The "Double Crush" and Carpal Tunnel Syndrome


Reprinted from The RSI Network - Issue 17 - Apr'94

Dr. Robert L. Kane, DC, CCUCS
April 1994

By Dr. Robert L. Kane, DC, CCUCS, a private practitioner in Redwood City, CA. For questions or concerns he may be reached at the Amalu Chiropractic Center, (415)361-8908.

Medical literature has repeatedly documented the involvement of multiple injury sites in repetitive strain injuries. This is commonly referred to as a "Double Crush" Syndrome. For example, Carpal Tunnel Syndrome (CTS) is a disorder involving the median nerve, which is one of the primary nerves to the hand. It's most commonly thought to be caused by an injury to the wrist which in turn causes inflammation of the nerve as it passes through the wrist. The resulting symptoms may manifest as wrist pain and/or weakness, hand pain and/or weakness, numbing, and tingling of the hand. However, research is now showing that the wrist is not the only site of injury to this nerve in CTS.

A nerve is similar to an electrical wire transmitting signals from one end to another. If a small amount of damage (injury) is done to the wire, we may not notice a change in the signal transmission (symptoms). But if a small amount of additional damage is done at another area further down the wire, the signal may then be affected by the cumulative effects of both injuries. This, in turn, causes noticeable transmission problems (symptoms) at the original site. And since the second area of damage was too small to create symptoms on its own, it may go undetected unless the entire wire is examined. This is often the case with CTS.

In CTS, many times the nerves to the hand are damaged due to injuries of the wrist along with concurrent injuries ranging from the forearm to the upper neck ("Double Crush"). Like the situation with the wire, the effects of the damage occurring at the wrist are exaggerated due to the other injury site, thus producing more pronounced wrist and hand symptoms. If this additional site of injury is overlooked and not treated, it will result in the incomplete resolution of CTS. It also will be a factor in the success of surgical procedures performed on the wrist itself.

If you're suffering from CTS, please be sure your doctor has thoroughly examined you to determine if your CTS is due to a Double Crush Syndrome. A hand specialist may overlook a Double Crush originating in the neck. A proper examination for CTS would include the entire arm and neck in order to trace the full length of the nerve. Since the neck is the most common site for a Double Crush to occur, a consultation with a cervical spine specialist would be in the best interests of the CTS sufferer, especially if they've been recommended for carpal tunnel surgery. Only by identifying all of the causative agents of a particular condition can a doctor implement the best treatment procedures to ensure its complete resolution.

* Upton ARM, McComas AJ: The double crush in nerve entrapment syndromes. Lancet 2:359-361, 1973
* Hurst LC, Weissberg D, Carrol RE: The relationship of the double crush to carpal tunnel syndrome: an analysis of 1,000 cases of carpal tunnel syndrome. Journal of Hand Surgery 10B(2):202-204, 1985

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