Surgery for carpal tunnel syndrome

INTRODUCTION — Carpal tunnel syndrome (CTS) is a common nerve entrapment disorder. The symptoms of carpal tunnel syndrome include numbness, tingling, and occasionally pain in the hand, especially if confined to the median nerve distribution (table 1). The symptoms are often worse at night but can also be present in the daytime in the worker with a provocative job. Symptoms are often worse with driving or holding a book, newspaper, or telephone [1,2].

Appropriate treatment can interrupt the progression of this disorder and avoid the development of permanent disability. Conservative therapy may be sufficient, although many patients require surgery. Surgical treatment may involve open or endoscopic technique. The goal of either approach is to decrease pressure upon the median nerve at the wrist by dividing the transverse carpal ligament and antebrachial fascia.

This topic review will discuss the surgical treatment of CTS. The clinical manifestations, diagnosis, and conservative therapy of this disorder are reviewed elsewhere. (See "Carpal tunnel syndrome: Clinical manifestations and diagnosis" and "Carpal tunnel syndrome: Treatment and prognosis".)

INDICATIONS — Indications for surgery include mild CTS unresponsive to conservative measures, or moderate-to severe CTS associated with axonal loss or denervation on electrodiagnostic testing (algorithm 1).

Diagnostic studies (eg, electrodiagnostic studies, ultrasound, and magnetic resonance [MR] imaging) can be helpful to assess the severity of disease or provide more information if the diagnosis is in question [3]. In addition, these studies provide baseline data and exclude other pathology that presents with similar symptoms. Although median nerve entrapment at the wrist is the most common and most well-studied manifestation, CTS is often confused with other disorders. Prior to contemplating surgical carpal tunnel release, the surgeon must be certain of the correct diagnosis. (See "Carpal tunnel syndrome: Clinical manifestations and diagnosis", section on 'Differential diagnosis'.)

If electrodiagnostic studies are normal, which can occur with symptomatic CTS [4], surgical intervention should only be considered if physical signs of median nerve dysfunction are present in addition to classic symptoms of CTS. (See "Carpal tunnel syndrome: Clinical manifestations and diagnosis", section on 'Electrodiagnostic testing'.)

ANATOMY OF THE CARPAL TUNNEL — To better appreciate the possible surgical approaches for carpal tunnel release, one must understand the anatomy of the carpal tunnel and the median nerve at the wrist. The carpal tunnel is a defined anatomic space with the following characteristics:

●The dorsal surface is formed by the carpal bones, while the volar surface is formed by the transverse carpal ligament (flexor retinaculum), which attaches ulnarly to the hamate and pisiform and radially to the trapezium and scaphoid tuberosity (figure 1).

●The antebrachial fascia of the forearm is continuous with the transverse carpal ligament of the palm. The four flexor digitorum profundus tendons, four flexor digitorum superficialis tendons, the flexor pollicis longus tendon, and the median nerve pass within this canal (figure 2).

●The superficial palmar arch lies 1 to 4 mm from the distal edge of the transverse carpal ligament.

Median nerve — The median nerve lies directly under the transverse carpal ligament (figure 1). The median nerve at the level of the distal forearm and wrist has three main branches: two sensory and one motor. The first sensory branch is the palmar cutaneous nerve, which branches from the median nerve approximately 5 cm proximal to the wrist crease. This nerve gives sensation to the thenar eminence and, because its takeoff is proximal to the carpal canal, it is not affected by CTS. However, it can easily be injured in the release of the transverse carpal ligament if the incision is not meticulously placed.

The second sensory branch passes through the carpal canal as part of the main trunk. After passing through the canal, it divides into multiple branches to innervate the thumb, index, middle, and radial half of the ring finger. Because these sensory branches pass through the canal, they are affected by compression of the median nerve at the level of the transverse carpal ligament. Branches of these sensory nerves can also be injured during surgery, more commonly with an endoscopic carpal tunnel release.

The motor branch innervates the two radial lumbricals, opponens pollicis, abductor pollicis brevis, and the superficial head of the flexor pollicis brevis. The motor branch takes a more variable route to its destination. It most often branches off distal to the transverse carpal ligament. However, it may branch off within the tunnel or pass directly through the transverse carpal ligament. The motor branch is in jeopardy during carpal tunnel release if meticulous planning is not carried out.

SURGICAL TECHNIQUES — Surgery can be divided into two main techniques:

●The open carpal tunnel release, which can be performed through a standard incision or a limited incision. (See 'Open technique' below.)

●Endoscopic carpal tunnel release, which can be performed through a single or double portal. (See 'Endoscopic techniques' below.)

●Ultrasound-guided minimally invasive carpal tunnel release, which can be performed through a minimal skin incision (skin nick) or entirely percutaneously. (See 'Ultrasound-guided ultra-minimally invasive techniques' below.)

Each procedure has its risks and benefits, and there is controversy among prominent hand surgeons as to the best technique. Surgeon experience and preference is therefore the main determining factor in the technique selection. (See 'Outcomes' below.)

Surgery for carpal tunnel release is usually performed using local anesthesia only, or local anesthesia with intravenous sedation, according to patient preference. It is usually carried out with the use of a tourniquet. However, if the local anesthetic is used with epinephrine, tourniquet use can be avoided.

In addition to performing the carpal tunnel release, some surgeons will selectively perform tenosynovial biopsy in at-risk patients to identify early amyloidosis. Carpal tunnel syndrome is one of the earliest clinical manifestations of this disease [5,6]. (See "Musculoskeletal manifestations of amyloidosis".)

Open technique — The open approach provides a complete view of the anatomy and possible anomalies, thereby decreasing the risk of injury to critical structures. This approach also allows exploration of the carpal canal (eg, mass) or biopsy of the tenosynovium to rule out systemic inflammatory disease, which may not be possible with the endoscopic technique.

Prior to making an incision, the surgeon must keep in mind the anatomy of associated structures (figure 3) such as the superficial palmar arch, the motor branch of the median nerve, the ulnar canal (Guyon's canal), and the palmar cutaneous branch.

Standard incision — A variety of longitudinal incisions can be employed. Most commonly, the incision starts just proximal to Kaplan's cardinal line, which is drawn from the apex of the interdigital fold between the thumb and index finger toward the ulnar side of the hand, parallel with the middle crease of the hand (figure 4) [7,8]. The incision is extended in a curvilinear manner staying just ulnar to the thenar crease. This keeps the incision ulnar to the palmaris longus, which reduces the likelihood of affecting the small palmar cutaneous nerve branches that pass from radial to ulnar in the palm.

Few surgeons carry this incision proximal to the wrist crease unless the patient needs a repeat release. If the incision does cross the crease, it should do so obliquely to avoid a flexion contracture at the wrist, and it should be directed ulnarly to avoid the palmar cutaneous nerve. The incision is then deepened either bluntly or sharply through the palmar fascia to the transverse carpal ligament.

The transverse carpal ligament and antebrachial fascia are divided longitudinally, and the median nerve may be identified. The division should occur along the ulnar border of the transverse carpal ligament to avoid damage to the motor branch. Care must be taken to obtain a complete release while avoiding damage to the vital structures. The flexor tendons can be retraced radially to inspect the floor of the canal for lesions. Meticulous hemostasis must be achieved prior to closure. A technique that includes subneural reconstruction of the transverse carpal ligament has been described and, in one trial, appeared to improve postoperative grip strength [9].

With open carpal tunnel release, the question often arises whether or not to perform internal neurolysis. At one time, neurolysis was felt to be important to a primary carpal tunnel release [10,11]. However, later studies found no significant difference between primary carpal tunnel release performed with or without internal neurolysis [12,13]. This applies even to patients with severe CTS defined by thenar atrophy and/or a fixed sensory deficit [12]. Neurolysis is accomplished by incising the epineurium to further decompress the nerve fascicles.

Small palmar incision — Open carpal tunnel release can also be performed through a small palmar (or "limited") incision [14]. This permits better exposure to avoid complications and keeps the incision out of the painful portion of the palm.

Carpal tunnel release through a small palmar incision uses a longitudinal palmar incision that starts just proximal to Kaplan's cardinal line and moves proximally for 2 to 2.5 cm. This allows visualization of the transverse carpal ligament; the more proximal portion of the ligament can be identified by elevating the tissue proximally above and below it. Then, under direct vision, the ligament can be incised or cut with a carpal tunnel tome.

The improved exposure with this technique decreases the risk of injury to vital structures and avoids a longer scar at the base of the palm that increases morbidity. Furthermore, the palmar fascia is left intact over the proximal portion of the transverse carpal ligament, reducing postoperative incision pain [14].

Endoscopic techniques — Due to preservation of the palmar fascia, subcutaneous fat, and skin, endoscopic median nerve decompression may result in less scar tenderness and an earlier return to work compared with the open technique. However, good visualization is essential for the endoscopic technique. If this cannot be achieved, one must switch to the open technique.

Both a one-portal and a two-portal approach have been used [15-20]. The success rates are equivalent, and the choice is surgeon dependent [18,19].

One-portal approach — The one- and two-portal techniques use a transverse portal at the wrist. A flap of antebrachial fascia is elevated and dilators are passed distally. The path is just radial to the hook of the hamate, in line with the ring finger. Care must be taken not to pass Kaplan's cardinal line to avoid injury to the palmar arch. The neurovascular bundle is 1 to 4 mm from the distal edge of the transverse carpal ligament [21].

If the one portal technique is used, the endoscopic device is then passed. One should immediately see the fibers of the transverse carpal ligament. If these are not seen, an attempt to clear the ligament of synovial tissue from the ligament is carried out. If the exact position of the transverse carpal ligament cannot be determined, the endoscopic approach must be aborted. If the fibers are clearly seen, the device is inserted just distal to the fibers. The knife device is then elevated and pulled proximally, cutting the transverse carpal ligament under endoscopic vision. Assessment to verify complete transection of the fibers is carried out. The antebrachial fascia can be cut under direct vision, through the portal at the wrist, using scissors.

Two-portal approach — If a second portal is desired, a transverse incision is made in the palm just over the end of the transverse carpal ligament. This portal permits distal visualization and can be used to depress structures, such as the superficial palmar arch, out of the operative field.

Ultrasound-guided ultra-minimally invasive techniques — Ultrasound is commonly used in the initial evaluation of carpal tunnel syndrome and can also be used to guide nonsurgical therapies. (See "Carpal tunnel syndrome: Clinical manifestations and diagnosis", section on 'Imaging' and "Carpal tunnel syndrome: Treatment and prognosis", section on 'Initial nonsurgical treatment for most patients'.)

A novel technique to release the median nerve using an ultrasound-guided minimally invasive technique has been described and may become an alternative to conventional open surgery or endoscopic treatment [22,23]. Several techniques have been described that vary in access, with some involving a very small incision and others describing a totally percutaneous technique, access location, and approach to the flexor retinaculum (antegrade, retrograde) [22,24-26].

Conceptually, the ultrasound-guided technique is like endoscopic carpal tunnel release but instead of viewing anatomic structures directly using the endoscope, the operator visualizes the contents of the carpal tunnel using ultrasound. With the hand sterilely prepared and draped, a sterile ultrasound probe is used to identify and mark key anatomic structures. Local anesthesia is administered over the predetermined incision site. Using ultrasound guidance, local anesthetic is administered into the carpal canal, which improves visualization and allows for hydrodissection. A small incision (3 to 5 mm), which must penetrate the fascia, is made with a no. 15 blade at the level of the proximal flexion crease. Under ultrasound guidance, a retrograde cutting tool is placed through the incision and advanced distally between the hook of the hamate and the median nerve to the distal end of the transverse carpal ligament. The cutting blade is deployed, and the transverse carpal ligament is released from distal to proximal. Following confirmation that the transverse carpal ligament is completely released, the cutting tool is removed. The wound can be closed with steristrips or a suture.

POSTOPERATIVE CARE — A soft dressing is placed postoperatively and left in place for three days, after which it is removed and replaced with a small adhesive dressing overlying just the wound [27,28]. The hand is elevated postoperatively until all swelling resolves. Active motion of all the digits and of the wrist should be encouraged. Postoperative immobilization (eg, splint, cast) is unnecessary and may adversely affect rehabilitation [29].

COMPLICATIONS — With proper surgical training, experience, and technique, it is estimated that the combined incidence of long-term disability related to complications from carpal tunnel release surgery should not exceed 1 to 2 percent [30]. The types of complications seen with open, endoscopic techniques and ultrasound-guided ultra-minimally invasive techniques are similar [31-34].

Complications of surgery for CTS include the following [30,35]:

●Inadequate division of the transverse carpal ligament

●Injuries of the recurrent motor and palmar cutaneous branches of the median nerve

●Lacerations of the median and ulnar trunk

●Vascular injuries of the superficial palmar arch

●Postoperative wound infections

●Painful scar formation

●Complex regional pain syndrome

Incomplete release of the transverse carpal ligament may be the most frequent complication of surgery for CTS and is usually due to errors in surgical technique, such as poor choice of incision and inadequate exposure [30]. It is also the most common problem leading to reoperation for CTS, in one series accounting for 49 percent of 185 reoperations [36].

In an early series of 186 patients, 34 various complications occurred in 22 patients (12 percent), including incomplete division of the transverse carpal ligament in 11 (6 percent) and development of complex regional pain syndrome in 4 (2 percent) [35].

OUTCOMES — Outcome studies have demonstrated that both open surgery and endoscopic release produce subjective improvement in preoperative symptoms [14,18,31,37-40]. The choice of technique is largely surgeon dependent. Each has its advantages and disadvantages, and each technique has a learning curve, which is greatest with the endoscopic technique.

Proponents of the ultrasound-guided ultra-minimally invasive and endoscopic techniques cite evidence that it leads to less postoperative incision pain and an earlier return to work compared with open techniques [31,41,42]. However, critics of the endoscopic approach cite an apparent increased rate of complications, which are related to the experience of the surgeon [43,44].

Evaluation of pain relief and function is essential in determining the effectiveness of treatment for musculoskeletal disorders. One study used a standardized, self-administered questionnaire to assess the severity of symptoms and functional status at six weeks, three months, six months, and two years after open (primarily limited open) surgery [45]. The following findings were noted:

●Nocturnal pain, tingling, and numbness improved within six weeks.

●Weakness and functional status improved more gradually, and grip and pinch strength initially worsened, returned to preoperative levels at approximately three months, and improved significantly by two years. Grip and pinch strength improve after carpal tunnel release despite the effect of transverse carpal ligament release on flexor tendon pulley function [46].

●Although 90 percent of patients had relief of either nighttime or daytime pain, only 73 percent said that they were completely or very satisfied with the results of the surgery.

These temporal patterns should be discussed with the patient to promote realistic expectations about the results of surgery.

Using the same questionnaire, a prospective study was performed to determine the predictors of return to work after carpal tunnel release (primarily open surgery) in a community-based cohort [17]. Within six months, 77 percent had returned to their previous employment. The major risk factors for poor outcome were scar tenderness and failure to relieve symptoms. Other negative predictors of return to work included lack of an education beyond high school, consumption of more than two drinks per day, smoking, female sex, use of an attorney or workers' compensation before surgery, and the presence of physical stresses such as multiple repetitive motion in the workplace. Later follow-up of a related cohort showed that 82 percent of workers' compensation recipients had returned to work at 30 months [47].

A single-surgeon study involving 113 patients followed over a mean of 13 years also evaluated patient satisfaction [39]. The most common residual complaint was very mild daytime tingling, but 88 percent of the patients were "completely" or "very" satisfied with the results of the surgery; 74 percent reported complete relief of symptoms. Only 2 patients out of 113 (1.8 percent) required a repeat carpal tunnel release.

In a review of 42 operations in 35 patients, the outcomes of endoscopic carpal tunnel release were "satisfactory" in 86 percent [38]. The mean time to return to ordinary daily activities and work were 14 and 25 days, respectively. One year after surgery, night pain and paresthesia were absent in 95 and 81 percent, respectively.

Open versus endoscopic techniques — In trials comparing open versus endoscopic carpal tunnel release, the outcomes appear to be equivalent [48,49].

●While some trials suggest a more rapid postoperative recovery and earlier return to work with the endoscopic technique [31,50,51], others have found no significant difference for time to return to work between the two techniques [52-54].

●The endoscopic technique may result in less postoperative pain and tenderness of the scar [31,55,56], but the degree of this benefit appears to be modest [54].

●Digital flexor tendon mechanics are closer to normal following endoscopic carpal tunnel release than with the open technique [57].

●A trial that randomly assigned 128 patients to open or two-portal endoscopic carpal tunnel release followed the patients over an extended period of time [58]. Complete data for all outcome survey measures were available for 124 of the patients with a mean follow-up of 12.9 years after surgery (range: 11.3 to 15.7 years). At extended follow-up, there were no significant differences between open and endoscopic carpal tunnel release.

Open versus ultrasound-guided ultra-minimally invasive techniques — The benefits of ultrasound-guided ultra-minimally invasive techniques are potentially no incision and quick recovery, but there is possibly a higher recurrence rate [23,59,60]. Two prospective studies have compared mini-open techniques to the ultrasound-guided technique [41,42]. In one trial, return to normal daily activities occurred significantly sooner in the ultrasound-guided technique group (4.9 versus 25.4 days) [41]. In another trial, the ultrasound-guided technique had lower scores on the Italian modified version of the Boston Carpal Tunnel Questionnaire (BCTQ) compared with the mini-open group at 19 months, but not at 30 months. Disease recurred in 7 of 82 patients in the ultrasound-guided technique group and only 1 of 103 in the mini-open group. There are no prospective studies comparing the various ultrasound-guided techniques.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Carpal tunnel syndrome".)

SUMMARY AND RECOMMENDATIONS

●Carpal tunnel syndrome – Carpal tunnel syndrome is a common nerve entrapment disorder manifested by pain, paresthesias, and ultimately muscle wasting of the hand. Conservative therapy may be sufficient, although many patients require surgery. (See 'Introduction' above.)

●Indications for surgery – Indications for surgery include persistent numbness and pain, motor dysfunction with diminished grip or pinch grasping, or thenar eminence flattening. Electrodiagnostic studies are suggested, even if the history and/or physical examination is suggestive of carpal tunnel syndrome. (See 'Indications' above.)

●Surgical approach – Carpal tunnel release can be performed as an open procedure, endoscopically, or by using ultrasound-guided ultra-minimally invasive techniques. (See 'Surgical techniques' above.)

●Complications – The most frequent complication of carpal tunnel surgery is incomplete release of the transverse carpal ligament, which often requires reoperation. (See 'Complications' above.)

●Outcomes – The long-term outcomes of open, endoscopic, and ultrasound-guided ultra-minimally invasive carpal tunnel release are equivalent. Ultra-minimally invasive techniques have the advantage of quicker recovery but the potential for a higher rate of recurrence. (See 'Outcomes' above.)