eMedicine Specialties > Radiology > Musculoskeletal

Carpal Tunnel Syndrome

Author: Patrick D Browning, MA, MD, Partner, Redwood Regional Medical Group; Clinical Staff, University of California at Davis Medical Center; Founder and Principle Partner, Conceptus Partners Consulting
Contributor Information and Disclosures

Updated: Apr 16, 2009

Introduction

Background

Carpal tunnel syndrome (CTS) is defined as the impairment of motor and/or sensory function of the median nerve as it traverses through the carpal tunnel.

Recommendation 1

A course of nonoperative treatment is an option in patients diagnosed with carpal tunnel syndrome (CTS). Early surgery is an option when there is clinical evidence of median nerve denervation or the patient elects to proceed directly to surgical treatment. (Grade C, level V)

Recommendation 2

We suggest another nonoperative treatment or surgery when the current treatment fails to resolve the symptoms within 2-7 weeks. (Grade B, level I and II)

Recommendation 3

We do not have sufficient evidence to provide specific treatment recommendations for carpal tunnel syndrome when found in association with the following conditions: diabetes mellitus, coexistent cervical radiculopathy, hypothyroidism, polyneuropathy, pregnancy, rheumatoid arthritis, and carpal tunnel syndrome in the workplace. (Inconclusive, No evidence found)

Recommendation 4a

Local steroid injection or splinting is suggested when treating patients with carpal tunnel syndrome, before considering surgery. (Grade B, level I and II)

Recommendation 4b

Oral steroids or ultrasound are options when treating patients with carpal tunnel syndrome. (Grade C, level II)

Recommendation 4c

We recommend carpal tunnel release as treatment for carpal tunnel syndrome. (Grade A, level I)

Recommendation 4d

Heat therapy is not among the options that should be used to treat patients with carpal tunnel syndrome. (Grade C, level II)

Recommendation 4e

The following treatments carry no recommendation for or against their use: activity modifications, acupuncture, cognitive behavioral therapy, cold laser, diuretics, exercise, electric stimulation, fitness, Graston instrument, iontophoresis, laser, stretching, massage therapy, magnet therapy, manipulation, medications (including anticonvulsants, antidepressants, and nonsteroidal anti-inflammatory drugs [NSAIDs]), nutritional supplements, phonophoresis, smoking cessation, systemic steroid injection, therapeutic touch, vitamin B6 (pyridoxine), weight reduction, yoga. (Inconclusive, level II and V)

Recommendation 5

We recommend surgical treatment of carpal tunnel syndrome by complete division of the flexor retinaculum regardless of the specific surgical technique. (Grade A, level I and II)

Recommendation 6

We suggest that surgeons do not routinely use the following procedures when performing carpal tunnel release: skin nerve preservation (Grade B, level I); epineurotomy (Grade C, level II)

The following procedures carry no recommendation for or against use: flexor retinaculum lengthening, internal neurolysis, tenosynovectomy, ulnar bursa preservation. (Inconclusive, level II and V)

Recommendation 7

The physician has the option of prescribing preoperative antibiotics for carpal tunnel surgery. (Grade C, level III)

Recommendation 8

We suggest that the wrist not be immobilized postoperatively after routine carpal tunnel surgery. (Grade B, level II)

We make no recommendation for or against the use of postoperative rehabilitation. (Inconclusive, level II)

Recommendation 9
We suggest physicians use one or more of the following instruments when assessing patients’ responses to CTS treatment for research:

• Boston Carpal Tunnel Questionnaire (disease-specific)
• DASH—Disabilities of the Arm, Shoulder, and Hand (region-specific; upper limb)
• MHQ—Michigan Hand Outcomes Questionnaire (region-specific; hand/wrist)
• Patient Evaluation Measure (region-specific; hand)
• SF-12 or SF-36 Short Form Health Survey (generic; physical health component for global health impact) (Grade B, level I, II, and III)

Pathophysiology

The most common cause of carpal tunnel syndrome is chronic repetitive stress upon the carpal tunnel, and thus the median nerve within it. This stress can result from abnormal positioning of the wrist as occurs during typing, repeated flexion or extension stress (eg, carpentry, carpet weaving), or rapid jarring of the wrist (eg, operating a jackhammer). Fractures or dislocations of the wrist, soft-tissue injuries or abnormalities, infection, infiltrative disease, or intraneural hemorrhage also may cause CTS.

Frequency

United States

It has been estimated that 4-10 million persons in the United States have carpal tunnel syndrome.² A prevalence of 56.77% has been reported in workers who hold data entry/typing positions.³  As many as 50% of cases are bilateral.

Mortality/Morbidity

• Mortality: The likelihood of mortality resulting from carpal tunnel syndrome or complications of conservative treatment is exceedingly low. A small risk of death is associated with attempted surgical relief. Deaths are likely to be associated with the patient's prior health status and complications related to anesthesia. Mortality risk has no doubt decreased with the increasing acceptance of endoscopic techniques for carpal tunnel release and the subsequent decrease in both general anesthesia use and time under anesthesia.
• Morbidity: Morbidity of CTS is extremely variable and depends highly on duration and severity at presentation, cause, success of conservative therapy (if any), general preoperative health and attitude of the patient, type of surgical release, and numerous psychosocial factors postoperatively. Throughout the medical literature, a large number of articles have shown a correlation between these factors and treatment outcome. Conservative therapy failure rates from 1-50% and surgical failure rates from 2-31% have been reported.

Sex

There is a strong female predominance with a male-to-female ratio of 1:3-5.

Age

Rates of CTS increase with age, peaking in middle age (45-54 years) and then declining.³ However, several other factors influence age of onset.

Anatomy

Knowledge of carpal tunnel anatomy is important in understanding the pathophysiology of the syndrome. The carpus (composed of the carpal bones) has a concave bony contour on its flexor surface and is covered by the flexor retinaculum. This structure forms the floor and walls of the carpal tunnel and the rigid flexor retinaculum forms its roof. The flexor retinaculum, or transverse carpal ligament, attaches to the scaphoid tubercle, the ridge of the trapezium, and the ulnar aspect of the hook of the hamate and pisiform (see Images 1 through 4 ).

All 8 flexor tendons are covered with a common synovial sheath. The flexor pollicis longus tendon, contained in its own synovial sheath, is located on the radial aspect of the flexor tendons within the carpal tunnel. The median nerve resides just under the flexor retinaculum and abuts its inner surface. It is located on the lateral side of the flexor digitorum superficialis between the flexor tendon of the middle finger and the flexor carpi radialis.

The nerve is round or oval at the level of the distal radius; it becomes elliptical at the pisiform and hamate. Both its position and its morphology are altered during flexion and extension. With the wrist in a neutral position, the median nerve lies anterior to the flexor digitorum superficialis tendon of the index finger or posterolaterally between the flexor digitorum tendon of the index finger and flexor pollicis longus tendon.

The nerve is forced against the transverse carpal ligament in dorsiflexion or palmoflexion of the wrist. In wrist extension, the median nerve assumes a more anterior position, deep to the flexor retinaculum and superficial to the flexor digitorum superficialis tendon of the index finger. In wrist flexion, the median nerve can be found anterior to the flexor retinaculum or between the flexor digitorum superficialis tendons of the index finger and thumb or middle and ring fingers. In the flexed position, the elliptical shape of the median nerve flattens.

Alteration of median nerve morphology is less pronounced in wrist extension. As much as 20 mm of excursion of the median nerve can occur and frictional forces between the median nerve, adjacent tendons, and the transverse carpal ligament compound the potential irritation caused by morphologic plasticity during flexion and extension.

Presentation

Clinical presentation typically includes pain and numbness, often with increased nocturnal pain and/or burning. The thumb, index finger, middle finger, and radial side of the ring finger are most commonly affected.

• Sensory findings range from minimal loss of sensation to complete anesthesia.
• Muscular atrophy and function loss are late findings, although the abductor pollicis brevis muscle may show earlier involvement.
• Direct pressure measurement in patients with carpal tunnel syndrome reveals increased pressures in the carpal canal (up to 32 mm Hg, compared with 2.5 mm Hg in asymptomatic patients). Pressure changes also can be recorded in extremes of dorsiflexion and palmoflexion.
• Axial CT studies of patients with carpal tunnel syndrome reveal a decrease in the cross-sectional area of the carpal canal. Various processes can cause decreased volume of the carpal tunnel, including infections, tenosynovitis of the flexor tendons, Colles fracture, and fracture-dislocation of the radiocarpal, carpal, and carpometacarpal joints. These processes also may cause posttraumatic scarring, fibrosis, or both. Inflammatory processes causing decreased volume within the carpal tunnel include rheumatoid arthritis, gout, pseudogout, amyloid deposition, and granulomatous infection. All of these may produce a tenosynovitis with hyperplastic synovium.
• Tumors of the median nerve (eg, neuromas, fibromas, hamartomas) and tumors extrinsic to the median nerve (eg, ganglion cysts, lipomas, hemangiomas) can create space-occupying masses within the carpal canal.
• Disorders that enlarge the normal structures within the carpal tunnel and may increase the risk for carpal tunnel syndrome include acromegaly, hypothyroidism, pregnancy, diabetes mellitus, and systemic lupus erythematosus. Both the frequency and the severity of carpal tunnel syndrome may be greater in persons with metabolic syndrome.⁴
• For reasons not yet understood, volumetric increases occasionally are seen in women who are postmenopausal.
• Developmental causes of increased carpal tunnel pressures include a persistent median artery, hypertrophied lumbricals, anomalous muscles, and a distal positioning of the flexor digitorum superficialis muscle. All of these conditions can produce carpal tunnel syndrome as a result of compression or of irritation, edema, and subsequent swelling of the median nerve.
• Median nerve damage proximal to the carpal tunnel is an important consideration in the differential diagnosis of carpal tunnel syndrome. Such damage may affect the palmocutaneous branch of the median nerve, thereby causing weakness of the corresponding flexor muscles of the forearm, including the flexor pollicis longus. This contrasts with carpal tunnel syndrome, in which the terminal phalanx of the thumb demonstrates normal flexion without motor impairment. Although the median nerve is composed of both sensory and motor nerve fibers, sensory fibers predominate at the level of the carpal tunnel, explaining the initial findings of sensory deficit and numbness.
• As the disease progresses, wasting and weakness of the thenar muscles occur, with decreased ability to oppose the thumb and anesthesia of the 3.5 digits on the radial side of the hand. No anesthesia of the thenar eminence occurs because the cutaneous branch of the median nerve supplies this structure.

Preferred Examination

The clinical examination is the most important part of the evaluation for CTS. Guidelines regarding the clinical diagnosis have been issued by the American Academy of Orthopaedic Surgeons⁵ and the Work Loss Data Institute.³

A positive Tinel sign (tingling in the digits supplied by the median nerve) is an indication of nerve entrapment. The Phalen test, tourniquet compression, and direct compression also are used to detect signs of median nerve entrapment. A positive flick sign (having to shake the hand for relief) is suggestive of CTS.³  
 
Electromyography (EMG) and nerve conduction studies are useful for confirming the diagnosis of CTS and are most helpful in localizing the level and determining the severity of median nerve compression. A prolonged sensory conduction or distal motor latency test provides quantitative information in this regard. Electrodiagnostic tests such as EMG and nerve conduction studies are 85-90% accurate in patients with carpal tunnel syndrome, with a false-negative rate of 10-15%. Therefore, in cases of clinically symptomatic CTS with normal EMG and conduction findings, radiology studies can have a strong complementary role in diagnosis.⁶

Of radiologic imaging methods, MRI has consistently shown the greatest sensitivity and specificity in the diagnosis and evaluation of carpal tunnel syndrome.

Plain radiographs have no role in the evaluation of CTS except for their ability to show the anatomic relationship of the carpal bones and evidence of severe prior trauma or fractures.

Helical CT is more sensitive than plain radiography in revealing subtle bony trauma and misalignments and can be used to measure the cross-sectional area of the carpal tunnel.

Ultrasound can be useful in the evaluation of soft tissues of the carpal tunnel and the median nerve. An increasing number of studies have supported early suggestions that measurement of the cross-sectional area and morphology of the median nerve with high-resolution sonography compares favorably with physical examination alone; thus, this technique is proving to be a useful tool for diagnosis. Additionally, ultrasound may prove to be a beneficial adjunct in the conservative treatment of CTS.

Limitations of Techniques

As noted above, electrodiagnostic tests such as EMG and nerve conduction studies are 85-90% accurate in patients with carpal tunnel syndrome, with a false-negative rate of 10-15%.

Plain radiographs usually do not reveal ligamentous or soft tissue abnormalities but may be useful to exclude frank fractures or chronic degenerative/posttraumatic morphologic abnormalities.

CT does not reveal ligamentous or soft tissue abnormalities to any degree. Axial scanners are even more limited since they do not allow adequate multiplanar or 3-dimensional reconstructions.

Ultrasound is operator and equipment dependent. Although musculoskeletal ultrasound using high-frequency transducers is widely used in Europe, familiarity with and training in the performance and interpretation of carpal tunnel ultrasonography is still variable, more so in the United States.

MRI is useful for the evaluation of all of the intrinsic structures of the wrist (including the carpal bones) but may not be widely available, is technique and equipment dependent, can require up to 45 minutes to complete an examination, and has a number of contraindications (eg, cardiac pacemakers, older aneurysm clips, new stents or aortic valves, ferromagnetic ocular fragments).

Patient Education: 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.

Differential Diagnoses

Other Problems to Be Considered

Cervical radiculopathy
Proximal median nerve damage
Arthritic conditions
Muscle and nerve diseases

 

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