Double Crush Syndrome

Introduction

• The double crush hypothesis was first formulated in 1973 and states that axons that have been compressed at one site become especially susceptible to damage at another site.
  
• This theory was originally described by Upton (1973) in a study of 115 patients.
• The existence of double crush syndrome was further substantiated by Massey's (1981) study of nineteen cases of carpal tunnel syndrome co-existing with a cervical radiculopathy. 
  

Hypothesis

• It is suggested that compression of an axon at one location makes it more sensitive to effects of compression in another location,because of impaired axoplasmic flow.
• Hypothetically, two lesions with little or no independent clinical ramifications, when combined, lead to appearance or magnification of symptoms
• Two areas of compression affecting the same axons do not, alone, meet the criteria of the hypothesis.
• By definition, a first lesion must render axons more susceptible to effects of a second, leading to more than just the combined, independent effects of two lesions
• Upton and McComas used the double crush hypothesis to explain why patients with carpal tun-nel syndrome (CTS) sometimes feel pain in the forearm, elbow, upper arm, shoulder, chest, and upper back.
  
• They also used it to explain failed attempts at surgical repairs when neither surgery nor CTS diagnosis appeared faulty.
• They claimed that most patients with CTS not only have compressive lesions at the wrist, but also show evidence of damage to cervical nerve roots.