Relevant Anatomy

The radial nerve in the distal arm passes anteriorly, 10 cm proximal to the lateral epicondyle (Fig. 80-2).⁸⁰ At the level of the radiocapitellar joint, it divides into its major branches, the deep and the superficial radial nerves. In this passage, the radial nerve passes just deep to the fascia of the brachioradialis. Above the elbow, the radial nerve innervates the brachioradialis and the extensor carpi radialis longus. The motor branch to the extensor carpi radialis brevis arises from the superficial radial nerve in 58% of the population.¹⁵⁵ It frequently arises as a separate terminal branch of the radial nerve with the posterior interosseous and superficial radial nerves.

FIGURE 80-2 A, Dissection of the anterior aspect of the elbow demonstrating the anatomic relationship with the radial nerve. B, An enlarged view of the antecubital fossa shows the relationship of the posterior interosseous nerve to the supinator muscle and the arcade of Frohse. Note how the proximal superficial radial nerve is spared from compression by the arcade.

(Redrawn from Spinner, M.: Injuries to the Major Branches of Peripheral Nerves of the Forearm, 2nd ed. Philadelphia, W. B. Saunders, 1978.)

At the elbow, the deep branch passes between the two heads of the supinator muscle, where it becomes the posterior interosseous nerve.³¹ The proximal edge of the supinator forms an arch for the posterior interosseous nerve, the arcade of Frohse. The superficial radial nerve passes superficial to the supinator muscle. It is covered anteriorly by the brachioradialis. Recurrent vessels of the radial artery cross superficial and deep to these radial nerve branches. The posterior interosseous nerve courses in a dorsoradial direction in the proximal forearm. As it passes through the supinator, it innervates this muscle by multiple branches. Approximately 6 to 8 cm below the elbow joint, this nerve emerges from the supinator muscle, where it divides into its terminal motor branches to the extensor digitorum communis, extensor digiti minimi, extensor carpi ulnaris, abductor pollicis longus, extensor pollicis longus and brevis, and extensor indicis proprius.

Posterior Interosseous Nerve Syndrome

In cases of a high bifurcation, the deep branch may be compressed at the lateral intermuscular septum, 4 cm proximal to the lateral epicondyle. There is focal tenderness and often wrist and finger extensor weakness. In these rare cases, the superficial radial nerve lies anterior to the lateral intermuscular septum.

The deep branch can be compressed by a fibrous band or thickened proliferating rheumatoid synovium from the radiocapitellar joint,^18,114,116 the radial recurrent artery, or the leading tendinous edge of the extensor carpi radialis brevis.¹¹⁹ Next, the posterior interos-seous nerve can be compressed at the arcade of Frohse,^{54,118,134,152,163,168,196} the most common site of compression. It may also be compressed by fibrotic bands within the midportion of the supinator²⁶ and its distal end. Other causes of compression include adhesions at the anterior aspect of the distal humerus, muscular anomalies, vascular aberrations,⁴¹ bursae,² inflammatory thickening, and adherence of the extensor carpi radialis brevis¹¹⁹ tendinous origin to the proximal edge of the supinator on its radial side.^19,20 Some have identified focal constriction within the posterior interosseous nerve.^71,94 Posterior interosseous nerve palsy may result from fractures^124,179 or fracture-dislocations (Fig. 80-3).^122,171 Tardy posterior interosseous nerve palsy may also occur years after unreduced Monteggia fracture-dislocations^73,105 or after radial osteomyelitis (Fig. 80-4).¹⁷⁶ Tumors may compress the nerve primarily, which can be secondarily compressed by a structure such as the arcade of Frohse.^{7,11,17,151,178,200}

FIGURE 80-3 Fractures of the proximal radius often demonstrate posterior angulation, which places the posterior interosseous nerve in jeopardy.

(Redrawn from Spinner, M., and Spinner, R. J.: Management of nerve compression lesions of the upper extremity. In Omer, G. E., Spinner, M., and Van Beek, A. L. [eds.]: Management of Peripheral Nerve Problems, 2nd ed. Philadelphia, W. B. Saunders, 1998.)

FIGURE 80-4 This patient presented with a partial posterior interosseous nerve palsy. Plain films showed thickened cortices and a widened radial metaphysis, bony changes from an old osteomyelitis.

(From Spinner, R. J., and Spinner, M.: Tardy posterior interosseous nerve palsy due to childhood osteomyelitis: A case report. J. Hand Surg. 22A:1049, 1997.)

Classically, the clinical presentation of this nerve paralysis is thought to be typically motor because the posterior interosseous nerve basically carries motor fibers destined to innervate the extensor digitorum communis, extensor digiti minimi, extensor carpi ulnaris, abductor pollicis longus, extensor pollicis longus and brevis, and extensor indicis proprius. However, pain simulating lateral epicondylitis is also recognized as a common early presentation (see later discussion).¹⁹ Because of the segmental innervation of the supinator, the proximal or distal location of the compression of this nerve in the supinator can be determined by evaluating the electromyogram occasionally. Fibrillations in the supinator muscle suggest that the compression is proximal, at the arcade of Frohse. The pattern of involvement of this nerve varies depending on whether the entire nerve is compressed or whether there is a partial paralysis. When the entire posterior interosseous nerve is compressed, the fingers and thumb cannot extend at the metacarpophalangeal level and the wrist deviates in a radial direction with wrist extension (because the branches to the extensor carpi radialis longus and brevis usually take off more proximally) (Fig. 80-5).^15,197 An untreated partial paralysis commonly evolves into a complete paralysis. Wristdrop signifies a lesion proximal to the posterior interosseous nerve branch (Fig. 80-6).

FIGURE 80-5 Patient with a complete posterior interosseous nerve paralysis showing inability to extend the fingers at the metacarpophalangeal joints as well as an inability to extend the thumb. The patient can dorsiflex his wrist. Wrist dorsiflexion is in a radial direction through the intact extensor carpi radialis longus, which is innervated at or above the elbow. Sensation in the hand is intact.

(From Spinner, M.: Injuries to the Major Branches of Peripheral Nerves of the Forearm, 2nd ed. Philadelphia, W. B. Saunders, 1978.)

FIGURE 80-6 This patient has a complete radial nerve paralysis at the mid-arm level. Note the wristdrop with loss of finger extension at the metacarpophalangeal joints. The brachioradialis is paralyzed. Sensory loss is present in the autonomous zone of the radial nerve, that is, the dorsum of the thumb and first web space. In addition there is sensory loss in the distributions of the posterior cutaneous nerve of the forearm and the lower lateral cutaneous nerve of the arm.

With partial paralysis, some of the digits, for example the fourth and fifth fingers at the metacarpophalangeal joints, do not extend but the others do.^41,66,78,126 This attitude looks like a “pseudoulnar” claw hand. In reality, there is no clawing but only a drop at the metacarpophalangeal joint and no true hyperextension of the metacarpophalangeal joints of the fourth and fifth fingers, as is present in a typical ulnar nerve palsy (Fig. 80-7).

FIGURE 80-7 This patient has a complete low ulnar nerve palsy of the right hand with typical ulnar nerve clawing of the ring and little fingers. Note in this type of ulnar nerve palsy that there is hyperextension at the metacarpophalangeal joint typically seen with a claw finger. If a digit cannot be passively hyperextended at the metacarpophalangeal joint, a claw finger would not develop in the event of a low ulnar nerve paralysis. Sensation is absent in the palmar aspect of the little finger and ulnar half of the ring finger. Sensibility on the dorsal side is intact.

(From Spinner, M., and Spinner, R. J.: Management of nerve compression lesions of the upper extremity. In Omer, G. E., Spinner, M., and Van Beek, A. L. [eds.]: Management of Peripheral Nerve Problems, 2nd ed. Philadelphia, W. B. Saunders, 1998.)

Understanding the branching pattern of the posterior interosseous nerve can assist in further localization of partial lesions. Different patterns of presentation have been described and localized.^{72,77,173,181} These include dropped finger (all) and thumb deformity; dropped long-ring, and little finger (and extensor carpi ulnaris) deformity; dropped thumb (abductor pollicis longus, extensor pollicis brevis and longus, and extensor indicis proprius) deformity; and dropped long and ring fingers only (“sign of the horns”). If surgery is entertained for incomplete lesions, the exit of the supinator should also be explored. In both partial and complete posterior interosseous nerve paralysis, sensation in the autonomous region on the dorsum of the first web space of the hand is uninvolved.

On occasion, isolated superficial radial nerve entrapment may occur in the elbow or proximal forearm region, but it is more commonly involved in the distal forearm or wrist. Isolated radial sensory paresthesias are usually secondary to irritations to the nerve in the region of the radial styloid. A compression neuropathy may occur in which this nerve penetrates the deep fascia in the midforearm between the brachioradialis and extensor carpi radialis longus.³⁷ Focal tenderness usually identifies the involved site.

Plain radiographs may be helpful in showing a fat stripe of a lipoma or a bony lesion in the vicinity of the radial neck (see Fig. 80-4). Ultrasound or magnetic resonance imaging (MRI) may demonstrate an occult ganglion or elucidate a palpable mass by its imaging characteristics (Fig. 80-8).¹⁷⁸ MRI is helpful in demonstrating denervation atrophy and hyperintensity in the nerve, which may help confirm a diagnosis or localization of nerve compression, or both. Electrical studiestypically demonstrate denervational changes in the muscles innervated by the posterior interosseous nerve. If there are no EMG abnormalities in the supinator, then one should have a suspicion that the compression lesion of the posterior interosseous nerve is at the distal end of this muscle rather than at its proximal end. The brachioradialis and the extensor carpi radialis longus and brevis should not reveal any abnormalities in the typical posterior interosseous nerve syndrome because these muscles are innervated by the radial nerve proximal to the arcade of Frohse. Because of the overlap of posterior interosseous nerve syndrome with many cases of Parsonage-Turner syndrome, EMG should examine other muscles (e.g., shoulder muscles) to identify a more diffuse neurologic process that would favor the diagnosis of an inflammatory disease. The favorable response of operative decompression in some patients with posterior interosseous nerve “entrapment” may well be due to a favorable natural history of Parsonage-Turner syndrome. I believe that Parsonage-Turner syndrome is underrecognized. For this reason, I recommend performing decompression after 6 months of observation in patients with spontaneous onset of symptoms in whom mass lesions are not discovered and there has not been any clinical recovery.

FIGURE 80-8 This patient had a near complete posterior interosseous nerve palsy associated with a 2.5 cm mass. Plain radiographs were unremarkable. Sagittal T1 (a)-weighted MR images show a mass (^*) iso-intense to muscle in the region of the radial neck and the supinator muscle (S).

(From Spinner, R. J., Lins, R. E., Collins, A. J., and Spinner, M.: Posterior interosseous nerve compression due to an enlarged bicipital bursa confirmed by MRI. J. Hand Surg. 18B:753, 1993.)

Resistant Tennis Elbow (Radial Tunnel Syndrome)

For the most part, resistant tennis elbow is caused by degeneration or fascial tears at the lateral epicondyle. On occasion, persistent complaints have been attributed to either compression of the posterior interosseous nerve or to a combination of nerve compression and persistent localized epicondylitis.^20,153,165 Resistant pain localized to the proximal forearm should suggest that entrapment of the adjacent posterior interosseous nerve may be an unrecognized factor.

Physical findings frequently reveal tenderness, both over the lateral epicondyle and anteriorly over the course of the nerve as it passes through both heads of the supinator. On occasion, pain can be localized to the distal end of the supinator posteriorly at the junction of the middle and upper thirds of the proximal forearm. Pain may be increased with resisted active supination of the forearm or with resisted extension of the long finger with the elbow extended. There are no sensory abnormalities in the hand.

EMG studies in cases of resistant tennis elbow due to entrapment of the posterior interosseous nerve are often normal, even if the condition has been present for months and with definite clinical findings. Conduction delays are observed rarely. Stress testing as described by Werner¹⁹³ has sometimes been helpful in confirming the diagnosis. Fibrillations in the muscles innervated by the posterior interosseous nerve are usually sparse, but if present, they are most likely in the extensor indicis proprius. If fibrillations are widespread in the more severe lesions, weakness of the finger extensors and extensor carpi ulnaris is also usually evident.

Patients suspected of having coexisting lateral epicondylitis and posterior interosseous nerve compression, who fail conservative treatment, should have both conditions treated simultaneously. Patients with persistent pain after surgery for lateral epicondylitis should be suspected of having posterior interosseous nerve compression.¹²¹

Preferred Operative Exposure for the Entire Course of the Posterior Interosseous Nerve

When exposure of the entire posterior interosseous nerve is needed, the plane between the extensor carpi radialis brevis and the extensor digitorum communis (Fig. 80-9) is developed. The incision begins 5 cm proximal to the lateral epicondyle and passes over the lateral epicondyle down to the region of the origin of the outcropping muscles (abductor pollicis longus, extensors pollicis longus and brevis). The aponeurotic plane between the extensor carpi radialis brevis and the extensor digitorum communis is developed from distal to proximal (Fig. 80-10). Identification of the plane is facilitated by passive motion of the fingers while the wrist is held steady, and the plane can be developed by blunt dissection. The supinator muscle is seen in the depth of the wound as these muscles are liberated. To gain complete exposure to the proximal end of the supinator, the extensor carpi radialis brevis tendon can be detached from its origin at the lateral epicondyle. At times, the distal portion of the origin of the extensor carpi radialis longus is detached, if necessary, for complete exposure of the underlying arcade of Frohse. This is facilitated with elbow flexion. Adherence of the tendinous origin of this muscle to the lateral portion of the supinator muscle is frequently found and is freed to give exposure to the proximal end of the supinator. One can identify the posterior interosseous nerve by flexing the elbow and by palpating the nerve’s course as it passes obliquely through the supinator in a dorsoradial direction. By gently spreading longitudinally through the fat on both sides of the nerve with a right-angled hemostat, the nerve can be isolated. Because there are recurrent vessels in the vicinity, dissection must be gentle. Any vessels crossing the nerve should be clamped and tied individually. When the posterior interosseous nerve is identified proximal to the arcade of Frohse, a vasoloop is passed about it so that its identity and continuity are maintained. The arcade of Frohse may be found to be thickened. A hemostat is placed deep to the arcade but superficial to the nerve, and the arcade is incised, liberating the most proximal portion of the nerve. If further surgery is necessary, the entire posterior interosseous nerve can be traced and brought into direct view. Compression of the proximal and distal region has been described, as well as compression of the nerve in its midportion.¹⁷⁷ Epineurotomy of the posterior interosseous nerve at the site of its compression on occasion may be deemed necessary. Microsurgical technique should be used when this is indicated.

FIGURE 80-9 A, Incision for extensile exploration of the radial nerve is helpful for exploring the radial nerve, the proximal half of the posterior interosseous nerve, and the superficial radial nerve. B, The interval between the brachioradialis and the brachialis and pronator teres is developed. C, The radial nerve and its major forearm branches, the posterior interosseous and the superficial branches are exposed.

(Redrawn from Spinner, M.: Injuries to the Major Branches of Peripheral Nerves of the Forearm, 2nd ed. Philadelphia, W. B. Saunders, 1978.)

FIGURE 80-10 Details of the innervation provided by the posterior interosseous nerve. The nerve may be traced to the supinator showing the terminal branches(BR, brachioradialis; ECRB, extensor carpi radialis brevis; ECRL, extensor carpi radialis longus; ECU, extensor carpi ulnaris).

(Redrawn from Spinner, M.: Injuries to the Major Branches of Peripheral Nerves of the Forearm, 2nd ed. Philadelphia, W. B. Saunders, 1978.)

The detailed anatomy of the nerve supply to the extensor digitorum communis is important because this muscle obtains its innervation from branches of the terminal portion of the posterior interosseous nerve that run at right angles to the plane of the forearm in the distal portion of the proximal third of the forearm (see Fig. 80-10).¹⁷³ The operating surgeon should not sweep the planes between the extensor digitorum communis and the supinator because these branches are vulnerable. Furthermore, strong retraction posteriorly of the extensor digitorum communis in this area could damage the nerve supply to this important muscle.

The tendinous origin of the extensor carpi radialis brevis tendon is not reattached. Increasingly it has been recognized that the thick tendon of origin of this muscle in its distal prolongation passes directly over the arcade of Frohse. The combination of frictional and compressive irritation from this structure may be a major factor in the development of the radial tunnel syndrome. For this reason, a 3- to 4-cm portion of its most proximal tendinous origin may be excised. The tourniquet is released, and hemostasis is obtained. If the patient had lateral epicondylar pain and tenderness preoperatively, then at this time, the lateral epicondyle can be drilled or a small portion excised. The skin is closed, and the arm is immobilized in long arm plaster splints with the elbow at 90 degrees, the forearm in mid-position, and the wrist in a functional position. The immobilization is continued for 2 weeks, and the limb is gradually mobilized.

If a limited approach to the proximal portion of the supinator is needed, I prefer an anterior exposure of the posterior interosseous nerve. The lesion localized to the arcade of Frohse is approached by developing the plane proximal to the elbow between the brachialis and brachioradialis (see Fig. 80-9). Distal to the elbow, the anatomic dissection is continued, and the plane between the brachioradialis and the pronator teres is developed. If the dissection is difficult because of scarring or muscle anomalies, the superficial radial nerve can be identified distally and traced proximally to the main radial nerve and then to the deep branch. Any obstructing collateral vessels are ligated. The proximal third of the posterior interosseous nerve can be best visualized with this exposure. If necessary, the rest of the nerve can be followed by a separate posterior approach.

A longitudinal transmuscular approach through the brachioradialis has been popularized by Lister and associates.¹⁰⁷ It provides direct access to the nerve from the radiohumeral level to the midsupinator (Fig. 80-11).

FIGURE 80-11 An extensile exposure of the forearm to demonstrate the radial nerve may be accomplished by the surgical excisions shown here. The data outlined by Lister may be used to aid in performing an extensile exposure to the radial tunnel.

When there has been prior surgery in the region, an anterior and separate posterior incision may be necessary to expose the radial nerve and its branches safely.

Relevant Anatomy

At the elbow, the ulnar nerve⁹⁰ passes posterior to the medial epicondyle through the cubital tunnel. The cubital tunnel retinaculum¹³⁷ (Fig. 80-12) seems to be the predominant site of pathology for patients with primary symptoms. In the proximal arm, the nerve descends in the anterior compartment. In the majority of upper extremities, the ulnar nerve crosses from the anterior to the posterior compartment in the distal arm. The anatomy of the region (about 8 cm proximal to the medial epicondyle), corresponding to the so-called arcade of Struthers, is controversial.¹⁶⁴ The ulnar nerve, similarly, passes from posterior to the medial epicondyle to the anterior compartment of the forearm a few centimeters distal to the medial epicondyle and the cubital tunnel.

FIGURE 80-12 The cubital tunnel retinaculum seems to be the predominant site of pathology for patients with primary ulnar nerve symptoms at the elbow.

(Redrawn from O’Driscoll, S. W., Horii, E., Carmichael, S. W., and Morrey, B. F.: The cubital tunnel and ulnar neuropathy. J. Bone Joint Surg. 73B:613, 1991.)

In the arm, there usually are no branches of the ulnar nerve of significance. Occasionally there is a variant high take-off of a motor branch to the flexor carpi ulnaris in the distal arm. The dorsal cutaneous nerve of the forearm, the sensory branch to the dorsoulnar aspect of the hand, rarely has been observed to arise in the proximal rather than the distal forearm. At the elbow level, the first branch is usually an expendable articular branch that arises just distal to the medial epicondyle; next are usually varying branches of the flexor carpi ulnaris and the motor branch to the fourth and fifth flexor digitorum profundus muscles. Stimulation of these branches can help the physician in deciphering whether the branch is a motor branch to an end organ or an articular branch. In addition, fascicular mobilization of these branches can be performed safely for a distance up to 6 cm to facilitate ulnar nerve transposition.¹⁹²

Etiology

Ulnar nerve compression lesions may be due to many factors.^{4,69,110,140,141,189,190} At the elbow level, spontaneous compression neuritis is well known as the cubital tunnel syndrome.⁴⁹ It is second only to carpal tunnel syndrome in its frequency.

Ulnar nerve lesions may be due to compression, stretch, traction, friction, or a combination of these. Direct pressure on the posterior aspect of the elbow can compress the nerve and is seen in patients following coma, in surgical cases, or even in those who use wheelchairs. Flexion of the elbow may exacerbate symptoms, because it causes tightening and narrowing of the cubital tunnel and traction-related deformation of the nerve.⁶⁰ The tendinous origin of the flexor carpi ulnaris can compress this nerve between its ulnar and humeral heads with elbow flexion.⁶ Extrinsic pressure on the nerve may result from the anconeus epitrochlearis,^29,102 a variant muscle crossing the ulnar nerve in the region of the medial epicondyle, or from adhesions. Tumors¹³⁰ such as ganglia^14,89 may also be a causative factor.

A hypermobile ulnar nerve can produce symptoms.²³ This usually occurs during elbow flexion, as the nerve dislocates from the undersurface of the medial epicondyle to a position anterior to the epicondyle. Snapping of the medial triceps^{43,75,149,154,175} may be found in association with a dislocating ulnar nerve, and this can result in elbow pain, snapping, and ulnar nerve symptoms (Figs. 80-13 and 80-14). Persistent pain after an otherwise successful ulnar nerve transposition may represent unrecognized snapping of the triceps.

FIGURE 80-13 The ulnar nerve can be palpated within the cubital tunnel with the elbow in extension. Then with passive or active flexion of the elbow, the examiner can assess whether the ulnar nerve or another structure, such as a portion of the medial head of the triceps or an anomalous triceps tendon, moves anterior to the medial epicondyle.

(Redrawn from Spinner, R. J., and Goldner, R. D.: Snapping of the medial head of the triceps and recurrent dislocation of the ulnar nerve: Anatomical and dynamic factors. J. Bone Joint Surg. 80A:239, 1998.)

FIGURE 80-14 A, Magnetic resonance imaging can demonstrate a snapping triceps and dislocating ulnar nerve. Here the ulnar nerve (1) and a portion of the medial head of the triceps (2) are anterior to the medial epicondyle (E) with the elbow fully flexed. Computed tomography or real-time ultrasonography can also confirm the diagnosis. Imaging, however, is not necessary for confirmation of a diagnosis. Patients undergoing ulnar nerve surgery should be examined preoperatively and intraoperatively, with the elbow in flexion and extension, so that the surgeon can evaluate whether the medial head of the triceps snaps over the medial epicondyle. R, radius; U, ulna. B, Corresponding artist drawing shows the position of the ulnar nerve and the medial head of the triceps to the medial epicondyle in full extension and flexion. O, olecranon; T, triceps.

(A from Spinner, R. J., Hayden, F. R., Jr., Hipps, C. T., and Goldner, R. D.: Imaging the snapping triceps. A.J.R. Am. J. Roentgenol. 167:1550, 1996; B redrawn from Khoo, D., Carmichael, S. W., and Spinner, R. J.: Ulnar nerve anatomy and compression. Orthop. Clin. North Am. 27:317, 1996.)