Interscalene

Indications

Analgesia and anaesthesia for:

  • Shoulder surgery
    • Particularly open surgery
      Arthroplasty, arthroscopy, rotator cuff repair, subacromial decompression.
    • Mobilisation
      Frozen shoulder.
  • Proximal humerus surgery
  • Sympathicolysis

Contraindications

Absolute:

  • Contralateral recurrent laryngeal or phrenic nerve injury
    Risk of bilateral phrenic nerve palsy.
  • Contralateral pneumonectomy/pneumothorax

Relative:

  • Reduced respiratory reserve

Anatomy

The upper limb is supplied by the brachial plexus:

  • Formed by the anterior primary rami of C5 to T1
    • Variably C4 to T2
  • Divided into roots, trunks, devisions, cords, and branches
    Blocking the plexus at different levels will give a different distribution of sensory block.
  • Runs between the clavicle and third rib
  • Runs with the axillary artery into the upper limb, where it forms the major terminal branches

Sections of Brachial Plexus

The brachial plexus has five key sections:

  • Five roots
    The nerve roots that give rise to the plexus. May be imaged as they emerge from the vertebral foramen.
  • Three trunks
    Roots merge together to form three trunks:
    • May be imaged at the interscalene level
      Deep to SCM, between anterior and middle scalene. Key landmarks:
      • Lateral border of SCM
      • Scalenus anterior
      • Interscalene groove
    • Superior trunk
      From C5 & C6.
    • Middle trunk
      From C7.
    • Inferior trunk
      From C8 and T1.
  • Six divisions
    Three anterior and three posterior, which then re-merge to form the cords.
    • Lie posterior and cephalad to the subclavian artery
    • May be imaged at the supraclavicular level.
  • Three cords
    Imaged wrapping around the axillary artery at the infraclavicular level, and include:
    • Lateral cord
    • Posterior cord
    • Medial cord
  • Branches
    • Divided into major and minor terminal branches
    • Major terminal branches may be imaged in the axilla

Major Terminal Branches

The major terminal branches include:

  • Radial nerve
    • Sensation to the dorsum of the hand, generally the lateral 2.5 digits.
    • Motor: Extension of elbow and fingers
  • Median nerve
    • Sensation to the palm, and the palmar surface and dorsum of the distal phalanges of the lateral 3.5 digits
    • Motor: Flexion of fingers
  • Ulnar nerve
    • Sensation to the medial 1.5 fingers, the ulnar border of the hand (including the dorsum), and sometimes the ulnar part of the forearm
    • Motor: Flexion of 4th and 5th digits and opposition of 1st digit
    • Most effectively blocked with a targeted axillary block
  • Musculocutaneous nerve
    • Sensation to the lateral aspect of the forearm
    • Motor: Flexion and supination of forearm
  • Axillary nerve
    • Sensation over the “regimental patch” of the shoulder

Minor Terminal Branches

From the roots:

  • Dorsal scapular nerve
  • Long thoracic nerve
  • Branch to phrenic nerve

From the trunks:

  • Nerve to subclavius
  • Suprascapular nerve

From the cords:

  • Lateral pectoral nerve
  • Subscapular nerve
  • Thoracodorsal nerve
  • Median pectoral nerve
  • Intercostal brachial nerve
  • Medial brachial cutaneous nerve
  • Medial antebrachial cutaneous nerve Supplies upper medial part of the forearm, and can be covered with a subcutaneous bleb just distal to the axillary hairline.

Equipment

  • 22G 4cm needle
  • Local anaesthetic:
    10-20ml of:
    • 1% lignocaine
    • 0.5% bupivacaine
    • 0.75% ropivacaine
      0.2-0.5% ropivacaine at the C5-C6 level.
    • 1% lignocaine with 0.5% ropivacaine
      i.e. 1:1 of 2% lignocaine with 1% ropivacaine.

Technique

  • Position:
    May be either:
    • Supine, head up and rotated away with, ipsilateral arm on patient’s lap
    • Lateral
  • Place ultrasound probe lateral to larynx
    Identify thyroid, carotid, and IJV.
  • Translate laterally and slightly caudally to identify:
    • Lateral border of SCM
    • Scalenus anterior
      Under SCM and lateral to the carotid artery.
    • Scalenus medius
    • Interscalene plexus
      Appears as three nerves (‘traffic light’) between the anterior and middle scalene muscles.
  • Occasionally a scalenus intermedius muscle/fascial layer divides the plexus into a superficial and deep plexus.
  • Insert needle IP:
    • From posterolateral to anteromedial
    • Through middle scalene
    • Aiming deep to the plexus
      This position minimises the risk of nerve injury.
  • Nerve stimulation
    May be used to identify improper positioning:
    • Contraction of levator scapulae indicates too posterior
    • Contraction of diaphragm (via phrenic nerve) indicates too anterior

Complications

Specific complications include:

  • Blockage of additional nerves, leading to:
    • Horner’s syndrome
    • Facial numbness
    • Vocal cord paralysis
      Due to recurrent laryngeal nerve blockade.
  • Vertebral artery injection
    May lead to seizure.
  • Subarachnoid/epidural injection
  • Pneumothorax

References