Lesson-Interscalene

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).

4 – The cutaneous innervation of the shoulder

The cutaneous innervation of the shoulder is:

1) the axillary nerve (C5-C6; superior lateral brachial cutaneous nerve)

2) the supraclavicular nerve (C4; from the cervical plexus)

3) intercostal nerves (T2-T4; anterior cutaneous branches)

4) radial nerve (C5-T1; inferior lateral brachial cutaneous branches)

The interscalene brachial plexus block typically covers only C5-C6

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Innervation: Axillary nerve (cyan), supraclavicular nerve (pink), lateral cutaneous nerves (purple), medial brachial cutaneous nerve (green), inferior lateral brachial cutaneous nerve (from radial nerve, yellow).

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)

8 – Indications of the interscalene block

The indications of the interscalene block are:

– Anaesthesia for shoulder surgery & shoulder
procedures

– Analgesia after shoulder surgery & shoulder
procedures

The ultrasound guided interscalene brachial plexus block is a basic level block

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A dislocated shoulder joint can be reduced using an interscalene brachial plexus block

9 – How to perform an ultrasound guided interscalene brachial plexus block

– Select a high-frequency linear probe
– Adjust gain, focus, and depth 2-3 cm
– Turn the orientation mark on the probe postero-lateral on the right side and antero-lateral on
the left side of the patient
– Place the probe behind the clavicle on top of the first rib oriented practically in the
parasagittal plane
– Locate the black, pulsatile subclavian artery (SA) on top of the first rib between the anterior
and the middle scalene muscles
– Locate the branches of the brachial plexus (BP) posterior to the SA
– Track the BP branches proximally until the profiles of the C5 and C6 spinal nerve roots line
up like a string of black pearls in the interscalene groove. C5 appears as one profile, C6 as
two
– Capture the best possible cross sectional image by tilting the probe and fine-tuning gain,
focus, and depth

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(A) Starting position (B) subclavian artery (A), costa I (CI) and brachial plexus branches (PB) (C) Track the brachial plexus branches proximally (D) C5 and C6 spinal nerve branches into the intescalene groove where they are sandwiched between the anterior scalene (SA) and the middle scalene (SM)

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.

19 – Do not penetrate the brachial plexus nerves in the interscalene groove

It is important to advance the needle tangential to the target nerves and NOT penetrate the nerves

Click on the VIDEO CLIP button to view the video

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By advancing the needle tangentially to the nerves, it is possible to avoid piercing the nerves
C5 = spinal nerve root of C5; C6 = spinal nerve root of C6; C7 = spinal nerve root of C7; ASM = anterior scalene muscle; MSM = middle scalene muscle

14 – The in-plane approach to the interscalene brachial plexus block

The in-plane approach to the interscalene brachial plexus block

Local anaesthetic is deposited lateral to C5 and C6

You often feel a “pop” as you enter the interscalene groove

Click on the VIDEO CLIP button to view the video

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The video shows the in-plane approach to the interscalene block of the brachial plexus
ASM = anterior scalene muscle; MSM = middle scalene muscle; C5 = spinal nerve root of C5; C6 = spinal nerve root of C6

15 – Tracking the brachial plexus from the subclavian artery to the interscalene groove

To localise the brachial plexus you should start by localising the pulsating subclavian artery where it runs across the first rib

The branches of the brachial plexus are located just lateral to the artery

Track the branches of the brachial plexus proximally until they line up as a string of black pearls in the interscalene groove

Click on the VIDEO CLIP button to view the video

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The video shows the tracking of the branches of the brachial plexus from the level of the subclavian artery to the interscalene groove
SA = subclavian artery; BP = cluster of branches of the brachial plexus; ASM = anterior scalene muscle; MSM = middle scalene muscle