Carpal Tunnel Release

Carpal tunnel syndrome (CTS) is the most common entrapment neuropathy, affecting approximately 2% of men and 3% of women, most commonly between 40 and 60 years of age. ¹ The symptoms of CTS are caused by compression of the median nerve at the wrist within the carpal tunnel. The pathophysiology of this compression injury is incompletely understood; however, various studies have hypothesized that the symptoms of CTS may be related to ischemia-induced nerve damage, mechanical trauma, inflammation, ectopic impulse generation from nerve irritation, demyelination, or elevated carpal tunnel pressures.

Most cases of CTS are idiopathic or related to occupations with repetitive wrist strain; however, CTS may also be associated with multiple clinical conditions that lead to either an increase in the volume of carpal tunnel contents or a decrease in the size of the carpal tunnel.

59.1.1 Clinical Presentation

The most common clinical presentation of CTS is painful paresthesias or burning pain in the radial aspect of the hand and the lateral three fingers. A classic feature of CTS is worsening of the pain or paresthesias at night, which may be relieved by vigorously shaking (flick sign) and massaging the affected hand. ² Venous stasis in the upper extremity has been suggested as the culprit in nocturnal symptom exacerbation. ³ Patients also complain of numbness and swelling in the hand, tingling sensations in the hand and forearm, and clumsiness. The pain can often be made worse by repetitive use of the hand, such as in typing and driving. Infrequently, patients experience weakness without any pain; however, physical examination findings in patients with CTS are usually mild compared with their subjective complaints.

On clinical examination, the patient may exhibit wasting of the thenar eminence in advanced cases, and this is highly predictive of CTS. ⁴ In moderate or severe cases of CTS, sensory loss in the median nerve distribution and weakness or atrophy of the abductor pollicis brevis or the opponens pollicis muscle may be noticed. Percussion or manual compression over the median nerve at the level of the distal wrist crease may elicit Tinel’s sign, or paresthesias distally in the median nerve distribution. The Phalen wrist flexion test is performed by placing the patient’s wrists in complete flexion for 1 minute and is positive if the patient’s symptoms are reproduced. Other provocative tests to elicit CTS symptoms include the median nerve compression test (applying firm pressure for 30 seconds over the palmar course of the nerve), ⁵ reverse Phalen test (maintaining full wrist and finger extension for 2 minutes), ⁶ and the Gilliatt pneumatic-tourniquet test (inflating brachial blood pressure cuff to a suprasystolic pressure), ⁷ or the scratch collapse test, which has been proposed more recently in an attempt to provide a more objective means of diagnosing CTS. ⁸

Confirmatory Testing

Electrophysiological studies are helpful in confirming the diagnosis and evaluating the severity of CTS, particularly with detecting early sensory changes. The palmar sensory latency test, the most sensitive test for CTS, is measured by stimulating sensory fibers in the palm and recording over the wrist. ⁹ In addition, distal motor latency may be prolonged, but this measure carries a false-negative rate of 25%. ¹⁰ Electromyography tests of the thenar muscles are also measured, which may reveal signs of denervation, characterized by the presence of positive sharp waves, spontaneous fibrillation potentials, and prolonged polyphasic motor unit potentials. ¹⁰ Reference electrophysiological data should be obtained from the ipsilateral radial and ulnar nerves instead of relying solely on the contralateral median nerve in the case of subclinical CTS in the contralateral arm. A recent prospective study combined electrophysiological data with provocative testing to add diagnostic and prognostic value in the evaluation of mild CTS. The cuff sign signifies the increase in sensory latency of the median nerve measured 1 minute after the application of a blood pressure cuff above diastolic pressure for 3 minutes compared with the pre–blood pressure cuff value. The authors suggest a cutoff of 2-milliseconds increase in sensory latency, above which their study patients were more likely to benefit after surgery. ¹¹

Other clinical testing modalities, such as vibrometry threshold testing, Semmes-Weinstein monofilament testing, two-point discrimination, and current perception testing may aid in making the diagnosis of CTS but have a much lower sensitivity than electrophysiological studies.

Imaging

High-resolution ultrasonography appeared in the literature nearly 25 years ago as a useful tool in the diagnosis of CTS. ¹² Quantification of median nerve cross-sectional area due to its swelling in the carpal tunnel has been found to be a promising target of ultrasonographic study. ¹³^, ¹⁴ Ultrasonography has favorable diagnostic accuracy when compared with electrophysiological studies and may be useful when the latter presents equivocal data.

Magnetic resonance imaging (MRI) has been studied for correlations between the abnormalities seen on the images and the intraoperative findings. All the patients clinically diagnosed with CTS had abnormalities of the median nerve by MRI, most with increased signal of the nerve or flexor tendon sheath, increased distance between flexor tendons, or abnormal nerve configuration. Abnormal nerve configuration on MRI correlated with favorable outcomes after surgical release of the carpal tunnel. Diffusion tensor imaging, tractography, and magnetic resonance neurography have also been used to study median nerve characteristics in patients with CTS versus healthy controls. ¹⁵^, ¹⁶^, ¹⁷^, ¹⁸ Neurography has also been used to demonstrate changes in postsurgical nerve morphology. ¹⁹ Despite the utility of MRI in evaluation of CTS, the evidence has not supported the routine use of MRI in the diagnosis or management of CTS ²⁰; however, imaging may be a useful adjunct in cases with normal electrophysiological studies or a diagnostic picture muddled by concurrent systemic disease. ²¹^, ²²

59.2 Patient Selection

59.2.1 Nonoperative Treatment

Most patients with CTS are treated with nonsurgical measures first. The goals of early therapy for CTS include not only improving symptoms but also preventing disease progression and muscle weakness. Most nonsurgical therapy is a combination of anti-inflammatory agents such as nonsteroidal anti-inflammatory drugs and steroid injections with activity modification and splinting of the wrist in a neutral position. Other therapies include ultrasound and laser therapy. ²³^, ²⁴^, ²⁵ These therapies are often effective in the short term. Local steroid injections have been one of the more widely studied therapies. ²⁶^, ²⁷^, ²⁸^, ²⁹ The duration of symptom relief and the benefits of multiple injections are controversial. ³⁰^, ³¹ Overall, some patients experience long-term relief with conservative therapy, but many others later require additional therapy or surgery. Nonsurgical therapy generally requires a minimum trial of 6 weeks before surgical options may be considered.

59.2.2 Surgical Candidates

Surgical intervention should be considered in two groups of patients: (1) patients who continue to be symptomatic despite conservative treatment and (2) patients with progressive disease, including those with thenar eminence flattening and diminished hand function.

Many options are available for surgical decompression of the median nerve in the carpal tunnel, including open carpal tunnel release (OCTR), endoscopic carpal tunnel release (ECTR), and various mini-open and minimally invasive techniques. A recent meta-analysis of randomized controlled trials compared the safety and efficacy of OCTR versus ECTR in patients with idiopathic CTS. ³² A review of 13 randomized trials yielded no statistical difference in patient satisfaction, return to work, postoperative grip and pinch strength, length of procedure, and overall complication rate. ECTR did show reduced postoperative hand pain, but conversely it increased the chance of reversible postoperative nerve injury. We describe our method for OCTR in this chapter; ECTR is discussed in more depth in Chapter 60.

In patients with bilateral CTS, we usually choose to decompress the more severely affected hand first. Sometimes the symptoms in the less severely affected hand spontaneously resolve in the interim and will not need surgical intervention; however, if the patient continues to have symptoms in the remaining hand, operations on that hand can be performed 2 to 3 months later, when the patient has recovered from the first surgery. Some surgeons perform simultaneous bilateral carpal tunnel release with reportedly good results ³³; this practice has not been widely adopted as yet.

59.3 Preoperative Preparation

In our practice, the procedure is performed with the patient under local anesthesia with mild sedation, or monitored anesthesia care (MAC). Many surgeons prefer to use a regional block or straight local anesthesia.

59.4 Operative Procedure

59.4.1 Surgical Anatomy

The carpal tunnel is a fibro-osseous canal, with its floor and lateral walls formed by carpal bones and its roof formed by the transverse carpal ligament (also called the flexor retinaculum) ( ▶ Fig. 59.1). The transverse carpal ligament is ~ 4 cm wide, 3 mm thick, and begins ~ 1 cm proximal to the distal wrist crease and extends ~ 3 cm distal to the crease. The transverse carpal ligament attaches on the ulnar side to the hamate and pisiform and on the radial side to the trapezium and scaphoid tuberosity. The carpal tunnel contains four flexor digitorum profundus tendons, four flexor digitorum superficialis tendons, the flexor pollicis longus tendon, and the median nerve. In 10% of patients, there is a small, persistent median artery coursing through the tunnel along with the median nerve.

Fig. 59.1 Surgical anatomy of the carpal tunnel (left hand). (a) Flexor retinaculum (transverse carpal ligament); (b) median nerve; (c) palmar cutaneous branch; (d) palmaris longus tendon; (e) recurrent motor branch.

The median nerve lies immediately underneath the transverse carpal ligament and consists of two sensory branches and one motor branch. The median nerve gives off the palmar cutaneous branch, which provides sensory innervation to the proximal thenar eminence, before entering the carpal tunnel. The palmar cutaneous branch leaves from the radial side of the median nerve and descends lateral to the palmaris longus tendon. Therefore, this sensory branch is not usually affected by carpal tunnel compression; however, the palmar cutaneous nerve has rare anatomical variations and may be injured during surgery.

The second sensory component of the median nerve travels with the main branch through the carpal tunnel and is responsible for the painful symptoms of CTS. It divides into multiple branches to provide sensation to the radial portion of the palm, the thumb, index, middle, and radial half of the ring finger.

As it exits the tunnel, the median nerve gives off the important recurrent motor branch. This branch curves laterally to innervate two thenar muscles: the abductor pollicis brevis and opponens pollicis muscles. It is essential for surgeons to recognize numerous anatomical variations in the course of the recurrent motor branch: It may pierce the flexor retinaculum without wrapping around it; it may have a duplicate branch; it may also leave the ulnar side of the median nerve and extend over the median nerve toward the thenar muscles. Motor components of the median nerve also innervate the two radial lumbricals and the superficial head of the flexor pollicis brevis.

59.4.2 Patient Positioning and Surgical Procedure

The patient is positioned supine with the arm abducted and the forearm supinated on a hand table or an arm board. Many surgeons prefer to use a tourniquet, but we do not routinely use one. After meticulous skin preparation, the hand is enclosed in a stockinette. The stockinette is opened over the palm and proximal wrist. The incision is marked along the ulnar border of the major thenar crease in line with the radial border of the ring finger ( ▶ Fig. 59.2). The incision begins just distal to the distal wrist crease and extends no farther than Kaplan’s cardinal line, which extends along the distal border of the outstretched thumb obliquely toward the pisiform. On rare occasions, if the incision needs to be extended proximally (e.g., in a revision case), it can be extended 1 cm proximally to cross the wrist crease with a short S-shaped extension ( ▶ Fig. 59.2). Alternatively, a mini-open carpal tunnel release may be performed with a shorter incision to achieve the same result ( ▶ Fig. 59.3).

Fig. 59.2 The surgical incision for a standard open carpal tunnel release. The incision (solid line) can be extended 1 cm proximally (dotted line) if necessary.

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