4.1
Brachioradialis
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Surface anatomy : Lateral border of the antecubital fossa and palpable with forearm flexion at neutral position.
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Origin : Lateral supracondylar ridge of the distal humerus.
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Insertion : Radial styloid process (distal radius).
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Function : Elbow flexion at forearm neutral position.
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Motor point (MP) : Midpoint between biceps brachii tendon (lateral side, A) and lateral epicondyle (B) 13 .
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Injection tip : At sitting or supine position, keep the forearm in neutral position and elbow flexion 30–40 degrees (positioning is very important). MP is superficial. Make sure the elbow flexion at forearm neutral position with electrical stimulation (brachialis is a major elbow flexor at forearm neutral position).
4.2
Pronator teres
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Surface anatomy : Medial border of the antecubital fossa and palpable with forearm pronation.
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Origin : Medial supracondylar ridge of distal humerus.
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Insertion : Middle of the lateral surface of the radius.
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Functio n: Pronation of forearm and elbow flexion.
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Motor point (MP) : Midpoint between the medial epicondyle of the elbow (A) and half point of the lateral forearm (B). B is the midpoint between lateral antecubital fossa (C) and wrist lateral end (D).
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Injection tip : At sitting or supine position, keep the forearm in neutral position and slight elbow flexion (about 30 degrees). The muscle is superficial. If the needle is inserted deep, it may stimulate median nerve and wrist/finger flexors. Make sure the forearm pronation without finger or wrist flexion with electrical stimulation.
4.3
Pronator quadratus
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Surface anatomy : It lies deep to the distal anterior of forearm and runs obliquely from ulnar to radius.
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Origin : Distal one-quarter of the anterior ulnar.
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Insertion : Distal end of the anterior radius.
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Function : Forearm pronation when elbow is flexed.
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Motor point (MP) : Draw a line of twice length of the wrist (volar side, line AB) from the wrist ulnar end (point A) upward along the ulnar side (point C) (2 × AB = AC), then draw another line to the wrist radius end (point B). MP is the midpoint of the line BC.
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Injection tip : It is deep to the tendons of wrist-finger flexors. Make sure pronation of the forearm at elbow flexion position (pronator quadratus is a major forearm pronator at elbow flexion position). To minimize the median nerve stimulation, insert the needle through the medial side of palmaris longus tendon. Volar approach (described here) is recommended in two reasons. First, dorsal approach needs forearm pronation so it is difficult to see pronation with electrical stimulation and second, this muscle has narrower widow between the radius and ulnar at forearm pronated position (ultrasound image of the left forearm, b) than at forearm supinated (ultrasound image of the left forearm, a).
4.4
Palmaris longus
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Surface anatomy : Superficial and small located between flexor carpi radialis and flexor carpi ulnaris. Not always present (15% population absent). Prominent with wrist flexion.
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Origin : Medial supracondylar ridge of distal humerus.
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Insertion : Mid-wrist (palmar aponeurosis).
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Function : Wrist flexion.
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Motor point : Proximal one-third between medial epicondyle (A) and midpoint of distal wrist crease (Palmaris longus tendon insertion) (B).
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Injection tip : At sitting or supine position, keep the forearm in supinated position. The muscle is superficial. If Insert the needle deep, it may stimulate median nerve and/or wrist and finger flexors.
4.5
Flexor carpi radialis
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Surface anatomy : Superficial and medial to the pronator teres.
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Origin : Medial supracondylar ridge of the distal humerus.
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Insertion : Second and third metacarpal bones.
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Function : Wrist flexion and radial deviation.
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Motor point (MP) : Proximal one-third point of the line between medial epicondyle (A) and wrist radial end (B).
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Injection tip : At sitting or supine position, keep the forearm in supinated position. The muscle is superficial. If Insert the needle deep, it may stimulate median nerve and/or finger flexors. Make sure the wrist flexion without finger flexion.
4.6
Flexor carpi ulnaris
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Surface anatomy : Superficial and medial side of the forearm volar side.
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Origin : Medial supracondylar ridge of distal humerus.
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Insertion : Carpal bones and fifth metacarpal bone.
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Function : Wrist flexion and ulnar deviation.
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Motor point (MP) : Proximal one-third between medial epicondyle (A) and wrist joint ulnar end (B). 1 4
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Injection tip : At sitting or supine position, keep the arm abduction and forearm supination. If the needle is inserted deeply, it may stimulate ulnar nerve and/or finger flexors.
4.7
Flexor digitorum superficialis
