Author
Lars Grimm, MD, MHS
House Staff
Department of Internal Medicine
Duke University Medical Center
Durham, North Carolina
Lars Grimm, MD, MHS, has disclosed no relevant financial relationships.
Editor
David A. Fuller, MD
Assistant Professor of Surgery
Director of Hand Surgery
University of Medicine and Dentistry of New Jersey
Cooper University Hospital
David A. Fuller, MD, has disclosed no relevant financial relationships.
Carpal tunnel syndrome is the impairment of motor and/or sensory function of the median nerve as it traverses through the carpal tunnel. It is the most commonly diagnosed and treated entrapment neuropathy, affecting millions of Americans. Intrinsic swelling or extrinsic compression of the nerve causes progressively worsening symptoms that can be debilitating and prevent individuals from engaging in hobby or work activities. The image shown is of an individual who has undergone bilateral carpal tunnel repair surgery with a flexor retinaculum release on the left and ulnar nerve mobilization on the right. Image courtesy of Wikimedia Commons.
An estimated 4-10 million people in the United States suffer from carpal tunnel syndrome, with a prevalence of approximately 50 cases per 1000 subjects in the general population. Up to half of cases are bilateral. There is a roughly 4 to 1 predominance for females, with a peak incidence at 50 years of age. The vast majority of cases requiring days away from work are for non-Hispanic whites, as shown. Image courtesy of the Centers for Disease Control.
Carpal tunnel syndrome is caused by compression of the median nerve from elevated pressure within the carpal canal. A number of different etiologies have been identified to cause increased pressure, including fracture callus, osteophytes, anomalous muscle bodies, tumors, hypertrophic synovium, infection, gout, and other inflammatory conditions. Systemic conditions such as diabetes mellitus, hypothyroidism, pregnancy, alcoholism, renal failure, and mucopolysaccharidoses have also been associated with carpal tunnel syndrome either directly or indirectly. Normal pressures are less than 20 mm Hg. Venular flow is retarded at 20-30 mm Hg, axonal transport is impaired at 30 mm Hg, sensory and motor dysfunction occurs at 40 mm Hg, and complete cessation of blood flow occurs at 60-80 mm Hg. Image courtesy of Wikimedia Commons.
The typical clinical presentation is a patient complaining of hands that fall asleep or things slipping from fingers without notice. Nighttime symptoms and symptomatic relief with hand shaking are more specific to carpal tunnel syndrome. Pain and numbness are typically in the thumb, index finger, middle finger, and radial side of the ring finger. Muscular atrophy of the thenar muscles and function loss are late findings (black arrow). Autonomic symptoms include tightness or a swollen feeling in the hands, or a sense of temperature changes.
A number of physical examination tests have been advocated, but most have limited sensitivity and specificity. They include the Hoffman-Tinel sign (tingling with tapping on the median nerve), Phalen sign (tingling with full wrist flexion), and carpal compression test (reproduction of symptoms with firm pressure on the carpal tunnel). Electromyography and nerve conduction studies are useful for confirming the diagnosis of carpal tunnel syndrome, with an accuracy of 85%-90%. The image shown demonstrates sensory nerve delayed conduction of 29.8 and 25.5 m/sec for digits 3 and 1, respectively (underlined), compared to a normal rate of > 50 m/sec.
No imaging studies are considered routine for the diagnosis of carpal tunnel syndrome. Radiography is the most commonly used modality, but can only identify fractures or degenerative/posttraumatic boney changes. High-resolution ultrasonography (7-15 MHz) can be used to noninvasively evaluate the median nerve and adjacent tendons. Compared to magnetic resonance imaging (MRI), ultrasound is faster and less expensive, while also evaluating blood flow and providing dynamic images. Good correlation between the measured ultrasound area of the median nerve and electromyography studies has been established.
The image shown is a 5- to 12-MHz ultrasound scan of a normal wrist at the proximal level of the carpal tunnel delimited by the pisiform (P) and scaphoid (S). The flexor retinaculum (open arrowheads) forms the roof of the carpal tunnel, overlying the median nerve (MN). Ulnar nerve (U), ulnar artery (solid arrowhead), and flexor pollicis longus tendon (*) are shown for reference.
MRI is the most sensitive and specific modality to detect carpal tunnel syndrome, but is not routinely ordered unless a space-occupying lesion in the carpal tunnel is suggested. It allows for excellent visualization of the soft tissue structures and associated inflammatory changes. Common findings are swelling of the median nerve, flattening of the median nerve, palmar bowing of the flexor retinaculum, and changes in the T2-weighted signal intensity of the median nerve. MRI can also depict space-occupying lesions, such as neuromas, ganglion cysts, lipomas, and hemangiomas.
The axial fast spin-echo T2-weighted MRI with fat saturation shows increased signal within the median nerve (white arrow). There is a slight increase in the cross-sectional area, consistent with mild inflammation.
One of two abnormal patterns of median nerve enhancement is typically identified. The nerve will show increased signal if there is hypervascular edema or decreased signal if there is nerve ischemia.
The fast spin-echo T2-weighted MRI shows increased signal within the median nerve (white arrow), indicating moderate disease. A small amount of fluid, visible as increased signal on T2 imaging, is present within the carpal tunnel (red arrow), a secondary sign of inflammation.
MRI allows for the early detection of subtle changes before they are present on standard radiographs or computed tomography. Preoperative and postoperative images can be compared to evaluate the change in cross-sectional area.
The axial spin-echo T2-weighted MRI shows increased signal and loss of definition of the median nerve (arrow) with surrounding inflammatory changes adjacent to the flexor digitorum superficialis tendon. This is consistent with more advanced disease.
The American Academy of Orthopaedic Surgeons has published detailed guidelines for the treatment of carpal tunnel syndrome. For most patients, initial treatment is nonoperative with surgery reserved for those with signs of nerve denervation. Steroid injections (shown), splinting, therapeutic ultrasound, nonsteroidal anti-inflammatory drugs, and oral steroids are all approved first-line recommendations.
Wrist immobilization with a splint helps to limit symptoms by preventing wrist flexion, which can be especially useful at night. Unfortunately, there is limited evidence that it prevents disease progression. It is mainly limited for use in patients with mild symptoms and has been shown to be effective in reducing symptoms over a period of weeks, but with less impressive results after a year. Image courtesy of Wikimedia Commons.
Carpal tunnel release can be performed either as an open procedure or endoscopically. In an open release, a longitudinal incision is made with the ring finger flexed. Dissection is made down to the transverse carpal ligament, which is dissected under direct visualization. Postoperative treatment is minimal, with splinting not demonstrating any proven benefit.
Endoscopic carpal tunnel surgery involves either a 1- or 2-incision technique. With use of endoscopy, a reverse cutting knife is used to cut the transverse carpal ligament. If visualization is not satisfactory, then the procedure is converted into an open release. Compared to open surgery, the incisions used are much smaller and recovery is faster, although the cost is higher and complications are more frequent. The most common complication is incomplete release of the transverse carpal ligament.
There is controversy regarding the role of repetitive motion and carpal tunnel syndrome in the scientific community. The Occupational Safety and Health Administration (OSHA) has adopted rules and regulations regarding cumulative trauma disorders, with repetitive tasks, force, posture, and vibration cited as risk factors. They also provide extensive guidelines for appropriate ergonomic designs for workers in a wide variety of industries. The use of tools that provide a more natural hand and wrist positioning in people who do highly repetitive tasks such as kitchen work is recommended by OSHA. Image courtesy of Occupational Safety & Health Administration.
Author
Lars Grimm, MD, MHS
House Staff
Department of Internal Medicine
Duke University Medical Center
Durham, North Carolina
Lars Grimm, MD, MHS, has disclosed no relevant financial relationships.
Editor
David A. Fuller, MD
Assistant Professor of Surgery
Director of Hand Surgery
University of Medicine and Dentistry of New Jersey
Cooper University Hospital
David A. Fuller, MD, has disclosed no relevant financial relationships.
