. One of the most important is to be able to confirm the distribution of the local anesthetic around the nerve by direct vision. The use of ultrasound also improves safety, since we observe at all times the trajectory of the needle and its relation with neighboring structures (vascular, pleura, and solid organs). Another notable advantage is that the volume of local anesthetic is considerably lower. The correct extension of the anesthetic around the nerve allows a shortening of the latency of the

Brachial plexus block at interscalene level has been well described and widely used (**Figure 2**). The lack of impact of suprascapular nerve block on respiratory function makes it a good

**3.** It provides an adequate muscular relaxation for the correct position of the patient.

**4.** Reduces intraoperative bleeding and promotes hemodynamic stability.

**4. Intraoperative analgesic techniques**

post-operatively.

tion of the anesthetic.

guided by ultrasound is not conceived.

blockade and a longer duration of the effect.

decreases the average stay.

Multiple advantages present loco-regional anesthesia:

**Figure 1.** Division of the brachial plexus into its terminal branches.

The axillary plexus is responsible for both internal and cutaneous innervation of the shoulder, except for the upper part of the shoulder, which is innervated by the supraclavicular nerve originated in the lower part of the superficial cervical plexus (C3–C4). The articular innervation and the structures that surround it are mainly in charge of the axillary nerve or circumflex and the suprascapular nerve. To a lesser extent, they can be innervated by the musculocutaneous and subscapular nerve.

The suprascapular nerve is a mixed, motor and sensory nerve, formed by the direct union of the upper primary trunk of C5 and C6, with occasional contributions of C4 in some variants. It occurs laterally below the trapezius and omohyoid, and enters the supraspinatus fossa. The transverse scapular ligament closes the fossa on the nerve. In the suprascapular fossa, the nerve sends motor branches to the supraspinatus and infraspinatus muscles and some to the teres minor. It provides sensitive branches to the posterior glenohumeral capsule, acromioclavicular joint, and the coracohumeral ligament. In 15% of patients, the suprascapular nerve receives cutaneous sensory fibers from the upper side of the arm (deltoid) [8].

The axillary or circumflex nerve is a branch of the posterior secondary trunk (C5–C6). It forms on the lateral border of the subscapularis muscle, and is directed toward the posterior part of the surgical neck of the humerus. It runs below the shoulder joint about 2–3 mm below the lower capsule. Along with the posterior humeral circumflex artery, the nerve passes through a quadrilateral space forming a small aperture delimited by teres minor, teres major below, long head of medial biceps, and proximal humerus laterally. It provides motor innervation mainly to deltoids with branches to the teres minor, provides sensitive innervation to the lower, lateral, and anterior joint capsule, and innervates the humeral head and upper humeral neck. It has a cutaneous branch, which contributes sensitivity of the skin on the deltoids.
