Arm and Neck Pain

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Chapter 29 Arm and Neck Pain

Evaluation of the patient with arm and/or neck pain is based on a careful history and clinical examination. Diagnosis of the common causes and a treatment plan can almost always be accomplished in the office before laboratory investigation, but further study may be required if the patient fails to improve or has other specific indications for imaging or electrical studies.

A useful approach is to consider the diagnosis in terms of pain-sensitive structures in the neck and upper limbs. These structures may be part of the nervous system or may involve joints. Neurological causes should be considered in terms of the innervation of the neck and arm, and non-neurological causes are based on dysfunction of the other anatomical structures of the arm or neck. Because nerve root irritation generates neck muscle spasm, this type of pain is usually lumped into the “neurological” category. Some essentially non-neurological conditions have neurological complications and are grouped in this chapter as “in-between” disorders.

Clinical Assessment

History

Neurological Causes of Pain

Peripheral pathology may involve the brachial plexus (Fig. 29.1) or individual nerves extending to the hand. Infiltrative or inflammatory lesions of the brachial plexus produce severe brachialgia radiating down the upper limb and also spreading to the shoulder region. Radiation to the ulnar two fingers suggests that the origin is in the lower brachial plexus, and radiation to the upper arm, forearm, and thumb suggests an upper plexopathy. Patients with a thoracic outlet syndrome complain of brachialgia and numbness or tingling in the upper limb or hand when working with objects above the head.

Fig. 29.1 Brachial plexus: schema.

Ulnar Nerve Pain

Ulnar nerve entrapment causes numbness or pain radiating down the medial aspect of the arm to the little and ring fingers. Symptoms are often worse at night when the patient sleeps with a flexed elbow, and they may interrupt sleep. Ulnar paresthesias are also triggered by pressure on the nerve when the patient rests the elbow on the arm of a chair or desk. Tapping on the nerve in the ulnar groove at the elbow may evoke a tingly electrical sensation in the little and ring fingers—Tinel sign.

Median Nerve Pain

Median nerve entrapment in the carpal tunnel classically awakens the patient from sleep with numbness and tingling in the thumb, index, and middle fingers, which is relieved by “shaking out” the hand. Pain generated in the median nerve can be sharp and lancinating and radiates to the thumb, index, and middle fingers. While entrapment at the wrist is common, occasionally the site of entrapment is at the elbow under the pronator muscle.

Non-Neurological Causes of Neck Pain and Brachialgia

Pain arising in muscle is deep, aching, and boring. In the cervical region, it is localized to the shoulders and sometimes radiates down the arm. If the patient is over 50 years of age, a sedimentation rate should be checked; if it is markedly elevated, the diagnosis of polymyalgia rheumatica should be considered. Patients with fibromyalgia may have pain in the neck, shoulders, and arms, with trigger spots or nodules that are exquisitely tender even to light pressure.

If pain is triggered or aggravated by movement of the upper limb, arthritis or tendonitis is the likely cause. Particular attention should be paid to these characteristics; pain on shoulder joint movement is unlikely to be neuropathic. The pain of epicondylitis may radiate down the forearm in a pseudoneuralgic fashion, but precipitation of pain by movement at the fingers or wrist indicates a rheumatological cause.

Examination

The physical examination is designed to localize a neurological deficit related to spinal cord, nerve roots, or peripheral nerves. Evaluation for non-neurological pathology is required because rheumatological problems often complicate a primarily neurological problem. A detailed knowledge of motor and sensory neuroanatomy is required for accurate localization.

Motor Signs

The examination begins with inspection. Particular attention is paid to atrophy of muscles of the shoulders, arms, and the small muscles of the hands. Fasciculations are often due to anterior horn cell disease, but they may be part of the neurology of cervical spondylosis and radiculopathy. Significant sensory signs would argue against anterior horn cell degeneration.

Muscles in the various myotomes must be tested individually. When there is unilateral weakness, the contralateral side can act as a control, but some standard measure of strength is necessary for accurate evaluation when bilateral weakness is present. If one can overcome the action of a patient’s muscle by resisting or opposing its action close to the joint it moves, using an equivalent equipotent muscle of the examiner (fingers test fingers, whole arm tests biceps), then that muscle in the patient is, by definition, weak. The degree of weakness can be graded, and the 5-point (Medical Research Council [MRC]) grading scale is often used. Grade 5 represents normal strength. Grade 4 represents “weakness” somewhere between normal strength and the ability to move the limb only against gravity (grade 3). Grade 4 covers such a wide range of weakness that it is usually expanded. One simple expansion is into “mild, moderate, or severe.” When the muscle can move the joint with the effect of gravity eliminated, it is graded at 2, and grade 1 is just a flicker of contraction.

The lower limbs must always be examined, even when the patient complains of symptoms only in the upper limbs. Evidence of a myelopathy as evidenced by the finding of sensory or motor dysfunction in the lower limbs, when combined with the presence of radicular signs in the upper limbs, indicates a spinal cord lesion in the neck.

The distribution of weakness is all important in localizing the problem to nerve root, plexus, peripheral nerve, muscle, or even upper motor neuron (central weakness). It is useful to use a simplified schema of radicular anatomical localization when evaluating nerve root weakness because overlap of segmental innervation of muscles can complicate the analysis (Table 29.1).

Table 29.1 Segmental Innervation Scheme for Anatomical Localization of Nerve Root Lesions

Segment Level	Muscle(s)	Action
C4	Supraspinatus	First 10 degrees of shoulder abduction
C5	Deltoid	Shoulder abduction
	Biceps/brachialis/brachioradialis	Elbow flexion
C6	Extensor carpi radialis longus	Radial wrist extension
C7	Triceps	Elbow extension
C7	Extensor digitorum	Finger extension
C8	Flexor digitorum	Finger flexion
T1	Interossei	Finger abduction and adduction
	Abductor digiti minimi	Little finger abduction

The thoracic outlet syndrome, or brachial plexus entrapment, is an overdiagnosed condition. Maneuvers designed to test for compromise of the neurovascular structures passing through the thoracic outlet are often difficult to interpret. In these maneuvers, the arm is extended at the elbow, abducted at the shoulder, and then rotated posteriorly. The examiner palpates the radial pulse while listening with a stethoscope over the brachial plexus in the supraclavicular fossa. The patient takes a deep inspiration and turns the head to one or the other side. Many normal individuals lose their radial pulse, but the emergence of a bruit does suggest at the least vascular entrapment (Adson test). The patient then exercises the hands held above the head with extended elbows—numbness, pain, or paresthesias, often with pallor of the hand, support the diagnosis (Roos test).

A distribution of weakness that does not conform to a clearly defined anatomical distribution of a single peripheral nerve in the upper limb suggests plexopathy. Upper plexus lesions cause mainly shoulder abduction weakness, and lower plexus lesions will affect the small muscles of the hand.

Sensory Signs

Skin sensation is tested in a standardized manner starting with pinprick appreciation at the back of the head (C2), followed by sequentially testing sensation in the cervical dermatomes, down the shoulder, over the deltoid, down the lateral aspect of the arm to the lateral fingers, and then proceeding to the medial fingers and up the medial aspect of the arm (Fig. 29.2). The procedure is repeated with a wisp of cotton to test touch sensation and test tubes filled with cold and warm water to test temperature sensation. Vibration sense is rarely abnormal in the fingers. Position sense in the distal phalanx of a finger is tested by immobilizing the proximal joint and supporting the distal phalanx on its medial and lateral sides and then moving it up or down; the patient, with closed eyes, reports movement and its direction. Loss of position sense in the fingers usually indicates a very high cervical cord lesion.

Fig. 29.2 Diagram of the dermatomes in the upper limbs. A, Anterior aspect. Although variability and overlap across the interrupted lines are evident, little or no overlap occurs across the continuous lines (i.e., dorsal and ventral axial lines). The examiner should routinely choose one spot in the “middle” of a dermatome and test at that point in all patients. C4 usually terminates at the point of the shoulder, T3 is almost always in the axilla, and T4 spreads across the chest so that C4 abuts T4 approximately at the nipple line. B, Posterior aspect.

Tendon Reflexes

Examination of the tendon reflexes helps localize segmental nerve root levels, but in cervical spondylosis, which is by far the most common underlying pathology, the reflexes are often preserved or even increased despite radiculopathy because of an associated myelopathy. An absent or decreased biceps reflex localizes the root level to C5, and an absent triceps reflex localizes the level to C6 or C7. An absent biceps reflex but with spread so that triceps or finger flexors contract is called an inverted biceps jerk and is strong evidence for C5 radiculopathy.

Non-Neurological Signs

The arm is passively abducted and internally and externally rotated at the shoulder. The complaint of pain on movement or at a point in the abductor arc indicates local shoulder joint pathology, usually shoulder tendonitis or pericapsulitis. The tendons anteriorly and at the lateral point of the shoulder may be tender to pressure. More diffuse tenderness anterior to the shoulder joint indicates bursitis. Tenderness over the medial or lateral epicondyle at the elbow indicates local inflammation, and pain on active or passive wrist or finger joint movement suggests tendonitis or arthritis.

Pathology and Clinical Syndromes

Spinal Cord Syndromes

Intramedullary Lesions

Primary intramedullary lesions may be neoplastic, inflammatory, or developmental. The most common presenting symptom of spinal cord tumor is pain, which is present in about two-thirds of patients, usually radicular in distribution, often aggravated by coughing or straining, and worse at night. A minority of patients show dissociated sensory signs (segmental loss of pin prick and temperature sensation with preserved light touch, vibration, and position sense) in the upper limbs to suggest central cord pathology. Long-tract signs in the lower limbs will ultimately develop. Magnetic resonance imaging (MRI) reveals swelling of the spinal cord. The most common tumors are glioma, lymphoma, and ependymoma.

Cervical myelitis presents with rapid onset of radicular and long-tract symptoms and signs and may be due to MS, postinfectious encephalomyelitis, or may be without an obvious cause (idiopathic).

Syringomyelia, a cystic intramedullary lesion of variable and unpredictable progression, may present with deep aching or boring pain in the upper limb, often characteristically referred to the ear. Asymmetrical lower motor neuron signs in the upper limbs, with dissociated suspended sensory loss (i.e., has an upper and lower border to the impairment of pin prick and temperature sensation), is very suggestive of a syrinx. However, the most common cause of intramedullary cord dysfunction is extrinsic spinal cord compression.

Extramedullary Lesions

Extramedullary lesions may result in any combination of root, central cord, and long-tract signs and symptoms. The most common cause of extrinsic nerve root and spinal cord compression is cervical spondylosis. This is a degenerative disorder of the cervical spine characterized by disc degeneration with disc space narrowing, bone overgrowth producing spurs and ridges, and hypertrophy of the facet joints, all of which can compress the cord or nerve roots. Hypertrophy of the spinal ligaments, with or without calcification, may contribute to compression. Hypertrophic osteophytes are present in approximately 30% of the population, and the incidence increases with age. The presence of such degenerative changes does not indicate that the patient has symptoms due to these changes; astuteness in diagnosis is necessary. Furthermore, the degree of bony change does not always correlate with the severity of the signs and symptoms it produces. This degenerative process is sometimes referred to as hard disc as opposed to an acute disc herniation or soft disc in which the onset is acute with severe neck pain and brachialgia. Patients with cervical spondylosis often awake in the morning with a painful stiff neck and diffuse nonpulsatile headache that resolves in a few hours. The lesion is most commonly at C5/6 and C6/7, and focal signs are likely to be at these levels. Wasting and weakness of the small muscles of the hands, particularly weakness of abduction of the little finger, is also frequently seen. These signs localize to lower segmental levels, but there may be no observable anatomical change at those levels, and then they are referred to as false localizers. Restricted neck movement is always present with significant cervical spondylosis. Bladder dysfunction, indicated by frequency, urgency, and urgency incontinence or the finding of long-tract signs or symptoms, indicates the need for imaging of the cervical spine both to exclude other pathology and to define the severity of the spinal cord compression. Immobilization in a cervical collar often helps with the symptoms and signs of cervical spondylosis. The role of surgery in treatment is discussed in Chapter 75.

Extramedullary compression in the extradural space is usually due to primary or metastatic tumors. Of the primary tumors commonly encountered, a schwannoma produces signs and symptoms related to the nerve root on which it arises, and as it enlarges, progressive myelopathic dysfunction occurs. Plain radiographs of the cervical spine may demonstrate an enlarged intervertebral foramen, but MRI is diagnostic. A meningioma may present in a somewhat similar fashion but is more frequent in the thoracic region.

Epidural spinal cord compression due to metastatic malignancy presents initially with spine pain in over 90% of patients. Malignant bone pain is usually localized to the vertebra involved, and percussion tenderness is a good localizing sign, even in the neck. As the pathology spreads to the epidural space, radicular pain appears. Plain radiographs of the cervical spine may show bony pathology with preservation of disc spaces, and again, the imaging modality of choice is MRI. The whole spinal column should be scanned because the pathology is often at multiple sites and may be subclinical. Spinal cord compression due to metastatic disease is a neurological emergency requiring treatment with immediate high-dose steroids and local irradiation. Occasional patients are referred for surgery.

Epidural infection (abscess) may be either acute and pyogenic or more chronic when the organism is mycobacterial or fungal. Pyogenic epidural abscess usually presents acutely with fever, severe pain localized to a rigid neck, radicular pain, and rapidly progressing root and myelopathic signs. Sometimes the presentation is more subacute with less systemic evidence of infection. Imaging will usually reveal early destruction of the disc, with spread into the epidural space; only later is there spread to bone, with vertebral collapse. Optimal therapy is surgical decompression and evacuation combined with 6 to 12 weeks of appropriate antimicrobial therapy for pyogenic infections and more prolonged treatment for tuberculosis.

The differential diagnosis of a very rapidly progressing painful epidural lesion includes spinal epidural abscess and spinal subarachnoid, subdural, or epidural hemorrhage. The latter are usually associated with some form of coagulopathy or anticoagulant therapy and sometimes with vascular anomalies or trauma. The sudden onset of severe pain in the neck, with or without radicular pain, may be due to hemorrhage. Reversal of the coagulation deficit, if present, should be followed by decompression.

The sudden onset of pain at the back of the neck with associated posterior fossa signs suggests vertebral artery dissection. The diagnosis is easily made with MRI and fat suppression sequences.

Repetitive sudden shooting pains radiating from the occipital region to the temporal areas or vertex suggests the diagnosis of occipital neuralgia. There may be local tenderness over the greater or lesser occipital nerve, and a local injection of corticosteroid plus local anesthetic is both diagnostic and therapeutic. Failure to respond suggests that the craniovertebral junction area should be imaged.

Radiculitis

Herpes zoster may infect cervical sensory root ganglia. The pain is typically radicular, and the diagnosis becomes clear when, after 2 to 10 days, the typical vesicular rash appears. Motor involvement occasionally occurs, and when it does, it has a predilection for C5/6 segments. Myelitis with long-tract signs is seen in less than 1% of patients. If the pain lasts longer than 3 months after crusting of the skin lesions, postherpetic neuralgia has developed. The pain is described as constant, nagging, burning, aching, tearing, and itching, upon which are superimposed electric shocks and jabs. Treatment of postherpetic neuralgia pain is discussed in Chapters 69 and 75.

Brachial Plexopathy

Brachialgia and signs not respecting a single nerve root, associated with tenderness to palpation in the supraclavicular notch, should arouse suspicion of a brachial plexopathy.

Brachial Neuritis (Neuralgic Amyotrophy, Parsonage-Turner Syndrome)

Brachial neuritis is characterized by the abrupt onset of severe pain in one shoulder and arm, which is constant and unrelenting, worse at night, and rarely bilateral. The syndrome afflicts mainly young adult men. Within a week or so, muscle weakness, atrophy, and fasciculations are evident, mainly in the shoulder girdle but at times more distally and not in one particular myotome. There is usually little or no sensory loss despite the pain. Pathogenesis is thought to be autoimmune/inflammatory, and a number of antecedent inciting events have been described, including immunization, infections, and trauma. The syndrome is associated with autoimmune diseases and Hodgkin disease. There is no proven specific treatment, but a short course of corticosteroids is usually given. In general, treatment is supportive, and the pain often runs its course in 6 to 8 weeks. In some patients, recovery from paralysis can take up to a year, and occasionally there is some permanent mild weakness.

A subset of patients who have a familial history have recurrent attacks. Hereditary neuralgic amyotrophy is an autosomal dominant, and many have deletions of the PMP-22 gene in a portion of the distal long arm of chromosome 17.

Brachial Plexopathy in Cancer Patients

Plexopathy in patients with cancer, particularly those with breast cancer or lymphoma who have been irradiated, poses a problem: is this radiation plexopathy or malignant infiltration of the brachial plexus? Malignant infiltration is more likely to trigger severe brachialgia, a Horner syndrome, and to affect the lower plexus. Irradiation damage is less likely to cause severe pain and often affects the upper plexus. Both are slowly progressive, but radiation plexitis is more likely to be of longer duration. Electroneurophysiological studies (see Chapter 32B) are helpful; myokymia and fasciculations support the diagnosis of radiation plexitis. MRI for detecting infiltration with tumor has a sensitivity of 96%, a specificity of 95%, and positive predictive value of 95%. Occasionally a locally malignant, relentless, and recurrent schwannoma occurs in a plexus that has been irradiated many years before.

Thoracic Outlet Syndrome

Brachial plexus involvement as an entrapment syndrome in the thoracic outlet is rare. The very existence of this entrapment remains open to debate, partly because it is rare and difficult to diagnose, and partly because it has been used as a disability issue, often in the absence of proven pathology. Consequently, questions remain about diagnosis and the efficacy of surgical treatment. Entrapment may involve the plexus, the subclavian artery, or both. Sagging musculature with postural abnormalities including droopy shoulders and a long neck contribute to the predisposition for thoracic outlet syndrome.

A supernumerary cervical rib or simply an elongated transverse process of the seventh cervical vertebra may be seen on plain radiographs. The rib may articulate with the superior surface of the first true rib, or a fibrous band may extend from its tip or the tip of the abnormal transverse process connecting to the first true rib. The abnormal structure compresses the plexus, particularly when the upper limb is elevated above head level. Pain and paresthesias radiate to the ulnar side of the hand and fingers, and weakness of the intrinsic muscles of the hand secondary to lower plexus compression may be evident. Thoracic outlet maneuvers described earlier are generally considered to be unreliable but do raise suspicion. The examination may be normal, or there may be weakness of abductor digiti minimi and hypothenar sensory loss. Occasionally, the abductor pollicis brevis is particularly atrophic and weak.

The diagnosis is often one of exclusion; imaging of the cervical spine is normal, and nerve conduction studies below the clavicle are also normal. Venous and arterial anatomy can be studied by catheter angiography, Doppler flowmetry, or MR angiography and venography. Electrophysiological studies that show partial denervation of the small muscles of the hand and a decreased sensory nerve action potential amplitude from digit 5 are compatible with the diagnosis of thoracic outlet syndrome.

In all cases, a conservative approach should be tried initially. Postural exercises and thoracic outlet muscle strengthening exercises, instructions in proper sitting at work, and correction of unusual sleep positions should provide relief in 50% to 90% of patients, usually within 6 weeks. Failure of conservative treatment prompts consideration of a surgical opinion.

Suprascapular Nerve Entrapment

The suprascapular nerve may be entrapped or injured as it passes through the suprascapular notch (see Chapter 76). It is occasionally cut in the process of lymph node biopsy. The branch to the infraspinatus muscle can be entrapped at the spinoglenoid notch by a hypertrophied inferior transverse scapular ligament. The patient complains of deep pain at the upper border of the scapula, aggravated by shoulder movement, and there may be atrophy and weakness of the supra- and more commonly the infraspinatus muscles. The supraspinatus muscle accounts for the first 10 degrees of shoulder abduction, and the infraspinatus muscle externally rotates the arm.

Carpal Tunnel Syndrome

Carpal tunnel syndrome, the most common entrapment neuropathy, is more frequent in females. It is now accepted as an occupational hazard secondary to repetitive stress and occasionally is the presenting symptom of underlying systemic disease. The nerve is entrapped in the bony confines of the carpal tunnel, which is roofed by the transverse carpal ligament.

Pregnancy, diabetes, rheumatoid arthritis, hypothyroidism, sarcoidosis, acromegaly, and amyloid infiltration of the ligament are possible predisposing factors, and appropriate screening studies should be performed on all patients with carpal tunnel syndrome.

Numbness or pain radiates to the thumb, index, and middle fingers and often wakes the patient at night. At times there is diffuse brachialgia. Atrophy of the abductor pollicis brevis muscle may be marked, but the motor deficit is rarely the cause of disability. Significant sensory loss in median nerve distribution can be a handicap because of poor feedback when using the hand out of sight.

In advanced cases, examination reveals atrophy of the abductor pollicis brevis muscle, which produces a longitudinal furrow in the thenar eminence. There is weakness of thumb abduction. In theory there should also be weakness of the opponens, but patients recruit the long flexor tendons when testing opposition, so weakness is hard to identify. The palmar cutaneous nerve branch leaves the median nerve proximal to the flexor retinaculum and supplies the skin over the thenar eminence and proximal palm on the radial aspect of the hand. Hence, sensory loss secondary to dysfunction of the median nerve in the carpal tunnel, if present, is likely to involve the distal thumb, index, and middle fingers but not the thenar eminence, a diagnostic point helpful in localization of the lesion. The Phalen test is performed by holding the wrist in complete flexion, and the test is considered positive when numbness or tingling in a median nerve distribution is seen within 20 seconds, but the latency before the sensory symptoms occur can be up to a minute. Sensitivity is about 74% and the false-positive rate is about 25%. The Tinel sign, distal tingling on tapping the median nerve at the wrist, may be elicited. Confirmation of the diagnosis is provided by nerve conduction studies and electromyography (EMG); distal motor and sensory latencies are prolonged, and polyphasic reinnervation potentials are seen in the abductor pollicis brevis muscle. More extensive and expensive investigations are usually not warranted, but sonography and MRI have been utilized. Initial relief of the sensory symptoms can be obtained with the use of wrist splints, but patients with unremitting pain or significant motor and sensory signs, together with confirmatory nerve conduction studies, should be offered decompressive surgery. This is usually curative. The surgeon should always send the excised flexor retinaculum for histopathological examination to search for amyloid deposition.

Occasionally, carpal tunnel syndrome may be mimicked by entrapment of the median nerve more proximally at the elbow. Here it passes beneath the thick fascial band between the biceps tendon and the forearm fascia and then between the two heads of the pronator teres muscle. As the nerve passes between the heads of the pronator teres, it supplies that muscle as well as the flexor carpi radialis (which flexes and abducts the hand at the wrist) and the flexor digitorum superficialis (which flexes the fingers at the interphalangeal joints with the proximal phalanx fixed) muscles. After it passes between the two heads of the pronator teres muscle, it supplies the flexor pollicis longus muscle (which flexes the distal phalanx of the thumb with the proximal phalanx fixed), the flexor digitorum profundus muscle to the first and second digits (which flexes the distal phalanx with the middle phalanx fixed), and the pronator quadratus muscle (which pronates the forearm with the elbow completely flexed). Nerve conduction studies may localize the site of pathology, and the EMG precisely defines which muscles are involved.

Ulnar Entrapment at the Elbow

The ulnar nerve may be entrapped proximal to the epicondylar notch or as it passes through the cubital tunnel at the elbow, where a fibro-osseous canal is formed by the medial condyle, ulnar collateral ligament, and flexor carpi ulnaris muscle. Structural narrowing of the canal aggravated by occupational stress and a sustained flexion posture, especially when sleeping, and repetitive flexion/extension movements contribute to entrapment. Although numbness and tingling are more common than pain, both are referred to the hypothenar eminence and the little and ring fingers. A positive Tinel sign at the elbow over the ulnar nerve helps localize the site. In severe cases, there is wasting and weakness of the small muscles of the hand (excluding the abductor pollicis brevis and opponens muscles which are median innervated). There is decreased sensation over the palmar aspect of the ring and little finger, and there may be decreased sensation on the medial dorsal aspect of the hand and ulnar two fingers owing to involvement in the distribution of the dorsal branch of the ulnar nerve. In severe chronic cases, clawing of the fourth and fifth digits results from weakness of the third and fourth lumbrical muscles. Nerve conduction studies localize the area of entrapment. If the symptoms do not resolve by avoiding prolonged elbow flexion, and the physical signs are significant, surgical decompression should be considered (see Chapter 76).

Radial Nerve–Posterior Interosseus Nerve Syndrome

Having passed through the spiral groove of the humerus, the radial nerve pierces the lateral intermuscular septum to lie in front of the lateral condyle of the humerus between the brachialis and brachioradialis muscles. There it bifurcates to form the superficial branch, which provides sensory innervation to the lateral dorsal hand and the deep branch, referred to as the posterior interosseus nerve. This branch supplies the finger and thumb extensors and the extensor carpi radialis brevis muscle, which is of lesser importance for radial wrist extension (extensor carpi radialis longus is dominant, and its nerve supply comes off slightly more proximally, so radial wrist extension is spared in lesions of the posterior interosseus nerve). The deep branch passes through the fibrous edge of extensor carpi radialis muscle through a slit in the supinator muscle (arcade of Frohse). Entrapment of the posterior interosseous nerve produces symptoms similar to those of lateral epicondylitis—lateral arm pain or a dull ache in the deep extensor muscle area, which radiates proximally and distally and is increased with resisted active supination of the forearm. Extension of the elbow, wrist, and middle fingers against resistance increases the lateral elbow pain. Tenderness may be elicited over the posterior interosseous nerve just distal and medial to the radial head. Pain secondary to posterior interosseous entrapment is typically seen in manual laborers and occasionally in typists. The site of pathology is easily localized by EMG and nerve conduction studies, and surgical decompression is usually successful. Occasionally a neoplasm of the nerve causes the same symptoms, and some surgeons prefer MRI prior to surgery.

Complex Regional Pain Syndrome

Complex regional pain syndrome (CRPS) encompasses syndromes previously called reflex sympathetic dystrophy (RSD), causalgia, shoulder-hand syndrome, Sudeck atrophy, transient osteoporosis, and acute atrophy of bone (see Chapters 44, 76, and 77). By consensus, the syndrome requires the presence of regional pain and sensory changes following a noxious event. The pain is of a severity greater than that expected from the inciting injury and is associated with abnormal skin color or temperature change, abnormal sudomotor activity, or edema. Type I CRPS refers to patients with RSD without a definable nerve lesion, and type II CRPS refers to cases where a definable nerve lesion is present (formerly called causalgia). A soft-tissue injury is the inciting event in about 40% of patients, a fracture in 25%, and myocardial infarction in 12%.