eMedicine Specialties > Orthopedic Surgery > Hand & Upper Extremity
Carpal Tunnel Syndrome
Updated: Aug 12, 2008
Introduction
Carpal tunnel syndrome (CTS) is the most commonly diagnosed and treated entrapment neuropathy. The syndrome is characterized by pain, paresthesia, and weakness in the median nerve distribution of the hand. Surgical and nonsurgical treatments exist that can produce excellent outcomes for patients.
For excellent patient education resources, visit eMedicine's Hand, Wrist, Elbow, and Shoulder Center and Arthritis Center. Also, see eMedicine's patient education article Carpal Tunnel Syndrome.
Related eMedicine topics:
Carpal Tunnel Syndrome [Emergency Medicine]
Carpal Tunnel Syndrome [Physical Medicine and Rehabilitation]
Carpal Tunnel Syndrome [Radiology]
Related Medscape topics:
Resource Center Joint Disorders
Resource Center Pain Management: Pharmacologic Approaches
Resource Center Rheumatoid Arthritis
Specialty Site Orthopaedics
History of the Procedure
In 1854, Sir James Paget first reported median nerve compression at the wrist following a distal radius fracture.1 In 1880, James Putnam presented the first series of patients with pain and paresthesia in the median nerve distribution of the hand. In 1913, Pierre Marie and Charles Foix described the pathology of median nerve compression underneath the transverse carpal ligament (TCL).2 In 1933, Sir James Learmonth reported the first TCL release to treat median nerve compression at the wrist.3 Since these early reports, much work has described the signs and symptoms of CTS, as well as its treatments.
Frequency
Carpal tunnel syndrome (CTS) is common in the general population.4 It has previously been reported with acute onset following trauma to the wrist; it has also been detailed as a gradual progression of symptoms typically occurring in women who are in the late middle-aged years of life. A new population at risk has been reported to be industrial workers whose hands and wrists are subjected to repetitive motion and trauma.5,6
Controversy exists regarding the clinical and electrophysiologic findings necessary to diagnose CTS. Despite this controversy, several surveys have been conducted to determine the prevalence of CTS in the general population. In the Netherlands, the prevalence of undetected CTS was 5.8% in women and 0.6% in men.4 In Sweden, the overall prevalence of CTS in the population was 2.7%. These prevalence rates were based on clinical and electrophysiologic criteria and probably represent minimum prevalence rate estimates.
Etiology
The etiology of carpal tunnel syndrome (CTS) is multifactorial, with local and systemic factors contributing to varying degrees. Symptoms of CTS are a result of median nerve compression at the wrist, with ischemia and impaired axonal transport of the median nerve across the wrist.7 Compression results from elevated pressures within the carpal canal.
Elevated pressures can develop within the carpal canal even though the canal is not a separate, closed compartment within the upper extremity. Direct pressure or a space-occupying lesion within the carpal canal can increase pressure on the median nerve and produce CTS. Fracture callus, osteophytes, anomalous muscle bodies, tumors, hypertrophic synovium, and infection, as well as gout and other inflammatory conditions, can produce increased pressure within the carpal canal. Extremes of wrist flexion and extension also elevate pressure within the carpal canal.
Compression of a nerve affects intraneural blood flow.8,9,10 Pressures as low as 20-30 mm Hg retard venular blood flow in a nerve. Axonal transport is impaired at 30 mm Hg. Neurophysiologic changes manifested as sensory and motor dysfunction are present at 40 mm Hg. Further increases in pressure produce increasing sensory and motor block. At 60-80 mm Hg, complete cessation of intraneural blood flow is observed. In one study, the carpal canal pressures in patients with CTS averaged 32 mm Hg, compared with only about 2 mm Hg in control subjects.8
The double crush syndrome, in which there is pressure on the median nerve at a second site (remote from the wrist), can further lower the median nerve's pressure threshold for producing symptoms of CTS. If a nerve is compressed at multiple sites, traction within the nerve with joint motion may be produced. In addition to pressure, traction or stretch has been demonstrated to produce alterations in intraneural circulation. Elongation of only 8% can impair venular flow, and all intraneural microcirculation can cease at 15% nerve elongation.
Many systemic conditions are strongly associated with CTS. These conditions may directly or indirectly affect microcirculation, pressure thresholds for nerve conduction, nerve cell body synthesis, and axon transport or interstitial fluid pressures. Perturbations in the endocrine system, as observed in individuals with diabetes and hypothyroidism and in women who are pregnant, are linked to CTS. Conditions affecting metabolism (eg, alcoholism, renal failure with hemodialysis, mucopolysaccharidoses) also are associated with CTS.
The international debate regarding the relationship between CTS and the performance of repetitive motion and work is ongoing.5,6 The Occupational Safety and Health Administration (OSHA) has adopted rules and regulations regarding cumulative trauma disorders. Occupational risk factors — repetitive tasks, force, posture, and vibration — have been cited. However, the American Society for Surgery of the Hand has issued a statement that the current literature does not support a causal relationship between specific work activities and the development of diseases such as CTS.
Psychosocial and socioeconomic issues are increasingly being studied. In a study of risk factors for CTS in women, the greatest risk factor was found to be a previous history of another musculoskeletal complaint.11 Perceptions of health and tolerance to pain also may influence the development of CTS.
Pathophysiology
The pathophysiology of carpal tunnel syndrome (CTS) is typically demyelination. In more severe cases, secondary axonal loss may be present. The most consistent findings in biopsy specimens of tenosynovium from patients undergoing surgery for idiopathic CTS have been vascular sclerosis and edema.12 Localized amyloid deposition in the tenosynovium also has been reported in persons with idiopathic CTS. Inflammation, specifically tenosynovitis, is not part of the pathophysiologic process in chronic, idiopathic CTS.
Presentation
Acute carpal tunnel syndrome (CTS) can develop following a major trauma to the upper extremity (typically a distal radius fracture), a carpal dislocation, or a crush injury. Swelling, pain, and paresthesia in the median nerve distribution of the hand (palmar and radial) are observed.
In the more common idiopathic or chronic CTS, symptoms are more gradual in onset.13 Pain and paresthesia in the median nerve distribution of the hand are common. Symptoms are often worse at night and can wake a patient from sleep. As the condition worsens, daytime paresthesia becomes common and is often aggravated by daily activities, such as driving, combing the hair, and holding a book or phone. Weakness can be present. With long-standing or severe cases of CTS, thenar atrophy is frequently observed.
Because of the motor and sensory disturbances, manual dexterity is diminished, and difficulty with such daily activities as buttoning clothes and holding small objects is often encountered. Pain and paresthesia can also occur proximally in the forearm, elbow, shoulder, and neck in up to one third of patients. Pain and paresthesia in the hand are not always isolated to median nerve distribution but can involve the ulnar aspect or the entire hand.
Indications
Acute carpal tunnel syndrome (CTS) can be thought of as a compartment syndrome of the carpal canal, and decompression should be performed as soon as possible, assuming that reduction of associated fractures or dislocations or removal of tight splints does not relieve the symptoms. Other medical and surgical factors may impact the opportunity to operate emergently, but relieving pressure on the median is a priority in order to reduce the risk of permanent nerve injury. Acute CTS can be diagnosed through history and physical examination alone. Electrophysiologic studies are not required. Sometimes, carpal canal pressure measurements are made to help support the diagnosis of acute CTS, with pressures greater than 30 mm Hg being consistent with the diagnosis.
Chronic CTS presents over time and is treated in an operative and nonoperative fashion. Patients with milder symptoms and shorter nerve conduction delays on electrodiagnostic studies respond most favorably to nonoperative treatments. Patients with more severe symptoms — duration longer than 1 year, weakness, atrophy, radial-sided hand numbness, 2-point discrimination greater than 6 mm, and longer nerve conduction delays — often do not benefit from nonoperative care. Failure or findings that are predictive of nonoperative treatment failure are indications for surgical treatment of CTS.
Relevant Anatomy
The carpal canal is a fibro-osseous tunnel at the wrist through which 9 flexor tendons and the median nerve pass.14 The carpal bones define the dorsal aspect of the carpal canal and are shaped in a concave arch. The palmar aspect of the carpal canal is defined by the TCL, which bridges the 2 sides of the carpal arch. Intrinsic and extrinsic ligaments of the wrist and hand further stabilize the carpal bones. The carpal canal is narrowest at the level of the hook of the hamate, where the canal averages 20 mm in width.
The TCL attaches to the scaphoid tuberosity and trapezial crest on the radial side of the wrist, as well as to the pisiform and hook of the hamate on the ulnar side of the wrist (see Image 1). The TCL is 1.5 mm thick and 21.7 mm in length on average. Proximally, the TCL is a continuation of the antebrachial fascia in the forearm, and distally, the TCL attaches to the fibers of the midpalmar fascia. The TCL is under tension and helps to maintain the carpal arch. It serves as a retinacular pulley for the flexor tendons. Cutting the TCL increases the volume of the carpal canal. Cutting the TCL has also been postulated to alter the kinematics of the carpus, risk bowstringing of the flexor tendons, and decrease grip strength.
A combination of the lateral (C6-7) and medial (C8-T1) cords of the brachial plexus forms the median nerve. At the wrist and into the palm, the median nerve divides into terminal motor and sensory branches, with some anatomic variability. The variability is caused in part by the branching point of the recurrent motor branch. An extraligamentous pattern, with a branching point distal to the TCL, is the most common. The recurrent motor branch can also divide from the median nerve underneath the TCL in a subligamentous fashion; it can then either wrap around the distal end of the TCL or pass directly through the TCL to innervate the thenar muscles. Other less common patterns, such as a branch point proximal to the TCL, exist as well. These variations can have major surgical implications.
The ulnar nerve is the other major motor and sensory nerve of the hand. The ulnar nerve does not pass through the carpal canal but instead goes through the Guyon canal, which is located adjacent to the carpal canal, at the wrist. Division of the TCL will change the morphology of the Guyon canal from triangular to ovoid.
See also the following related eMedicine topic:
Carpal Bone Injuries
Contraindications
No specific contraindications exist for surgical treatment of carpal tunnel syndrome (CTS). Medical conditions should be stabilized prior to surgery. Pregnancy should be allowed to proceed to term, because CTS often resolves after the pregnancy. Unrealistic expectations can influence surgical outcomes, and risk factors for poor outcomes should be sought pre-operatively. Individuals with severe CTS should be cautioned that their numbness may persist, at least to some degree, despite a complete surgical release. Patients receiving worker's compensation have a lower return-to-work rate. A greater preference for improved strength pre-operatively also has been associated with lower satisfaction.15
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Further Reading
Keywords
carpal tunnel syndrome, carpel tunnel syndrome, carpal tunnel surgery, carpal, carpal tunnel, repetitive stress injury, cumulative trauma disorder, median nerve entrapment, median neuropathy, mononeuropathy, nerve compression syndrome, CTS, median nerve compression at the wrist, double crush syndrome, carpal canal, median nerve
