| Carpal tunnel syndrome (CTS) is a common problem among manual wheelchair users (MWU), which is no surprise given the high force, high repetition nature of wheelchair propulsion. Since MWU rely heavily on the upper extremities for mobility, a greater focus should be placed on prevention of this overuse syndrome rather than treatment. In order to achieve this, there needs to be a better understanding of the pathophysiology of CTS, specifically median nerve characteristics related to wheelchair propulsion. Ultrasonography provides the means necessary to study the median nerve characteristics and physiologic changes associated with wheelchair propulsion. In this research, we used ultrasound and image analysis techniques to quantify median nerve shape and size characteristics. We developed a standardized imaging protocol to reliably assess median nerve changes in response to manual wheelchair propulsion. We also developed methodology for assessing dynamic characteristics of median nerve entrapment and compression during finger movements. Participants underwent ultrasound examinations of the wrist before and after a strenuous wheelchair propulsion task. Comparing individuals with and without symptoms of CTS, we found no significant differences at baseline, but did see significantly different and opposite median nerve changes in response to propulsion. Specifically, the three most common ultrasound characteristics previously related to CTS, including median nerve cross-sectional area at the pisiform level, flattening ratio at the hamate level, and swelling ratio, were significantly different between symptom groups. We were unable to determine any significant relationships between median nerve changes and propulsion biomechanics variables, including resultant force, stroke frequency, and wrist joint angles. In a subsample of subjects, we found dynamic signs of median nerve entrapment and compression in individuals with symptoms of CTS. While making a loose fist, symptomatic participants showed significantly less median nerve displacement within the carpal tunnel and significantly greater compression of the median nerve compared to asymptomatic participants. In conclusion, quantitative ultrasound measures of the median nerve are useful for studying CTS and assessing the nerve response to activity. The techniques presented here may be useful in developing interventions to prevent or reduce the likelihood of median nerve damage among both MWU and other populations affected by CTS. |
