Approach Considerations
No specific conditions contraindicate the surgical treatment of median nerve compression, other than general contraindications for minor outpatient surgery. Some would prefer the patient to be off anticoagulant medications (eg, warfarin and clopidogrel), especially when an axillary block is used. Individuals with severe median nerve compression should be cautioned that some of their symptoms may persist after surgery.
There has been controversy over whether any of the various surgical techniques commonly used to treat carpal tunnel syndrome (CTS) is superior to any of the others in terms of final patient outcomes. (See Orthopedic Surgery for Carpal Tunnel Syndrome.) The techniques most commonly used at present include the following:
-
Traditional surgical open release
-
Limited-incision open release
-
Limited-incision device-assisted release
-
Single- or dual-port endoscopic release
Endoscopic carpal tunnel release offers the advantages of decreased scar formation, less scar sensitivity, and avoidance of an incision directly over the carpal tunnel between the thenar and hypothenar muscles. A number of studies comparing the two basic techniques (endoscopic and open) suggested that endoscopic techniques are superior to open techniques in terms of earlier functional recovery and earlier return to work. Various multicenter studies did not find endoscopic carpal tunnel release to be associated with a higher complication rate than open release.
In an evidence-based review by Shores and Lee, endoscopic release provided no demonstrable added benefit as compared with open carpal tunnel release, [82] though review of current literature suggests that the operative technique chosen should ultimately be based on patient and surgeon preference. This analysis included an updated systematic review by the Cochrane Collaboration in 2007, as well as a 5-year follow-up of patient outcomes by Atroshi et al in 2009.
A 2014 Cochrane review (admittedly based on low-quality evidence only) found that open and endoscopic approaches to carpal tunnel release were approximately equally effective with respect to symptomatic relief and functional improvement. [83] Endoscopic release appeared to yield better improvement in grip strength and to have a lower rate of minor complications (though there was no difference in the rate of major complications); it was also associated with quicker return to work. The applicability of these conclusions is limited by the flaws of the studies included.
In a 2020 systematic review that included 27 studies, Orhurhu et al compared open with endoscopic carpal tunnel release. [84] They noted that whereas both approaches were satisfactory in terms of pain relief, symptom resolution, patient satisfaction, time to return to work, and adverse events, there was growing evidence in favor of the endoscopic approach with respect to pain relief, functional outcomes, and satisfaction, at least in the early postoperative period (though the difference might disappear over time).
A learning curve should be anticipated with endoscopic carpal tunnel release, and prior cadaveric practice would be advisable. The fear of catastrophic nerve injuries and the absence of any clear increase in overall benefits of endoscopic release have prompted many surgeons to continue using the traditional approach, with or without modifications of the incision to reduce postoperative discomfort.
Minimally invasive percutaneous ultrasonography (US)-guided approaches to carpal tunnel release has been described as alternatives to the open and endoscopic approaches now in use. [4, 85, 86, 87]
Medical Therapy
Carpal tunnel syndrome
Most cases of median nerve entrapment neuropathy improve after several weeks of conservative therapy. A change in lifestyle and work activities is necessary. Patients should be advised to decrease or avoid weightbearing repetitive hand movements and the use of vibrating tools. Wrist splinting is frequently suggested for nonoperative treatment of CTS. Wrist splinting in a neutral position at night is recommended. Avoiding wrist extension in splints minimizes intratunnel pressure. [88]
If significant lifestyle changes or financial burden would be inflicted by avoiding activities, a more aggressive treatment should be considered. Operative treatment is recommended for physically active patients and those with severe or long-standing symptoms.
Oral anti-inflammatory medications and corticosteroid injections can be used for transient relief or in high-risk patients. Improvement of symptoms confirms the diagnosis and may be a predictor of satisfactory surgical outcome, if necessary. [89]
A 1-mL combination of 0.5 mL of lidocaine 1% and 0.5 mL of triamcinolone is a common choice for injection in the area around the median nerve at the proximal wrist crease. US has been employed to guide injection. [90] Side effects include irritation and postinjection flare, which may last for a couple of days, and skin discoloration around the injection site. Infection and tendon rupture are rare complications.
Addition of oral vitamin B6 [91] has also been reported as a nonoperative treatment for CTS.
Nerve gliding exercises have been used to improve symptoms. [92] Aerobic exercise without wrist strain that results in weight reduction could help alleviate CTS. [93]
In addition to assessing clinical symptoms, some hand surgeons follow the improvements resulting from carpal tunnel therapy by conducting routine nerve conduction studies. Deterioration of nerve conduction in some cases prompts surgical intervention to avoid axonal loss.
Pronator syndrome and anterior interosseous nerve syndrome
Initial treatment of pronator syndrome (pronator teres syndrome [PTS]) and anterior interosseous nerve (AIN) syndrome (AINS) is typically nonsurgical and includes rest, activity modification, anti-inflammatory medications, and splints for at least several months, unless a motor deficit is noted. Patients who do not respond to conservative treatment or who experience motor deficits require decompressive surgery.
The results of decompressive surgery may vary. Before treating PTS, the authors ensure that any carpal tunnel pathology is addressed. If symptoms persist, any proximal nerve compression should be examined, and if signs of thoracic outlet compression are present, the patient is referred for physical therapy.
Surgical treatment of PTS is offered if the above measures yield no improvement.
Surgical Therapy
Carpal tunnel syndrome
When a regimen of conservative treatment fails to relieve patient symptoms of CTS or signs of thenar muscle weakness and atrophy are present, surgical decompression of the median nerve is usually recommended. The following are some of the predictors of nonoperative treatment failure [94] :
-
Age greater than 50 years
-
Symptom duration exceeding 10 months
-
Constant paresthesia
-
Stenosing flexor tenosynovitis
-
Positive Phalen test result in less than 30 seconds
The traditional exposure (see the image below) remains more common, though minimally invasive approaches confer the advantage of less postoperative discomfort. (See Orthopedic Surgery for Carpal Tunnel Syndrome.) A minimally invasive percutaneous US-guided approach has been described. [4, 85, 86, 87]
The surgeon should choose the method that offers the best visualization of the median nerve so as to avoid injury to the nerve and its branches. A curved longitudinal incision is made paralleling the thenar crease and crossing the wrist crease obliquely in an ulnar direction to a point in line with the long axis of the flexed ring finger. The distal end stops before or beyond the proximal wrist crease in order to afford good visualization of the scissor cut on the retinaculum.
Postoperative wrist pain is somewhat proportional to the length of the incision. Accordingly, some surgeons use minimally invasive incisions, sparing the extended proximal incision with special retractors (see the first image below) and/or using blade guide instruments (see the second image below) to visualize and divide the retinaculum. The ulnar cutaneous branch, which is sometimes found in the distal portion of the incision, should be avoided.
Lighted retractor allows direct visualization of transverse carpal ligament, which can be divided under direct vision with knife or scissors.
Blade (swivel knife) and blade guide (grooved Mickey Mouse director) are used to divide transverse carpal ligament when minimally invasive incision is made.
The incision in the retinaculum should follow the course of the nerve as it is exposed gradually by the advancing cut, preferably with visualization of the thenar motor and sensory branches. Care should be taken not to injure the superficial palmar arch. [95] The completeness of the distal cut is confirmed by checking for remaining cross bands and the yellow fat at the end of the carpal tunnel.
Endoscopic retinaculotomy with various techniques, including either the two-portal or the single-portal technique, has been advocated to decrease the length of the incision and thus potentially decrease postoperative incisional discomfort. Numerous endoscopic systems have been described, [96, 97] but the risk of complications, including iatrogenic nerve injury, [98] poor visualization, inability to identify anatomic variations, incomplete release, and apparent beneficial cost savings, remains to be defined. [99, 98] (See the images below.)
Instruments used in endoscopic carpal tunnel surgery. From left to right: endoscopic camera, endoscopic knife, cannula, scraper, custom-made plastic tube, and elevator.
The following is a brief description of the endoscopic technique used by the authors’ group. After a longitudinal palmar skin incision, the palmar fascia is split longitudinally, and a self-retaining retractor is applied. The distal edge of the carpal ligament is exposed and partially divided. Similarly, a transverse proximal incision is made in the wrist, exposing the carpal ligament. (See the image below.)
Two red lines show correct locations of incisions for endoscopic carpal tunnel surgery. FCR=flexor carpi radialis tendon; H=hook of hamate; P=pisiform; PL=palmaris longus tendon.
With the wrist in hyperextended position, an elevator is passed from proximal to distal under the transverse carpal ligament. A cannula is then passed through the same path, and the endoscope is applied. Under endoscopic observation, a meniscus knife is pushed forward along the groove (positioned superiorly) in the cannula to release the flexor retinaculum. (See the images below.)
Endoscope is inserted in cannula attached to endoscopic knife. Knife is pushed forward along cannula's groove, and carpal ligament is divided under direct vision.
After all instruments have been removed, a custom-made glass or plastic tube is inserted. The clear tube allows a view of pathology in the carpal tunnel and confirmation of release of the flexor retinaculum.
Pronator syndrome and anterior interosseous nerve syndrome
Before surgical treatment of PTS or AINS, compression points are determined by physical examination, either with stress on a particular tendon or muscle unit or with the elicitation of pain with direct palpation.
The incision to explore the median nerve in the proximal forearm begins a few centimeters above the elbow crease at the antecubital fossa and continues distally in an S or zigzag fashion (see the image below).
Incision for pronator teres syndrome (PTS) and anterior interosseous nerve syndrome (AINS) exposure.
The bicipital aponeurosis (lacertus fibrosus) should always be divided. The median nerve is then exposed by dividing the superficial fibers of the pronator teres where the areas of compression are addressed individually.
For exposing the AIN, division or retraction of the superficial head of the pronator teres is usually necessary. The fibrous tissue arch of the flexor digitorum superficialis (FDS) should also be addressed as a potential site of compression, and the deep head of the pronator teres is often divided. If a ligament of Struthers is identified, the incision is extended above the elbow crease to divide this structure.
Vascular abnormalities can also be a cause of constriction that must be addressed. A compression site can usually be identified by noting a discoloration at a narrowing of the nerve after the area of constriction.
Another favorite approach for PTS and AINS is to use two transverse skin incisions that allow adequate exploration and decompression distally and proximally. This approach is thought to be associated with less postoperative discomfort and scarring. [100] (See the image below.)
Alternative incision for pronator teres syndrome (PTS) and anterior interosseous nerve syndrome (AINS) is marked by horizontal thickened lines. Relative locations of underlying pertinent structures are marked on skin. Bicep=biceps tendon; BR=ulnar border of brachioradialis; LABN=lateral antebrachial cutaneous nerve; MABN=medial antebrachial cutaneous nerve; PT=radial border of pronator teres.
Postoperative Care
After carpal tunnel decompression, volar wrist splints are used to restrict range of motion in the wrist during the first 2 weeks after the procedure. Movement of the metacarpophalangeal (MCP) and interphalangeal (IP) joints is encouraged.
Some prefer early movement of the wrist within 24-48 hours after surgery, when the splint and dressings are removed and early physical therapy is initiated. [101] Some have reported that earlier mobilization decreases the risk of flexor tendon “bowstringing” (see Complications) and hastens the process of returning to work and engaging in daily activities, unlike with long-term immobilization.
The sutures are removed 12-14 days after carpal tunnel release. Within 2 weeks, patients are allowed to return to work with one-handed duty. At 1 month after surgery, patients are allowed to work with weight restriction, and at 6-8 weeks after surgery, they are allowed full activity without restrictions.
Most surgeons use soft dressing postoperatively for proximal median nerve entrapment. Splinting, however, is done by keeping the elbow slightly flexed and the wrist in a neutral position.
Complications
Recurrent symptoms after surgical decompression of the carpal tunnel usually result from incomplete sectioning of the anterior carpal ligament, flexor tendon synovitis, and scarring in the carpal tunnel. [102] Further surgery, in particular to deal with scarring, leads to relief in only 50% of this minority group of patients.
Injury to both the ulnar and the median nerve has been reported for all carpal tunnel release techniques. Most of these are self-limited problems with paresthesias that resolve.
Scar tenderness at the incision site in the wrist occurs in nearly all patients, but a small number of patients find the sensitivity disabling, especially with the open carpal tunnel release technique. Cseuz et al found that 36% of their patients reported unpleasant scar sensitivity when queried months or years postoperatively. [47] Most patients with scar symptoms reported "minor discomfort which did not interfere with their daily activities."
The median nerve proper, the recurrent thenar motor branch, the median palmar cutaneous nerve branch, the ulnar palmar cutaneous nerve branch, the superficial radial nerve, and digital nerve branches are all vulnerable to injury at the time of carpal tunnel surgery.
Reflex sympathetic dystrophy (RSD) can occur, presumably from irritation of the median nerve. The hand may be swollen, warm, and dry. Later, the skin may become cool, pale, or shiny with trophic changes. The patient may describe hyperalgesia and hyperesthesia.
The transverse carpal ligament is the stabilizing structure for the origin of the abductor pollicis brevis (APB) and the abductor digiti minimi (ADM). Patients frequently note "pillar" pain for several months near these muscle origins, weakening their grip until stable scar tissue forms.
In rare cases, after division of the flexor retinaculum, the flexor tendons move anteriorly with wrist flexion (ie, "bowstringing" of the flexor tendons). [103] When these patients flex their wrists, they may experience pain, a snapping sensation, and paresthesias in a median distribution.
Rarely, patients describe increased stiffness in finger joints after carpal tunnel surgery.
The risk of deep postoperative wound infection after carpal tunnel surgery is small. At the Mayo Clinic, the incidence of infection was 0.5% in 3600 patients. [104]
-
Anatomy of median nerve along its course in upper extremity.
-
Ligament of Struthers.
-
Lacertus fibrosus (bicipital aponeurosis).
-
Pronator teres.
-
Fibrous arch of flexor digitorum superficialis.
-
Gantzer's muscle.
-
Traditional open carpal tunnel incision.
-
Lighted retractor allows direct visualization of transverse carpal ligament, which can be divided under direct vision with knife or scissors.
-
Blade (swivel knife) and blade guide (grooved Mickey Mouse director) are used to divide transverse carpal ligament when minimally invasive incision is made.
-
Two red lines show correct locations of incisions for endoscopic carpal tunnel surgery. FCR=flexor carpi radialis tendon; H=hook of hamate; P=pisiform; PL=palmaris longus tendon.
-
Cannula is inserted inside carpal space, with groove of instrument facing up.
-
Endoscope is inserted in cannula attached to endoscopic knife. Knife is pushed forward along cannula's groove, and carpal ligament is divided under direct vision.
-
Type of endoscopic knife used in carpal tunnel surgery.
-
Instruments used in endoscopic carpal tunnel surgery. From left to right: endoscopic camera, endoscopic knife, cannula, scraper, custom-made plastic tube, and elevator.
-
Incision for pronator teres syndrome (PTS) and anterior interosseous nerve syndrome (AINS) exposure.
-
Alternative incision for pronator teres syndrome (PTS) and anterior interosseous nerve syndrome (AINS) is marked by horizontal thickened lines. Relative locations of underlying pertinent structures are marked on skin. Bicep=biceps tendon; BR=ulnar border of brachioradialis; LABN=lateral antebrachial cutaneous nerve; MABN=medial antebrachial cutaneous nerve; PT=radial border of pronator teres.
