METHODS: Peer-reviewed journal articles on double crush syndrome were found through PubMed, MANTIS, and the Index to Chiropractic Literature, using the search terms “double crush syndrome”, “double crush carpal tunnel”, and “chiropractic carpal tunnel syndrome.” Many other related papers were found through cross reference and fortunate happenstance. Many of the articles that were included have also been quoted by a number of other sources, while some less popular papers offer ideas or perspectives not found elsewhere. Other papers were omitted because of redundancy, obscurity, and/or age. Many articles describing animal experiments were not used because doing so would have added little of clinical import, and those have been reviewed extensively by other authors. Papers used fell into several categories: experimental attempts to create double crush syndromes in animals; case series, case reports, and retrospective records reviews of carpal tunnel syndrome patients; double crush syndrome literature reviews with pertinent commentary; and alternative proposals to the original hypothesis. All information was chosen with the thoughts of presenting the pros and cons of double crush syndrome to chiropractic practitioners, students, and educators.
DATA SYNTHESIS: Many studies support that 2 or more sites of nerve compression cause a greater degree of dysfunction than a single site, but it is not clear that additional sites magnify the effects of compression. It appears that a significant percentage of carpal tunnel syndrome patients also have cervical spine problems, but the nature of the relationship between the anatomical regions has not been definitively explained. The original double crush syndrome hypothesis, based upon a theorized interference with axoplasmic flow, is probably not valid for sensory disturbances in carpal tunnel syndrome. For these reasons, the double crush syndrome hypothesis has remained controversial and a number of alternative explanations are presented.
DISCUSSION: Many authors of papers about double crush syndrome have suggested that patients may have more than a single problem at a time, and that examination and treatment should be directed toward multiple sites. This thinking might allow a greater role for chiropractic. However, the chiropractic profession needs to further develop theoretical models to relate cervical dysfunction to carpal tunnel syndrome, and would do well to look beyond axoplasmic flow and incorporate some of the alternatives to the original double crush syndrome hypothesis.
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