There have been numerous descriptions of muscular variations in the axillary region, in the axillary fossa or in the walls that form it, including Langer's axillary arch which is a muscle-fascial arch that originates in the lateral edge of the latissimus dorsi muscle and passes in front of the axillary vessels and nerves to join the fascia of the
coracobrachialis muscle (Ortiz et al., 2009; Stanching, 2016).
Caption: Figure 6: Axial T1 MRI: (1) humerus, (2) deltoid muscle, (3)
coracobrachialis muscle, (4) teres major muscle, and (5) triceps muscle.
Is the musculocutaneous nerve really in the
coracobrachialis muscle when performing an axillary block?
(13) Protecting the
coracobrachialis muscle during coracoid osteotomy and subsequent transfer can help prevent transient or permanent musculocutaneous nerve injury.
The musculocutaneous nerve arises from the lateral cord, perforates the
coracobrachialis muscle and leaves the neurovascular sheath usually at the level of the lateral edge of the pectoralis major.
Musculocutaneous nerve arise in axilla from lateral cord of brachial plexus and passes downward & laterally, pierces the
coracobrachialis muscle, then run downward between the biceps and the brachialis muscle, and further continues as the lateral cutaneous nerve of the forearm.
Usually
coracobrachialis muscle arises from the apex of the coracoid process, together with the tendon of the short head of the biceps, and also by muscular fibres from the proximal 10 cm of this tendon.
The musculocutaneous nerve coursed laterally to supply the
coracobrachialis muscle. The first lateral root is labeled as LR -1, which is indicated by a single arrow coursed medially towards the medial root of median nerve and joined with it in front of the third part of axillary artery.
Anesthesia of the forearm is incomplete unless the musculocutaneous nerve is also blocked, either at the antecubital fossa or the
coracobrachialis muscle. (3) Anesthesia at the antecubital fossa is described in the section on elbow blocks.
The MCN gives off a branch for the
coracobrachialis muscle (CbM) before piercing it, and then innervates the biceps brachii muscle and brachialis muscle (Standring, 2016).
Two bellies of the
coracobrachialis muscle associated with a third head of the biceps brachii muscle.
AA--axillary artery, ACHA--anterior circumflex humeral artery, BA--brachial artery, CBM--
coracobrachialis muscle, CSA -circumflex scapular artery, IT--intermediate trunk, LT--lateral trunk, LTA- -lateral thoracic artery, MCN-- musculocutaneous nerve, MN--median nerve, MT -medial trunk, PB--pectoral branch, PCHA--posterior circumflex humeral artery, Pm-- pectoralis minor muscle, SBRA--superficial brachioradial artery, SSA--subscapular artery, TA-- thoracodorsal artery, UN--ulnar nerve.
