In vitro Investigation of Carpal Tunnel Volume and Morphology Changes with Non-Neutral Wrist Postures
Carpal tunnel syndrome (CTS) is a debilitating neuropathy resulting from compression of the median nerve within the carpal tunnel, a fibro-osseous compartment in the palmar aspect of the wrist. Non-neutral wrist postures are a commonly reported risk factor for CTS, due to changes in the geometry of the carpal tunnel leading to median nerve impingement. This thesis investigates the effects of wrist posture on carpal tunnel volume (CTV) and morphology. Analysis was performed in vitro using computed tomography imaging of cadaveric upper-extremities positioned in flexion-extension (FE) and radial-ulnar deviation (RUD) postures using a custom active joint motion simulator. This thesis presents four studies of the carpal tunnel. The first quantifies previously unreported reliability and variability of CTV measurement. Given excellent inter- and intra-rater reliability, the methods outlined in the first study were applied to investigate the effects of slight FE and RUD on CTV. Over the range of FE postures examined, no significant changes in CTV were observed, while a significant decrease in CTV was noted moving from radial to ulnar deviation. The third study introduces a novel approach to quantifying carpal tunnel morphology using one-dimensional centroid-to-boundary shape signatures. The fourth study investigated changes in volume distribution and morphology with FE and RUD postures. The results indicated the greatest shape changes occurred in the proximal and distal regions of the tunnel and that, even if the overall CTV does not change with posture, local changes in morphology could contribute to compression of the median nerve. Further, twisting between the proximal and distal ends of the tunnel may also play a role in median nerve impingement. Collectively this work advances our current state of knowledge on how the carpal tunnel deforms in non-neutral postures. Measures of CTV are enhanced by morphology and volume distribution metrics to further understand the effects of both FE and RUD postures. The techniques used represent advanced methods to both capture and visualize tunnel geometry changes, offering insight into anatomical mechanisms for CTS aetiology. The findings of this work may be applied toward treatment and prevention of CTS and contribute towards reducing the CTS burden of illness.
Anderson, D.A., Agur, A.M., Oliver, M.L., Gordon, K.D., 2022. Effects of slight flexion- extension and radial-ulnar deviation postures on carpal tunnel volume. Clin. Biomech. 92, 105575. https://doi.org/10.1016/j.clinbiomech.2022.105575