Monday, June 04, 2012

Carpal Tunnel Syndrome - Introduction

Table of Contents

The median nerve travels through a compartment in the wrist called the carpal tunnel. The ligaments that traverse the nerve are not very flexible. Any swelling within the wrist compartment can put excessive pressure on structures such as the blood vessels and the median nerve. Excessive pressure can constrict blood flow and cause nerve damage. The symptoms from the compression cause pain, loss of sensation, and decreased function in the hand.

The Carpal Tunnel Syndrome Process

It is not completely known how the process leading to carpal tunnel syndrome actually evolves, and how nerve conduction (the transmission of the nerve signal) through the wrist changes. In general, carpal tunnel syndrome develops when the tissues around the median nerve swell and press on the nerve. Early in the disorder, the process is reversible. Over time, however, the insulation on the nerves may wear away, and permanent nerve damage may develop.

The following events have been observed in the hands of people with carpal tunnel syndrome:

  • The protective lining of tendons (called the tenosynovium) swells within the carpal tunnel. Some research suggests that this swelling is caused by a buildup of fluid (called synovial fluid) under the lining. Synovial fluid normally lubricates and protects the tendons.
  • The transverse ligament, the band of fibrous tissue that forms the roof over the median nerve, becomes thicker and broader.
  • The swollen tendons and thickened ligament press on the median nerve fibers, just as stepping on a hose slows the flow of water through it. This compression reduces blood flow and oxygen supply to the nerve, while slowing the transmission of nerve signals through the carpal tunnel. Some cases of carpal tunnel syndrome may be due to enlargement of the median nerve rather than compression by surrounding tissues.

The result of these processes is pain, numbness, and tingling in the wrist, hand, and fingers. Only the little finger is unaffected by the median nerve.

Click the icon to see a depiction of carpal tunnel syndrome.

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Review Date: 02/17/2011
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org)