Lesson-Interscalene

5 – Anatomy of the brachial plexus in the interscalene groove

The brachial plexus is sandwiched between the anterior and the middle scalene muscles in the interscalene groove

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The figure shows the yellow branches of the brachial plexus (yellow arrows) emerging from between the anterior and middle scalene muscles
MSM = middle scalene muscle (blue arrow); ASM = anterior scalene muscle (green arrow)

3 – The muscle innervation of the shoulder

The shoulder muscles are innervated by

1) the axillary nerve (C5-C6; deltoid and teres minor)
2) the suprascapular nerve (C5-C6; supraspinatus and infraspinatus)
3) the subscapular nerve (C5-C6; subscapularis and teres major)
4) the medial and lateral pectoral nerves (C5-T1; major and minor pectorals)
5) the musculocutaneous nerve (C5-C7; coracobrachialis and long and short heads of biceps brachii)
6) the thoracodorsal nerve (C6-C8; latissimus dorsi)
7) the radial nerve (C5-T1; long and lateral heads of the triceps brachii)

The muscles innervated by the axillary and suprascapular nerves are the most clinically important for shoulder surgery

1)-3) and the major part of 4)-7) are anaesthetised by an interscalene brachial plexus block

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Some of the muscle innervation of the shoulder from an anterior and a posterior view. Deltoid (blue, axillary nerve), teres major and minor (grey, subscapular and axillary nerve), long and short heads of biceps brachii (yellow, musculocutaneous nerve), long and lateral heads of triceps brachii (orange, radial nerve).

1 – Anatomy of the brachial plexus

The brachial plexus (BP) innervates the upper limb

The BP originates from five spinal nerve roots: C5 to T1

The shoulder is innervated by the suprascapular nerve and the axillary nerve. They both originate from the spinal nerve roots C5 and C6

Anaesthesia of the shoulder requires blockade of the BP proximal to the level of the trunks, because the suprascapular nerve branches off the superior trunk

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The brachial plexus is displayed with the suprascapular nerve (red arrow) and the axillary nerve (blue arrow). The five spinal nerve roots of the brachial plexus are indicated by C5 to T1. Green asterix = superior trunk; red asterix = middle trunk; blue asterix = inferior trunk.

2 – The bone innervation of the shoulder

The shoulder and the shoulder joint is innervated by the axillary nerve and the suprascapular nerve

Minor contributions from the long thoracic nerve and capsular filaments from the infraspinatus nerve are not clinically significant

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The figure shows the bony structures of the shoulder from an anterior and a posterior view. The axillary nerve innervates the anterior side (purple). The suprascapular nerve innervates the posterior side (“bone” color). The blue color is innervated by the radial nerve.