Chapter 18: Evaluation of neuropathic/nerve entrapment about the elbow and forearm.

Publicado em: 15 de maio de 2020 por Dr. José Carlos Garcia Jr.
Categorias: Capítulos de Livros

The Art of the Musculoskeletal Physical Exam, ISAKOS Book, Editors John Lane, Alberto Gobbi, João Espregueira-Mendes, Camila Kaleka Cohen, Nobuo Adachi

Jose Carlos Garcia Jr

Rafael Gadioli 

Leandro Sossai Altoé

NAEON Institute – Sao Paulo – Brazil

Musculocutaneous Nerve

The musculocutaneous nerve originates from C5–C8 nerve roots and is a continuation of the lateral cord. It innervates the major elbow flexors, the biceps and brachialis, and continues through the brachial fascia lateral to the biceps tendon, terminating as the lateral antebrachial cutaneous nerve. The motor branch enters the biceps and the brachialis approximately 15 and 20 cm below the tip of the acromion.

Lateral Cutaneous Nerve of Forearm

Originating from the musculocutaneous nerve, the lateral cutaneous nerve of the forearm innervates the anterolateral region of the forearm until the thenar eminence. Its compression site is in the distal third of the arm, between the biceps and the fascia of the brachial muscle, which tenses in the forearm extension and pronation.

Compression of the lateral cutaneous nerve of the forearm is a rare and badly understood condition. It presents a poor clinical picture, with burning pain in the anterolateral aspect of the forearm with worsening in passive pronation and hyperextension of the elbow. In full pronation forced supination of the forearm with elbow flexion can also reproduce the symptoms. In chronic cases, the patient reports vague discomfort in the forearm that can intensify and worsen with pronation supination activities with the elbow extended.

On physical examination, an area of hypoesthesia on the anterolateral surface of the forearm can be identified by applying a light touch to the skin with a blind spot.

Thinking about differential diagnoses the lateral epicondylitis and radial tunnel syndrome are highlighted.

For diagnostic confirmation, the use of electroneuromyography has an action potential with prolonged latency or decreased amplitude, however a negative result will not predict patient does not present this nerve entrapment. Imaging tests have little or no value.

Radial Nerve

The radial nerve and its major branches, the posterior interosseous nerve and the superficial radial nerve, are vulnerable to compression forces from the level of the lateral head of the triceps through the region of the elbow, proximal forearm, and even into the distal forearm.

Depending on which branch of the nerve is involved at the elbow, either motor and sensory (posterior interosseous nerve) or just sensory (superficial radial nerve) symptoms can occur. One needs to be aware that when sensory symptoms like tingling or numbness are present the superficial radial nerve or a radial nerve before the division of this nerve are highly suspected. In occasions where pain on the anterolateral aspect of the elbow is present a posterior interosseous nerve impairment can be suspected, once it is not a sensitive nerve no tingling nor numbness are related to this nerve. 

Rarely, motor and sensory involvement can be due to a process in the proximal forearm affecting both branches rather than the radial nerve.

The radial nerve has its origin in the posterior fascicle of the brachial plexus and innervates the triceps, brachioradialis, anconeus, all extensors, supinator and abductor pollicis longus. In the distal region of the arm, it crosses anterior to 10 cm proximal to the lateral epicondyle. At the level of radiocapitellar articulation, divides into superficial and deep branches, passing the brachioradial fascia deep, innervating the m. brachioradialis radial and extensoris carpi radialis longus. The motor branch of the extensoris carpi radialis brevis originates from the superficial branch of the radial nerve in 58% of the population. In the elbow, the deep branch, crosses between the two heads of the supinator muscle, where it is called the posterior interosseous nerve (PIN) and innervates that muscle. The proximal edge of the supinator muscle forms the fibrous Fröhse’s arcade. The superficial radial nerve continues below the brachioradial until it emerges from the distal third of the forearm to the subcutaneous. Dorsoradial forearm tenderness until the hand can make one suspect of radial sensitive branch compression. The recurrent vessels of the radial artery cross superficial and deep to the branches of the radial nerve at the elbow, these structures can entrap the nerve, as well as fibrous adhesions of the anterior capsule. 

The PIN goes in the dorsoradial direction in the proximal forearm where 6-8 cm distal from the elbow it emerges from the supinator muscle and releases its terminal branches to the extensor digitorum communis, extensor digiti minimi, extensor carpi ulnaris, abductor policis brevis and longus, long and short thumb extensor, extensor indicis proprius and extensor digiti minimi.

Indeed, the compression sites are as follows: spiral groove of the humerus between the intermuscle septum of the triceps, and in the forearm: Fröse’s arch (most common compression site), fibrous band between the brachioraidalis and brachial muscles, Henry’s vascular complex (recurrent vessels art. Radial), tendon margin of the extensor radialis carpi brevis and distal edge of the supinator muscle.

Posterior Interosseous Nerve 

In cases of high bifurcation, the deep branch may be compressed in the lateral intermuscular septum, with local sensitivity and weakness of the wrist and finger extensors. In these cases, the superficial radial nerve is anterior to the intermuscular septum.

Classical clinical presentation of posterior interosseous nerve(PIN) paralysis is typically motor. Due to segmental innervation of the supinator, the proximal or distal location of the compression may determine an occasionally positive electromyographic study. A supine myofibrillation suggests a more proximal compression of the Fröse arcade.

If only the PIN is compressed, there will be a deficit in the extension of the fingers and thumb with radial deviation of the wrist. Because the branches for the long and short extensor carpi radialis brevis and longus of the wrist originate more proximally. In the case of partial paralysis or compression of the medial branch, weakness of the extensor carpi ulnaris, extensor digiti minimi and extensor digitorum will occur, which may lead to an attitude called the “pseudoulnar” claw.  In case of compression it occurs in the lateral branch, the weakness will be of the abductor pollicis longus, long and short extensor of the thumb and extensor proper of the fingers. There may be vague pain on the back of the forearm, but without sensory changes. Atrophy may be present in chronic cases.

The Maudsley test(Fig. 1) identifies pain at the origin of the Extensor carpi radialis brevis during movement of extension against resistance of the third finger with the extended member (differential diagnosis with lateral epicondylitis).

#Local tenderness along the Posterior interosseous nerve, and its branches need to be compared with the contralateral side, this region is regularly not very sensitive to pressure. Tenderness is particularly present on the main compression site, most commonly the Fröhse arcade on the anterolateral aspect of the elbow, located 5-10cm distal and anterior to the lateral epicondyle. 

# Supination of the forearm against resistance can reproduce pain in cases of PIN compression in the Fröhse’s arcade. This test needs to be done in two stages: 

  1. Elbow flexion: where pain can be reported in the proximal lateral forearm.
  2. Elbow extension: Pain can be equal or inferior 

When one tests the elbow in flexion the supinator muscle is more requested, because biceps is not under full tension. When elbow is extended biceps is under full tension assuming more control over the supination movement. Therefore, if pain is higher in forced supination with elbow’s flexion it’s the PIN compression is highly suggested, in opposite side when pain is higher during forced supination and elbow extension distal biceps partial lesions or tendinopathies are suggested. It is also not common that biceps pathologies cause tenderness on anterolateral aspect of the elbow when palped. Biceps will also cause high tenderness when patient in full pronation and extended elbow isometrically try to move to flexion and supination against resistance. Indeed, distal biceps tendinopathies are differential diagnosis of PIN in the Fröhse’s arcade.

Among the complementary exams that may assist in the diagnosis, there are few findings that define NIP compression. Dynamic electroneuromyography may show changes with denervation of the muscles innervated by PIN, but false negatives will not exclude the PIN syndrome.

Radial Tunnel Syndrome

The existence of the radial tunnel syndrome(RTS) is sometimes questionable, since the only symptom and complaint of the patient is constant pain, as soon as this condition is not associated with weakness of the extensor muscles and the electroneuromyography is negative.

The RTS, or also called the “tough tennis elbow”, presents a characteristic pain clinic located on the n. radial, ±5 cm lateral and distal to the epicondyle. The pain occurs during supination in a very similar manner to the PIN syndrome. Indeed, RTS is a slight PIN syndrome that predominantly presents sensitive symptoms and fatigue. Tests for RTS are the same of PIN syndrome. 

Wartenberg Syndrome

It is the compression of the sensory branch of the radial nerve, described by Wartenberg in 1926. This condition presents as clinical picture a middle or distal third of the forearm tenderness and paresthesia, between the brachioradialis and extensor carpi radialis longus (ECRL). The nerve arises in the proximal forearm at the bifurcation of the radial nerve, goes deeply to the brachioradial in the forearm, where there are 9 cm of the radial styloid emerging between the brachioradialis and the ECRL.

It has differential diagnosis with De Quervain’s tenosynovitis.

Compression can be caused extrinsically due to the use of a watch, bracelets and rubber bands or intrinsically by tumors, traumas, fibrous bands and anomalous muscles.

Symptoms are such as paresthesia on the dorsoradial aspect of the hand, with worsening with passive wrist flexion with ulnar deviation and wrist in pronation (for one minute), or active forearm supination and wrist extension against resistance(30 seconds)  The Tinel sign can be positive in the region proximal to the radial styloid (9cm). If positive over the radial styloid its compression is just of the dorsal branches. The Finkelstein test can also be positive for performing nerve traction.

The use of complementary exams is also restricted in this case, with electroneuromyography of low value. Local anesthetic block can be performed with lidocaine, which can lead to temporary improvement of the condition.

Anterior interosseous nerve

The Anterior Interosseous Nerve (AIN) can be compressed in anatomical sites such as: the supracondylar process at the distal humerus, within the Strüthers ligament of the supracondylar process, by the aponeurosis of the biceps (lacertus fibrosus), between the superficial and deep heads of the teres pronator muscle(most common site), arade of the superficial flexor digitorum superficialis, Gantzer muscle and at the Martin-Gruber anastomosis site, which is an anastomosis region that interconnects the motor branches of the median and ulnar nerves, present in 7 to 23% of the population.

The Strüthers ligament is present in 0.6% to 2.7% of the population and is a fibrous band that extends from the anteromedial aspect of the humerus to the medial epicondyle. Compression by the Strüthers ligament is responsible for 0.5% of all cases. This ligament can originate in the supracondylar process, when present in 1% of the population.

The AIN is the terminal motor branch of the median nerve, being responsible for innervating the second and third flexor digitorum profundus tendons, flexor pollicis longus, and pronator quadratus.

The compression of the true AIN has only motor deficit. There will be no sensitivity change in the forearm. The complaint will be of ill-defined pain in the forearm and a report of weakness of the thumb and forefinger.4

In the physical examination, the main test to be performed is the “ok” sign test, where the patient is unable to perform the OK sign (touching the tip of the thumb to the point of the indicator), performing flexion of the distal phalanx of the thumb and the index finger. The impairment of the flexor digitorum profundus tendon and the second flexor digitorum profundus tendon, will impede the patient to flex these tendons. A typical  incapacity of these tendons’ flexion during the ok is named as as the Kiloh-Nevin sign (Fig. 2).  

The pronator quadratus muscle can be examined separately by pronation against resistance with the elbow in flexion, in order to less tension on the humeral head of the teres pronator. Its examination needs to be comparative to the contralateral side. Other tests can be performed to help identify the most accurate location of the compression. Lacertus fibrosus can be assessed with supine resistance flexion. The pronator is round, with the pronated counter-resistance in flexion. The flexor arch, with the flexion against resistance of the intermediate phalanx of the annular finger.

Electromyographic studies are essential, which should show normal for sensitive conduction of the median nerve and changes to the quadratum pronator muscle, long flexor pollicis and flexor digitorum profundus tendon and the second flexor digitorum profundus tendon, with tapered waves, fibrillations and driving latency. MRI may show muscles with signs of edema and denervation.

Median nerve

The median nerve can be compressed within the elbow region by the supracondylar process, by the Struthers’s ligament, in the lacertus fibrosus, in rounded pronator muscle deep head or in the flexor arch. It can even be compressed by vascular malformations, anomalous muscles and synovial and bursal strains. Distal humerus fractures and elbow dislocation also can cause lesion of the median nerve. 

The passage of the nerve through the elbow region has close relationship with these anatomic structures, bringing the possibility of being affected by one or more of these structures. It can present motor and sensitive symptoms combinations, showing symptoms in the elbow, hand and forearm region. 

In this chapter it will be addressed forms of evaluate and differentiated its causes. 

Pronator syndrome 

This syndrome consists in the compression of the median nerve in the elbow region and also in the proximal part of the forearm.  The symptoms are always vague such as: pain, tingling, numbness, tiredness or fatigue, forearm discomfort with proximal irradiation. Laboral or sportive activities with pronosupination repetitive movements can trigger the symptoms. 

Generally, the symptoms are developed insidiously, but occasionally a specific event or sudden onset of pain in the forearm are related to the bigger susceptibility of the muscle stress.

It is estimated that ±5% of the symptoms related to median nerve are directly caused by the pronator teres syndrome, some studies suggest even higher percentages. Misunderstood, it is often misdiagnosed as an atypical carpal tunnel syndrome. However, unlike carpal tunnel syndrome, its symptomatology is more related to physical activities, night tingling isn’t an important complain and Phalen sign is not present. 

The pronator syndrome is characterized by the median nerve compression at the elbow and proximal forearm. Four potential compression sites include the supracondylar process and ligament of Stüthers, the lacertus fibrous, the rounded pronator and the superficial flexor digitorum superficialis ach. 

The compression region most proximal and less usual is the humerus supracondylar process. This bone process, existent in approximately 1-3% of the population, stems from the anteromedial aspect of the distal humerus, proximal 5cm to the medial epicondyle. The Struthers ligament is the fibrous band that can arise from the supracondylar process and attach to the medial epicondyle, forming a fibro-bone tunnel through which the median nerve crosses. The entrapment of the median nerve inside this tunnel is also called supracondylar process syndrome. 

The lacertus fibrosus arises from the distal bicipital tendon and inserts into the antebrachial fascia, crossing the flexor pronator muscle group. The thickened lacertus can produce median nerve compression. 

The pronator syndrome compression most frequent region is between the superficial heads (humeral) and deep (ulnar) of the rounded pronator, located from 2 to 4 cm distal to the medial epicondyle. It can be caused by muscle hypertrophy, fibrous adhesions or other teres pronator anomalies. 

The physical exam should be always comparative to the contralateral side. The hand’s palm symptoms are more related to higher compression sites out of the carpal tunnel once the sensitive branch to this hand’s region raises before the carpal tunnel.

Special care must be taken, because the forearm pronation can cause a depression into the proximal and medial forearm regions, suggesting constrictive strength of the lacertus fibrosus, also the extension of the elbow can increase compression on the humeral head of the pronator teres muscle, once it is anterior to the elbow’s rotation center.

The complete understanding related to the main compression site can be a difficult task. 

During the physical examination one needs to be aware in order to keep a suitable position avoiding median nerve compression on the carpal tunnel.

Symptoms can be reproduced by the following tests:

# Middle finger proximal interphalangeal flexion against resistance(Fig.3). The authors use to do this test with the patient’s forearm on a table. This test will tension flexor digitorum superficialis arch;

# Pronation against resistance(Fig.3) for 30 seconds can reproduce the symptoms. The authors use to do this test with the patient’s forearm on a table, with the elbow flexed, making lacertus fibrous relax.;

# The elbow flexion against resistance with supine forearm may trigger symptoms due to pressure from lacertus fibrosus(Fig. 4). One needs to be aware because if wrist is hyperextended the flexopronator mass can be overstretched, compressing the teres pronator site;

# Direct pression by the examiner on the rounded pronator proximal region, approximately 5 cm distal to the antecubital fossa (elbow pit) while making moderate resistance to pronation can also increase symptoms;

# The weakness of innervated median muscles is uncommon, but it is indicated the comparison between the two hands strength.  The pollicis longus flexor and the digitorum profundus index finger flexor are probably those which will present more evident weakness;

# Tinel signal can be present on the compression sites.

It is important to differentiate the simple compression from the double crush syndrome of the median nerve, thus cervical and wrist examination are also necessary. 

As a dynamic compression, electroneuromyographic tests in can sometimes show not significant alterations, however, when present will need to beconsidered. 

Ultrasound can allow dynamic, real-time visualization of nerves and also provide the means to precisely locate anatomical site of nerve compression. In addition, ultrasound can provide the examiner with more information about any underlying condition like ganglion cysts, lipoma, formation of neuroma or epineural hematoma. 

The pronator syndrome can also leads to forearm pronator flexor muscle atrophy, including the rounded pronator, the radial carpal flexor, long palmar and superficial flexor of the fingers. 

Nerve sheath tumors such as schwannoma and neurofibroma can also be related to nerve compression symptoms.

Ulnar Nerve

The cubital tunnel syndrome is the second most common compressive syndrome of the upper limb, second only to the carpal tunnel syndrome.

The ulnar nerve is localized medially the ulnar artery in the anterosuperior arm compartment, after crossing the intermuscular septum to the posterior compartment, it raises from the Strüthers ach on the distal arm. At the elbow, it passes at the back of the medial condylar groove, between the medial epicondyle of the humerus and the olecranon, and then enters in the cubital tunnel¹. 

In the cubital tunnel, the nerve is permanently subjected to compressive effects each time the elbow is flexed.

The most proximal compression locations are the Arcade of Strüthers and the medial edge of the intermuscular septum. Less frequent compression locations include Osborne’s fascia, a fibrous band that connects the proximal edge of the flexor carpi ulnaris muscle to the medial epicondyle and aponeurosis of the flexor pronator muscles.

The ulnar nerve is not a fixed structure and needs to move freely both longitudinally and medially during elbow movement.

Two major age ranges are described for cubital tunnel syndrome. The first is between 20 and 30 years old, predominantly secondary to the trauma. The second is developed between 50 and 60 years old, associated with degenerative disease.

Several factors can increase pressure on the ulnar nerve at the elbow. Postural addiction with flexion when sleeping, the hypermobility of the nerve at the cubital tunnel promoting subluxation in the medial epicondyle during the flexion. Other etiological factors of compression are muscle anomalies, such as epitrochlear anconeus, tumors, ganglia, cubit valgus deformity, sequelae of elbow fractures and dislocations, elbow arthrosis, thickening of the Arcade of Struthers, as well as sports.

Chronic compression may be secondary to mass lesions, including bursae, ganglia, synovitis, bruise, osteophytes, calcifications and ectopic ossifications. In athletes, lateral displacement of the ulna secondary to chronic medial collateral ligament laxity or lesion, and cubitus valgus deformity can also cause cubital tunnel syndrome.

The clinical picture is characterized by intermittent numbness and tingling in the ulnar nerve autogenous area, being related to the shoulder and elbow position increasing the pressure in the nerve and its symptomatology.

Patients can describe a difficulty in fine motor tasks, such as buttoning. Crossing fingers can be difficult because of interosseous weakness. Hypotrophy or atrophy of the intrinsic muscles and adductor pollicis, with ulnar claw, weakness of other extrinsic muscles innervated by the ulnar can be also present.

Pain is not a frequent complaint, there is no change in forearm sensibility. However, less sensibility, tingling and numbness in medial part of the annular finger and all the little finger are the frequent symptoms.

Tinel can be positive and helpful in delimitating the main compression area. 

The elbow flexion for 30 seconds may also reproduce sensitve symptoms in the patient. It happens because the ulnar nerve passes posterior to the elbow’s rotation center. Pressures within the cubital tunnel can increase until to 7-fold during elbow flexion. 

Collateral medial ligament tests are also important because lesions or attenuation of this ligament can also stretch the nerve when a valgus force is done on the elbow. Valgus stress test will be done with 30º elbow flexion. It is strongly suggested to make this test in supination and pronation, because in supination a false positive can take place when the patient presents posterolateral rotatory instability.

Ulnar nerve dislocation can be visible, usually during the elbow flexion. When one has difficulties on visualization one needs to full extends the patient’s elbow, feel the medial epicodyle, using 2nd and 3rd fingers and then the patient flexes his elbow. It is possible to feel the nerve dislocation using this maneuver. Snapping triceps can also be felt or visualized with this same maneuver.

X-ray examen can be useful in presence of bone lesions or deformities. The electroneuromyography is usually very helpful, however for some cases of dynamic or light compression it may not be altered. Ultrasound dynamic exams can make possible to determine ulnar dislocations and nerve narrowing. Unlike radial and median nerve neuropathies, ulnar neuropathy usually presents with increased ulnar nerve signal on T2-weighted examination. This change in the signal may be better appreciated in the ulnar nerve because of its larger size. Other pathological processes related to cubital tunnel neuropathy are identified by MRI imaging, including osteoarthritis, synovitis, valgus deformity, anomalous muscles and tumors.

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