Anatomy

The carpal tunnel is a fibro-osseous passageway in the anterior aspect of the wrist that is formed by the carpal bones and flexor retinaculum, also known as the transverse carpal ligament (TCL) (Fig. 236-1). The floor of the carpal tunnel is composed of the volar radiocarpal ligament and other bridging ligaments interconnecting the pisiform and hook of the hamate medially and the tubercles of the scaphoid and trapezium laterally. The TCL forms the roof by attaching medially to the pisiform and hook of the hamate and laterally to the scaphoid tuberosity and crest of the trapezium.^15,16 The carpal tunnel is approximately 4 to 6 cm in length and contains the median nerve and its vascular bundle, four tendons each of the flexor digitorum superficialis (FDS) and profundus (FDP) muscles, and the tendon of the flexor pollicis longus muscle. A persistent median artery or anomalous muscles and tendons may also run in the carpal tunnel.¹⁷ The TCL is approximately 3 to 4 cm in width and 2.5 to 3.5 mm in thickness. The ulnar nerve (UN) and ulnar artery run superficially on the ulnar side of the TCL, and the tendon of the flexor carpi radialis is enveloped by two layers of the TCL on the radial side of the wrist.¹⁸

FIGURE 236-1 Artist’s drawing demonstrating surgical anatomy of the carpal tunnel: A, flexor retinaculum; B, median nerve; C, palmar cutaneous branch; D, recurrent motor branch.

(Reprinted with permission from Huang JH, Zager EL. Mini-open carpal tunnel decompression. Neurosurgery. 2004;54:397.)

The median nerve arises from contributions of the lateral and medial cords and travels with the brachial artery and vein in the medial part of the arm. The median nerve courses through the cubital fossa and passes between the two heads of the pronator teres to enter the forearm. On a linear path through the forearm, the nerve travels on the deep surface of the FDS. The median palmar cutaneous nerve arises from the radial side of the median nerve approximately 5 cm proximal to the TCL and travels superficial to the carpal tunnel to provide sensory innervation to the thenar eminence. Immediately proximal to the carpal tunnel, the median nerve runs superficial to the FDS and deep to the palmaris longus tendon, and within the carpal tunnel, the median nerve runs parallel to the second and third FDS tendons.^18,19 Most often, the recurrent motor branch arises from the median nerve distal to the TCL, but anatomic variations do exist. Lanz classified these variations into three main groups: extraligamentous (50%), subligamentous (30%), and transligamentous (20%).²⁰ The recurrent motor branch provides innervation to the opponens pollicis, abductor pollicis brevis, and flexor pollicis brevis muscles. An important anatomic variant is the Riche-Cannieu anastomosis, in which innervation of thenar muscles is provided by the UN.²¹

The median nerve then divides into multiple palmar digital branches that provide motor innervation to the lateral two lumbricals and sensory innervation to the palmar surfaces and the distal dorsal portions of the thumb, index finger, middle finger, and lateral half of the ring finger.^15,16 The median nerve is vulnerable to compression at two particular sites in the carpal tunnel. The first site is the proximal edge of the TCL and the second is adjacent to the hook of the hamate.²²

Clinical Findings

Patients with CTS most often complain of pain and paresthesias in the median nerve distribution in the hand, particularly after strenuous wrist movements or at nighttime. The pain is often described as burning and may radiate proximally. Nocturnal occurrence of pain has been postulated by Sunderland to occur because of venous stasis within the upper extremity related to hypotonia during sleep.¹² Frequently, the patient will describe improvement of symptoms by shaking the affected hand, which may support the venous stasis theory.

Important questions for the patient include the duration, quality, and severity of symptoms, as well as aggravating/relieving activities. Certain conditions should be considered during the patient interview (Table 236-1): pregnancy (particularly the third trimester), renal failure/dialysis, rheumatoid arthritis, hypothyroidism, acromegaly, and amyloidosis. A thorough past medical and surgical history must be taken, including medical comorbid conditions and a history of trauma or fractures of the upper extremity. The social history should include questions about repetitive wrist motion with work or hobbies, but no conclusive evidence correlates repetitive stress with the development of CTS. Certain sports are associated with the development of CTS. Wheelchair athletes, archers, bicyclers, bodybuilders, football players, golfers, and wrestlers are prone to CTS.²³ Screening questions for alcoholism should also be asked. The patient’s family history should be obtained as well. Familial CTS often occurs through an autosomal dominant inheritance pattern, and other conditions associated with CTS include mucopolysaccharidoses, mucolipidoses, and hereditary susceptibility to pressure palsy.

TABLE 236-1 Common Conditions Associated with Carpal Tunnel Syndrome

On examination, the entire shoulder and limb should be inspected for atrophy or asymmetry. Thenar atrophy is important to identify because it is a clue to the severity of CTS, but it may be absent in severe cases in patients with a Riche-Cannieu anastomosis.²¹ Coexistent hypothenar or first dorsal interosseous muscle atrophy may signify compression at the thoracic outlet or an ulnar entrapment neuropathy. Palpation is performed over the entire length of the median nerve from the brachial plexus to the hand to check for masses, points of tenderness, and adjacent bony abnormalities (Table 236-2). Motor examination should include all median-innervated muscles. In CTS, motor strength should be normal in the pronator teres, flexor carpi radialis, the entire FDS, FDP going to the index and middle fingers, and the flexor pollicis longus. In the hand, the lumbrical muscles of the index and middle fingers should be tested by checking extension at the proximal interphalangeal joint, and abduction of the thumb with palpation of the abductor pollicis brevis muscle must be performed. A full sensory examination of the median nerve also needs to be performed. In particular, the presence of sensory abnormalities in the distribution of the palmar cutaneous branch of the median nerve implies that the median nerve lesion is above the wrist (see Table 236-2 for potential proximal entrapment sites). Semmes-Weinstein monofilament and vibratory testing has been reported in the literature to be more sensitive and specific than two-point discrimination.^24–26

TABLE 236-2 Possible Entrapment Sites of the Median Nerve

Certain provocative maneuvers can be used when examining a patient with suspected CTS. A positive finding occurs when the maneuver/position elicits symptoms in the distribution of the median nerve in the hand. The Tinel sign is performed by tapping over the carpal tunnel; sensitivity for the Tinel sign in patients with CTS ranges from 45% to 75%, and its specificity ranges from 40% to 67%.^25–31 The Phalen test is performed by having the patient flex the wrist as far as possible and holding that position for 60 seconds, and the sensitivity and specificity of this test range from 4% to 86% and 48% to 54%, respectively.^{24,25,28,29,32} The pressure provocation test (Durkan compression test) is performed by the examiner placing a thumb over the carpal tunnel and exerting downward pressure for 30 seconds. This test has a significantly better sensitivity and specificity of 82% to 89% and 90% to 99%, respectively.^25,33–35 Other provocative maneuvers reported in the literature are the reverse Phalen test, the Gilliat (tourniquet) test, and the ultrasonic stimulation test.

Diagnostic Evaluation

Electrophysiologic testing can provide important objective information to support the diagnosis of CTS. Palmar sensory latency, measured by stimulating sensory fibers in the palm and recording over the wrist, is the most sensitive test for CTS.³⁶ Distal motor latency is usually prolonged but may be normal in 25% of patients with other signs and symptoms of CTS. Sensory nerve action potentials (SNAPs) are either unrecordable or of low amplitude at the wrist. Electromyographic recording of the abductor pollicis brevis or opponens pollicis may reveal spontaneous fibrillation potentials and positive sharp waves, as well as an increased incidence of long-duration, polyphasic motor unit potentials. These electrophysiologic data are compared with recordings from the ipsilateral ulnar and radial nerves because the contralateral median nerve may be affected by subclinical CTS. Electrodiagnostic studies are also helpful in grading the severity of CTS. In mild CTS, the SNAP or mixed nerve action potential (NAP) is often prolonged, and SNAP amplitude may be below the lower limit of normal. In moderate CTS, there are findings of mild CTS plus prolongation of median motor distal latency. In severe CTS, median motor and sensory distal latencies are prolonged, with absent SNAPs or mixed NAPs or absent or reduced thenar compound motor action potentials, or both. Fibrillations, reduced recruitment, and changes in motor unit potential are often seen in severe cases.³⁷

Imaging can be a useful adjunct in the diagnosis of CTS. Plain films of the wrist can identify bony abnormalities such as fractures. Refinement of ultrasound techniques has allowed direct visualization of neural structures and associated sites of constriction, compression, or both. An entrapped peripheral nerve may appear hypoechoic, swollen, or flattened or exhibit any combination of these features.^38,39 Ultrasonography has been shown to be highly sensitive and specific in patients with clinical and electrophysiologic signs of CTS,⁴⁰ as well as in patients with clinical signs of CTS but negative electrodiagnostic studies.⁴¹

Improvements in magnetic resonance imaging (MRI) have resulted in greater sensitivity in the detection of peripheral nerve inflammation. Increased signal intensity within inflamed peripheral nerves may be seen on short tau inversion recovery (STIR) images or fat-suppressed T2-weighted spin echo images. Nerve thickening or nerve enlargement on MRI can also signify inflammation.^42,43 Magnetic resonance neurography, a technique based on enhancing signal differences between nerves and surrounding tissues, has increasingly been used for the diagnosis of entrapment neuropathies.⁴⁴ This technique is useful in demonstrating nerve position in relation to an adjacent joint placed in varying degrees of flexion. These images may suggest adhesion of nerve to surrounding tissue.⁴⁵ These MRI techniques may be useful in the diagnosis of CTS in patients with normal electrophysiologic studies or in those with an underlying systemic neuropathy altering the electrophysiologic results.^46,47 MRI evidence of nerve enlargement can be demonstrated at the level of the pisiform bone, where its diameter is 1.6 to 3.5 times that at the level of the distal radioulnar joint.^48–50 MRI is also useful in the detection of mass lesions. It is unlikely to be cost-effective in the diagnosis of routine CTS, but it may be useful in patients with complicated manifestations.

Conservative Treatment

CTS is usually a progressive condition, but a course of conservative therapy should be completed before surgical intervention. Wrist splints, physical therapy, lifestyle modification, ultrasound therapy, diuretics, nonsteroidal anti-inflammatory drugs (NSAIDs), and corticosteroids (either oral or direct carpal tunnel injection) are several conservative options available, but efficacy has yet to be proved for many of these approaches. Splinting of the affected wrist is the most commonly used nonoperative treatment and is supported by both anatomic and clinical studies. Anatomically, a wrist splint places the wrist in the neutral position, which has been shown to create the least amount of pressure or friction, or both, within the carpal tunnel.^51–54 Splinting has also been shown to temporarily improve functional deficits and the severity of symptoms.^51,53,55,56 Walker and colleagues compared nighttime with round-the-clock use of wrist splints for CTS and found that although full-time splinting provided better relief of symptoms and neurological improvement, splints limited the patient’s ability to perform normal daily activities.⁵³ Piazzini and associates recently performed an extensive review of the literature regarding the efficacy of conservative treatment of CTS. Their findings were the following: (1) locally injected steroids produce a significant, but temporary improvement; (2) wrist splints are effective, particularly if used full-time; (3) steroids are more effective than NSAIDs or diuretics; (4) ultrasound therapy may be effective, and laser therapy shows variable results; and (5) exercise therapy and pyridoxine (vitamin B₆) are both ineffective.⁵⁷ Randomized controlled studies have also shown that surgical decompression of the carpal tunnel is superior to both wrist splinting and steroids in terms of relief of symptoms and neurophysiologic outcome.^58,59 In regard to CTS in the setting of pregnancy, symptoms often resolve on delivery.^60,61

Surgical Techniques

Open Technique

The goal of the open approach is complete division of the TCL and decompression of the median nerve, with preservation of the palmar cutaneous and recurrent motor branches of the median nerve. This procedure is typically performed on an outpatient basis with local anesthesia and, in some cases, mild sedation administered by an anesthesiologist. Other anesthetic options are general anesthesia, regional block, or a Bier block.⁶² The patient is positioned supine with the arm abducted and forearm supinated on a hand table or arm board. Use of a tourniquet is optional. After careful skin preparation and draping, the wrist is often placed on a roll to provide wrist extension. Loupe magnification and headlights are useful adjuncts. A 3- to 4-cm (1.5 to 3 cm in a “mini-open” approach—see Fig. 236-2 and Video 236-1) straight or slightly curvilinear incision is marked starting at the distal wrist crease and ending at a point intercepting an imaginary line (Kaplan’s) drawn from the distal border of the extended thumb to the pisiform prominence, in line with the long axis of the radial side of the ring finger. The incision is placed ulnar to or in line with the tendon of the palmaris longus and the major thenar skin crease. The incision may have to be extended distally for better exposure in large hands. After infiltration of the proposed incision with local anesthetic, an incision is made with a No. 15 scalpel. Deep to the skin, subcutaneous fat and the palmar fascia are encountered, with care taken to protect the palmar cutaneous branch of the median nerve, which is not consistently visualized. A small self-retaining retractor such as an Alm or a small bur-hole retractor is placed, and meticulous hemostasis is maintained with bipolar electrocautery. The TCL is encountered deep to the palmar fascia; occasionally, the thenar and hypothenar muscles may obscure the ligament. The TCL is divided at its midpoint in layers with either a No. 15 scalpel or small scissors, and a fine instrument such as a Jacobson, McCabe, or a flat dissector is used to elevate each layer. The recurrent motor branch of the median nerve may be transligamentous or subligamentous. Once the median nerve is visualized, the TCL is incised both proximally and distally. Proximally, the skin is elevated to permit visualization 2 to 3 cm into the forearm. The proximal TCL and a distal portion of the antebrachial fascia are incised. The distal TCL is incised until the deep palmar fat pad is visualized. The proximal and distal portions of the incisions are probed with either the surgeon’s fifth finger or a Penfield No. 4 dissector.³⁶ At this point the carpal tunnel may be explored for tumor, ganglion cysts, muscle anomalies, or any other structural abnormality. Neurolysis of the median nerve is not generally recommended. Before closure, the wound is inspected for hemostasis and any bleeding points are coagulated with bipolar electrocautery; if used, the tourniquet should be released at this point. The wound is irrigated and then reapproximated with several absorbable subcutaneous sutures. The skin is closed with either absorbable or nonabsorbable monofilament in either a running or mattress configuration. A bulky hand dressing is then applied, and the patient is encouraged to perform gentle range-of-movement exercises as soon as possible.⁶³ Postoperative splinting is not usually recommended because splinting has not been shown to improve wound healing, reduce postoperative pain, or diminish scar tenderness.⁶⁴

FIGURE 236-2 Mini-open carpal tunnel release. A, Proposed incision measuring 2 cm starting at the distal wrist crease and extending distally in line with the third interspace. B, Intraoperative identification of the median palmar cutaneous nerve (identified with a No. 4 Penfield dissector). C, After division of the transverse carpal ligament (arrows), the median nerve (MN) is visualized. A Senn retractor is placed at the distal aspect of the incision to improve visualization.

Results from the open carpal tunnel release are generally excellent. From the Louisiana State University Health Sciences Center (LSUHSC) series of 376 carpal tunnel releases, 89% of the patients were satisfied with their results. Improvement in pain was seen in 87% of patients, improvement in paresthesias in 92%, improvement in numbness in 56%, and improvement in weakness in 42% of patients. Major symptoms persisted in 6% of patients, and complications included wound infections, reflex sympathetic dystrophy, and hematoma.⁶⁵

Anatomy

The UN is composed of contributions from C7, C8, and T1 and is the terminal continuation of the medial cord of the brachial plexus (Fig. 236-3). The UN enters the medial part of the arm by traveling in a groove between the coracobrachialis and triceps. The nerve initially travels into the arm with the axillary artery but diverges posteriorly and medially from the brachial artery. The UN pierces the medial intermuscular septum near the midpoint of the arm and then travels along the anterior aspect of the medial head of the triceps. In some cases, the UN will run within the triceps muscle. As the UN approaches the postcondylar groove, it may traverse a thickened fascial structure known as the arcade of Struthers approximately 8 cm proximal to the elbow. The nerve enters the postcondylar groove posterior to the medial epicondyle and then gives off articular branches to the elbow. The UN courses between the medial epicondyle and olecranon within the cubital tunnel, the most common site of entrapment.⁸⁴ The roof of the cubital tunnel is formed by the cubital tunnel retinaculum or arcuate ligament of Osborne, which extends from the tip of the olecranon to the medial epicondyle. The fibers of the retinaculum are oriented in transverse fashion and become taut with elbow flexion. The floor is formed by the capsule of the elbow joint and the medial collateral ligament; the walls are formed by the medial epicondyle and olecranon. The distal extent of the retinaculum fuses with the common aponeurosis of the flexor carpi ulnaris (FCU) muscle, also referred to as Osborne’s fascia, another common site of entrapment.^83,85,86 The UN enters the forearm between the ulnar and humeral heads of the FCU and provides muscular branches for innervation of this muscle. Approximately 3 cm distal to the cubital tunnel, the UN pierces the flexor pronator aponeurosis, another potential site of entrapment.^86,87 The UN continues down the forearm and gives off muscular branches to the ulnar half of the FDP muscle. The palmar cutaneous branch of the UN originates approximately 16 cm proximal to the ulnar styloid and provides sensation to the distal ulnar aspect of the forearm.⁸⁸ In the distal part of the forearm, the dorsal cutaneous branch of the UN passes medial to the FCU and enters the dorsal ulnar portion of the hand. The UN enters the hand through Guyon’s canal, which is a fibro-osseous tunnel between the pisiform and hook of the hamate. The floor of this canal is the pisohamate ligament, and the roof is the superficial volar carpal ligament. Guyon’s canal is another potential site of entrapment (Table 236-3), and within the canal the UN divides into a superficial and a deep branch. The superficial branch of the UN innervates the palmaris brevis muscle and continues to the fourth and fifth fingers as a sensory nerve. The deep or motor branch of the UN innervates the hypothenar muscles, the interosseous muscles, and the third and fourth lumbricals and ends by supplying the adductor pollicis and medial head of the flexor pollicis brevis.⁸⁹

FIGURE 236-3 A, Artist’s illustration of the surface anatomy with right ulnar decompression (right elbow, medial surface). The solid line in the inset indicates our preferred incision over the course of the nerve. B, Artist’s illustration of the surgical anatomy of the ulnar nerve in the elbow (right elbow, medial view).

(Reprinted with permission from Huang JH, Samadani U, Zager EL. Ulnar nerve entrapment neuropathy at the elbow: Simple decompression. Neurosurgery. 2004;55:1150.)

TABLE 236-3 Possible Entrapment Sites of the Ulnar Nerve

Clinical Findings