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*Indicates abnormal value.

*Indicates abnormal value.

Electromyographic Study Results

There was no evidence of abnormal spontaneous activity in the right flexor dig-itorum profundus, abductor digiti minimi, or the abductor pollicis brevis. In the right first dorsal interosseous muscle there was increased insertional activity with 2+ (present at multiple sites) fibrillations and 2+ positive sharp waves; recruitment frequency was 30 to 40 Hz (normal: 5 to 15 Hz); the interference pattern was decreased and discrete, indicating marked loss of motor units; amplitude was decreased with the first recruitment = 1000 pV and the duration of the voluntary motor unit potentials was increased.

Differential Diagnosis

Brachial plexus injury Upper plexus Lower plexus Cervical root compression Ulna nerve tunnel compression Elbow Wrist Corvical disk disease

The ulnar nerve, containing fibers from the ventral rami of C8 andTl, is the terminal branch of the medial cord of the brachial plexus. Pathologic compression of the ulnar nerve occurs most commonly either at the elbow (cubital tunnel syndrome) or at the wrist where the ulnar nerve passes through the confines of the canal of Guyon (ulnar tunnel syndrome). With either of these conditions the patient may present with numbness along the little finger and ulnar half of the ring finger, often accompanied by weakness of grip, particularly in activities in which torque is applied to a tool, and rarely by wasting of the intrinsic musculature in the hand. The site of the compression may be determined by a careful physical examination; pain at the medial aspect of the elbow, a positive percussion test at the cubital tunnel, or exacerbation of symptoms by full flexion of the elbow suggests cubital tunnel syndrome. Sensory involvement on the ulnar dorsal aspect of the hand also suggests cubital tunnel syndrome, as the dorsal cutaneous branch of the ulnar nerve originates proximal to the canal of Guyon. Weakness of the deep flexors to the ring and little fingers as well as weakness of the flexor carpi ulnaris signal proximal ulnar nerve entrapment. Grip and pinch strength measurements may demonstrate weakness in more advanced lesions.

Examination of the patient with symptoms of ulnar nerve compression should begin at the neck to rule out cervical disk disease or arthritis. Provocative maneuvers including Adson's, hyperabduction, military brace positioning, and 3-minute elevation should be used to screen for thoracic outlet syndrome. Range of motion of the elbow should be observed and the ulnar nerve palpated during flexion-extension to determine subluxation. Percussion over the ulnar nerve can be performed to evoke a positive Tinel's sign; however, nearly 24% of asymptomatic people have this finding. The elbow flexion test in cubital tunnel syndrome is analogous to the wrist flexion test (Phalen's test) in diagnosing carpal tunnel syndrome. It is performed by maximally flexing the patient's elbow with forearm supination and wrist extension. Symptoms of paresthesias in the ulnar nerve distribution within 1 minute constitute a positive test. False positives, however, occur in 24% of the normal population.

Sensory examination of the hand including the dorsum should be performed using Semmes-Weinstein monofilaments. Sensibility testing is an important part of the workup of a patient with an ulnar nerve compression lesion. Much of the misunderstanding over which test is better at detecting an abnormality has been cleared up with our understanding the fundamental nature ofwhat each test is measuring. Four sensory tests are available which test different fiber populations and receptor systems. Touch fibers, group Ap, can be divided into slowly and quickly adapting fiber systems. A quickly adapting fiber signals an on-off event, and a slowly adapting fiber continues its pulse response throughout the duration of the stimulus. Static two-point discrimination and Semmes-Weinstein monofilament tests evaluate the slowly adapting fibers, whereas vibration and moving two-point discrimination tests evaluate the quickly adapting fibers. Each fiber system is associated with a specific sensory receptor. Each clinical test of sensibility is related to a receptor group and is classified as either a threshold test or a test of innervation density. A threshold test measures a single nerve fiber innervating a receptor or group of receptors. An innervation density test measures multiple overlapping peripheral receptive fields and the density of innervation in the region being tested. Static and moving two-point discrimination are innervation density tests, which require overlapping of different sensory units and complex cortical integration. These are reliable tests in assessing functional nerve regeneration after nerve repair where brain input is radically altered but are not sensitive to the gradual decrease in nerve function seen in nerve compression. Cortical organization is intact in compression neuropathy, as the integrity of the sensory relay system remains uninterrupted. Two-point discrimination may remain intact even if only a few fibers are conducting normally to their correct cortical end points. Semmes-Weinstein monofilament and vibration tests are threshold tests and are more likely to detect a gradual, progressive change in nerve function as a greater proportion of large nerve fibers are lost whereas smaller fibers maintain their normal central connections. Clinically, threshold tests are clearly more sensitive in evaluating compressive neuropathies. At present, Semmes-Weinstein monofilament testing is simpler, less expensive, and equally as reliable and sensitive as vibration testing.

The value of nerve conduction studies is that often they provide the only objective evidence of the neuropathic condition. Electrodiagnostic testing remains the diagnostic gold standard, yet it entails several pitfalls. It is highly operator dependent, and so should be done with the same equipment and operator each time. Nerve conduction velocities and latencies can be compared with published popula tion norms, to the contralateral nerve, to other nerves in the same extremity, or to previous tests in the same patient. Systemic conditions (including age-dependent alterations in nerve conduction) may confound the comparisons. Decreased dorsal ulnar sensation can help localize a lesion to be proximal to the wrist. Motor examination should carefully grade the flexor carpi ulnaris, flexor digitorum profundus, little and ring fingers, and the intrinsic muscles of the hand. One must keep in mind that median nerve fibers may supply some of the intrinsic hand muscles in 7.5% of limbs via a Martin-Gruber anastomosis.

Electrodiagnosis is helpful in establishing the diagnosis of cubital tunnel syndrome, localizing the level of the lesion, and differentiating other or concomitant neuropathic lesions. The classic finding is focal slowing of conduction in the ulnar nerve segment that crosses the elbow. The lower limit of normal motor conduction velocity across the elbow is 49 m/second, with the elbow flexed to 135 degrees, and the across-elbow segment normally has a conduction velocity within 11 m/second of the forearm segment. Short segment stimulation studies can increase the sensitivity of the exam and be highly specific in identifying the precise point of conduction block; however, they are prone to error in velocity calculations. A latency change greater than 0.4 millisecond (ms) over a 1-cm segment of nerve is considered abnormal. Electromyography demonstrates whether or not axonal degeneration has occurred. The first dorsal in-terosseous muscle is affected most commonly. The abductor pollicis brevis should be examined to exclude a C8/T1 nerve root or inferior brachial plexus lesion. Thoracic outlet syndrome most commonly involves the medial components of the brachial plexus and may be mistaken for ulnar nerve compression.

Plain radiographs in two orthogonal planes should be obtained to rule out post-traumatic deformity, neoplasm, cervical ribs, or other possible bony causes of the nerve condition. A carpal tunnel view can sometimes show a hook of the hamate fracture, but often computed tomography is needed to visualize this injury. Magnetic resonance imaging (MRI) has a specific role in the workup of this condition. For instance, MRI can be extremely helpful in assessing the extent of a soft tissue mass like a ganglion causing ulnar tunnel syndrome. An apical tumor of the lung can also compress or invade the inferior brachial plexus, causing ulnar nerve symptoms. A chest x-ray to rule out a Pancoast tumor should be obtained whenever the patient gives a history of smoking, ulnar nerve symptoms, and shoulder pain.


In 1861 Guyon, a French urologist, described a "loge" or a space in the hypothenar region of the wrist where the ulnar nerve bifurcates, and he prophesied compression of the ulnar nerve could be found here. Written in French, his word loge was subsequently translated to mean "canal," and thus originated the name for the anatomic region we now call Guyon's canal. Entrapment at this level may present with pure motor, sensory, or mixed symptoms depending on the precise location of compression. Space-occupying bony or soft tissue lesions may be causative; ganglia and other soft tissue masses are responsible for 32% to 48% of cases of ulnar tunnel syndrome. Another 16% of cases are due to muscle anomalies. Ganglia arising from the triquetrohamate joint are responsible for over 85% of the nontraumatic causes of ulnar tunnel syndrome. Other causes of ulnar tunnel syndrome include thrombosis or pseudoaneurysms of the ulnar artery, edema secondary to burns, and inflammatory arthritis.

The distal ulnar tunnel, which is 4 to 4.5 cm in length beginning at the proximal edge of the palmar carpal ligament and ending at the fibrous arch of the hypothenar

Figure 16—1. Schematic drawing of the distal ulnar tunnel showing the location of the three zones. Zone 1 (coarse stippling), zone 2 (lines), zone 3 (fine stippling). P, pisiform; H, hamulus; A, ulnar artery; N, ulnar nerve. (With permission from Gross MS, Gelberman RH. The anatomy of the distal ulnar tunnel. Clin

Orthop 1985;196:238-247.)

muscles, is divided into three zones to allow more accurate localization of ulnar nerve compressive lesions (Fig. 16—1). Zone 1 is the area proximal to the bifurcation of the nerve. Beginning at the edge of the palmar carpal ligament, it is ~3 cm in length, bounded dorsally by the flexor digitorum profundus and transverse carpal ligament, palmarly and laterally by the palmar carpal ligament, and medially by the pisiform and flexor carpi ulnaris. Compression in zone 1 causes combined motor and sensory deficits and is most likely due to ganglions or fractures of the hook of the hamate but has been reported to occur from an anomalous muscle. Even though the hook of the hamate is in zone 2, compression of the ulnar nerve by fracture just proximal to its bifurcation can produce mixed motor and sensory symptoms. Compression in this zone has also been reported to occur from an anomalous arching pattern of the ulnar nerve piercing the flexor carpi ulnaris tendon. Zones 2 and 3 travel alongside each other from the bifurcation of the ulnar nerve to just beyond the fibrous arch of the hypothenar muscles. Although bifurcation is the most common pattern, the ulnar nerve may trifurcate at this point into two common digital sensory branches and a motor branch. Zone 2 is bounded palmarly by the palmaris brevis muscle, fibrous arch, and hypothenar muscles; dorsally by the pisohamate and pisometacarpal ligaments, triquetrohamate joint, and opponens digiti minimi muscle; laterally by the transverse carpal ligament, flexor digiti minimi muscle, and the hook of the hamate; and medially by the superficial branch of the ulnar nerve and the abductor digiti minimi muscle. Zone 2 surrounds the deep motor branch, and compression in this region produces motor deficits without sensory disturbances. Again, ganglions and fractures of the hook of the hamate are the most likely causes, but an anomalous intrinsic muscle can also be responsible for symptoms.

Ulna Pisiform Ligament

The motor branch leaves the tunnel, passing underneath the fibrous arch of the hypothenar muscles, entering the interval between the abductor digiti minimi and flexor digiti minimi muscles, piercing the opponens digiti minimi, and then curving radially and dorsally around the hook of the hamate. Zone 3 is bounded pal-marly by the palmaris brevis muscle and ulnar artery; dorsally by the hypothenar fascia; laterally by the motor branch of the ulnar nerve; and medially by the abductor digiti minimi muscle. Zone 3 surrounds the superficial branch of the ulnar nerve, and compression in this zone produces pure sensory deficits. Synovial inflammation has been reported to cause compression in zone 3. More frequently, however, compression in zone 3 is due to a vascular lesion resulting from thrombosis or aneurysm of the ulnar artery, but an anomalous abductor digiti minimi, which has an incidence of 1.5%, can also be responsible. Just distal to the ulnar nerve bifurcation, the superficial branch gives off two small motor branches to the palmaris brevis muscle and then becomes purely sensory coursing deep and ulnar to the artery.

The clinical characteristics of nerve compression in the ulnar tunnel can largely be correlated with the distinct regional anatomy in this area of the wrist. Symptoms include pain in the wrist with numbness, tingling, or burning, with radiation into the ring and little fingers. Pain is usually a less significant aspect of the presentation than in carpal tunnel syndrome. Sustained hyperextension or hyperflexion of the wrist accentuates symptoms. Intrinsic weakness, which occurs, progresses to atrophy in the hand if compression is not relieved.

The diagnosis of an ulnar tunnel syndrome consists of first demonstrating the presence of an ulnar nerve lesion at the wrist and then determining the underlying cause. Although the cause may be purely mechanical, it may be potentiated by a coexisting systemic disorder like diabetes or a more proximal lesion of the same nerve (double crush phenomenon). It is important not to develop "tunnel" vision early in the diagnostic process, but rather to consider the possibility of additional places where the nerve may be compressed.

Nonsurgical Management

In the absence of an identifiable lesion, alterations of repetitive activities, splint immobilization of the wrist in neutral, and nonsteroidal antiinflammatory drugs (NSAIDs) may alleviate symptoms.

Surgical Management

Operative intervention is recommended for those patients refractory to conservative care or with documented anatomic lesions. Regardless of the suspected site of compression, the ulnar nerve should be visualized and released in its entirety within Guyon's canal. Acute ulnar neuropathy following a wrist fracture is unusual but warrants special concern. This injury is seen in young patients with high-energy distal radius fractures with marked dorsal displacement of the distal fragment. Based on clinical and anatomic studies, Vance and Gelberman recommended that any patient with immediate complete ulnar neuropathy following a wrist fracture should undergo immediate fracture reduction, with particular attention to eliminating dorsal displacement of the radial and/or ulnar fracture(s). If ulnar nerve function does not improve in 24 to 36 hours, Guyon's canal should be explored and the ulnar nerve decompressed. Any patient with progressive ulnar neuropathy after treatment for a wrist fracture should have immediate exploration and decompression of the ul-nar nerve.

Regardless of the expected pathology, the ulnar nerve should be explored proxi-mally from the distal forearm into the palm throughout all three zones. Some surgeons routinely release the carpal canal when decompressing Guyon's canal and perform this operation via an extended carpal tunnel incision. Regional or general anesthesia is used as is a tourniquet. A consideration in planning the skin incision is the anatomy of the palmar cutaneous branch of the ulnar nerve. According to Engber, the classic position for this nerve is ulnar to the ring finger ray. Although only found to be present in 5 of 21 cadaver dissections, injury to it may lead to painful neuromas. Although it is widely believed that there exists an internervous plane in the palm in the axis of the ring finger between the palmar cutaneous branches of the median and ulnar nerves, more careful dissections have demonstrated that this area in the palm is variably innervated by the nerve of Henle (the nervi vasorum of the ulnar artery) and multiple ulnar cutaneous branches. Dissection in the palm should avoid these small cutaneous nerves whose injury may lead to persistent incisional tenderness. The pisiform and hook of the hamate, which is 1 cm distal and radial to the pisiform, are used as anatomic landmarks. The incision begins 3 cm proximal to the wrist along the radial border of the flexor carpi ulnaris tendon, crosses the wrist crease at an angle of 60 degrees, with the apex radial, continues distally bisecting the interval between the pisiform and the hamate directed toward the web space between the little and ring fingers, and then is angled across the palm proximal and parallel to the proximal transverse palmar crease (Fig. 16—2). In the proximal incision, the flexor carpi ulnaris is reflected ulnarly and the ulnar nerve is identified dorsal and medial to the ulnar artery and tagged with a small rubber drain. Blunt dissection of the subcutaneous fat safeguards the palmar cutaneous branch of the ulnar nerve. The forearm and palmar fascia are divided in line with the skin incision. The ulnar nerve is traced distally into Guyon's canal between the

Palmar Fascial CordHenle Ligament

Figure 16—3. The ulnar nerve courses through

New York: Churchill Livingstone; 1999:1431.)

Entrapment and compression neuropathies. In:

the volar carpal ligament and the transverse carpal ligament. P, pisiform;

Green DP, ed. Operative Hand Surgery. 4th ed.

Guyons canal between

Pisiform H, hamate. (Withpermission from: Szabo RM.

Figure 16—3. The ulnar nerve courses through

New York: Churchill Livingstone; 1999:1431.)

Entrapment and compression neuropathies. In:

the volar carpal ligament and the transverse carpal ligament. P, pisiform;

Green DP, ed. Operative Hand Surgery. 4th ed.

Guyons canal between volar carpal ligament and the transverse carpal ligament (Fig. 16-3). The palmaris brevis muscle is elevated ulnarly and the volar carpal and pisohamate ligaments are incised. The fibrous origin of the hypothenar muscles often forms a thick arch just distal to the pisohamate ligament inserting on the hamate that should be incised. The motor branch is traced underneath the fibrous arch between the abductor digiti minimi and flexor digiti minimi and through the opponens digiti minimi. The floor of Guyon's canal is explored looking for masses, fibrous bands, anomalous muscles, fractures particularly of the hook of the hamate, and any other unusual pathology. The ulnar artery is examined, the tourniquet is deflated, the ulnar artery is reexam-ined, and hemostasis is obtained. The skin is approximated and a bulky plaster reinforced hand dressing applied with the wrist in slight dorsiflexion.

Sutures are removed in 10 days and splinting is continued in 20-degree wrist dorsiflexion for an additional 2 weeks. Tenderness may persist in the palm, particularly if the hook of the hamate was excised. A gel-padded sleeve to protect the palm along with scar massage and desensitization therapy is often appreciated. Sensibility and motor function will return depending on the severity and length of time of compression.

Suggested Readings

Campbell WW, Pridgeon RM, Sahni KS. Short segment incremental studies in the evaluation of ulnar neuropathy at the elbow. Muscle Nerve 1992;15:1050-1054.

Denman EE. The anatomy of the space of Guyon. Hand 1978;10:69-76.

Engber WD, Gmeiner JG. Palmar cutaneous branch of the ulnar nerve. J Hand Surg 1980;5A:26-29.

Fahrer M, Millroy PJ. Ulnar nerve compression neuropathy due to an anomalous abductor digiti minimi—clinical and anatomic study. J Hand Surg 1981;6A:266-268.

Failla JM. The hypothenar adductor muscle: an anomalous intrinsic muscle compressing the ulnar nerve. J Hand Surg 1996;21A:366-368.

Gelberman RG. Ulnar tunnel syndrome. In: Gelberman RH, ed. Operative Nerve Repair and Reconstruction. Philadelphia: Lippincott; 1991:1131-1143.

Gross MS, Gelberman RH. The anatomy of the distal ulnar tunnel. Clin Orthop 1985;196:238-247.

Guyon F. Note sur une disposition anatomique propre à la face antérieure de la région du poignet et non encore décrite par le docteur. Bull Soc Anat Paris 1861;6:184-186.

Hilburn JW. General principles and use of electrodiagnostic studies in carpal and cubital tunnel syndromes. Hand Clin 1996;12:205-221.

Kang HJ, Yoo JH, Kang ES. Ulnar nerve compression syndrome due to an anomalous arch of the ulnar nerve piercing the flexor carpi ulnaris: a case report. J Hand Surg 1996;21A:277-278.

Kleinert HE, Hayes JE. The ulnar tunnel syndrome. Plast Reconstr Surg 1971;47: 21-24.

Lindsey JT, Watumull D. Anatomic study of the ulnar nerve and related vascular anatomy at Guyon's canal: a practical classification system. J Hand Surg 1996;21A: 626-633.

Rayan GM, Jensen C, Duke J. Elbow flexion test in the normal population. J Hand Surg 1992;17A:86-89.

Shea JD, McClain EJ. Ulnar-nerve compression syndromes at and below the wrist. J Bone Joint Surg 1969;51A: 1095-1103.

Szabo RM, Gelberman RH. Peripheral nerve compression. Etiology, critical pressure threshold, and clinical assessment. Orthopedics 1984;7:1461-1466.

Szabo RM, Gelberman RH. The pathophysiology of nerve entrapment syndromes. J Hand Surg 1987;12A:880-884.

Szabo RM, Gelberman RH, Dellon AL, Yaru NC, Dimick MP. Vibratory sensory testing in acute peripheral nerve compression. J Hand Surg 1984;9A:l04-109.

Taleisnik J, Szabo RM. Compression neuropathies of the upper extremity. In: Chapman MW, Madison M, eds. Operative Orthopaedics. Philadelphia: Lippincott; 1993:1419-1435.

Thomson A. Third annual report on the Committee of Collective Investigation of the Anatomical Society of Great Britain and Ireland for the year 1891-1892. J Anat Physiol 1893;27:183.

Vance RM, Gelberman RH. Acute ulnar neuropathy with fractures at the wrist. J Bone Joint Surg 1978;60A:962-965.

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  • bisrat
    What surrounds the hamate?
    8 years ago
  • Aran
    How to pull free trapped nerves in the shoulder?
    4 years ago

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