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Management of Ulnar Nerve Compression
Compression of the ulnar nerve is a well-known cause of neurologic dysfunction. Compression at the elbow (cubital tunnel syndrome) is the second most common entrapment neuropathy (only carpal tunnel is more common). Ulnar nerve compression at the wrist (within Guyon’s canal) is relatively rare in comparison. Both of these entities must be differentiated from each other and from other neurologic disorders, including cervical radiculopathy. Indications and techniques for surgical management, and their comparative outcomes studies, are provided. The ulnar nerve arises from the medial cord of the brachial plexus and innervates some muscles in the forearm and hand. It also carries sensory neurons supplying the skin of the back of the forearm, the palm, and the fourth and fifth digits. Entrapment of the ulnar nerve at the elbow is the second most common neuropathy in adults, after entrapment of the median nerve at the carpal tunnel.
History
Before surgical options were explored, conservative treatments employed included hydrotherapy, immobilization, electrotherapy/application of electric current, , massage, and application of ointments and solutions. In 1818, Granger described a patient with ulnar palsy after fracture of the medial condyle of the humerus and advised nonsurgical management with anatomic repositioning and immobilization. The earliest known report of surgical treatment of ulnar nerve entrapment dates to 1816 when Henry Earle (1789–1838) , attempted to alleviate pain caused by it in a 14-year-old girl by nerve sectioning.
In the Archives Générales de Médecine , in 1878, Photinos Panas was the first to describe the relationship between ulnar nerve compression at the elbow and clinical ulnar nerve palsy—what has been called “tardy ulnar palsy.” He presented three cases in which either prior trauma or osteoarthritis gradually caused damage to the ulnar nerve and eventually clinical manifestations. The term tardy was applied to this scenario where deficits appeared late after an injury. Panas attempted to improve the “bed” for the ulnar nerve by deepening the epicondylar groove.
In 1888, Poncet performed the first definitive surgical treatment for a subluxated ulnar nerve by creating a groove or a sulcus in the bone, placed the ulnar nerve in it, and then sutured the periosteum over the nerve to create a roof over the tunnel. Benjamin Farquhar Curtis (1857–1924) in 1898 developed the technique that is known today as the anterior subcutaneous transposition. Albert Mouchet (1869–1963) in 1914, described ulnar neuropathy secondary to a fracture of the humerus (maladie de Mouchet) , and developed the technique of supracondylar cuneiform osteotomy of the humerus for ulnar neuritis from cubitus valgus. In 1917, Rudolf Klauser described a technique of transposing the nerve in a muscular bed to prevent repetitive direct trauma to the relatively superficially placed nerve from a simple subcutaneous transposition and was the first to describe anterior “intramuscular” transposition. Decompression or “liberation” of the ulnar nerve (without transposition) was first suggested by Sir Edward Farquhar Buzzard, a British physician, in the year 1922. In 1942, James Rögnvald Learmonth described the anterior “submuscular” transposition placing it deep to the flexor pronator group of muscles alongside the median nerve. Feindel and Stratford defined the cubital tunnel anatomically in 1958. ,
In 1959, Geoffrey Vaughan Osborne postulated that a fibrous band bridging the two heads of the flexor carpi ulnaris and directly laying over the ulnar nerve may be responsible for compressing the ulnar nerve leading to ulnar neuritis rather than by the previously postulated friction or traction on nerve. This fibrous band later came to be known as the “Osborne band.” King and Morgan proposed medial epicondylectomy as another surgical option for the treatment of this problem.
Ulnar nerve entrapment at the elbow is now more frequently grouped under the broad category of repetitive strain injuries. This acknowledges the fact that this syndrome is seen more frequently in individuals that work with the arm in a flexed position for long periods of time (e.g., typists, secretaries) or those that repetitively flex and extend the arm (e.g., manual laborers).
Anatomy
The ulnar nerve derives its contributions from C8 and T1 (occasionally from C7) nerves and is the largest nerve derived from the medial cord of the brachial plexus.
ARM
The ulnar nerve descends in the arm posterior to the pectoralis major muscle and medial or posteromedial to the brachial artery. At the inferior border of the pectoralis major, the nerve moves medially and pierces the medial intermuscular septum about 6 to 8 cm above the medial epicondyle. It descends medially on the anterior surface of the medial head of the triceps muscle and then enters the interval between the medial epicondyle of the humerus and the olecranon. As it descends, the nerve is usually invested by some triceps fibers that are given the name the “arcade of Struthers.” The arcade, located about 6 to 8 cm proximal to the medial epicondyle, is a musculofascial band and is about 1.5 to 2 cm wide. Its anterior border is the medial intermuscular septum, and its lateral border is formed by the deep fibers of the medial head of the triceps. The arcade typically passes obliquely and superficial to the nerve. The Struthers arcade should not be confused with “Struthers ligament”—a rare finding that bridges the supracondylar spur on the medial aspect of the humerus to the junction of the medial epicondylar ridge and medial epicondyle. Struthers ligament is usually associated with compression of the median nerve.
Cubital Tunnel
The nerve passes into the ulnar groove on the dorsal aspect of the medial epicondyle, at the entrance to the cubital tunnel —the term first coined by Feindel and Stratford in 1958. , ,
The nerve is most superficial here during its entire course down the length of the arm. Laying over a bony floor, it is therefore most susceptible to trauma in this location. The nerve is surrounded by fat throughout the cubital tunnel, except for adjacent to the medial epicondyle. The roof of the cubital tunnel is formed by a fibrous aponeurosis that thickens to form the cubital tunnel retinaculum or the arcuate ligament of Osborne (also called triangular ligament, arcuate ligament, or humero-ulnar arch or humero-ulnar arcade/HUA), which connects the tendinous origin of the humeral and ulnar heads of the flexor carpi ulnaris. This fibrous band is approximately 4 mm wide and extends from the medial epicondyle to the tip of the olecranon. Its fibers are oriented transversely and are taut in elbow flexion. The walls of the cubital tunnel are formed by the medial epicondyle, and the olecranon and the floor is formed by the medial collateral ligaments and the joint capsule. The proximal and mid-portions of the cubital tunnel alter with flexion from round to elliptical. , Studies show that the pressure within the cubital tunnel rises up to 7-fold with elbow flexion and further up to 20-fold with contraction of the flexor carpi ulnaris muscle causing microvascular ischemia and pressure injury to the nerve. As it traverses through the cubital tunnel, the ulnar nerve passes from the extensor surface of the arm to the flexor surface of the forearm and the nerve gives off one or more articular branches to the elbow joint. Anatomical and vascularization studies demonstrate a consistent but segmental extraneural and intraneural vascular supply from the superior ulnar collateral, inferior ulnar collateral, and posterior ulnar recurrent arteries. The inferior ulnar collateral artery, which is typically sacrificed with ulnar nerve transposition procedures, provides the only direct vascularization to the nerve in the region just proximal to the cubital tunnel.
Forearm
As the nerve exits the cubital tunnel, it does so between the two heads of the flexor carpi ulnaris. It lies on the palmar surface of the flexor digitorum profundus and travels in this position down through the middle of the forearm. In the distal third of the forearm, it becomes superficial, lying just radial to the flexor carpi ulnaris. After emerging from under the flexor carpi ulnaris, the nerve enters the wrist radial to the pisiform bone. In the proximal third of the forearm, the ulnar nerve innervates the flexor carpi ulnaris and the flexor digitorum profundus III/IV.
Wrist
Approximately 6 to 8 cm proximal to the wrist, the ulnar nerve gives off the dorsal cutaneous sensory branch leaving the terminal motor and palmar sensory branches to traverse the wrist into the hand. The dorsal cutaneous nerve passes posteriorly, deep to the tendon of the flexor carpi ulnaris, pierces the deep fascia, and continues distally along the dorsomedial side of the wrist. It supplies sensation to the dorsal surface of the ulnar innervated fingers—that is, the fifth digit and medial half of the fourth digit. The remainder of the ulnar nerve continues into the wrist, traveling with the ulnar artery and vein as it passes lateral to the pisiform bone. Guyon’s canal, named after French surgeon Jean Casimir Félix Guyon (1831–1920), who, in 1861, described this space at the wrist between the pisiform bone and the hook of the hamate through which the ulnar artery nerve travels into the hand as a “loge,” now also known as the ulnar tunnel. Compression in the ulnar tunnel can occur in one of three zones. Zone 1 is in the most proximal portion of the canal, where the nerve is a single structure in one epineural sheath containing both motor and sensory fascicles. Zones 2 and 3 are further along the canal where the ulnar nerve has already bifurcated into motor and sensory branches. The clinical picture will correlate with the zone in which compression is occurring. A fibrous arch overlying the motor branch of the ulnar nerve as it passes beneath the origin of the hypothenar muscles in Guyon’s canal is often encountered. Awareness of this fibrous arch facilitates appropriate surgical management of ulnar-innervated intrinsic muscle weakness or wasting associated with ulnar compression at the wrist. The nerve fibers cross beneath the pisohamate ligament and the fibrous arch of the hypothenar muscles. They then split off into sensory palmar digital nerves to the fifth and fourth digits, motor branches to ulnar-innervated intrinsic muscles of the hand, and a communicating branch to the median nerve. The ulnar nerve in the hand supplies motor function to the abductor digiti minimi, opponens digiti minimi, and flexor digiti minimi muscles of the fifth digit, as well as the lumbricales III and IV. It also supplies the interossei, both dorsal and palmar, and finally the adductor pollicis and a portion of the flexor pollicis brevis.
As the ulnar nerve crosses the extensor aspect of the elbow in a superficial site with little supporting epineurium, it is prone to injury after upper extremity trauma. The motor fibers that supply the intrinsic muscles of the hand occupy a more superficial location, and those that supply the flexor carpi ulnaris and ulnar half of the flexor digitorum profundus are in a deeper location. This fact is offered as an explanation of why intrinsic weakness of the hand muscles is more often seen in patients with cubital tunnel syndrome. It then follows that as the sensory fibers are also located more superficially as the ulnar nerve traverses the extensor elbow, that paresthesias and sensory disturbances are the most common early features of cubital tunnel syndrome ( Table 187.1 ).
Table 187.1
Ulnar Nerve
| Motor |
Forearm, via the muscular branches of the ulnar nerve:
|
Hand, via the deep branch of the ulnar nerve:
|
Hand, via the superficial branch of ulnar nerve:
|
| Sensory |
| Sensory innervation to the fourth and fifth digits |
Anatomic Variations
Numerous anatomic variations have been reported in the literature, mainly between the median and the ulnar nerve in the forearm. The Martin-Gruber anastomosis is the most commonly encountered anatomical variation and was first described by the Swedish anatomist Martin in 1763 and later by Gruber in 1840. Here a variant neural pathway is seen in the proximal forearm, where motor fibers from the median nerve cross over to the ulnar nerve. Another rare entity in the hand, the Riche-Cannieu anomaly consists of the abnormal connection between the motor branch of the ulnar nerve and the recurrent motor branch of the median nerve.
Etiology of Ulnar Nerve Compression
The ulnar nerve responds in a proportional manner by exhibiting increasingly altered intraneural microvascular blood flow, axonal transport, and nerve function as the pressure exerted upon it increases. The main etiologies of ulnar nerve damage at the elbow joint are thought to be compression, , ischemia, , traction, , , longitudinal strain, and friction. In previous studies , increased cubital tunnel pressures of up to six times have been reported with elbow flexion, wrist extension, and shoulder abduction. In 1973, Apfelberg demonstrated that with elbow flexion, due to the increasing tension of the arcuate ligament and the bulging of the medial collateral ligament, there is a change in the cross-sectional contour of the cubital tunnel from a smooth, round configuration to a flattened triangle, narrowing by approximately by 55%. , , Friction on the nerve may result from subluxation or dislocation of the nerve because of congenital or developmental laxity of the soft-tissue restraints that normally hold the ulnar nerve in its groove at the cubital tunnel.
Along its path around the elbow, five anatomic sites of potential entrapment/compression of the ulnar nerve exist. The Arcade of Struthers, , , the medial intermuscular septum, the cubital tunnel, the arcade of the flexor carpi ulnaris, and the flexor-pronator aponeurosis have all been described. After transposition, the ulnar nerve may be compressed proximally as the nerve passes over the edge of the medial intermuscular septum, when it has not been excised or excised incompletely. Particular attention must be paid to structures that may tether the nerve distally after transposition as well, including branches of the medial antebrachial cutaneous nerve, vascular branches from the ulnar artery, the Osborne fascia, ulnar motor branches to the flexor carpi ulnaris, the distal intermuscular septum, the flexor-pronator muscle origin, and the investing fascia of the flexor digitorum superficialis overlying the ulnar nerve. In the wrist, the deep branch of the ulnar nerve can also be compressed by the arch of origin of the hypothenar muscles. A well-defined band of tissue either at the point where the deep branch crosses the third metacarpal or where it penetrates the adductor pollicis muscle can also be found.
There are many potential causes of ulnar neuropathy, including compression within the cubital tunnel or by constricting fascial bands; perineural adhesions; the presence of a variant muscle (the anconeus epitrochlearis ); a hypertrophied medial head of triceps, as seen in some bodybuilders; and compression of the ulnar nerve in the ulnar groove, as is common in people who lean on their elbows, particularly in the flexed position (e.g., truck drivers leaning their arms on the edge of the window frame, people working on computers). Ulnar compressive neuropathy is also seen after suboptimal intraoperative padding to on the medial side of the arm and in patients confined to bed for acute or chronic illnesses. It may also be due to extrinsic or intrinsic compression by tumors (such as ganglion cysts or hemangiomas ) and postradiation changes. Ulnar neuropathy may be due to repetitive strain (with “neuritis” perhaps associated with medial epicondylitis or “golfer’s elbow”). Friction neuritis may occur from ulnar nerve dislocation from repetitive elbow extension and flexion. Trauma (i.e., direct injury from fractures, elbow dislocation, hematoma) and posttraumatic deformities (e.g., cubitus valgus or varus; malunited supracondylar fracture) or degenerative changes (e.g., osteophytes associated with osteo or rheumatoid arthritis or gouty tophus ) may be associated with ulnar neuropathy at the elbow. Iatrogenic injuries to the nerve, such as after total elbow replacement, are also well described.
The common causes of compression at the wrist at the Guyon’s canal are repeated blunt trauma to the hypothenar region (e.g., bicycle riders), ganglionic cysts arising from the underlying carpus (usually from the triquetrohamate joint), lipoma, use of bilateral forearm crutches, vascular lesions, and fractures of the distal ulna and carpal bones, especially the hook of the hamate.
Diagnosis
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