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Anatomy for Needle Electromyography


Upper Extremity

Median Nerve

Abductor Pollicis Brevis (APB) ( Fig. 13.1A,B )

Innervation

  • Median nerve, medial cord, lower trunk, C8–T1

    Fig. 13.1, (A) Abductor pollicis brevis insertion point. (B) Cross-section anatomy. a a All cross-section anatomy figures adapted from Eycleshymer AC, Schoemaker DM. A Cross-Section Anatomy . New York: D Appleton Century Company; 1911. All figures are in the public domain.

Needle Insertion

  • Insert the needle tangentially into the lateral thenar eminence, just lateral to the mid-point of the first metacarpal.

Activation

  • Abduct the thumb with arm and hand in the supinated position.

Key Clinical Points

  • The APB is the best median muscle to sample distal to the carpal tunnel.

  • May be abnormal in carpal tunnel syndrome, proximal median neuropathies, lower trunk/medial cord plexopathy, thoracic outlet syndrome, C8–T1 radiculopathy, and distal polyneuropathy.

  • Spared in anterior interosseous nerve syndrome.

  • The APB often is perceived as more painful to sample than other intrinsic hand muscles.

Cross-Section Anatomy Key Points

  • If the needle is inserted too medially, it may be in the flexor pollicis brevis, which has both median and ulnar innervation.

  • If the needle is inserted too deeply, it may be in the opponens pollicis, also innervated by the median nerve.

Opponens Pollicis (OP) ( Fig. 13.2A,B )

Innervation

  • Median nerve, medial cord, lower trunk, C8–T1

    Fig. 13.2, (A) Opponens pollicis insertion point. (B) Cross-section anatomy. a

Needle Insertion

  • With the needle parallel to the hand, insert the needle into the patient’s lateral thenar eminence, just above the first metacarpal bone.

Activation

  • Have the patient oppose the thumb to little finger with the arm and hand in the supinated position.

Key Clinical Points

  • May be abnormal in carpal tunnel syndrome, proximal median neuropathies, lower trunk/medial cord plexopathy, thoracic outlet syndrome, C8–T1 radiculopathy, distal polyneuropathy.

  • Spared in anterior interosseous nerve syndrome.

Cross-Section Anatomy Key Points

  • The OP muscle lies below the APB. If the needle is inserted too medially or superficially, it will be in the APB.

Flexor Pollicis Brevis (FPB) ( Fig. 13.3A,B )

Innervation

  • Median and ulnar nerves, medial cord, lower trunk, C8–T1

    Fig. 13.3, (A) Flexor pollicis brevis insertion point. (B) Cross-section anatomy. a

Needle Insertion

  • Insert the needle just medial to the mid-point of the first metacarpal in the thenar eminence.

Activation

  • Have the patient flex the thumb at the metacarpal-phalangeal joint.

Key Clinical Points

  • Sampling this muscle is often perceived as more painful than the APB.

  • The superficial head usually is median innervated; the deep head usually is ulnar innervated.

  • Innervation varies widely in normal subjects. In some individuals, both heads are median innervated; in others, both are ulnar innervated.

  • Because of normal anatomic variation, abnormalities should be interpreted with caution when trying to separate median from ulnar lesions.

Cross-Section Anatomy Key Points

  • If the needle is inserted too laterally, it will be in the APB.

Pronator Quadratus (PQ) ( Fig. 13.4A,B )

Innervation

  • Anterior interosseous nerve, median nerve, lateral-medial cords, middle-lower trunks, C7– C8 –T1

    Fig. 13.4, (A) Pronator quadratus insertion point. (B) Cross-section anatomy. a

Needle Insertion

  • With the patient’s hand in mid-position between supination and pronation, insert the needle in the patient’s dorsal forearm three fingerbreadths proximal to the mid-point of a line drawn from the ulnar to radial styloids. Insert the needle deep through the interosseous membrane.

Activation

  • Have the patient pronate the hand with the elbow flexed.

Key Clinical Points

  • May be abnormal in anterior interosseous nerve syndrome or proximal median neuropathies.

  • The PQ is a distal C8 median-innervated muscle above the wrist.

  • Spared in carpal tunnel syndrome.

  • The muscle is deep to the finger and thumb extensor muscles and their tendons.

Cross-Section Anatomy Key Points

  • Before reaching the muscle, one must go through the thick interosseous membrane.

Flexor Pollicis Longus (FPL) ( Fig. 13.5A,B )

Innervation

  • Anterior interosseous nerve, median nerve, lateral-medial cords, middle-lower trunks, C7– C8 –T1

    Fig. 13.5, (A) Flexor pollicis longus insertion point. (B) Cross-section anatomy. a

Needle Insertion

  • With the patient’s forearm supinated, insert the needle straight down one-third the distance up from the lateral wrist toward the lateral elbow, over the radius.

Activation

  • Have the patient flex the thumb at the interphalangeal joint.

Key Clinical Points

  • Often abnormal in anterior interosseous nerve syndrome or proximal median neuropathies.

  • The FPL is a distal C8 median-innervated muscle above the wrist.

  • Spared in carpal tunnel syndrome.

Cross-Section Anatomy Key Points

  • Caution : the radial artery is just lateral to the insertion point.

  • Caution : the superficial radial sensory nerve is lateral to the insertion point.

  • If the needle is too superficial, it may be in the flexor digitorum sublimis.

Flexor Digitorum Profundus to Digits 2, 3 (FDP 2, 3) ( Fig. 13.6A,B )

Innervation

  • Anterior interosseous nerve, median nerve, medial cord, lower trunk, C7– C8 –T1

    Fig. 13.6, (A) Flexor digitorum profundus to digits 2, 3 insertion point. (B) Cross-section anatomy. a

Needle Insertion

  • With the patient’s elbow flexed, hand pointing toward the head and the back of the hand facing down, insert the needle three to four fingerbreadths distal to the olecranon.

Activation

  • Have the patient flex the fingers (digit 2 or digit 3) at the distal interphalangeal (DIP) joints.

Key Clinical Points

  • Deeper layers are median-innervated (anterior interosseous nerve) to digits 2 and 3.

  • Superficial layers are ulnar-innervated to digits 4 and 5.

  • Median slips (deep) are difficult to study. The individual muscle slip can be identified by having the patient flex one finger at a time.

  • The median FDP may be abnormal in anterior interosseous nerve syndrome or proximal median neuropathies.

Cross-Section Anatomy Key Points

  • Caution : when placing the needle deep to reach the median slips, the main ulnar nerve is within reach of the needle. To avoid the ulnar nerve, the needle should be angled medially toward the body. Indeed, this muscle is best avoided unless it is absolutely needed to establish the diagnosis (e.g., anterior interosseous neuropathy).

Flexor Digitorum Sublimis (FDS) ( Fig. 13.7A,B )

Innervation

  • Median nerve, medial-lateral cords, middle-lower trunks, C7– C8

    Fig. 13.7, (A) Flexor digitorum sublimis insertion point. (B) Cross-section anatomy. a

Needle Insertion

  • With the patient’s forearm supinated, insert the needle just medial to the mid-point between the antecubital fossa and the mid-wrist.

Activation

  • Have the patient flex the digits at the proximal interphalangeal joints.

Key Clinical Points

  • May be abnormal in proximal median neuropathies.

  • Spared in anterior interosseous nerve syndrome.

Cross-Section Anatomy Key Points

  • The FDS supplies digits 2–5. The slips to different fingers can be determined by placing the needle slightly lateral or medial to the original location and having the patient move individual fingers.

  • If the needle is too deep, it will be in the FDP.

  • Caution : if the needle is placed in the midline and too deeply, it may reach the median nerve.

  • More difficult muscle to localize than other proximal median-innervated muscles (e.g., flexor carpi radialis [FCR] and pronator teres [PT]).

Flexor Carpi Radialis (FCR) ( Fig. 13.8A,B )

Innervation

  • Median nerve, lateral cord, upper-middle trunks, C6–C7

    Fig. 13.8, (A) Flexor carpi radialis insertion point. (B) Cross-section anatomy. a

Needle Insertion

  • With the patient’s forearm supinated, insert the needle four fingerbreadths distal to the mid-point between the biceps tendon and medial epicondyle on a line to the center of the wrist.

Activation

  • Have the patient flex the wrist radially.

Key Clinical Points

  • Often abnormal in C6 or C7 radiculopathy.

  • Often abnormal in proximal median neuropathies including pronator syndrome.

  • Spared in anterior interosseous nerve syndrome.

Cross-Section Anatomy Key Points

  • If the needle is too medial, it may be in the FDS.

  • If the needle is too lateral and deep, it may be in the PT.

  • Caution : if the needle is placed too deeply, it may reach the median nerve.

Pronator Teres (PT) ( Fig. 13.9A,B )

Innervation

  • Median nerve, lateral cord, upper-middle trunks, C6–C7

    Fig. 13.9, (A) Pronator teres insertion point. (B) Cross-section anatomy. a

Needle Insertion

  • With the patient’s forearm supinated, insert the needle two fingerbreadths distal to the mid-point between biceps tendon and medial epicondyle.

Activation

  • Have the patient pronate the hand with the elbow fully extended.

Key Clinical Points

  • Often abnormal in C6 or C7 radiculopathy.

  • Often abnormal in proximal median neuropathies but may be spared in pronator syndrome.

  • Spared in anterior interosseous nerve syndrome.

  • It is easily located and activated.

Cross-Section Anatomy Key Points

  • The PT is the first muscle medial to the antecubital fossa.

  • If the needle is too lateral, it will be in either the FCR or the FDS.

  • Caution : if the needle is placed deeply, it can easily reach the median nerve.

Ulnar Nerve

First Dorsal Interosseous (FDI)( Fig. 13.10A,B )

Innervation

  • Ulnar nerve, medial cord, lower trunk, C8–T1

    Fig. 13.10, (A) First dorsal interosseous insertion point. (B) Cross-section anatomy. a

Needle Insertion

  • Insert the needle into the patient’s dorsal hand, halfway between the first and second metacarpal-phalangeal joints.

Activation

  • Have the patient abduct the index finger (spread the fingers).

Key Clinical Points

  • The FDI is easy to study.

  • It is the least painful of the intrinsic hand muscles to sample.

  • Often abnormal in ulnar lesions at Guyon’s canal. May be abnormal in ulnar neuropathy, lower trunk/medial cord plexopathy, thoracic outlet syndrome, C8–T1 radiculopathy, and distal polyneuropathy.

Cross-Section Anatomy Key Points

  • If the needle is too deep, it will be in the adductor pollicis muscle, which is also supplied by the ulnar nerve.

Abductor Digiti Minimi (ADM)( Fig. 13.11A,B )

Innervation

  • Ulnar nerve, medial cord, lower trunk, C8–T1

    Fig. 13.11, (A) Abductor digiti minimi insertion point. (B) Cross-section anatomy. a

Needle Insertion

  • Insert the needle into the medial hand at the mid-point of the fifth metacarpal.

Activation

  • Have the patient abduct the little finger (spread the fingers).

Key Clinical Points

  • The ADM may be involved but also may be spared in some ulnar lesions at Guyon’s canal. May be abnormal in ulnar neuropathy, lower trunk/medial cord plexopathy, thoracic outlet syndrome, C8–T1 radiculopathy, and distal polyneuropathy.

  • This muscle often is perceived as more painful to sample than the FDI.

Cross-Section Anatomy Key Points

  • If the needle is inserted too deeply, it will be in the flexor or opponens digiti minimi; however, both of these muscles are also supplied by the ulnar nerve in the hypothenar eminence.

Flexor Digitorum Profundus to Digits 4, 5 (FDP 4, 5) ( Fig. 13.12A,B )

Innervation

  • Ulnar nerve, medial cord, lower trunk, C7– C8 –T1

    Fig. 13.12, (A) Flexor digitorum profundus to digits 4, 5 insertion point. (B) Cross-section anatomy. a

Needle Insertion

  • With the patient’s elbow flexed, hand pointing toward the head and the back of the hand facing down, insert the needle three to four fingerbreadths distal to the olecranon.

Activation

  • Have the patient flex the fingers (digit 4 or digit 5) at the DIP joints.

Key Clinical Points

  • Superficial layers are ulnar-innervated to digits 4 and 5.

  • Deeper layers are median-innervated (anterior interosseous nerve) to digits 2 and 3.

  • Ulnar slips (superficial) are easy to study. The individual muscle slip can be identified by having the patient flex one finger at a time.

  • The ulnar FDP often is involved in ulnar neuropathy at the elbow.

Cross-Section Anatomy Key Points

  • Caution : the main ulnar nerve is within reach of the needle. To avoid the ulnar nerve, the needle should be angled slightly medially toward the body.

Flexor Carpi Ulnaris (FCU) ( Fig. 13.13A,B )

Innervation

  • Ulnar nerve, medial cord, lower trunk, C8 –T1

    Fig. 13.13, (A) Flexor carpi ulnaris insertion point. (B) Cross-section anatomy. a

Needle Insertion

  • With the patient’s forearm supinated, insert the needle into the medial forearm at the mid-point between the elbow and wrist.

Activation

  • Have the patient flex the wrist in ulnar deviation or abduct the fifth finger.

Key Clinical Points

  • To ensure proper needle location, ask the patient to spread his or her fingers. During fifth-finger abduction, the FCU contracts to fix the pisiform bone, the origin of the ADM. The FCU is the only muscle in the forearm that will be contracted with spreading of the fingers.

  • The FCU muscle is very superficial and thin.

  • The muscle often is spared in ulnar neuropathy at the elbow, especially in mild cases.

Cross-Section Anatomy Key Points

  • If the needle is inserted too deeply, it will be in the FDP.

Radial Nerve

Extensor Indicis Proprius (EIP)( Fig. 13.14A,B )

Innervation

  • Posterior interosseous nerve, radial nerve, posterior cord, middle-lower trunks, C7– C8

    Fig. 13.14, (A) Extensor indicis proprius insertion point. (B) Cross-section anatomy. a

Needle Insertion

  • With the patient’s hand and forearm pronated, insert the needle straight down slightly medial to the point two fingerbreadths proximal to the ulnar styloid.

Activation

  • Have the patient extend the index finger.

Key Clinical Points

  • Can be abnormal in all radial nerve lesions, including posterior interosseous nerve palsy.

  • The EIP is the most distal radial-innervated muscle.

  • May be abnormal in lower trunk/posterior cord plexopathy, thoracic outlet syndrome, C8 radiculopathy, and distal polyneuropathy.

Cross-Section Anatomy Key Points

  • This muscle is often deep. If the needle is too superficial, it will be in the extensor carpi ulnaris or extensor digiti quinti.

  • The needle passes near several superficial tendons.

Extensor Carpi Ulnaris (ECU) ( Fig. 13.15A,B )

Innervation

  • Posterior interosseous nerve, radial nerve, posterior cord, middle-lower trunks, C7– C8

    Fig. 13.15, (A) Extensor carpi ulnaris insertion point. (B) Cross-section anatomy. a

Needle Insertion

  • With the patient’s forearm pronated, insert the needle just rostral to the mid-point of the ulna.

Activation

  • Have the patient extend the wrist in ulnar deviation.

Key Clinical Points

  • Can be abnormal in all radial nerve lesions, including posterior interosseous nerve palsy.

  • May be abnormal in lower trunk/posterior cord plexopathy, thoracic outlet syndrome, C7–C8 radiculopathy, and distal polyneuropathy.

Cross-Section Anatomy Key Points

  • If the needle is too medial, it will be in the extensor digiti quinti or extensor digitorum communis.

Extensor Digitorum Communis (EDC)( Fig. 13.16A,B )

Innervation

  • Posterior interosseous nerve, radial nerve, posterior cord, middle-lower trunks, C7 –C8

    Fig. 13.16, (A) Extensor digitorum communis insertion point. (B) Cross-section anatomy. a

Needle Insertion

  • With the patient’s forearm pronated, insert the needle three to four fingerbreadths distal to the olecranon, three fingerbreadths above the ulna.

Activation

  • Have the patient extend the middle finger.

Key Clinical Points

  • The EDC is a superficial muscle and easily palpated when the patient activates the muscle.

  • Can be abnormal in all radial nerve lesions, including posterior interosseous nerve palsy.

  • This muscle often is selected for study for single-fiber electromyography (EMG).

Cross-Section Anatomy Key Points

  • If the needle is too lateral, it may be in the ECU.

  • If the needle is too medial, it may be in the extensor carpi radialis (ECR).

  • Caution : if the needle is placed too deeply, it may reach the radial motor nerve. However, the muscle is very easy to sample just below the surface.

Extensor Carpi Radialis–Long Head (ECR-LH) ( Fig. 13.17A,B )

Innervation

  • Radial nerve, posterior cord, upper–middle trunks, C6–C7

    Fig. 13.17, (A) Extensor carpi radialis (long head) insertion point. (B) Cross-section anatomy. a

Needle Insertion

  • With the patient’s forearm pronated, insert the needle just above the lateral epicondyle.

Activation

  • Have the patient extend the wrist radially.

Key Clinical Points

  • The long head of the ECR is the only forearm extensor spared in posterior interosseous nerve palsy.

  • May be abnormal in radial nerve lesions at or proximal to the spiral groove.

Cross-Section Anatomy Key Points

  • If the needle is inserted distally into the extensor mass, it is difficult to separate this muscle from other wrist and finger extensors innervated by the posterior interosseous nerve.

  • If the needle is inserted too medially, it will be in the brachioradialis (BR).

Brachioradialis (BR) ( Fig. 13.18A,B )

Innervation

  • Radial nerve, posterior cord, upper trunk, C5–C6

    Fig. 13.18, (A) Brachioradialis insertion point. (B) Cross-section anatomy. a

Needle Insertion

  • Insert the needle three to four fingerbreadths distal to the mid-point between the biceps tendon and lateral epicondyle.

Activation

  • Have the patient flex the elbow with the wrist in the mid-position between supination and pronation.

Key Clinical Points

  • May be abnormal in lesions of the radial nerve at or proximal to the spiral groove.

  • Spared in posterior interosseous nerve palsy.

  • May be abnormal in upper trunk plexopathy or C5 or C6 radiculopathy.

Cross-Section Anatomy Key Points

  • The BR is the first muscle lateral to the antecubital fossa.

  • If the needle is too lateral and deep, it will be in the ECR.

Anconeus (ANC) ( Fig. 13.19A,B )

Innervation

  • Radial nerve, posterior cord, upper-middle-lower trunks, C6– C7 –C8

    Fig. 13.19, (A) Anconeus insertion point. (B) Cross-section anatomy. a

Needle Insertion

  • With the patient’s forearm pronated, insert the needle one to two fingerbreadths distal to the olecranon slightly above the ulna.

Activation

  • Have the patient extend the elbow.

Key Clinical Points

  • The ANC is effectively an extension of the medial head of the triceps.

  • It is the only radial muscle in the forearm innervated from above the spinal groove.

  • Spared in radial neuropathy at the spiral groove.

Cross-Section Anatomy Key Points

  • If the needle is too anterior, it will be in the ECU or EDC.

Triceps Brachii–Lateral Head (TB)( Fig. 13.20A,B )

Innervation

  • Radial nerve, posterior cord, upper-middle-lower trunks, C6– C7 –C8

    Fig. 13.20, (A) Triceps brachii (lateral head) insertion point. (B) Cross-section anatomy. a

Needle Insertion

  • With the patient’s forearm pronated and the elbow flexed, insert the needle just below the mid-point between the lateral epicondyle and shoulder.

Activation

  • Have the patient extend the elbow.

Key Clinical Points

  • The lateral head is the easiest of the three heads of the triceps to study.

  • Often abnormal in C7 radiculopathy.

  • Spared in radial neuropathy at the spiral groove.

  • The most consistently abnormal muscle in C7 radiculopathy.

  • If sampled too distally (near the elbow), the muscle is more tendinous and more painful.

Cross-Section Anatomy Key Points

  • As long as this muscle is sampled from the lateral approach, there are no other nearby vascular structures or major nerves.

Musculocutaneous Nerve

Biceps Brachii (BB) ( Fig. 13.21A,B )

Innervation

  • Musculocutaneous nerve, lateral cord, upper trunk, C5–C6

    Fig. 13.21, (A) Biceps brachii insertion point. (B) Cross-section anatomy. a

Needle Insertion

  • With the patient’s forearm supinated, insert the needle at the mid-point between the biceps tendon and the anterior shoulder.

Activation

  • Have the patient flex the elbow with the hand supinated.

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