Carpal tunnel release for compression of the median nerve at the wrist is one of the most common and successful procedures in hand surgery. Complications, though rare, are potentially devastating and may include intraoperative technical errors, postoperative infection and pain, and persistent or recurrent symptoms. Patients with continued complaints after carpal tunnel release should be carefully evaluated with detailed history and physical examination in addition to electrodiagnostic testing. For those with persistent or recurrent symptoms, a course of nonoperative management including splinting, injections, occupational therapy, and desensitization should be considered prior to revision surgery.
Key points
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Complications of carpal tunnel release are rare and include intraoperative technical errors, postoperative infection and pain, and persistent or recurrent symptoms.
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Evaluation should include a detailed history and physical examination in addition to electrodiagnostic examination and other imaging.
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A course of nonoperative management including splinting, injections, occupational therapy, and desensitization should be considered.
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Revision carpal tunnel release may be indicated if symptoms fail to improve and electrodiagnostic results worsen compared with preoperative values.
Introduction
Carpal tunnel syndrome is the most common peripheral compression neuropathy and one of the most frequent disorders of the hand, affecting 4.9% to 7.1% of the population. It was originally described in 1854 and has been treated surgically since Learmonth’s description of release of the transverse carpal ligament in 1933. Today, carpal tunnel release (CTR) surgery is among the most common hand procedures. The number of CTRs performed in the United States increased 38% from 360,000 per year in 1996 to 577,000 in 2006.
Although this surgery has been shown to be reliably safe and effective, complications do occur. These complications include intraoperative injury to nerves, vessels, and tendons; postoperative complications, such as infection, pain syndromes, and wrist instability; and treatment failures. The ability to competently evaluate and manage these complications is an essential part of hand surgery.
Introduction
Carpal tunnel syndrome is the most common peripheral compression neuropathy and one of the most frequent disorders of the hand, affecting 4.9% to 7.1% of the population. It was originally described in 1854 and has been treated surgically since Learmonth’s description of release of the transverse carpal ligament in 1933. Today, carpal tunnel release (CTR) surgery is among the most common hand procedures. The number of CTRs performed in the United States increased 38% from 360,000 per year in 1996 to 577,000 in 2006.
Although this surgery has been shown to be reliably safe and effective, complications do occur. These complications include intraoperative injury to nerves, vessels, and tendons; postoperative complications, such as infection, pain syndromes, and wrist instability; and treatment failures. The ability to competently evaluate and manage these complications is an essential part of hand surgery.
Review of anatomy
An understanding of the normal anatomy of the carpal tunnel as well as the common variants guide incision placement and operative technique for CTR and can help prevent iatrogenic injury.
The carpal tunnel is defined by the curved carpus dorsally and the transverse carpal ligament volarly, which runs from the scaphoid tuberosity and medial ridge of the trapezium to the hook of the hamate and the pisiform ( Fig. 1 ). It is narrowest at the level of the hook of the hamate where the tunnel is only 20 mm wide and 10 mm deep. This constriction is 2.0 to 2.5 cm distal to the start of the canal and is caused by prominence of the capitate, increased thickness of the transverse carpal ligament, and the position of the hamate. This area often corresponds to the hourglass deformity of the median nerve seen in cases of severe carpal tunnel syndrome.
The carpal tunnel contains 10 structures: 4 flexor digitorum superficialis (FDS) and 4 flexor digitorum profundus (FDP) tendons, the flexor pollicis longus tendon, and the median nerve. The nerve is the most superficial structure and overlies the FDS and FDP tendons to the index finger.
The median nerve gives off 2 branches in the vicinity of the carpal tunnel that may be injured during release. The palmar cutaneous branch provides sensory innervation to the thenar eminence and arises from the radial side of the median nerve an average of 6 cm proximal to the transverse carpal ligament. The nerve then pierces the antebrachial fascia proximal to the wrist and travels in the subcutaneous tissue into the palm before branching out. The palm may also be innervated by transverse palmar branches that leave the ulnar nerve in the Guyon canal and course radially across the hand.
The thenar branch of the median nerve innervates the thenar muscles and generally branches off after the carpal tunnel but can branch within the tunnel and continue with the main nerve (subligamentous) or perforate the transverse carpal ligament (transligamentous). The thenar branch generally stems from the radial side of the nerve, but anomalous branches from the ulnar aspect that cross over the top of the nerve have been described.
Although there are usually no major vessels in the carpal tunnel proper, there are several nearby that may be injured during release. The ulnar artery runs through the Guyon canal with the ulnar nerve and is usually ulnar to the hook of the hamate but is often found radial to the hamate, putting it at risk. The superficial palmar arch is the transverse anastomosis between the ulnar and superficial radial arteries in the palm and lies in a fat pad 5 mm distal to the edge of the transverse carpal ligament. There may also be an anomalous persistent median artery that travels with the median nerve.
Intraoperative complications
The normal anatomy and common anatomic variants of the volar palm and wrist have been well described, and this understanding contributes to the overall low rates of intraoperative complications. Permanent injury to the palmar cutaneous branch, thenar branch, and common digital nerves occur in only 0.03%, 0.01%, and 0.12% of cases, respectively. Injury to the median nerve proper occurs in 0.06% of cases. Risk of nerve injury has been found to be higher in patients undergoing endoscopic CTR compared with open, though most are temporary neurapraxias.
The palmar cutaneous branch of the median nerve may be injured during superficial skin dissection or while releasing the proximal portion of the transverse carpal ligament with scissors or an endoscopic device. Nerve injury can lead to persistent paresthesias or painful neuroma formation.
If surgical dissection is taken too far distally, the common digital nerves may be injured. Similar to the palmar cutaneous branch, damage to these nerves can result in persistent paresthesias or the formation of painful neuromas. In addition, innervation to the first and second lumbricals may be compromised, potentially leading to weakened metacarpophalangeal flexion and interphalangeal extension of the index and long fingers.
The thenar branch may be damaged by surgical dissection distal to the carpal tunnel or may be encountered proximally beneath the transverse carpal ligament, piercing the ligament, or crossing the carpal tunnel in the case of a subligamentous, transligamentous, or ulnar-originating variant. Loss of function of the thenar branch causes weakness of thumb abduction and apposition, leading to markedly decreased grip strength and loss of hand function. Careful distinction must be made, however, between preexisting thenar atrophy from carpal tunnel syndrome and new or worsening dysfunction after iatrogenic injury.
Injury to the median nerve proper may occur during incision of the transverse carpal ligament, as it is the most superficial structure within the carpal tunnel. The nerve is mixed, containing both motor and sensory fibers, so injury may present with a variable pattern of deficit. The nerve may also be damaged during intraneural dissection while attempting to release fascicles from an area of internal scarring. In addition to direct injury, this procedure may lead to recurrence of more severe scarring and should not be done routinely.
While attempting to avoid the branches of the median nerve, which usually reside on the radial side of the carpal tunnel, surgeons may err to the ulnar side of the tunnel, increasing the risk of injury to the contents of the Guyon canal. The ulnar nerve is inured in 0.03% of cases. Injury to the deep motor branch may occur, leading to loss of innervation to most of the intrinsic muscles of the hand. These muscles include the ulnar 2 lumbricals, the dorsal and palmar interosseous muscles, the abductor digiti minimi, the opponens digiti minimi, and the flexor digiti minimi. Loss of the intrinsic musculature can result in ulnar clawing with hyperextension of the metacarpophalangeal joints and flexion of the interphalangeal joints of the fourth and fifth digits. Patients may also have weakened or absent finger abduction.
Also within or superficial to the Guyon canal, the ulnar artery may be damaged by an incision placed too far ulnarly. If patients have an incomplete arch and, thus, no collateral circulation from the radial artery, loss of the ulnar artery would lead to ischemia of the ulnar side of the hand. In either case, damage to the artery could result in serious bleeding. Furthermore, the injury might not be appreciated until after the wound was closed if a tourniquet is used, complicating its diagnosis and management.
As the superficial palmar arch lies just distal to the transverse carpal ligament and is obscured in fat, it is vulnerable to injury and is damaged in 0.1% of CTRs. Damage to the arch is unlikely to cause ischemia but again may cause significant bleeding when the tourniquet is released.
Injury to flexor tendons occurs in 0.1% of cases and generally involves a partial tenotomy as opposed to a complete transection. This injury may leave the flexor tendons more prone to rupture in the future and may also lead to adhesions and triggering.
Postoperative complications
In the absence of technical errors during the surgery, patients may still have complications after CTR, including infection, postoperative pain, and tendon problems. As with most soft tissue surgeries of the hand, postoperative wound infection is rare after CTR, occurring in only 0.36% of cases. Most of these are superficial, with only 0.13% of cases having deep infections.
After CTR, some patients may develop pain in the area of the scar that can be invoked by pressure or light touch. Scar tenderness is less common after endoscopic release compared with open and more common in patients with depressive symptoms. Although most of these resolve spontaneously within a few months, some patients do have more persistent pain. This pain may be due to a failure to protect the crossing cutaneous nerve branches or from adhesions to the median nerve.
Patients may also develop pain in the thenar and/or hypothenar eminence that is worse with pressure or grasping. The cause of this so-called pillar pain is unknown but may be due to postoperative swelling or temporary instability of the insertions of the thenar and hypothenar musculature on the transverse carpal ligament. Nearly all cases resolve spontaneously in 6 to 9 months. There is no difference in the rates of pillar pain between patients undergoing open or endoscopic release.
Postoperative hypothenar pain that does not resolve may localize to the pisotriquetral joint. The pisiform is stabilized by the flexor carpi ulnaris and abductor digiti minimi ulnarly and the transverse carpal ligament radially and may be destabilized after transection of the ligament in certain patients with preexisting chondromalacia or subluxation of pisotriquetral joint, causing pain. The pain will intensify with pressure on pisotriquetral joint and flexion, extension, or ulnar deviation of the wrist. Patients will experience temporary pain relief with intra-articular anesthetic injection. Surgical excision of the pisiform can provide permanent relief.
Complex regional pain syndrome (formerly known as causalgia and reflex sympathetic dystrophy) may rarely occur after CTR without any clear predisposing factors. Patients may have a constellation of sensory, motor, vasomotor, and pseudomotor complaints. Treatments include hand therapy; medications, such as gabapentin, antidepressants, and bisphosphonates; and interventions including sympathetic blocks and botulinum toxin injections. Referral to a pain specialist should be considered early for these patients as well as careful evaluation for iatrogenic nerve injury.
In addition to pain, patients may have mechanical symptoms related to the flexor tendons contained in the carpal tunnel after release of the transverse carpal ligament. Damage to the tendons during release may cause inflammation and adhesions leading to triggering at the wrist. Patients may also develop triggering at the A1 pulleys, which may be due to overloading after loss of the pulley effect of the transverse carpal ligament. Alternatively, this may simply be unrecognized or new-onset stenosing tenosynovitis as carpal tunnel syndrome and trigger fingers are commonly seen together. Patients may also rarely have bowstringing of the flexor tendons with wrist flexion or symptomatic subluxation of the FDS to the ring and small finger over the hook of the hamate.
Treatment failure
After CTR, many patients feel immediate relief, particularly of their nocturnal symptoms. However, particularly in cases whereby the median nerve has been severely compressed for many years, symptoms of numbness may not begin to improve for 6 months and may never completely resolve. Patients need to be counseled on this possibility before CTR. If patients have no improvement in symptoms after 12 months or have initial improvement in symptoms followed by clinical deterioration, they may be considered to have failed treatment. Failure of primary CTR occurs rarely but has been reported in 7% to 25% of patients in some series with approximately 5% to 12% requiring secondary surgery. Causes of treatment failure can be thought of in 3 categories: incomplete release, recurrent compression, and incorrect diagnosis.
Incomplete release of the transverse carpal ligament proper (usually at the distal end), the flexor retinaculum distally, or the antebrachial fascia proximally can cause persistent carpal tunnel syndrome and is the most common reason for reoperation. Although there has been controversy about different surgical techniques, a recent meta-analysis found no difference in the rates of persistent symptoms between patients undergoing open or endoscopic release.
Some patients may have good improvement of their symptoms initially, only to have them recur in the months after surgery. This pattern accounts for nearly 20% of revision surgeries and is more common in patients with diabetes and hypertension. Early recurrence may be due to incomplete release as the unreleased structure becomes a new site of nerve compression. Late recurrence is thought to be due to dense scar formation from the cut ligament ends that can entrap the intact nerve. The nerve itself is uninjured but is encased in fibrous tissue for the length of the ligament and, occasionally, proximally into the forearm. This extraneural scarring impedes gliding of and blood flow to the nerve, in addition to mechanical compression ( Fig. 2 ). To avoid this, some authors recommend splinting the wrist in slight extension after CTR to keep the nerve seated in the tunnel and away from the cut ligament ends.
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