Strain elastography that uses the body's cardiorespiratory pulsations to determine tissue stiffness (referred to here as “ambient strain elastography”) has not been previously described for the assessment of carpal tunnel syndrome (CTS). The objective of this study is to assess the reliability of ultrasonographic ambient strain elastography in the evaluation of CTS and compare median nerve stiffness between patients and healthy controls.Methods:
Ambient strain elastography was used to examine the wrists of 17 patients and 26 controls in cross-sectional and longitudinal views, twice by two observers. The strain ratio between the median nerve and nearby tendons was obtained and tested for intrarater and interrater reliability and differences between patients and healthy controls.Results:
Intrarater and interrater reliabilities were strong, even for the less experienced rater (lowest r = 0.566, highest r = 0.905; P < 0.001 for all comparisons). No significant difference in strain ratio between those with CTS and controls was detected (cross-sectional image P = 0.32; longitudinal image P = 0.20). Strain ratio did not correlate significantly with traditional ultrasound measures of CTS (lowest P = 0.26) but did correlate significantly with body mass index if obtained from cross-sectional images (r = 0.346; P = 0.02).Conclusions:
This strain elastography method is reliable but does not show changes in median nerve stiffness with CTS. Body mass index may influence elastography and further studies should be conducted to clarify this relationship.