Abstract
Upton and McComas claimed that most patients with carpal tunnel syndrome not only have compressive lesions at the wrist, but also show evidence of damage to cervical nerve roots. This "double crush" hypothesis has gained some popularity among chiropractors because it seems to provide a rationale for adjusting the cervical spine in treating carpal tunnel syndrome. Here I examine use of the concept by chiropractors, summarize findings from the literature, and critique several studies aimed at supporting or refuting the hypothesis. Although the hypothesis also has been applied to nerve compressions other than those leading to carpal tunnel syndrome, this discussion mainly examines the original application – "double crush" involving both cervical spinal nerve roots and the carpal tunnel. I consider several categories: experiments to create double crush syndrome in animals, case reports, literature reviews, and alternatives to the original hypothesis. A significant percentage of patients with carpal tunnel syndrome also have neck pain or cervical nerve root compression, but the relationship has not been definitively explained. The original hypothesis remains controversial and is probably not valid, at least for sensory disturbances, in carpal tunnel syndrome. However, even if the original hypothesis is importantly flawed, evaluation of multiple sites still may be valuable. The chiropractic profession should develop theoretical models to relate cervical dysfunction to carpal tunnel syndrome, and might incorporate some alternatives to the original hypothesis. I intend this review as a starting point for practitioners, educators, and students wishing to advance chiropractic concepts in this area.
Highlights
Upton and McComas [1] formalized the hypothesis of the "double crush" syndrome (DCS)
Upton and McComas coined the term "double crush syndrome," and wrote: "...our hypothesis is that neural function is impaired because single axons, http://www.chiroandosteo.com/content/16/1/2 having been compressed in one region, become especially susceptible to damage at another site."
What's Wrong with the Double Crush Hypothesis? Upton and McComas based their hypothesis on an interference with axoplasmic flow, the mechanism by which trophic substances manufactured in a neuronal cell body are carried away along the peripheral processes of the neuron and products of lysosomal breakdown are transported back to the cell body [10]
Summary
Upton and McComas [1] formalized the hypothesis of the "double crush" syndrome (DCS). Upton and McComas [1] used the double crush hypothesis to explain why patients with carpal tunnel syndrome (CTS) sometimes feel pain in the forearm, elbow, upper arm, shoulder, chest, and upper back. They used it to explain failed attempts at surgical repairs when neither surgery nor CTS diagnosis appeared faulty. They claimed that most patients with CTS have compressive lesions at the wrist, and show evidence of damage to cervical nerve roots
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