3106 · 3 Motor System

Peripheral Nerve Syndromes

Transection of a mixed peripheral nerve causes flaccid paresis of the muscle(s) supplied by the nerve, a sensory deficit in the distribution of the interrupted afferent fibers of the nerve, and autonomic deficits.

When the continuity of an axon is disrupted, degeneration of the axon as well as of its myelin sheath begins within hours or days at the site of the injury, travels distally down the axon, and is usually complete within 15­20 days (socalled secondary or wallerian degeneration).

Damaged axons in the central nervous system lack the ability to regenerate, but damaged axons in peripheral nerves can do so, as long as their myelin sheaths remain intact to serve as a template for the regrowing axons. Even when a nerve is completely transected, resuturing of the sundered ends can be followed by near-complete regeneration of axons and restoration of functional activity. Electromyography (EMG) and nerve conduction studies are often very helpful in assessing the severity of a peripheral nerve injury and the chances for a good recovery.

Figure 3.35 illustrates the anatomical course of a number of important peripheral nerves that are commonly injured. Figure 3.36 shows typical clinical pictures of radial, median, and ulnar nerve palsies.

The more common causes of isolated peripheral nerve palsies are: compression of a nerve at an anatomically vulnerable point or bottleneck (scalene syndrome, cubital tunnel syndrome, carpal tunnel syndrome, peroneal nerve injury at the fibular head, tarsal tunnel syndrome); traumatic injury (including iatrogenic lesions, e. g., puncture and injection injuries); and ischemia (e. g., in compartment syndrome and, less commonly, in infectious/inflammatory processes).

Carpal Tunnel Syndrome

Carpal tunnel syndrome (Fig. 3.37a) is caused by median nerve damage in the carpal tunnel, which can be narrowed at the site where the nerve passes under the transverse carpal ligament (flexor retinaculum). Patients typically complain of pain and paresthesiae in the affected hand, which are especially severe at night and may be felt in the entire upper limb (brachialgia paresthetica nocturna), as well as of a feeling of swelling in the wrist or the entire hand. Trophic abnormalities and atrophy of the lateral thenar muscles (abductor pollicis brevis and opponens pollicis) are common in advanced cases. The median nerve contains an unusually large proportion of autonomic fibers; thus, median nerve lesions are a frequent cause of complex regional pain syndrome (previously called reflex sympathetic dystrophy, or Sudeck syndrome).

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Complex Clinical Syndromes due to Lesions of Specific Components of the Nervous System · 107	3

Fig. 3.36 Typical appearance of peripheral nerve palsies affecting the hand. a Wrist drop (radial nerve palsy).

b Claw hand (ulnar nerve palsy). c Pope’s blessing (median nerve palsy).

d Monkey hand (combined median and ulnar nerve palsy). The areas of sensory deficit are shaded blue.

Ulnar Nerve Lesions—Cubital Tunnel Syndrome

Ulnar nerve palsy is the second most common peripheral nerve condition, after median nerve palsy. The ulnar nerve is particularly vulnerable to injury at the site of its passage through the cubital tunnel, on the medial side of the extensor aspect of the elbow (Fig. 3.37b). It can be damaged here by acute trauma or, even more commonly, by chronic pressure, e. g., by habitually propping up the arm on a hard surface, which may be an unavoidable posture in certain occupations. Paresthesia and hypesthesia in the ulnar portion of the hand are accompanied, in advanced cases, by atrophy of the hypothenar muscles and of the adductor pollicis (ulnar nerve palsy with claw hand).

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3 108 · 3 Motor System

Flexor	Median n.
retinaculum

Carpaltunnel

Ulnar n.

a

b

Fig. 3.37 a Carpal tunnel with median nerve (carpal tunnel syndrome). b Cubital tunnel syndrome: pressure palsy of the ulnar nerve due to external compression or dislocation.

Polyneuropathies

A pathological process affecting multiple peripheral nerves is called polyneuropathy, and an infectious or inflammatory process affecting multiple peripheral nerves is called polyneuritis. Polyneuropathies can be classified by histological­structural criteria (axonal, demyelinating, vascular-ischemic), by the systems they affect (sensory, motor, autonomic), or by the distribution of neurological deficits (mononeuropathy multiplex, distal-symmetric, proximal). Polyneuropathies and polyneuritides have many causes, and their diagnosis and treatment are accordingly complex. A more detailed discussion of these disorders would be beyond the scope of this book.

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Complex Clinical Syndromes due to Lesions of Specific Components of the Nervous System · 109	3

Differential Diagnosis of Radicular and Peripheral Nerve Lesions

The functions of individual muscles and their radicular (segmental) and peripheral nerve innervation are listed in Table 3.1. The information in this table can be used to determine whether muscle weakness in a particular distribution is due to a radicular or a peripheral nerve lesion, and to localize the lesion to the particular root or nerve that is affected.

Table 3.1 Segmental and Peripheral Innervation of Muscles

Function	Muscle	Nerve
I. Cervical plexus, C1–C4
		Cervical nerves

Flexion, extension, rotation, and lateral flexion of the neck

Deep muscles of the neck C1–C4 (also sternocleidomastoid

and trapezius)

Elevation of the upper rib cage,	Scalene muscles	C3	–C5
inspiration
		Phrenic nerves
Inspiration	Diaphragm	C3, C4, C5
II. Brachial plexus, C5–T1
		Medial and lateral
		pectoral nerves
Adduction and internal rotation of the	Pectoralis major	C5	–T1
arm and depression of the shoulder from	Pectoralis minor
posterior to anterior
		Long thoracic nerve
Fixation of the scapula on lifting of the	Serratus anterior	C5	–C7
arm (protraction of the shoulder)
		Dorsal scapular
		nerve
Elevation and adduction of the scapula	Levator scapulae	C4	–C5
toward the spine	Rhomboids
		Suprascapular nerve
Elevation and external rotation of the arm	Supraspinatus	C4	–C6
External rotation of the arm at the	Infraspinatus	C4	–C6
shoulder
		Thoracodorsal nerve
Internal rotation of the arm at the	Latissimus dorsi	C5	–C8
shoulder, and adduction from anterior to	Teres major	(from the posterior
posterior as well as depression of the ele-	Subscapularis	cord of the brachial
vated arm		plexus)

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3110 · 3 Motor System

Table 3.1 (Continued)

Function

Lateral elevation (abduction) of the arm up to the horizontal position

External rotation of the arm

Flexion of the arm and forearm, supination

Elevation and adduction of the arm Elbow flexion

Flexion and radial deviation of the hand Pronation

Wrist flexion

Flexion of the interphalangeal (IP) joint of the thumb

Flexion of the proximal IP joints of the 2nd through 5th fingers

Flexion of the distal IP joints of the 2nd and 3rd fingers

Abduction of 1st metacarpal

Flexion of the metacarpophalangeal (MP) joint of the thumb

Opposition of 1st metacarpal

Flexion of MP joints and extension of IP joints of 2nd and 3rd fingers

Flexion of MP joints and extension of IP joints of 4th and 5th fingers

Flexion and ulnar deviation of the hand

Flexion of the distal IP joints of the 4th and 5th fingers

Abduction of 1st metacarpal Abduction of 5th finger Opposition of 5th finger Flexion of MP joint of 5th finger

Flexion of MP and extension of IP joints of 3rd, 4th, and 5th fingers; also aband adduction of these fingers

Muscle	Nerve
	Axillary nerve
Deltoid	C5	–C6
Teres minor	C4	–C5
	Musculocutaneous
	nerve
Biceps brachii	C5	–C6
Coracobrachialis	C5	–C7
Brachialis	C5	–C6
	Median nerve
Flexor carpi radialis	C6	–C7
Pronator teres	C6	–C7
Palmaris longus	C7	–T1
Flexor pollicis longus	C6	–C8
Flexor digitorum superfi-	C7	–T1
cialis
Flexor digitorum profun-	C7	–T1
dus (radial part)
Abductor pollicis brevis	C7	–T1
Flexor pollicis brevis	C7	–T1
Opponens pollicis brevis	C6	–C7
Lumbricals I, II	C8	–T1
	Ulnar nerve
Lumbricals III, IV	C8	–T1
Flexor carpi ulnaris	C7	–T1
Flexor digitorum profun-	C7	–T1
dus (ulnar part)
Adductor pollicis	C8	–T1
Abductor digiti quinti	C8	–T1
Opponens digiti quinti	C7	–T1
Flexor digiti quinti brevis	C7	–T1
Interossei (palmar and	C8	–T1
dorsal)

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Complex Clinical Syndromes due to Lesions of Specific Components of the Nervous System · 111 3

Table 3.1 (Continued)

Function	Muscle	Nerve
		Radial nerve
Elbow extension	Triceps brachii, anconeus	C6–C8
Elbow flexion	Brachioradialis	C5–C6
Extension and radial deviation of hand	Extensor carpi radialis	C6–C8
Extension at MP joints of 2nd through	Extensor digitorum	C6–C8
5th fingers; spreading of the fingers;
dorsiflexion of the hand
Extension of 5th finger	Extensor digiti quinti	C6–C8
Extension and ulnar deviation of hand	Extensor carpi ulnaris	C6–C8
Supination	Supinator	C5–C7
Abduction of 1st metacarpal, radial	Abductor pollicis longus	C6–C7
extension of the hand
Extension of thumb at MP joint	Extensor pollicis brevis	C7–C8
Extension of thumb at IP joint	Extensor pollicis longus	C7, C8
Extension of 2nd finger at MP joint	Extensor indicis proprius	C6–C8
		Intercostal nerves
Elevation of the ribs, expiration, Valsalva	Thoracic and abdominal
maneuver, anteroflexion and lateral flex-	muscles
ion of the trunk
III. Lumbar plexus, T12–L4
		Femoral nerve
Hip flexion and internal rotation	Iliopsoas	L1	–L3
Hip flexion and external rotation; knee	Sartorius	L2	–L3
flexion and internal rotation
Knee extension	Quadriceps femoris	L2	–L4
		Obturator nerve
Thigh adduction	Pectineus	L2	–L3
	Adductor longus	L2	–L3
	Adductor brevis	L2	–L4
	Adductor magnus	L3	–L4
	Gracilis	L2	–L4
Thigh adduction and external rotation	Obturator externus	L3	–L4
IV. Sacral plexus, L5–S1
		Superior gluteal nerve
Thigh abduction and internal rotation	Gluteus medius	L4	–S1
	Gluteus minimus
Hip flexion; thigh abduction and internal	Tensor fasciae latae	L4	–L5
rotation
Thigh abduction and external rotation	Piriformis	L5	–S1

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3 112 · 3 Motor System

Table 3.1 (Continued)

Function	Muscle	Nerve
		Inferior gluteal nerve
Hip extension	Gluteus maximus	L4	–S2
	Obturator internus	L5	–S1
External rotation of the thigh	Gemelli	L4	–S1
	Quadratus femoris	L4	–S1
		Sciatic nerve
Knee flexion	Biceps femoris	L4	–S2
	Semitendinosus	L4	–S1
	Semimembranosus	L4	–S1
		Deep peroneal nerve
Dorsiflexion and supination of the foot	Tibialis anterior	L4	–L5
Extension of toes and foot	Extensor digitorum	L4	–S1
	longus
Extension of 2nd through 5th toes	Extensor digitorum brevis	L4	–S1
Extension of great toe	Extensor hallucis longus	L4	–S1
	Extensor hallucis brevis	L4	–S1
		Superficial peroneal
		nerve
Dorsiflexion and pronation of the foot	Peroneal muscles	L5	–S1
		Tibial nerves
Plantar flexion of the foot in supination	Gastrocnemius	L5	–S2
	Soleus
	(together called triceps
	surae)
Supination and plantar flexion of the foot	Tibialis posterior	L4	–L5
Flexion of distal IP joints of 2nd through	Flexor digitorum longus	L5	–S2
5th toes; plantar flexion of the foot in
supination
Flexion of IP joint of great toe	Flexor hallucis longus	L5	–S2
Flexion of proximal IP joints of 2nd	Flexor digitorum brevis	S1–S3
through 5th toes
Flexion of MP joints of toes, abduction	Plantar muscles of the	S1–S3
and adduction of toes	foot
		Pudendal nerve
Closure of bladder and bowel	Vesical and anal	S2–S4
	sphincters

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