Residency · Residency · Anesthesiology

Ultrasound-Guided Upper Extremity Blocks

Brachial Plexus Anatomy

Root Formation

The brachial plexus arises from the ventral rami of C5-T1, with variable contributions from C4 and T2. The roots exit the spinal column and pass between the anterior and middle scalene muscles.

Trunks (Supraclavicular Fossa)

The roots reorganize into three trunks as they cross the posterior triangle of the neck above the clavicle. The superior trunk is formed by C5 and C6, the middle trunk by C7 alone, and the inferior trunk by C8 and T1.

Divisions

Behind the clavicle, each trunk divides into an anterior and a posterior division. The anterior divisions supply the flexor compartments of the upper extremity, while the posterior divisions supply the extensor compartments.

Cords (Infraclavicular Region)

The divisions regroup into three cords named by their relationship to the axillary artery. The lateral cord forms from the anterior divisions of the superior and middle trunks (C5-C7). The posterior cord forms from all three posterior divisions (C5-T1). The medial cord forms from the anterior division of the inferior trunk (C8-T1).

Terminal Branches

The cords give rise to five terminal branches. The musculocutaneous nerve arises from the lateral cord (C5-C7) and innervates the biceps and brachialis muscles and the lateral cutaneous nerve of the forearm. The median nerve receives contributions from both the lateral and medial cords (C6-T1). The ulnar nerve arises from the medial cord (C8-T1). The radial nerve arises from the posterior cord (C5-T1). The axillary nerve arises from the posterior cord (C5-C6) and innervates the deltoid and teres minor muscles along with the "regimental badge" area of the lateral shoulder.

<image>Comprehensive anatomical illustration of the brachial plexus from roots (C5-T1) through trunks, divisions, cords, and terminal branches. The diagram uses color coding to trace each root contribution through the plexus. Key landmarks are labeled including the scalene muscles, clavicle, axillary artery, and the relationship of cords to the artery. Major terminal branches (musculocutaneous, median, ulnar, radial, axillary) are shown with their motor and sensory distributions on an arm diagram.</image>

Interscalene Block

Indications

The interscalene block is primarily indicated for shoulder surgery, including arthroscopy, arthroplasty, and rotator cuff repair. It is also used for proximal humerus fractures and clavicle surgery, the latter typically requiring supplementation with a superficial cervical plexus block.

Sonoanatomy

A linear high-frequency probe is placed in transverse orientation at the level of the cricoid cartilage. The sternocleidomastoid muscle is identified superficially, followed by the anterior and middle scalene muscles. The brachial plexus roots or trunks appear as hypoechoic round structures in the interscalene groove between the scalenes, often described as the "traffic light" sign. The carotid artery and internal jugular vein serve as medial landmarks.

Technique

The block is performed with an in-plane approach from lateral to medial. The needle is directed between the C5 and C6 roots or around the superior trunk. A volume of 15-20 mL is typically used. A catheter can be placed for continuous analgesia.

Coverage

The interscalene block provides excellent coverage of the shoulder (C5-C6 dermatomes) and lateral arm. However, it characteristically spares the inferior trunk territory (C8-T1), leaving the ulnar side of the forearm and hand without anesthesia. This "ulnar sparing" pattern makes it inappropriate as the sole technique for hand or forearm surgery.

Complications and Side Effects

Phrenic nerve paralysis occurs in virtually 100% of standard-volume interscalene blocks because the phrenic nerve (C3-C5) runs on the anterior surface of the anterior scalene muscle in close proximity to the injection site. This produces a 25-30% reduction in ipsilateral diaphragmatic function and is an absolute contraindication in patients who cannot tolerate unilateral phrenic nerve palsy, such as those with contralateral phrenic palsy, severe COPD, or restrictive lung disease. Other complications include Horner syndrome (from stellate ganglion blockade, producing ptosis, miosis, and anhidrosis), recurrent laryngeal nerve block (causing hoarseness), vertebral artery injection (which is catastrophic), epidural or intrathecal injection (which can cause total spinal anesthesia), and pneumothorax (rare with ultrasound guidance).

Phrenic Nerve-Sparing Strategies

Several strategies have been developed to reduce phrenic nerve involvement: using reduced volumes (5-10 mL) with ultrasound-targeted injection of C5-C6, performing a superior trunk block (targeting the injection away from the C5 root), and combining a suprascapular nerve block with an axillary nerve block (which avoids the interscalene groove entirely). However, the evidence is mixed, and no technique reliably eliminates phrenic nerve involvement.

Supraclavicular Block

Indications

The supraclavicular block is indicated for surgery of the arm, elbow, forearm, and hand. It is often called the "spinal of the arm" because it blocks all three trunks in a compact area, providing the most complete upper extremity block from a single injection.

Sonoanatomy

A linear probe is placed in the supraclavicular fossa in a coronal oblique orientation. The brachial plexus appears as a "cluster of grapes" -- a collection of hypoechoic nodules -- located lateral and superficial to the subclavian artery. The first rib appears as a hyperechoic line deep to the plexus and serves as the critical safety landmark. The pleura is visible as a sliding bright line deep to the first rib.

Technique

An in-plane approach is used from lateral to medial. The target is the "corner pocket" between the plexus and the first rib, where the inferior trunk lies. A volume of 20-25 mL is injected, with care taken to ensure spread around the entire cluster of nerve structures.

Coverage

The supraclavicular block provides the most complete upper extremity anesthesia from a single injection site. It may spare the intercostobrachial nerve (T2), which can be supplemented with local infiltration at the medial arm tourniquet site. The musculocutaneous nerve may occasionally be spared if it has already departed the plexus at this level.

Complications

The primary concern is pneumothorax, though the first rib provides a safety backstop when needle tip position is carefully monitored. Phrenic nerve palsy occurs in 50-60% of cases, less frequently than with the interscalene approach. Subclavian artery puncture and Horner syndrome are also possible.

<image>Ultrasound image illustration of the supraclavicular brachial plexus block showing the linear probe position on the patient's neck/shoulder area, and the corresponding sonographic view with labeled structures: subclavian artery (round anechoic), brachial plexus (grape-like cluster of hypoechoic nodules), first rib (bright hyperechoic line with acoustic shadow), and pleura. The needle path is shown in-plane from lateral to medial, with the target "corner pocket" area highlighted between the plexus and the first rib.</image>

Infraclavicular Block

Indications

The infraclavicular block is indicated for surgery of the elbow, forearm, and hand. It is particularly well-suited for catheter placement because the pectoralis muscle holds the catheter in a stable position with low migration rates. It is also commonly used for AV fistula creation.

Sonoanatomy

A linear or curvilinear probe is placed inferior to the clavicle, medial to the coracoid process, in a parasagittal orientation. The axillary artery is identified deep to the pectoralis major and minor muscles. The three cords surround the artery: the lateral cord is cephalad, the posterior cord is deep, and the medial cord is caudal. The axillary vein lies caudal and superficial to the artery.

Technique

An in-plane approach is used from cephalad to caudal. The target is posterior to the axillary artery (the posterior cord position), often described as the "6 o'clock" position relative to the artery. Adequate distribution is indicated by a U-shaped spread of local anesthetic around the artery. A volume of 25-30 mL is typical.

Coverage

The infraclavicular block reliably covers all four terminal nerves: median, ulnar, radial, and musculocutaneous. The musculocutaneous nerve is blocked more reliably at this level than at more distal levels because it has not yet departed from the lateral cord. The intercostobrachial nerve (T2) is spared and requires supplementation for tourniquet pain.

Complications

Pneumothorax is possible due to the deeper needle trajectory compared to the supraclavicular approach. Vascular puncture may occur. Phrenic nerve palsy is rare at this level.

Axillary Block

Indications

The axillary block is indicated for surgery of the forearm, wrist, and hand. It is the safest brachial plexus approach because there is no risk of pneumothorax or phrenic nerve palsy. This makes it ideal for bilateral blocks and for patients with respiratory compromise.

Sonoanatomy

A linear high-frequency probe is placed in the axilla with the arm abducted to 90 degrees. The axillary artery serves as the central landmark. The median nerve is located superficial and lateral (or anterolateral) to the artery. The ulnar nerve is superficial and medial (or anteromedial). The radial nerve is deep (posterior) to the artery, often between the artery and the conjoint tendon or triceps. The musculocutaneous nerve lies within the coracobrachialis muscle, appearing as a hyperechoic, elliptical structure separate from the other three nerves.

Technique

The axillary block requires individual targeting of four separate nerves using a multi-injection technique, with 5-8 mL of local anesthetic deposited around each nerve for a total volume of 20-30 mL. Critically, the musculocutaneous nerve must be specifically sought within the coracobrachialis muscle; it is not reliably blocked by perivascular injection alone.

Coverage

The axillary block provides complete coverage of the hand, wrist, and forearm through blockade of all four terminal nerves. It does not cover the shoulder or upper arm because the axillary nerve and superior trunk branches have already departed at more proximal levels. The intercostobrachial nerve (T2) must be supplemented for tourniquet pain.

Complications

Vascular puncture is the most common complication but is typically benign. Nerve injury is possible but has a low incidence. The absence of pneumothorax or phrenic nerve risk makes this the safest brachial plexus block approach.

Choosing the Appropriate Block Level

Clinical Pearls

The interscalene block provides the best shoulder analgesia but always causes phrenic nerve palsy; respiratory reserve must be assessed preoperatively. For catheter-based continuous blocks, the infraclavicular approach offers the most stable catheter fixation and the lowest migration rate. At the axillary level, the musculocutaneous nerve must be blocked separately within the coracobrachialis muscle; perivascular injection should not be assumed to reach it. The supraclavicular block provides the most reliable complete arm anesthesia from a single injection site. The needle tip must always be visualized in relation to the pleura during supraclavicular blocks, with the first rib serving as the safety margin. For patients with severe COPD or contralateral phrenic nerve palsy, the axillary approach should be used to avoid any phrenic nerve risk.

References

• Hadzic A, ed. Hadzic's Textbook of Regional Anesthesia and Acute Pain Management. 2nd ed. McGraw-Hill; 2017.
• Tran DQ, Elgueta MF, Aliste J, Finlayson RJ. Diaphragm-sparing nerve blocks for shoulder surgery. Regional Anesthesia and Pain Medicine. 2017;42(1):32-38.
• Soares LG, Brull R, Lai J, Chan VW. Eight ball, corner pocket: the optimal needle position for ultrasound-guided supraclavicular block. Regional Anesthesia and Pain Medicine. 2007;32(1):94-95.
• Neal JM, Gerancher JC, Hebl JR, et al. Upper extremity regional anesthesia: essentials of our current understanding. Regional Anesthesia and Pain Medicine. 2009;34(2):134-170.
• Koscielniak-Nielsen ZJ. Ultrasound-guided peripheral nerve blocks: what are the benefits? Acta Anaesthesiologica Scandinavica. 2008;52(6):727-737.

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