Fundamentals of Neurology: An Illustrated Guide

12. Diseases of the Spinal Nerve Roots and Peripheral Nerves

Fundamentals

Spinal Radicular Syndromes

Peripheral Nerve Lesions

Image  Fundamentals

Lesions of the peripheral nervous system cause flaccid weakness, sensory deficits, and autonomic disturbances in variable distributions and combinations depending on their localization and extent. They can be classified as lesions of the spinal nerve roots (radicular lesions), plexus lesions, or lesions of individual peripheral nerve trunks or branches.

Spinal Radicular Syndromes

Radicular lesions are usually due to mechanical compression; less commonly, they may be infectious/inflammatory or traumatic. Their main clinical manifestation is pain, usually accompanied by a sensory deficit in the dermatome of the affected nerve root. Depending on the severity of the lesion, there may also be flaccid weakness and areflexia in the muscle(s) innervated by the nerve root.

Preliminary anatomical remarks. The spinal nerve roots constitute the initial segment of the peripheral nervous system. The anterior (ventral) nerve roots contain efferent fibers, while the posterior (dorsal) nerve roots contain afferent fibers. The motor roots from T2 to L2 or L3 also contain the efferent fibers of the sympathetic nervous system. The anterior and posterior roots at a single level of the spinal cord on one side join to form the spinal nerve at that level, which then passes out of the spinal canal through the corresponding intervertebral foramen. At this point, the nerve roots are in close proximity to the intervertebral disk and the intervertebral (facet) joint (Fig. 12.1).

In their further course, the fibers of the spinal nerve roots of multiple segments form plexuses, from which they are then distributed to the peripheral nerves. The areas innervated by the nerve roots thus differ from those innervated by the peripheral nerves.

The sensory component of a spinal nerve root innervates a characteristic segmental area of skin, which is called a dermatome. The efferent fibers of a spinal nerve root, after redistribution into various peripheral nerves, innervate multiple muscles (the “myotome” of the nerve root at that level). Each muscle, therefore, obtains motor impulses from more than one nerve root, even if it is only innervated by a single peripheral nerve.

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Fig. 12.1 View of a cervical vertebra and intervertebral disk. The normal anatomy of the intervertebral (neural) foramen is shown on the left side of the figure; narrowing of the foramen by uncarthrosis is shown on the right. 1 Facets of the intervertebral joint; 2 root with spinal ganglion; 3 lateral/medial intervertebral disk herniation; 4 vertebral arteries; 5 uncarthrosis; 6 dorsal spondylosis; 7 ventral spondylosis; 8 spinal dura mater. (Modified from Mumenthaler M.: Der Schulter–Arm–Schmerz, 2nd edn, Huber, Bern 1982.)

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Table 12.1 lists the muscles that are often affected by radicular lesions in a way that is easily revealed by clinical neurological examination. The muscles that derive most of their innervation from a single nerve root are known as “root-indicating muscles.”

Causes of radicular syndromes. In most patients, the cause is compression of the nerve root by a space-occupying lesion, most often a herniated intervertebral disk, but sometimes a tumor, abscess, or other mass. In the cervical segments, spondylotic narrowing of the in tervertebral foramina, is a further common cause of radicular pain and brachialgia (Fig. 12.2). Infectious and inflammatory processes can cause monoradicular deficits, e.g., herpes zosterand borreliosis (Lyme disease, p. 117). Diabetes mellitus, too, can cause monoradiculopathy with pain and weakness. Finally, traumatic lesions, e.g., bony fractures, can affect individual nerve roots (Fig. 12.3).

Image Radiculopathy is often due to a mechanical injury or irritation of a nerve root by degenerative disease of the spine, particularly intervertebral disk herniation. A radicular deficit, however, should never simply be assumed to be due to disk herniation. Other etiologies (see above) must always be considered.

General clinical manifestations of radicular lesions. Regardless of the etiology, the following symptoms and neurological findings are characteristic:

Image pain in the distribution of the affected nerve root;

Image a sensory deficit and irritative sensory phenomena (paresthesia, dysesthesia) in the dermatome of the affected nerve root; in monoradicular lesions, these are easier to bring out by testing with noxious (painful) stimuli, rather than with ordinary somatosensory stimuli;

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Fig. 12.2 Stenosis of the left C3/4 intervertebral foramen (3D CT reconstruction).

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Fig. 12.3 Weakness of the abdominal wall musculature on the right in a 33-year-old man, 7 months after spinal and pelvic trauma. The muscle weakness is evident both from the front (a) and from the back (b). The CT scan (c) reveals a fracture of the right transverse process of a vertebra, which is the cause of the lesion of the motor spinal nerve roots.

Image paresis of the muscle(s) supplied by the affected nerve root, generally less marked than the paresis caused by a peripheral nerve lesion (no plegia!) because of the polyradicular innervation of most muscles, but possibly severe in the root-indicating muscles;

Image muscle atrophy is common, but usually less severe than in peripheral nerve lesions, while chronic radicular lesions can, rarely, cause fasciculations;

Image impaired reflexes in the segment corresponding to the affected nerve root.

The characteristic syndromes of the individual nerve roots supplying the upper and lower limbs are summarized in Table 12.1.

Differential diagnosis. Radicular syndromes must be differentiated from lesions in more distal components of the peripheral nervous system (plexuses, peripheral nerves). This can usually be done by careful clinical examination alone, but electromyography may be required for unambiguous confirmation. The lack of an autonomic deficit may be a useful clinical criterion in the differential diagnosis of radicular lesions that affect the limbs, because sympathetic fibers travel in the spinal nerve roots only at levels T12 through L2 (see above); therefore, an autonomic deficit in a limb always indicates a lesion distal to the nerve root. Some of the conditions that enter into the differential diagnosis of various radicular and peripheral nerve syndromes are listed in Table 12.1.

When there is a purely motor deficit, unaccompanied by a sensory deficit or pain, a lesion of the spinal motor neurons (e.g., spinal muscular atrophy or amyotrophic lateral sclerosis) should be suspected, rather than a radicular lesion. If the patient complains only of pain radiating into the periphery, in the absence of any demonstrable sensory deficit or weakness, the clinician should think of pseudoradicular pain (p. 261) due to mechanical overuse or other pathology of the musculoskeletal apparatus.

Radicular Syndromes Due to Intervertebral Disk Herniation

The proximity of the spinal nerve root to the intervertebral disk at the level of the intervertebral foramen carries with it the danger of root compression by disk herniation. The nerve root can be compressed either by a merely bulging disk or by a disk herniation in the truest sense, i.e., a prolapse of nucleus pulposus material (which is usually soft) through a hole in the annulus fibrosus.

General clinical manifestations. The typical manifestations of acute radiculopathy due to intervertebral disk herniation are the following:

Image local pain in the corresponding area of the spine, with painful restriction of movement and, sometimes, a compensatory, abnormal posture of the spine (scoliosis, flattening of lordosis).

Image usually, after a few hours or days, radiation of pain into the cutaneous area of distribution (dermatome) of the affected nerve root.

Image pain on extension (in the lower limb, a positive Lasègue sign).

Image exacerbation of pain by coughing, abdominal pressing (Valsalva maneuvers), and sneezing.

Image objectifiable neurological deficits (hyporeflexia or areflexia, paresis, sensory deficit, atrophy in the late stage; see above) depending on the severity of the root lesion.

Cervical Disk Herniation

Cervical disk herniation is a common cause of acute torticollis and of acute (cervico) brachialgia.

Etiology. Cervical disk herniation may occur as the result of nuchal trauma, a twisting injury of the cervical spine, an excessively rapid movement, or mechanical overload.

Clinical manifestations. The most commonly affected segments are C6, C7, and C8. Subjectively, patients usually complain of pain in the neck and upper limb, and sometimes of a sensory deficit, which does not necessarily cover the entire zone of innervation of the affected root.

Diagnostic evaluation. The clinical history and physical examination should already enable identification of the affected nerve root. The objectively observable neurological deficits are listed in Table 12.1. The Spurting test can provide further evidence of irritation of a cervical nerve root: the head is leaned backward and the face is turned to the side of the lesion. Carefully titrated axial compression by the examiner's hand may induce pain radiating in a radicular distribution (Fig. 12.4). Imaging studies (CT and/or MRI) are indispensable for the demonstration of nerve root compression by a herniated intervertebral disk. These are sometimes supplemented by neurography (i. e., measurement of nerve conduction velocities) and electromyography. One should not forget, however, that a mere disk protrusion without any detectable nerve root compression is a common radiological finding in asymptomatic persons.

Treatment. Temporary rest and physical therapy, with the addition of appropriate exercises as soon as the patient can tolerate them, usually suffice as treatment. Sufficient analgesic medication must also be provided, to prevent the chronification of the pain syndrome through the maintenance of an abnormal, antalgic posture (persistent fixation of the affected spinal segments by muscle spasm) and through nonphysiological stress on other muscle groups. If operative treatment is necessary (e.g., because of intractable pain, persistent, severe or progressive paresis, or signs of compression of the spinal cord), then the appropriate treatment is fenestration of the intervertebral space at the appropriate level for exposure of the nerve root and disk, widening of the bony intervertebral foramen (foraminotomy), then diskectomy, and, under some circumstances, spondylodesis (fusion) if there is thought to be a risk of spinal instability afterward. Fusion should be performed in such a way as to distract the vertebrae above and below and thereby maintain the patency of the intervertebral foramen.

Lumbar Disk Herniation

Lumbar disk herniation is one of the more common causes of acute low back pain and sciatica. The anatomical relationship of the lumbar roots to the intervertebral disks (both normal and herniated) is shown schematically in Fig. 12.5.

Clinical manifestations. A first bout of lumbar disk herniation (and often the first or second recurrence as well) may present with no more than acute low back pain (lumbago). The event may be precipitatedby a relatively banal movement in the wrong direction; in particular, the lumbar spine may suddenly freeze in a twisted position as the unfortunate individual attempts to lift a heavy load while the upper body is turned to one side. Any further movement of the lumbar spine is blocked by muscle spasm, a reflex response to the pain. Even the smallest movement is painful, as are coughing and abdominal pressing (Valsalva maneuvers). The pain usually resolves after a few days of bed rest. It is usually only when the herniation recurs later that the patient experiences pain radiating into the leg, i. e., sciatica, and possibly in combination with typical radicular neurological deficits.

In our experience, motor deficits generally arise only later in the course of this syndrome. The patient must be examined carefully to determine whether a deficit is present. The L5 root is most commonly affected, usually by an L4–5 disk herniation, and the S1 root is the next most commonly affected after that, usually by an L5–S1 disk herniation. The corresponding clinical findings are listed in Table 12.1.

Diagnostic evaluation. As in cervical disk herniation, the level of the nerve root that is affected can generally be determined from the pattern of referred pain and any motor, sensory, and reflex deficits that may be present. The peripheral nerve trunk containing the axons whose more proximal portions are located in the affected root is often sensitive to pressure (at the Valleix pressure points) and stretching of the nerve is often painful. The latter can be tested by passive raising of the supine patient's leg, extended at the knee (the Lasègue test). Pain caused by elevation of the leg on the side opposite the sciatica (the crossed Lasègue sign) usually indicates a large, prolapsed disk herniation. If a higher lumbar root (L3 or L4) is affected, one should look for the reverse Lasègue sign, i. e., test for pain on extension of the leg in the prone patient, which stretches the femoral n. rather than the sciatic n. (reverse Lasègue test). If the herniation is lateral or extraforaminal, pain will also be inducible by lateral bending of the trunk.

Imaging studies are not absolutely essential if the clinical picture is sufficiently characteristic, but they should be performed if there is any doubt as to the etiology of nerve root compression, or if the situation requires operative intervention. CT is the method of choice if the segmental level of the suspected disk herniation is clinically unambiguous; the main advantage of CT is that it can clearly demonstrate a far lateral disk herniation, if this turns out to be present (Fig. 12.6). It can also reveal bony deformities of the spinal canal and nerve root impingement by spondylotic changes, if present (Fig. 12.7). MRI is to be preferred over CT, however, if the level of the lesion is not fully clear on clinical grounds. The images should always be interpreted critically and in consideration of the associated clinical findings.

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Fig. 12.4 Spurling cervical compression test for the provocation of radicular pain in cervical disk herniation (after Mumenthaler M.: Der Schulter–Arm–Schmerz, 2nd edn, Huber, Bern 1982.) Pain can often be elicited by reclination and rotation of the head toward the affected side even without compression.

Neurography and electromyography are sometimes worth performing as supplementary tests.

Treatment. The initial treatment is conservative in practically all patients and is along the same lines as described above for cervical disk herniation. Operative treatment should be considered only if conservative treatment fails.

An incipient cauda equina syndrome (bladder and bowel dysfunction, saddle hypesthesia, bilateral pareses, and impairment of the anal reflex, cf. p. 144) is an absolute indication for urgent surgery.

Image When the clinical signs of cauda equina syndrome are present because of lumbar intervertebral disk herniation, an emergency neurosurgical procedure must be performed immediately.

Further indications for operative treatment are set forth in Fig. 12.8. At operation, the herniated disk tissue is removed, and, if there is a danger of postoperative instability at the level being operated on, a fusion (spondylodesis) is performed as well. This is more likely to be the case in older patients and when the intervertebral disk degeneration is very advanced. As in cervical disk procedures, spondylodesis must be performed in such a way as to keep the vertebral bodies above and below the disk a sufficient distance apart (in distraction), so that the intervertebral foramina are held open.

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Fig. 12.5 Anatomical relationships of the lumbar intervertebral disks to the exiting nerve roots.

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Fig. 12.6 Lateral L3/4 disk herniation (arrowheads), CT image. The normal spinal ganglion on the right side is visible in the intervertebral foramen (arrow).

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Fig. 12.7 Left S1 radicular compression in a 40-year-old man. Myelography (a) reveals a broadened and shortened left S1 nerve root (arrowhead) and an indentation of the dural sack from the right at this level. CT (b) reveals high-grade spondyloarthrosis and bilateral stenosis of the lateral recesses.

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Fig. 12.8 Diagnostic and therapeutic flowchart in lumbar disk herniation.

Radicular Syndromes Due to Spinal Stenosis

Slowly progressive mechanical compression of the intraspinal neural structures is usually seen in older patients in whom congenital narrowness of spinal canal has been accentuated by further, progressive, degenerative osteochondrotic and reactive-spondylogenic changes.

Cervical Spinal Stenosis

A narrow cervical spinal canal can compress not only the cervical nerve roots, but also the spinal cord itself, producing a myelopathy. Cervical spondylogenic myelopathy is discussed in detail above on p. 147.

Lumbar Spinal Stenosis

For anatomical reasons, a narrow lumbar spinal canal causes an entirely different clinical syndrome than cervical spinal stenosis:

Clinical manifestations. In addition to low back pain, which is usually chronic, neurogenic intermittent claudication is the most characteristic symptom: as the patient walks, sciatica-like pain arises on the posterior aspect of one or, usually, both lower limbs and then becomes progressively severe. The pain appears earlier if the patient is walking downhill, because of the additional lumbar lordosis that downhill walking induces. This historical feature differentiates neurogenic from vasogenic intermittent claudication, in which the pain tends to be more severe when the patient walks uphill. A further differentiating feature of neurogenic, as opposed to vasogenic, intermittent claudication is that standing still will not, by itself, cause the pain to go away. The patient must additionally bend forward, sit down, or crouch—these maneuvers induce kyphosis of the lumbar spine and thereby decompress its neural contents.

Diagnostic evaluation. Nowadays, the definitive diagnostic study is MRI, though radiculography and myelographic CT are still sometimes needed (Fig. 12.9).

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Fig. 12.9 Lumbar disk herniation in a 70-year-old man with neurogenic intermittent claudication due to degenerative lumbar spinal canal stenosis. The MRI (a) and myelogram (b) reveal compression of the dural sac and the nerve roots at the L2–3 (arrow) and L3–4 disk levels, as well as at L4–5 (less severe).

Treatment. If the symptoms are very severe, and the neurological deficits are progressive, then a treatment option to be considered is operative decompression of the affected segments by opening of the narrowed lateral recesses, possibly in combination with a stabilizing spondylodesis (fusion).

Radicular Syndromes Due to Space-Occupying Lesions

The term “space-occupying lesion,” in its narrowest sense, refers to a tumor. Neurinoma (Fig. 12.10) and meningioma are the most common types of intraspinal primary tumor, while ependymoma (Fig. 12.11), glioma (usually astrocytoma), and vascular tumors are rarer. Nerve root lesions can also be caused by a primary destructive process affecting a spinal vertebra (Fig. 12.12), particularly metastatic carcinoma. Finally, infectious and inflammatory processes of the vertebrae and intervertebral disks (e.g., spondylodiscitis), as well as spinal abscesses and empyema, can cause radicular or spinal cord compression.

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Fig. 12.10 Nerve root neurinoma filling the left L3/4 intervertebral foramen (MR images). Normal nerve roots, free of compression, are seen in the intervertebral foramina above and below the level of the lesion (a). The axial section (b) reveals an hourglass-shaped neurinoma, lying partly within and partly outside the spinal canal.

Clinical manifestations. The patient usually complains of pain radiating into the periphery; if the lesion is at a thoracic level, the pain tends to be in a bandlike distribution around the chest. Motor or sensory deficits may also be clinically detectable, depending on the level of the lesion. A space-occupying lesion within the lower lumbar canal can produce cauda equina syndrome, which may be of greater or lesser severity.

Diagnostic evaluation. Imaging studies are indispensable for diagnosis. If the underlying lesion is a nerve root neurinoma, plain films may already reveal the characteristic, widened intervertebral foramen, e. g., in the cervical region (Fig. 12.13). Nonetheless, CT or MRI (Fig. 12.14) is always necessary to demonstrate the full extent of the tumor.

Treatment. Operative treatment (resection of the lesion) is needed in most patients. Depending on the underlying illness, further treatment may be required (radiotherapy, antineoplastic chemotherapy, or antibiotics after the removal of an abscess or empyema).

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Fig. 12.11 Sausage-shaped cystic ependymoma filling the spinal canal from L1 to L3 and compressing the cauda equina (MR image).

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Fig. 12.12 Metastatic melanoma in the lumbosacral spinal canal, 8 years after resection of the primary tumor: sagittal (a) and axial (b) MR images. The patient presented with cauda equina syndrome. The nerve roots of the cauda equina are displaced dorsally and to the left by the compressive lesion.

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Fig. 12.13 Widened C5/6 intervertebral foramen caused by a neurinoma of the C6 root. The C5/6 foramen has opened up into the C6/7 foramen below it.

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Fig. 12.14 Left C3 root neurinoma. The sagittal MR image (a) reveals a compressive lesion anterior to the spinal cord. The axial image (b) shows the deformed cervical spinal cord posterior to the dens. The arrows indicate the left C3 root, which is expanded by the tumor.

Image  Peripheral Nerve Lesions

Fundamentals

When we speak here of the “peripheral nerves,” we are referring to the nerve plexuses formed by the junction and regrouping of fibers derived from the spinal nerve roots, as well as to the more distally lying peripheral nerve trunks and branches. The plexuses always contain mixed fiber types and the peripheral nerve trunks nearly always do, i. e., somatic motor, somatosensory, and often also autonomic (particularly sympathetic) fibers. The individual peripheral nerve trunks bear an anatomically invariant relationship to the muscles and cutaneous zones that they innervate. This pattern of innervation is fundamentally different from that of the spinal nerve roots, because, as we recall, the nerve root fibers undergo reassortment in the plexuses. This fact enables the clinical examiner to distinguish a peripheral nerve lesion from a radicular lesion based on the observed pattern of neurological deficits. The main clinical manifestations of peripheral nerve lesions are marked paresis, extensive sensory deficits, and diminished sweating in the zone of innervation of the affected nerve or nerve branch. Pain can be produced by either a radicular lesion or a peripheral nerve lesion and is thus not a distinguishing feature of either.

Preliminary anatomical remarks. A peripheral nerve is a cablelike bundle of nerve fibers of different functional types (see p. 3). The nerve fiber is the smallest “building block” of a peripheral nerve; it consists of an axon and an encasing myelin sheath (if present), which is the membrane of a Schwann cell wrapped around the axon numerous times. Individual nerve fibers are surrounded by a delicate connective tissue called endoneurium. The nerve fibers and the endoneurium are then bundled together into larger fascicles, each of which is surrounded by a tough perineurium. Along the length of the nerve, the individual fascicles make many plexus-like interconnections with one another; they are held together as a single peripheral nerve by an encompassing layer of epineurium. The epineurium is not a tough husk around the nerve, but rather a loose, lipid-rich layer of connective tissue, reinforced by transversely and longitudinally oriented collagen fibers. It contains not only the nerve fascicles, but also the vasa nervorum. The nerve trunks are fixed to the adjacent connective tissue at only a few points, at which they are especially vulnerable to mechanical damage. Larger nerve trunks are often found together with arteries and veins in so-called neurovascular bundles surrounded by a common connective tissue sheath. These bundles form an anatomical unit that is clearly demarcated from the surrounding structures.

Causes of peripheral nerve lesions. Most lesions of the nerve plexuses or the peripheral nerve trunks are either traumatic (caused by excessive traction, stab wounds, cuts, bony fractures, etc.), or else due to prolonged compression, which may occur through external influences, at anatomical bottlenecks, or because of space-occupying lesions in the vicinity of the nerve (especially tumors and hematomas). Less commonly, plexus and nerve lesions can be caused by infection and/or inflammation, e. g., neuralgic shoulder amyotrophy, which is probably an autoimmune disorder affecting the brachial plexus (p. 222). Nearly all lesions affecting a single peripheral nerve trunk or branch (mononeuropathy) are of mechanical origin; in contrast, most polyneuropathies (cf. Chapter 10) are of toxic, infectious/inflammatory, or paraneoplastic origin.

General clinical manifestations of peripheral nerve lesions. Depending on the particular segment of plexus or peripheral nerve trunk/branch that is affected, there may be a motor, sensory, autonomic, or (usually) mixed neurological deficit:

Image flaccid paresis of the muscle(s) innervated by the affected nerve;

Image usually marked atrophy of the affected muscle(s);

Image the corresponding reflex deficits;

Image diminished sensation and possibly also pain and paresthesia in the cutaneous area innervated by the nerve, though the pain is often felt beyond this area as well; all sensory modalities are affected to a comparable extent; in contrast to a radicular lesion, the affected area of skin is more easily demarcated by testing the sense of touch than by testing nociception;

Image because the sudomotor fibers travel together with the somatosensory components of the peripheral nerves, diminished sweating is often found in the hyp-esthetic area of skin and autonomic abnormalities of other kinds may also be present in the distribution of the affected nerve; radicular lesions affecting the limbs, in contrast, generally leave sweating intact (an important criterion for differential diagnosis);

Image fasciculations only in exceptional cases; these are much more common in anterior horn disease.

Grades of severity of peripheral nerve lesions. A peripheral nerve can be damaged more or less severely, with corresponding implications for treatment and prognosis. The traditional, clinically useful threefold distinction is as follows:

Image Neurapraxia: the nerve is dysfunctional, but its anatomical components are still in continuity (e.g., nerve dysfunction due to pressure on the nerve when the individual has slept for a prolonged period in an unusual posture); the functional deficit is completely reversible.

Image Axonotmesis: the axons within the nerve are interrupted, but the external structure of the nerve and its internal connective tissue sheaths remain intact; the full clinical picture of a peripheral nerve lesion results; under optimal conditions, full recovery may still be possible.

Image Neurotmesis: the axons and all surrounding structures are interrupted and the nerve is no longer in continuity (e.g., because of tearing or sharp transection of the nerve); a surgical procedure is needed to restore nerve integrity and the prognosis for recovery is uncertain.

Diseases of the Brachial Plexus

Anatomy of the brachial plexus. In the brachial plexus, the axons derived from the nerve roots of C4 to T1 (or T2) are regrouped and distributed to the various nerves that innervate the upper limb (Fig. 12.15). The brachial plexus passes through three anatomical bottlenecks on its way to the upper arm; the first two are the scalene hiatus, where it is accompanied by the subclavian a., and the costoclavicular space between the first rib and the clavicle. At this location, the caudal portion of the plexus is in close proximity to the apex of the lung. A bit further distally, the brachial plexus is covered by the pectoralis minor m., which originates from the coracoid process of the scapula, and it can be compressed at this location when the arm is elevated. These bottlenecks are sketched in Fig. 12.16.

General clinical manifestations of brachial plexus lesions. The complex structure of the brachial plexus and the redistribution of individual radicular elements within it make it very difficult to localize brachial plexus lesions exactly based on the neurological findings alone. Nonetheless, detailed functional testing of the affected muscles can reveal the root levels that are involved and this, in turn, permits localization of the lesion within the plexus with a fair degree of precision. The information provided in Fig. 12.17 will be helpful in this regard.

Classification of brachial plexus lesions. In addition to total paralysis of the entire upper limb, there are three types of partial lesion in the customary, topically oriented classification, namely, upper and lower brachial plexus lesions and C7 lesions. An alternative (or additional) classification is by etiology: traumatic, compressive, or infectious/inflammatory.

Topical Classification of Brachial Plexus Lesions

Upper brachial plexus lesion (Erb–Duchenne palsy).This type of lesion involves the fibers originating in the C5 and C6 nerve roots. The affected muscles are the abductors and external rotators of the shoulder joint, the flexor muscles of the upper arm, the supinator m., and sometimes the elbow extensors and the extensors of the hand. A sensory deficit is not necessarily present; if there is one, it is located in the area of the shoulder, on the outer surface of the upper arm, or on the radial edge of the forearm (Fig. 12.18).

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Fig. 12.15 The brachial plexus and its anatomical relationships to the surrounding bony structures.

pectoral nn. (med./lat.) C5–T1 

pectoralis major & minor mm.

2 lateral cord

3 dorsal (posterior) cord

4 medial cord

axillary n. C5, 6 

deltoid m. C5, 6 

teres minor m. C5, 6

musculocutaneous n. C5–7 

biceps brachii m. C5, 6 

coracobrachialis m. C6, 7 

brachialis m. C5, 6

radial n. C5–T1 

triceps brachii m. C7-T1 

anconeus m. C7, 8 

brachioradialis m. C5, 6

extensor carpi rad. long./brev. mm. C6–8 

extensor digit. m. C7, 8 

extensor indicis m. C7, 8 

extensor digiti minimi m. C7, 8 

ext. poll. long./brev. mm. C7, 8 

abd. poll. long. m. C7, 8

median n. C5–T1 

pronator teres m. C6, 7 

flexor carpi radialis m. C6–8 

palmaris longus m. C7, 8 

flexor digit. superf. m. C7–T1 

flexor digit. prof. m. (radial side, ll/lll) 

C7–T1 

pronator quadratus m. C7–T1 

opponens pollicis m. C7, 8

abductor poll. brev. m. C7, 8 

superf. head of flex. poll. brev. m. C6–8 

lumbrical mm. I & II C8–T1

ulnar n. (C7) C8–T1 

flexor carpi uln. m. C8–T1 

flexor digit. prof. m. (ulnar side, IV/V)

C8–T1 

palm./dors. interossei mm. C8–T1 

lumbrical mm. Ill & IV C8–T1 

adductor pollicis m. C8–T1 

deep head of flex. poll. brev. m. C8–T1 

palmaris brevis m. C8–T1

10 medial brachial cutaneous n. C8–T1

11 medial antebrachial cutaneous n. 

C8–T1

12 thoracodorsal n. C6–8 

latissimus dorsi m.

13 subscapular nn. C5–8 

subscapular m. C5–7 

teres major m. C5–6

14 long thoracic n. C5–7 

serratus anterior m.

15 nerve to the subclavius m. C5, 6 

subclavius m.

16 suprascapular n. C4–6 

supraspinatus m. C4-6 

infraspinatus m. C4–6

17 dorsal scapular n. C3–5 

levator scapulae m. C4-6 

rhomboid mm. C4–6

18 phrenic n. C3, 4

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Fig. 12.16 Anatomical bottlenecks in the shoulder region, at which nerves and/or blood vessels can be compressed.

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Fig. 12.17 Muscles of the upper limb and the nerve roots that innervate them. With the aid of this diagram, brachial plexus lesions can be localized from the pattern of muscle weakness that they cause.

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Fig. 12.18 Upper limb posture and sensory deficit in right upper brachial plexus palsy (diagram). The deltoid, biceps, and supra-and infraspinatus mm. are atrophic, the arm is internally rotated, and the palm of the hand points posteriorly.

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Fig. 12.19 Upper limb posture and sensory deficit in right lower brachial plexus palsy (diagram). The intrinsic muscles of the hand are atrophic, the sensory deficit corresponds to the C7 and C8 dermatomes, and there is an accompanying Horner syndrome.

Lower brachial plexus lesion (Dejerine–Klumpke palsy). This type of lesion involves the fibers originating in the C8 and Tl roots. Its prominent findings include weakness of the intrinsic muscles of the hand, sometimes also of the long flexors of the fingers, and rarely of the wrist flexors. The triceps brachii m. usually remains intact. The mechanism of the precipitating accident, and the anatomical relationships in this area, often lead to an accompanying dysfunction of the cervical sympathetic supply, resulting in Horner syndrome with impaired sweating. On the basis of these findings, a lesion of the Tl root is presumed to be present, proximal to the origin of its branch to the sympathetic chain. There is always a sensory deficit involving the ulnar edge of the forearm, hand, and fingers (Fig. 12.19).

C7 palsy. In the present context, we are speaking not of a lesion of the C7 root itself, but rather of the fibers derived from it that make up the C7 portion of the brachial plexus. This type of palsy involves deficits in the distribution of the radial n. (p. 226), while the function of the brachioradialis m. is preserved.

Etiologic Classification of Brachial Plexus Lesions

Traumatic Lesions

Traumatic lesions of the brachial plexus are usually due to motor vehicle accidents; rarer causes include occupational injury and direct stab or gunshot wounds. The initial clinical finding is not uncommonly a total upper limb paralysis (Fig. 12.20), which may later improve until it resembles one of the types of localized brachial plexus lesion described above. The prognosis is generally better for upper brachial plexus lesions; bloody CSF obtainable by lumbar puncture and, later, clinical evidence of myelopathy are poor prognostic signs indicating probable nerve root avulsion. In such patients, MRI may reveal empty nerve root pouches (Fig. 12.21). The treatment consists of the fitting of an abduction splint and the performance of passive exercises to prevent freezing of the shoulder joint. Brachial plexus surgery is highly complex and demanding and is occasionally resorted to in cases of upper brachial plexus injury.

Brachial plexus palsy caused by trauma during delivery is the result of obstetrical complications, such as breech delivery. When the damaged axons regenerate, they may reconnect to the “wrong” muscles and/or muscle groups, leading to pathological accessory movements and abnormal motor patterns.

Compressive Lesions of the Brachial Plexus

External compression can injure the brachial plexus in persons who carry heavy loads on their shoulders or wear heavy backpacks. Lesions of this type usually affect the upper brachial plexus and sometimes only individual branches of it. The long thoracic n. is most frequently involved (p. 224).

Compression at anatomical bottlenecks. The collective designation “thoracic outlet syndrome” (TOS) is commonly used for these conditions, usually in nonspecific fashion, and often, unfortunately, as a vague term for brachialgia of as yet undetermined origin, or for other unexplained symptoms relating to the brachial plexus. Scalene syndrome is usually due to the anomalous presence of a cervical rib, a fibrous band (which may be visible in a CT scan), or some other type of structural anomaly in the scalene hiatus. The typical manifestations of scalene syndrome include: clinical evidence of a lower brachial plexus lesion, worsening of symptoms on lowering of the arm, and fixed or motion-induced circulatory insufficiency of the subclavian a. (as revealed by a vascular bruit, and/or by disappearance of the radial pulse when certain maneuvers are performed, e. g., the Adson maneuver—turning the chin to the side of the lesion, with simultaneous backward bending of the head).

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Fig. 12.20 Complete right brachial plexus palsy. Atrophy of all muscles of the upper limb, internal rotation of the arm.

Costoclavicular syndrome. This syndrome, like the scalene syndrome, should be diagnosed only if a causative anatomical anomaly and objectifiable neurological deficits (usually, a lower brachial plexus palsy) can be found. An arteriogram is occasionally helpful in establishing the diagnosis, as it may demonstrate motion-dependent compression of the subclavian artery or vein (Fig. 12.22).

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Fig. 12.21 Right C7 and T1 nerve root avulsion after trauma to the brachial plexus. The T2-weighted coronal MR image reveals the empty nerve root sleeves containing only cerebrospinal fluid.

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Fig. 12.22 Costoclavicular syndrome in a 24-year-old patient with clinical evidence of a lower brachial plexus lesion. An arteriogram of the brachial a. reveals free passage of contrast medium (a) when the arm is dependent. When the arm is elevated, however, (b) the subclavian a. is compressed between the clavicle and the first rib.

Treatment of compression syndromes. Both the scalene syndrome and costoclavicular syndrome should be treated conservatively at first, once their diagnosis has been definitively established. Special exercises are used to strengthen the shoulder-elevating muscles. Surgical treatment is reserved for the small minority of patients with objectifiable, severe neurological deficits. A supra- or transclavicular approach gives the surgeon optimal access to the anatomical structures.

Neuralgic Shoulder Amyotrophy

Pathogenesis. This disorder is presumed to be due to an inflammatory/allergic affection of the brachial plexus. It usually arises spontaneously, but is sometimes seen in the aftermath of an infectious disease, or after the administration of serum (brachial plexus neuritis).

Clinical manifestations. This disease affects men more often than women and is usually located in the right arm. It always begins with intense local pain in the shoulder, which generally lasts for a few days. Rarely, the pain will persist at a milder intensity for a longer period. Once the pain subsides, motor weakness of the muscles of the shoulder girdle and/or of the arm develops. The weakness can, in principle, affect any muscle group of the upper limb, but it tends to affect the muscles innervated by the upper portion of the brachial plexus. Paresis of the serratus anterior m. is particularly common. There may be no objectifiable sensory deficit.

Treatment. No specific treatment is required beyond analgesic medication in the initial, painful phase.

Prognosis. The prognosis is generally good, but it may take many months for the weakness to resolve completely.

Other Causes of Brachial Plexus Lesions

Radiation-induced brachial plexus lesions usually appear with a latency of one or more years after radiotherapy, usually in women who have been treated with surgery and radiotherapy for breast cancer. In 15% of patients, pain is the main symptom; it can increase over the course of several years. The differentiation of radiation-induced brachial plexopathy from a recurrent malignant tumor is not always easy; a short interval between the completion of radiotherapy and the onset of pain (except when a very high radiation dose was given) and very intense pain, both tend to suggest a recurrent tumor rather than radiation injury as the cause. Imaging studies are helpful, but even these cannot always reliably distinguish scarring from new tumor tissue.

Pancoast tumors of the apex of the lung usually cause a lower brachial plexus palsy accompanied by severe pain. The sympathetic chain is usually involved as well; thus, Horner syndrome and diminished sweating in the upper body on the affected side are typical findings (Fig. 12.23).

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Fig. 12.23 Right-sided Pancoast tumor in a 68-year-old man. There is clinical evidence of compression of the lower brachial plexus and of the sympathetic chain. a Right Horner syndrome. b Atrophy of the intrinsic muscles of the right hand, especially the thenar muscles. cWeakness of the wrist and finger extensors on the right.

Other causes of brachial plexus palsy, some of which are very rare, are usually diagnosable only by the specialist: acute palsy due to occlusion of a small artery supplying the plexus, after medical procedures, in heroin addicts, in familial brachial plexus neuritis, parainfectious and serogenic forms, etc.

Differential Diagnosis of Brachial Plexus Lesions

A precise clinical and, if necessary, electrophysiological examination of the patient should always permit a reliable differentiation between brachial plexus lesions and lesions affecting multiple nerve roots or a peripheral nerve.Experience suggests, however, that it is not always easy to distinguish a lower brachial plexus lesion (affecting fibers derived from C8 and Tl) from an ulnar nerve lesion (p. 231). The same can be said for the distinction between a (traumatic) upper brachial plexus lesion and a lesion of the axillary n. or a rotator cuff injury.

Diseases of the Peripheral Nerves of the Upper Limbs

Suprascapular N. (C4–C6)

Anatomy. This nerve innervates the supraspinatus and infraspinatus mm. It reaches them after passing through the scapular notch and then running dorsally. It receives sensory branches from the shoulder joint, but not from the skin.

Typical deficits. A lesion of the suprascapular n. produces weakness and atrophy of the two muscles on the dorsal surface of the scapula (Fig. 12.24). The first 15° of lateral elevation of the arm are weak (supraspinatus m.), as is external rotation of the arm at the shoulder joint (infraspinatus m.) (Fig. 12.25).

Causes. Overuse of the arm can lead to mechanical compromise of the nerve in the scapular notch. Other causes include trauma and a ganglion lying in the notch.

Axillary N. (C5–C6)

Anatomy. This nerve provides motor innervation to the deltoid and teres minor mm. and sensory innervation to a palm-sized patch of skin on the proximal, lateral surface of the upper arm (superior lateral brachial cutaneous n.) (Fig. 12.26).

Typical deficits. Axillary nerve palsy manifests itself as marked weakness of lateral abduction and forward elevation of the arm. The normal roundness of the shoulder is flattened. External rotation of the arm at the shoulder joint is lessened at rest, so that the dependent arm is held in mild internal rotation (Fig. 12.27).

Causes. The most common cause of axillary n. palsy is dislocation of the shoulder (forward and downward). The prognosis in such patients is favorable.

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Fig. 12.24 Atrophy of the supra and infraspinatus muscles due to a lesion of the left suprascapular n. in a 25-year old man. The etiology remained unclear in this case.

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Fig. 12.25 Testing of the muscles innervated by the suprascapular n. a Weakness of the supraspinatus m. is most evident in the first 15° of lateral elevation of the arm. b Weakness of the infraspinatus m. is evident when the arm is externally rotated at the shoulder joint.

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Fig. 12.26 Anatomical course and distribution of the axillary n. Sensory (red) and motor branches (black). The autonomous sensory area of the superior lateral brachial cutaneous n. is shaded in red.

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Fig. 12.27 Left axillary nerve lesion in a 26-year-old man. Atrophy of the left deltoid m. with “pointed” shoulder contour. The sensory deficit in the territory of the superior lateral brachial cutaneous n. is indicated.

Differential diagnosis of axillary nerve palsy includes complex brachial plexus lesions affecting the upper portion of the plexus, rotator cuff lesions, and restriction of movement by pain in humeroscapular periarthropathy.

Long Thoracic N. (C5–C7)

Anatomy. This nerve is the longest branch of the brachial plexus. It is a purely motor nerve supplying the serratus anterior m.

Typical deficits. A long thoracic nerve palsy causes winging of the scapula, which is particularly evident when the arms are held high, or when the patient extends the arms and presses with the palms of the hands against a wall (Fig. 12.28).

Causes. Lesions of the long thoracic n. are usually due to excessive mechanical strain on the shoulder (carrying heavy loads) or to neuralgic shoulder amyotrophy (p. 222). Cryptogenic cases also occur.

Musculocutaneous N. (C5–C7)

Anatomy. This nerve innervates the biceps brachii and coracobrachialis mm. and a portion of the brachialis m. Its sensory terminal branch, the lateral antebrachial cutaneous n., innervates the skin on the radial side of the forearm (Fig. 12.29).

Typical deficits. Lesions of the musculocutaneous n. cause marked weakness of elbow flexion. This must be tested with the forearm in the supinated position, because, if the forearm is pronated or in neutral position, the elbow can still be flexed by the powerful brachioradialis m., which is innervated by the radial n.

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Fig. 12.28 Lesion of the right long thoracic n. Weakness of the serratus anterior m. causes winging of the scapula, which is particularly evident when the patient extends the arms forward and pushes against a wall.

Causes. The usual cause is trauma, in which case further signs of an upper brachial plexus lesion may be present. Cryptogenic lesions of the musculocutaneous n. and palsy of this nerve in the setting of neuralgic shoulder amyotrophy, are rarer events.

Differential diagnosis. A tear of the long tendon of the biceps brachialis m. only rarely causes weakness of elbow flexion when the forearm is held in the supinated position. This condition is easy to differentiate from musculocutaneous nerve palsy for two further reasons: one is the typical appearance of the belly of the muscle on the volar surface of the forearm; the other is the absence of a sensory deficit.

Radial N. (C5–C8)

Anatomy. The anatomy of the radial n. is depicted in Fig. 12.30. It provides motor innervation to the triceps brachii, brachioradialis, and supinator mm., as well as all of the extensors of the wristthumband finger joints. Its sensory innervation is to the dorsal skin of the upper arm and forearm as well as the dorsum of the hand, with an autonomic zone located between the first and second metacarpal bones.

Typical deficits. The clinical manifestations of radial nerve palsy depend on the level of the lesion:

Image Lesion in the upper arm: the radial n. is particularly vulnerable to injury in the radial nerve canal of the humerus, because it lies directly on the bone at this location. The corresponding, readily apparent neurological deficit is a wrist drop (Fig. 12.31), attributable to loss of action of the wrist and finger extensors. In addition, sensation is diminished on the radial portion of the dorsum of the hand.

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Fig. 12.29 Anatomical course and distribution of the musculocutaneous n.

Image “High radial nerve lesion”: if the nerve is injured more proximally in the upper arm or in the axilla, the triceps brachii m. is also weak and the elbow can no longer be actively extended against resistance.

Image Supinator canal syndrome: if the radial n. is compromised at the site of its passage through the supinator m., only its deeply penetrating motor terminal branch is affected. The resulting deficit is purely motor. The branch to the extensor carpi radialis m. and the brachioradialis m., which leaves the nerve proximal to its passage through the supinator m., is unaffected, but all of the other forearm muscles innervated by the radial n. are paretic. Finger extension is impaired, but wrist extension is preserved, particularly on the radial side (Fig. 12.32).

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Fig. 12.30 Anatomical course and distribution of the radial n. a Proximal muscle branches (black) and course of the sensory superficial branch (red). b Course of the motor deep branch. c Zones of cutaneous innervation of the branches of the radial n. and sensory autonomous area of the superficial branch.

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Fig. 12.31 Right wrist drop due to a radial nerve lesion. The shading indicates the sensory autonomous area in the distribution of the superficial branch of the radial n.

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Fig. 12.32 Right supinator tunnel syndrome in a 71-year-old woman. Marked weakness of the finger extensors (a) with preservation of wrist extension (b), particularly on the radial side of the wrist.

Causes. Radial nerve lesions can be produced by trauma and by pressure, e. g., by the use of crutches that press in the axilla, or by external pressure on the upper arm (humerus). The supinator canal syndrome is an anatomical bottleneck (entrapment) syndrome.

Differential diagnosis of radial nerve palsy must include predominantly distal weakness of central origin, which can also present with a wrist drop. The flexor weakness and enhanced intrinsic muscle reflexes that are present in central weakness serve to differentiate this condition from radial nerve palsy. Spinal muscular atrophy can, in rare cases, affect the wrist extensors on one side only. Steinert myotonic dystrophy (p. 268) commonly produces a bilateral wrist drop.

Median N. (C5–T1)

Anatomy. The anatomy of the median n. is shown in Fig. 12.33. All of the muscles innervated by this nerve are distal to the elbow. In the forearm, these include most of the long flexors of the fingers (with the exception of the deep flexors of the fourth and fifth fingers, which are innervated by the ulnar n.), as well as the flexor carpi radialis, pronator teres, and pronator auadratus mm. After the nerve passes through the carpal tunnel together with the long flexor tendons (see below), it innervates most of the thenar muscles (abductor pollicis brevis and opponens pollicis m. and the superficial head of the flexor pollicis brevis m.), as well as the first and second lumbrical mm. Its sensory innervation is to the radial side of the palm, the volar surface of the fingers from the thumb to the radial half of the fourth finger, and the dorsal surface of the terminal phalanges of these fingers.

Typical deficits. In median nerve lesions, too, the clinical manifestations depend on the level of the lesion:

Image Median nerve lesion in the upper arm (i. e., proximal to the origin of its motor branches to the forearm flexors): the typical clinical appearance is that of the “pope's blessing hand,” as depicted in Fig. 12.34, caused by weakness of the radial finger flexors.

Image Median nerve lesion at the wrist. A lesion of the median n. in the carpal tunnel causes weakness of the thenar muscles. Clinically, pain and paresthesia are the most prominent symptoms. Carpal tunnel syndrome is discussed separately, in detail, because of its special clinical importance (see below).

Image Kiloh–Nevin syndrome. An isolated lesion of the anterior interosseous n. is a rare event. This nerve is the motor terminal branch of the median n., which innervates the flexor pollicis longus m., the radial portion of the flexor digitorum profundus m. (flexion of the terminal phalanges of the 2nd and 3rd fingers), and the pronator quadratus m. A lesion of this terminal branch—due either to trauma or, occasionally, to entrapment—mainly impairs flexion of the terminal phalanges of the thumb and index finger. The patient can no longer form an “0” with these two fingers.

Causes. The median n. is the nerve most frequently injured by direct trauma, often by a cut in the wrist. Pressure palsies of the median n. also occur, both in the upper arm (due to prolonged maintenance of an awkward position, or to an Esmarch tourniquet) or in the palm of the hand (e. g., in occupational injuries). Compression at anatomical bottlenecks (entrapment) is a further cause of median nerve lesions. In many individuals, a bony spur is present just above the medial epicondyle of the humerus (the supracondylar process). A fibrous band (of Struther) may run from this spur to the medial epicondyle, forming a tunnel through which the median n. passes. The nerve can be compressed either by the supracondylar process or by the fibrous band. Further compression syndromes affecting the median n. are the Kiloh–Nevin syndrome (see above) and the carpal tunnel syndrome, which is described below.

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Fig. 12.33 Anatomical course and distribution of the median n. a Proximal course. b Course after traversal of the pronator teres m. c Zones of cutaneous innervation in the hand.

Carpal Tunnel Syndrome

The carpal tunnel syndrome (CTS) is caused by (mechanical) compression of the median n. as it passes through the carpal tunnel. It is considerably more common in women than in men and tends to develop around the time of the menopause. It usually affects the dominant hand, but it may affect the nondominant hand, or both. Factors that promote or precipitate the development of CTS include hormonal changes (menopause, pregnancy), weight gain, hypothyroidism, diabetes mellitus, and others.

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Fig. 12.34 “Preacher's hand” due to a proximal left median nerve lesion. The hypesthetic area is shaded dark red.

Typical deficits. CTS is characterized by the following manifestations:

Image in the first stage, which lasts several months or years, the manifestations are subjective: dull pain in the arm at night (brachialgia paresthetica nocturna),

Image which is felt not merely in the hand, but in the whole upper limb up to the shoulder,

Image wakes the patient from sleep and can be relieved by shaking and massaging the arms,

Image the fingers are stiff and uncoordinated for a short time after the patient arises in the morning,

Image in the more advanced stage, abnormal sensations (paresthesiae) develop and the sense of touch is impaired, mainly in the thumb and index finger,

Image careful clinical examination is needed to reveal objectifiable sensory and/or motor deficits.

Examination and diagnostic evaluation. An occasional objective finding is point tenderness to pressure at the root of the thenar muscles, or a positive Tinel sign (paresthesiae in the radial portion of the palm and the radial fingers induced by a tap on the transverse carpal ligament). Paresthesiae in the fingers can sometimes be induced by sustained passive hyperflexion or hyper-extension of the wrist (Phalen sign). Only later in the course of CTS can one find a discrete impairment of the sense of touch, particularly in the index finger (e.g., a worsening of two-point discrimination to > 5 mm). The major finding, however, is an inability to abduct the thumb fully, particularly when compared with the normal, opposite side, because of weakness of the abductor pollicis brevis m. This can be demonstrated by having the patient grasp a cylindrical object; a “positive bottle sign” is seen (Fig. 12.35). Impaired opposition of the thumb is more difficult to observe clinically (Fig. 12.36).

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Fig. 12.35 “Bottle” sign in right median nerve palsy. The thumb cannot be adequately abducted and opposed.

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Fig. 12.36 Inadequate opposition and pronation of the thumb in a patient with a right median nerve lesion. Because the thumb is insufficiently rotated, the thumbnail is seen tangentially rather than head on.

Overt CTS is unequivocally demonstrated by a finding of impaired conduction in the median n. across the carpal tunnel, as revealed by electroneurography (Fig. 12.37). This study should always be done before any operation is performed. Diminished conduction velocity alone, in the absence of characteristic symptoms, is not an indication for surgery.

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Fig. 12.37 Motor median neurography in right carpal tunnel syndrome. The recording is performed over the abductor pollicis m. The distal motor latency is prolonged (9.2 ms, compared to normal 3.9 ms). The nerve conduction velocities in the arm and forearm are normal.

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Fig. 12.38 Anatomical course and distribution of the ulnar n.

Treatment. Keeping the hand in the neutral position at night with a well-padded volar splint often brings relief. If it does not, or if objectifiable neurological deficits are already present, there should be no hesitation in proceeding to surgery. Operative carpal tunnel release involves splitting of the flexor retinaculum with an open or endoscopic technique (generally performed either by a neurosurgeon or by a hand surgeon).

Ulnar N. (C8–T1)

Anatomy. The anatomy of the ulnar n. is shown in Fig. 12.38. Among the muscles innervated by this nerve, the ulnar flexors of the wrist and fingers (the flexor carpi ulnaris m. and the ulnar portion of the flexor digitorum profundus m.) are functionally much less important than the ulnar-innervated intrinsic muscles of the hand. The ulnar n. is, indeed, the most important nerve for finger function: it innervates not only the hypothenar mm., but also all of the interossei, the 3rd and 4th lumbrical mm., and, in the thenar region, the adductor pollicis m. and the deep head of the flexor pollicis brevis m. It provides sensory innervation to the ulnar edge of the hand, the volar surface of the fifth finger, and ulnar half of the fourth finger. A sensory branch arising from the ulnar n. in the distal third of the forearm innervates the skin on the ulnar side of the dorsum of the hand, as well as on the dorsal surface of the fifth finger and the ulnar half of the fourth finger.

Typical deficits. The typical clinical picture of ulnar nerve palsy is a claw hand (Fig. 12.39): because the interossei and lumbrical muscles cannot contract, the ulnar digits are hyperextended at the metacarpophalangeal joints, while the remaining digits are flexed at these joints. The long fingers can no longer be fully adducted against one another, the fingers cannot be strongly spread apart, and the patient cannot flick the middle finger against the examiner's palm with full, normal strength. A key finding is that, when the patient grasps a flat object (such as a piece of paper) between the thumb and the index finger, weakness of the adductor pollicis m. (ulnar n.) leads to functional substitution by the flexor pollicis longus m. (median n.), and therefore to flexion of the thumb on the affected side at the interphalangeal joint. This finding, called Froment sign, is highly characteristic of ulnar nerve palsy (Fig. 12.40).

In addition to these general clinical manifestations of ulnar nerve palsy, there are other specific findings that depend on the level of the lesion:

Image If the lesion is proximal (at the elbow or higher), it will also affect the ulnar portion of the flexor digitorum profundus m., thereby impairing flexion of the distal phalanx of the fourth and fifth digits (Fig. 12.41).

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Fig. 12.39 Claw hand due to a right ulnar nerve lesion at the elbow. Typical features include hyperextension at the metacarpophalangeal joints and hyperflexion at the interphalangeal joints, particularly on the ulnar side of the hand. There is marked atrophy of the interossei and of the hypothenar muscles.

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Fig. 12.40 Froment sign in right ulnar nerve palsy. Flexion of the interphalangeal joint of the thumb when the patient pulls on a flat object (piece of paper).

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Fig. 12.41 A test for the function of the flexor digitorum profundus m. of the little finger (ulnar n.). Flexion of the little finger at the distal interphalangeal joint.

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Fig. 12.42 Typical appearance of the hand in a lesion of the deep branch of the ulnar nerve at the wrist. Marked muscle atrophy in the first interosseous space, with preservation of the hypothenar musculature. Sensation was intact in this case.

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Fig. 12.43 Weakness of the abdominal wall musculature, worse on the left side, due to neuroborreliosis affecting the caudal thoracic nerve roots.

Image If the lesion is at the wrist, it can be precisely localized by the involvement or noninvolvement of the palmaris brevis m. and the spatial configuration of the sensory deficit. The flexor muscles of the forearm that are innervated by the ulnar n. remain intact.

Image An isolated lesion of the purely motor terminal branch of the ulnar n. (its deep branch) causes weakness of the interossei, while the hypothenar and lum-brical mm. and the muscles of the forearm innervated by the ulnar n. are spared. There is usually no sensory deficit (Fig. 12.42).

Causes. Ulnar nerve palsy is often of traumatic origin. The nerve can be chronically dislocated at the elbow, where it can slip out of the ulnar groove on the medial epicondyle of the humerus; it is also vulnerable to external compression at this point (the “funny bone”), as well as to compression due to anatomical variations of the ulnar groove (sulcus ulnaris syndrome, cubital tunnel syndrome). Similarly, the ulnar n. can be damaged in the palm of the hand (e. g., by occupational tools), or by anatomical variations at the wrist (syndrome of the “loge de Guyon”).

Treatment. The treatment depends on the cause and location of the lesion. Chronic compression of the nerve is treated by removal of the source of compression. This may involve splinting or padding of the elbow, or even operative relocation of the nerve from a more dorsal to a more volar position.

Diseases of the Nerves of the Trunk

Anatomy. The peripheral nerves supplying the thoracic and abdominal wall are derived from nerve roots T2 through T12. Each peripheral nerve in this region contains fibers that are (nearly) exclusively derived from a single nerve root. We recall that this is not the case in the limbs, where there is an intervening plexus between the nerve roots and the peripheral nerves, in which the nerve fibers are reassorted. The clinical manifestations of a peripheral nerve lesion in the trunk are thus very similar to those of a nerve root lesion.

Typical deficits. The most characteristic neurological syndrome due to nerve dysfunction in this area is intercostal neuralgia, i.e., bandlike, usually burning pain radiating around the trunk from back to front, at a single dermatomal level.

Causes. The nerves of the trunk can be damaged by viral infection (e. g., herpes zoster), by mass lesions, or by a diabetic or infectious mononeuritis (e.g., borreliosis). Mononeuritis can produce unilateral weakness of the musculature of the abdominal wall; the corresponding segment of the abdominal wall becomes flaccid and pouches visibly outward (Fig. 12.43). Sensation in this area is diminished, too, and the abdominal skin reflex is absent at the corresponding level.

Rarely, painful entrapment neuropathy may affect individual sensory terminal branches of the nerves of the trunk. Notalgia paraesthetica is a neuropathy of this kind causing pain in the back: one of the dorsal rami of the thoracic spinal nerve roots becomes stuck in a small gap in the fascia, producing hypesthesia in a coin-sized, paravertebral area of skin, as well as pain. There are comparable entrapment syndromes of the ventral rami, causing, e. g., the so-called rectus abdominis syndrome.

Diseases of the Lumbosacral Plexus

Anatomy. The structure of the lumbosacral plexus is illustrated in Fig. 12.44. It lies in a well-protected location in the posterior wall of the pelvis. Its cranial portion (the lumbar plexus, L1–L4) gives off, as its main branches, the ilioinguinaliliohypogastricfemoral, and obturator nn. These nerves innervate most of the hip flexors and knee extensors. The caudal portion of the lumbosacral plexus (the sacral plexus, L5–S3) gives off the superior and inferior gluteal nn. for the gluteal muscles, as well as the sciatic n., which supplies the knee flexors and all muscles of the lower leg and foot.

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Fig. 12.44 Anatomy of the lumbosacral plexus.

iliohypogastric n. L1 (T12) 

lower abdominal wall muscles

ilioinguinal n. L1 

lower abdominal wall muscles

3 branch to iliacus m.

4 (femoral n., see 10, below) 

branch to psoas m.

5 branch to iliacus m.

genitofemoral n. L1, 2 

genital branch L2 

cutaneous branch L1 

(= femoral branch)

6a N. cutaneus femoris 

posterior S1–S3

superior gluteal n. L4–S1 

gluteus medius m. 

gluteus minimus m. 

tensor fasciae latae m.

inferior gluteal n. L5–S2 

gluteus maximus m.

sciatic n. L4–S3 

common fibular (peroneal) n. L4–S2 

tibial n. L4–S3

10 femoral n. L1–4 

psoas m. L1 –3 

iliacus m. L1–3

11 pectineus m. L2–4

12 sartorius m. L2–3

13 quadriceps m. L2–4

14 saphenous n. L2–4

15 common fibular 

(peroneal) n.
 L2-S2 

biceps m. (short head) 

L5-S2

fibularis (peroneus) 

longus m. L5-S2

fibularis (peroneus) brevis 

m. S1

tibialis anterior m. L4-5 

extensor dig. long. m. L4-S1 

extensor hallucis long. m. L4-5

16 lat. femoral cutaneous n. L2–3

17 anococcygeal nn.

18 coccygeus m.

19 levator ani m.

20 pudendal n. S1–4

21 obturator n. L2–4

22 ant. branch/add. brev. m. L2–4 

ant. branch/add. long./gracilis

23 post. branch/add. min. 

& magn. mm. L3–4

24 tibial n. L4–S3

25 common flexor head 

semitendinosus m. S1–2

26 add. magnus m. L4–5 

semimembranosus m. L4–S1

27 long head of biceps m. 

gastrocnemius m. S1–2 

popliteus m. L4–S1

soleus m. L5–S2

flexor dig. long. m. L5–S1

tibialis post. m. L5–S1

flex. hall. long. m. L5–S2 

plant. ped. mm., abductors, 

adductors, interossei, 

lumbricals, etc., L5–S2

28 lumbar plexus

29 sacral plexus

30 “pudendal plexus”

31 coccygeal plexus

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Fig. 12.45 Anatomical course of the iliohypogastric and ilioinguinal nn. 1 Psoas major m. 2 lliacus m. 3 Iliohypogastric n. 4 Ilioinguinal n.

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Fig. 12.46 Anatomical course and distribution of the lateral femoral cutaneous n. The nerve turns from a nearly horizontal to a nearly vertical course (in the standing patient) at the point where it traverses the inguinal ligament. 1 Psoas major m. 2 lliacus m.

Typical deficits. The clinical manifestations of a lumbosacral plexus lesion depend on its location; in general, one finds a combination of the deficits seen in lesions of the individual peripheral nerve trunks lying distal to the plexus lesion.

Causes. Lumbosacral plexus palsy is usually due to a local mass, but it may also be due to prior radiation therapy or to an autoimmune disorder known as chronic, progressive lumbosacral plexopathy.

Diagnostic evaluation. Ancillary testing, primarily with CT or MRI, is generally needed to identify the etiology of a lumbosacral plexopathy. These imaging studies can demonstrate the presence of a mass.

Diseases of the Peripheral Nerves of the Lower Limbs

Genitofemoral and Ilioinguinal Nn. (L1–L2)

Anatomy. The course of these two (almost) monoradicular, mixed nerves is depicted in Fig. 12.45.

Typical deficits. Lesions of these nerves cause local pain in the groin (ilioinguinal nerve syndrome), a sensory deficit in the corresponding zone(s) of cutaneous innervation, and sometimes, in men, loss of the cremaster reflex (because the afferent arm of the reflex loop is interrupted). The associated motor deficit only affects oblique muscles of the abdominal wall and is hardly noticeable.

Lateral Femoral Cutaneous N. (L2–L3)

Anatomy. This purely sensory nerve passes through the three layers of the abdominal wall and then penetrates the inguinal ligament, usually at a point three finger breadths medial to the anterior superior iliac spine, to emerge onto the anterior fascia of the thigh. It provides sensory innervation to a palm-sized area of skin on the anterolateral surface of the thigh (Fig. 12.46).

Typical deficits. The lateral femoral cutaneous n. is vulnerable to injury at the point where it penetrates the inguinal ligament. The resulting clinical disturbance is an entrapment neuropathy called meralgia paresthetica,characterized by burning pain in the cutaneous distribution of the nerve. The pain is better when the hip is flexed, e. g., when the patient raises the ipsilateral foot onto a low stool; it is worse on hyperextension of the leg (reverse Lasègue sign). The site where the nerve passes through the inguinal ligament is often tender to light pressure. Most patients find the symptoms bearable and need only be reassured that the condition is benign. Surgery is only rarely necessary; the goal of the operation is to widen the aperture in the ligament through which the nerve passes, relieving compression.

Causes. Meralgia paresthetica may be due to marked weight gain or pregnancy. It can also arise after prolonged, continuous extension of the hip joint (supine position). Some cases have no apparent cause.

Differential diagnosis. Meralgia paresthetica must be distinguished from an L3 nerve root lesion. L3 root lesions impair the quadriceps reflex; they also produce a more extensive sensory deficit, which, unlike that of meralgia paraesthetica, crosses over the midline of the thigh onto its anteromedial surface.

Femoral N. (L1–L4)

Anatomy. The femoral n. provides motor innervation to the hip flexors (iliacus and psoas major mm.) and the knee extensors (quadriceps femoris m.). It provides sensory innervation by way of anterior cutaneous branches to the anterior surface of the thigh, and, through its terminal branch, the saphenous n., to the medial quadrant of the anterior surface of the lower leg. Its anatomical course is shown in Fig. 12.47.

Typical deficits. A lesion of the femoral n. impairs hip flexion and knee extension. The hip flexors are examined with the patient sitting up and the knee extensors are examined with the patient supine (Fig. 12.48). In the standing patient, a low-lying patella is seen on the side of the lesion. The quadriceps reflex (patellar tendon reflex) is absent The patient cannot climb stairs with the affected leg and keeps it in a hyperextended position while walking (Fig. 3.2p. 15). Sensation is diminished in the territory of the sensory terminal branches (an-teromedial surface of the thigh and medial surface of the lower leg, Fig. 12.47).

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Fig. 12.47 Anatomical course and distribution of the femoral n.

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Fig. 12.48 Testing of knee extensors in the supine patient (the leg is able to hang freely downward). This testing position permits optimal use of the knee extensors that originate at the pelvis and thus span two joints, the hip joint and the knee joint (i.e., the rectus femoris and sartorius mm.).

Causes. Lesions of the femoral n. are commonly traumatic or iatrogenic (surgery). The nerve can also be involved by a pelvic tumor or, acutely, by a hematoma in the psoas sheath, e. g., in an anticoagulated patient.

Obturator N. (L3–L4)

Anatomy. The obturator n. supplies the thigh adductors (Fig. 12.49). Its sensory innervation is to a small area of skin just above the medial aspect of the knee.

Typical deficits. A lesion of the obturator n. impairs thigh adduction. The examining technique needed to demonstrate this is shown in Fig. 12.50. The adductor reflex, elicited by a tap on the medial condyle of the femur, is diminished and there is a small area of hypesthesia on the medial aspect of the thigh, just above the knee. Sometimes, irritation of the obturator nerve trunk can produce pain in this area as the sole clinical manifestation. This is called the Howship–Romberg phenomenon.

Causes. Masses in the pelvis or the obturator foramen are the usual causes; an obturator hernia is rarer.

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Fig. 12.49 Anatomical course and distribution of the obturator n. The area of cutaneous sensory innervation is shaded dark red.

Gluteal Nn. (L4–S2)

Anatomy. The gluteal nn. are purely motor. They innervate the hip abductors and extensors. The course of the two gluteal nn. is shown in Fig. 12.51.

Lesions of the superior gluteal n. produce weakness of the hip abductors (gluteus medius and minimus mm. and tensor fasciae latae m.). This impairs the stability of the pelvis on the side of the stationary leg when the patient walks; the pelvis tilts to the side of the swinging leg (so-called Trendelenburg gait). In an incomplete superior gluteal n. palsy, the patient barely manages to prevent tilting of the pelvis by inclining the trunk to the side of the stationary leg, thus displacing the body's center of gravity laterally (so-called Duchenne gait, cf. Fig. 3.2p. 15 and Fig. 14.3p. 266).

Lesions of the inferior gluteal n. (L5–S2) produce weakness of the gluteus maximus m., impairing hip extension. This makes it difficult for the patient to climb stairs (for example). Atrophy of the gluteus maximus m. is usually difficult to see because of the overlying fatty tissue, but, when the gluteus maximus mm. on either side are simultaneously and actively contracted, the lack of muscle tone on the affected side is easily appreciated by palpation. The natal fold is lower on the affected side.

Causes. The gluteal nn. are often injured by intramuscular injections with faulty technique.

Differential diagnosis. Trendelenburg gait can be observed in many diseases of the hip, e. g., in congenital hip dislocation. Weakness of the gluteus maximus m. can be caused by an S1 nerve root lesion (Fig. 12.52), while weakness of the gluteus minimus and gluteus medius mm. can be caused by an L5 nerve root lesion. Bilateral weakness of the hip abductors is found, for example, in muscular dystrophy.

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Fig. 12.50 Functional testing of the thigh adductors. a A patient lying in the lateral decubitus position can normally lift the lower leg off the examining table when the examiner lifts the upper leg. b A patient with adductor weakness cannot do this.

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Fig. 12.51 Anatomical course and distribution of the superior and inferior gluteal nn.

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Fig. 12.52 Weakness of the left gluteus maximus m. The left buttock, on active contraction, is less voluminous than the right, and the left gluteal fold hangs lower.

Sciatic N. (L4–S3)

Anatomy. The sciatic n. is the common trunk of the fibular (= peroneal or common peroneal) and tibial nn. It is the longest and thickest nerve in the human body. Its anatomy is shown in Fig. 12.53. The portions of the sciatic n. that are destined to become the fibular and tibial nn. are already clearly distinct from one another in the sciatic n. just distal to its exit from the pelvis, but they are usually ensheathed in a common epineurium nearly all the way down to the level of the popliteal fossa. The sciatic nerve trunk, in its proximal portion, gives off cutaneous branches to the buttock and the posterior surface of the thigh (the inferior cluneal nn. and the posterior femoral cutaneous n.). Along its further course, it gives off motor branches to the knee flexors (the semimembranosus, semitendinosus and biceps femoris mm., which may be collectively termed the ischiocrural muscles or hamstrings).

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Fig. 12.53 Anatomical course and distribution of the sciatic n.

Typical deficits. The clinical manifestations of a sciatic nerve lesion depend on the level of the lesion and the extent to which it involves the fibular and tibial portions of the nerve. Proximal lesions (but not distal ones) produce hypesthesia on the buttock and the posterior surface of the thigh and impair knee flexion. The strength and reflexes of the knee flexors are best tested in the prone patient (Fig. 12.54). For the clinical manifestations of fibular and tibial nerve lesions, see below.

Causes. The sciatic nerve trunk can be injured by fractures of the pelvic ring or proximal portion of the femur, by surgical procedures in the region of the hip, or by faultily delivered injections. Tumors are a less common cause of sciatic nerve palsy.

Fibular N. (L4–S2)

Anatomy. The fibular (peroneal or common peroneal) n., after it separates from the tibial portion of the sciatic n., travels to the lateral margin of the popliteal fossa, winds around the fibular neck, and then enters into the body of the fibularis longus (peroneus longus) muscle, where it divides into the superficial and deep fibular (peroneal) nn. The superficial fibular (peroneal) n. provides motor innervation to the fibular (peroneal) muscles and sensory innervation to the lateral surface of the lower leg and the dorsum of the foot, with the exception of the space between the first and second toes (the first interosseous space). The latter is supplied by the deep fibular (peroneal) n., which also innervates the dorsiflexors of the foot and toes and the intrinsic muscles of the dorsum of the foot.

The anatomy of the fibular n. is shown in Fig. 12.55.

Typical deficits. The clinical manifestations of a lesion of the deep fibular n. include foot drop and steppage gait (Fig. 3.2p. 15). Sensation is impaired on the dorsum of the foot and completely abolished in the first interosseous space. A lesion of the superficial fibular n. causes weakness of pronation of the foot (i. e., inability to elevate the lateral edge of the foot); when the patient walks, the lateral edge of the foot hangs downward. Sensation is impaired in the lower leg and on the dorsum of the foot. If the trunk of the fibular n. (= the common peroneal n.) is affected, all of the above deficits are seen.

Causes. The trunk of the fibular n. can be injured by penetrating or blunt trauma, e. g., by knee fractures. Injection palsies of the sciatic n. usually affect its fibular portion. The most common cause of fibular nerve palsy, however, is compression of the nerve at the fibular neck by local, external pressure (faulty surgical positioning, a cast, etc.). This type of palsy is spontaneously reversible. The site of the lesion can be precisely localized with the aid of electroneurography (Fig. 4.24p. 61).

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Fig. 12.54 Functional testing of the knee flexors. The patient is prone. This is mainly a test of the semimembranosus, semitendinosus, and biceps femoris mm.

Differential diagnosis. A foot drop combined with loss of sensation on the dorsum of the foot can be seen in combined lesions of the L4 and L5 nerve roots, but such lesions will additionally impair abduction of the hip and inversion of the foot. Bilateral foot drop caused either by Steinert myotonic dystrophy or by peroneal muscle atrophy in the setting of HMSN type I can mimic a bilateral fibular nerve palsy. An initially isolated, progressive, unilateral foot drop without any associated sensory deficit may be the first symptom of spinal muscular atrophy or ALS.

Tibialis anterior syndrome. This syndrome often causes difficulties in differential diagnosis. It is caused by infarction (due to compression) of the muscles in the anterior compartment of the lower leg, because of overuse, trauma, or a hematoma. Steadily rising local pressure within the anterior compartment, which is tightly encased in fascia, leads first to intense local pain, and then to muscle swelling. The pain increases on passive extension of the muscles by plantar flexion of the foot. The muscles become necrotic in 12 to 24 hours and are later replaced by connective tissue. The resulting contracture prevents the appearance of the flaccid foot drop that is otherwise characteristic of fibular nerve palsy. In the acute phase of the tibialis anterior syndrome, the deep fibular n. can be damaged, because its course passes through the anterior compartment of the lower leg. The resulting sensory deficit may be diagnostically misleading, because it may be taken to imply a peripheral nerve lesion as the primary causative event.

Tibial N. (L4–S3)

Anatomy. This nerve, derived from the medial portion of the sciatic n., innervates the plantar flexors of the foot and toes in the lower leg, as well as all of the intrinsic muscles of the foot, except those on the dorsum. It provides sensory innervation to the heel and sole (Fig. 12.56).

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Fig. 12.55 Anatomical course and distribution of the fibular (= peroneal) n.

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Fig. 12.56 Anatomical course and distribution of the tibial n.

Typical deficits. Weakness of plantar flexion makes tiptoe walking impossible, while weakness of the intrinsic muscles of the foot makes the patient unable to fan the toes. The sensory deficit on the sole of the foot is particularly troublesome because of the important protective function of sensation in this area.

Tarsal tunnel syndrome is an entrapment neuropathy affecting the terminal branch of the tibial n. as it passes under the medial malleolus. It is seen almost exclusively after fractures or sprains of the upper ankle joint. Its typical feature is local pain behind the medial malleolus or on the sole of the foot, which increases when the patient walks. The nerve trunk is tender to palpation behind the medial malleolus. Sensation is diminished on the sole of the foot and the plantar skin is abnormally smooth and dry. The patient can no longer fan the toes (Fig. 12.57).

Morton metatarsalgia. A painful neuroma can develop on a digital nerve (a sensory terminal branch of the tibial n.) if the nerve is chronically injured by being compressed between two adjacent metatarsal heads. This condition, called Morton metatarsalgia, causes pain in the forefoot, which is initially felt only on walking, but later also at rest. The pain can be induced by the examiner by laterally compressing the anterior arch of the foot or by squeezing the metatarsal heads against each other. An injection of local anesthetic along the course of the nerve, applied from the dorsal surface of the foot proximal to the site of the neuroma, will bring complete, though transient, relief. Specially padded shoe inserts may be therapeutically useful. If the pain persists, the neuroma should be surgically excised through a plantar approach (Fig. 12.58).

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Fig. 12.57 Weakness of the intrinsic muscles of the foot in tarsal tunnel syndrome (lesion of the tibial n. behind the medial malleolus).

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Fig. 12.58 Excised neuroma of an interdigital nerve. The neuroma was found at the branch point of the nerve. The patient had suffered from Morton metatarsalgia.