Magnetic resonance assessment of the double-crush phenomenon in patients with carpal tunnel syndrome: a bilateral quantitative study.

Our main goal was to assess the coexistence of narrowed cervical foramens and cervical canal stenosis in patients with carpal tunnel syndrome (CTS). We took magnetic resonance (MR) images of 120 wrists and 480 foramens in 60 age and sex matched subjects (30 patients with CTS and 30 controls). All patients had nerve conduction velocity tests before MR examination. We measured the volume of the carpal canal in all participants bilaterally. We also quantified the cross-sectional areas of the cervical foramens on both sides from C4 to T1 and measured the diameter of the cervical canal in all participants. We searched for the prevalence and location of cervical spondylosis and disc prolapse on the side of the symptomatic wrist(s). All patients had CTS-related neurophysiological findings. There was no correlation between the symptoms and the reduced carpal canal volume. The mean (SD) area of the foramens was 109.5 (12.8) mm2 in the patients compared with the controls 126.4 (28.7) mm2 (p = 0.007). Cervical spondylosis and disc prolapse were more common in the patients than the controls at the C5-C6 and C6-C7 levels, and their locations were on the same side as the symptoms in the wrist(s) in 50% of cases. There was no difference in the size of the cervical canal between the two groups. The higher incidence of narrowed cervical foramens in the patients and its concordance with affected nerve roots on the same side as the CTS symptoms support the hypothesis of a double-crush phenomenon.