What Is An Interscalene Nerve Block?

Interscalene nerve blocks are well-suited for surgeries involving the shoulder, clavicle, or uppermost arm. The nerve block is achieved by injecting an anesthetic adjacent to the brachial plexus, a cluster of nerves that control upper extremity function.

The brachial plexus resides in the interscalene groove, which is a potential space between the scalene muscles, middle and anterior.

An interscalene nerve block can elicit numbness during surgery, and provide pain relief in the post-surgical period.

Interscalene nerve blocks should not be used for surgeries below the elbow, due to the unreliability of achieving proper levels of numbness and pain relief.

How Is An Interscalene Nerve Block Performed?

Pain-Doctor-Interscalene-Nerve-Block-Injection-Procedure-5An interscalene nerve block is best performed by board-certified anesthesiologists who are familiar with the strengths and weaknesses of the procedure. Informed consent should be signed and properly documented at a pre-operative appointment for the patient.

After the patient arrives on the assigned date of surgery, sedation is administered and the patient is placed in a supine position with the head turned toward the non-operative side.

The anesthesiologist will trace the position of important landmarks using a surgical skin marker. These landmarks are the external jugular vein, clavicle, and clavicular belly of the sternocleidomastoid muscle (SCM).

The territory of injection for an interscalene nerve block is identified and washed with an antiseptic solution. The needle enters a point just beyond the posterior edge of the clavicular belly of the SCM and advances with care to avoid puncture of the external jugular vein.

The goal is the injection of a local anesthetic in the neighborhood of the brachial plexus, inducing numbness and providing pain relief.

Pain-Doctor-Interscalene-Nerve-Block-Injection-Procedure-3Needle placement using ultrasound guidance or a nerve stimulator is used to improve the reliability and accuracy of an interscalene nerve block. The desired effect can be achieved with injection of as little as 15 mL, but no more than 45 mL of local anesthetic. The nerve block onset time is relatively brief, less than 30 minutes, after the injection. A one-time injection of local anesthetic can provide eight to ten hours of anesthesia or upwards of 18 hours of analgesia.

Contraindications, or reasons to avoid, interscalene nerve blocks include:

  • Patient refusal
  • Allergy to the anesthetic being used
  • Active infection
  • Blood thinner treatment less than seven days prior to the procedure
  • Bleeding disorders
  • Dysfunction of the phrenic nerve, which controls the diaphragm
  • Severe chronic obstructive pulmonary disease (COPD)
  • Surgical procedures involving the forearm or hand
  • Pregnancy
  • Laryngeal nerve dysfunction

Pain-Doctor-Interscalene-Nerve-Block-Injection-Procedure-4_copyInterscalene nerve blocks have a low risk profile, but complications may include:

  • Infection at injection site
  • Hematoma, or mass of blood, beneath the skin
  • Allergic reaction
  • Seizures, which are usually self-limited and not a chronic disorder
  • Systemic reaction, caused by direct injection of anesthetic into vasculature
  • Paresthesias, which are abnormal skin sensations
  • One-sided paralysis of the diaphragm
  • Pneumothorax, or collapsed lung
  • Hoarseness or changes in voice, which is predominantly due to recurrent laryngeal nerve dysfunction
  • Vascular puncture
  • Total spinal anesthesia
  • Horner syndrome that consists of miosis (decreased pupil size), ptosis (drooping upper eyelids), and anhidrosis (absence of sweating)

Conditions Related To Interscalene Nerve Blocks

Rotator-Cuff-Tear-xrayInterscalene nerve block provides reliable and effective anesthesia or analgesia for surgery involving the clavicle, shoulder, elbow, or upper arm. Examples of upper extremity surgery include:

  • Hemiarthroplasty, or partial replacement, of the shoulder
  • Repair of a torn rotator cuff
  • Acromioplasty, or surgical repair of the part of the shoulder known as the acromion
  • Total shoulder replacement
  • Repair of humeral, or upper arm, fracture


Interscalene nerve blocks remain a favorite of health practitioners for induction of pre-surgical numbness and post-surgical pain relief in the arms and shoulders. Mostly anesthesiologists are charged with the task of administering the block. An intercostal nerve block is not appropriate for all patients with an indication for the procedure. It has a low risk profile, but complications do occur. Those complications are dealt with posthaste when they are uncovered. Overall, interscalene nerve blocks provide excellent anesthesia and analgesia for surgery of the upper extremity.


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