by Dr. Timothy Jameson
Doctor of Chiropractic
Castro Valley, CA

Illustrations by Judie Funicelli. All rights reserved. No duplication of photos or writing can occur without written consent of author.

The following is an exerpt from Dr. Jameson's book Repetitive Strain Injuries: The Complete Guide to Alternative Treatments and Prevention. (Keats Publishing, 1998). © 1998, Dr. Timothy Jameson.

Figure 21 - The Median Nerve shows the location of the carpal tunnel, and figure 22 (above) shows a cross section of the carpal tunnel. Notice on figure 22 how the median nerve, flexor tendons, along with an artery and vein traverse through the small tunnel within the wrist. The carpal bones form a U-shaped tunnel. The bones on either end of this "U" are connected by a tough unyielding ligament known as the flexor retinaculum, or transverse carpal ligament. The symptoms of true CTS are because of compression of the median nerve as it passes through this tunnel. (The reason I state "true CTS" is because of the many conditions that mimic CTS.) Compression of the median nerve is due to a number of factors. The first factor, and probably the most prevalent is inflammation of the flexor tendons.

The hand flexor tendons become inflamed due to overuse. Any occupation or hobby where the hand is contracted in a constant flexed position, or involves constant movement of the hand from extension to flexion (such as in grocery checkers) makes the tendon susceptible to injury. The flexor tendons are surrounded by a synovial sheath, or wrapping, where they pass under the flexor retinaculum. Inside this sheath is a substance called synovium, a lubricant aiding movement of the tendons within the sheath. Inflammation of the tendon leads to enlargement of the tendon/sheath complex due to overproduction of synovium, as well as a degradation of the synovium itself. The synovium transforms into a sticky, viscous compound. This leads to increased friction of the tendon/sheath complex, which instigates more inflammation. This irritation of the tendon and sheath is also known as tenosynovitis. If left untreated, a condition called "trigger finger" or stenosing tenosynovitis can result. (See under separate chapter headings). The enlargement of the tendon-sheath complex exerts pressure upon the median nerve in the uncompromising tunnel causing the symptoms of carpal tunnel syndrome.

A second factor involved in carpal tunnel syndrome is misalignment of the carpal bones. As shown in figure 22, if the carpal bones become misaligned, the transverse carpal ligament becomes taught, narrowing the carpal tunnel. Compression of contents of the carpal tunnel ensues, including the median nerve. Misalignment of the radius and ulna, the two forearm bones, can lead to carpal bones misalignments. In cases of CTS it is common to find the distal end (the end closest to the wrist) of the radius and ulna slightly spread apart from each other, causing stress to the interosseous membrane, the tough ligament that holds joins the two forearm bones together. Combined with this spreading is weakness, irritation, and myofascial trigger points in the pronator quadratus muscle. This muscle is responsible, along with the pronator teres muscle, for turning the palm of the hand downwards (pronation). This spreading is slight, but has a major affect on the carpal tunnel. The radius and ulna are connected to the carpal bones by ligaments, the radial collateral and Ulnar collateral ligaments, respectively. Spreading of the radius and ulna leads to tugging on the carpal bones, and the misalignments mentioned above.

The radius and ulna become misaligned and spread apart from compressive forces translating through the wrist up into the arm. Examples of this are weightlifting with barbells whereby the weight is forced into the wrist and arms. This is common in those who perform "benching" exercises, and "inclines." Pushing activities involving extension of the wrist and pushing with the palm lead to this condition. Any sufferer of carpal tunnel syndrome will tell you how difficult it is to push a grocery cart. This phenomenon is the cause. Chiropractors suffer from CTS because of the compressive forces up the arm from performing spinal adjustments. (I know of a number of chiropractors who had to change their techniques and adjusting style because of carpal tunnel syndrome.) Mail handlers who push large mail carts are susceptible to this forearm problem also. Anyone involved with pushing heavy objects with the hands can be affected by this condition.

A third factor in carpal tunnel syndrome is a combined myofascial syndrome with carpal bone misalignments. If the forearm and hand muscles which attach into the carpal bones are suffering from myofascial syndromes (see chapter under separate heading for more information), they will tighten and shorten, thus pulling on their attachments into the carpals. To be specific, the muscles susceptible to this are the flexor carpi ulnaris and abductor digiti minimi, which both attach into the pisiform bone, and the muscles involved in thumb movement which attach into the carpal bones. Myofascial syndromes in these muscles cause misalignments of the carpals leading to the series of events stated above.

A fourth factor is any occupation that involves direct compression upon the carpal tunnel itself. The major player here is use of a computer mouse. Most people will rest their wrists on mouse pad, and extend the hand and fingers to click the button. This posture puts direct pressure on the area of the carpal tunnel. A prolonged posture such as this will lead to nerve compression. Of course, the same goes for anyone who wrests their wrists on the wrist pad or table top.

A fifth factor is any occupation involving vibration. Laborers using jackhammers, chain-saws, buffers or grinders subject their wrists to excessive vibration. Studies indicate that vibration inhibits blood flow to the nervous tissue and other tissues in the hand. Researchers label this repetitive strain injury into its own classification. I have included a separate chapter on "Hand Arm Vibration Syndrome" which is the result of excessive vibration. This syndrome can lead to a disease called Raynaud's Disease.

The sixth factor is the environmental temperature. People who work in cold environments are much more susceptible to CTS. The cold temperature causes constriction of blood vessels, thus decreases the blood flow to the tissues. The same concept prevails for people who put ice packs on their arms and hands while working at a computer or other repetitive task. The decreased blood flow to the tissues because of the ice pack will predispose the person to increased injury if they attempt to perform repetitive movements with it on. Use ice only during rest, not during activity.

A seventh factor is underlying changes in the carpal bone structure. This may be due to previous wrist fractures which have caused changes to the size and shape of one or more carpal bones, hypertophic (enlargement) changes of the carpal bones due to imposed stresses over a long period of time, and callus formations in and around the bones from healing fractures. Changes to the bones because of pathological processes, such as tumors, must also be considered.

Last but not least, the eighth factor is spinal subluxations. Misalignments or subluxations of the lower cervical spine cause swelling in and around the nerves traveling to the hand. The pinched nerves cause irritation of the muscles and tissues they supply throughout the arm, making the subluxation a primary causative factor in the development of carpal tunnel syndrome. The irritated tissues cause abnormal tensions in the forearm, predisposing the person to developing carpal tunnel syndrome complaints.