3.1
Pectoralis major
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Surface anatomy : Superficial and thick muscle.
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Origin : Wide origin area such as medial clavicle, sternum, and cartilages of all ribs.
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Insertion : Narrowly converge to upper humerus anteromedial site (bicipital groove).
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Function : Shoulder adduction and medial (internal) rotation.
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Motor point (MP) : MP1, lateral 1/3 point between anterior axillary fold (A) and suprasternal notch (B) 10 . MP2, mid-point between anterior axillary fold (A) and nipple (C).
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Injection tip: The MP1 is in deep (MP2 is not as deep as MP1). Pneumothorax can be prevented, as long as the needle is not deeper than 4 cm (in adult). At supine or sitting position, abduct the shoulder about 60 degrees and then grab the pectoralis muscle lateral part with one hand. It helps to estimate the needle depth. If elbow or hand movement is noticed, the needle is close to the brachial plexus.
3.2
Corachobrachialis
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Surface anatomy : Just medial and posterior to biceps brachii short head.
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Origin : Coracoid process of scapula.
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Insertion : Medial humerus.
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Function : shoulder adduction and flexion.
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Motor point (MP) : MP is just inferior to the short head of biceps brachii where the lateral border of the pectoralis major meets medial border of short head of biceps brachii.
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Injection tip : Needs shoulder abduction (about 90 degrees) to identify the muscle. Starting with low electric stimulation. MP is close to the axillary artery and musculocutaneous nerve. Insert needle toward the acromion to avoid the nerve stimulation (if needle is close to the nerve, significant elbow flexion is noted) and axillary artery puncture. MP is adequately stimulated, only shoulder adduction without elbow flexion can be seen.
3.3
Latissimus dorsi
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Surface anatomy : Superficial, flat, large muscle on the lateral part of back. It runs lateral to the scapula.
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Origin : Lower thoracic and all lumbar spine, thoracolumbar fascia, and iliac crest.
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Insertion : Upper humerus anteromedial site (bicipital groove).
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Function : Shoulder adduction, medial (internal) rotation, and extension.
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Motor point (MP) : Two-three finger breadths inferolateral to the inferior scapular angle 10 .
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Injection tip : At side lying position, identify the scapular inferior angle. Two-three finger breadths inferolateral to the scapular angle. Since this is thin flat muscle, grab this area with one hand and then insert a needle slowly (45 degrees to the surface). To prevent pneumothorax, do not insert a needle through intercostal area.
3.4
Supraspinatus
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Surface anatomy : Deep to upper trapezius muscle. Scapula spine separates supraspinatus and infraspinatus. Palpable with shoulder abduction only.
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Origin : Supraspinatus fossa of scapula.
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Insertion : Greater tubercle of humerus.
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Function : Shoulder abduction and lateral (external) rotation.
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Motor Point (MP) : 1–2 finger breaths superior to the midpoint (C) between the point (A) where scapular spine meets medial border of the scapula and acromion lateral tip (B).
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Injection tip : At sitting or side lying positon, make sure the needle passes through upper trapezius. If the needle hit the scapula, then draw the needle slowly backward.
3.5
Infraspinatus
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Surface anatomy : Deep to mid trapezius muscle. Scapula spine separates infraspinatus and supraspinatus.
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Origin : Infraspinatous fossa of the scapula.
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Insertion : Greater tubercle of the humerus.
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Function : Lateral (external) rotation of the shoulder.
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Motor point (MP) : Center of the infraspinous fossa (center of triangle ABC, A: point where scapular spine meets medial border of scapula, B: acromion, C: inferior angle).
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Injection tip : At prone, sitting, or side lying position, insert the needle through the center of the infraspinous fossa. The needle has to penetrate mid-trapezius muscle. If the needle hits the bone (scapula), draw the needle backward slowly.
3.6
Subscapularis
