Date Presented Accepted for AOTA INSPIRE 2021 but unable to be presented due to online event limitations.
Repetitive wrist and hand movement is a risk factor for carpal tunnel syndrome. During daily functional hand use, some people develop carpal tunnel syndrome. However, the exact mechanism of injury remains unknown. We evaluated the effect of functional hand use on the median nerve and assessed the compression and displacement of the median nerve using state-of-the-art sonography.
Primary Author and Speaker: Buwen Yao
Contributing Authors: Shawn C. Roll
PURPOSE: Carpal tunnel syndrome (CTS) is a prevalent upper extremity condition and commonly seen in hand therapy, with an estimated prevalence of 3% to 6% of adults in the US (Calandruccio & Thompson, 2018). The essential injury mechanism of the median nerve (MN) is compression, often due to repetitive or forceful hand use (Abichandani, Shaikh, & Nadiger, 2013). However, little is known regarding the mechanism in which hand use during daily activities causes compression and why heterogeneous susceptibility exists among individuals. We aimed to examine the effect of functional hand use on the MN in healthy individuals to examine potential mechanisms of nerve injury.
DESIGN: A cross-sectional descriptive study was conducted with asymptomatic participants. Individuals with a history of carpal tunnel release surgery, MN pathology, or other polyneuropathy involving the MN were excluded.
METHOD: Sonographic imaging was conducted on both wrists while participants slowly closed and opened the hand to simulate functional grasp. The transverse view of the MN was collected using the pisiform bone as a landmark. During the gripping process, any compression causing a shape change of the MN was noted. Also, two static images (before and after the gripping action, respectively) were captured, and nerve shapes were categorized as ovoid, angular, or irregular due to different amounts of compression caused by the surrounding structures. Next, endpoint displacement of the nerve's center of mass was calculated based on the relative position at full grip to the position at rest. Finally, a longitudinal view was used to determine the amount of nerve gliding relative to surrounding tendons.
RESULTS: Across 167 participants, the MN shifted from being primarily ovoid shaped at rest (48.7% ovoid, 37.2% angular, and 14.1% irregular shape) to primarily angular shaped (24.4% ovoid, 53.8% angular, and 21.8% irregular shape) when the hands were in a full fist position. 72.4% of nerves were compressed at some point during the gripping action, represented by a noticeable shape change. Compared to resting position, nerves in the carpal tunnel moved to dorsal-radial (32.9%), dorsal-ulnar (26.7%), volar-ulnar (16.2%), and volar-radial (24.3%) directions after gripping. The majority of nerves moved within the realm of 1mm vertically and 3 mm horizontally. Compared to nerves with no or little longitudinal movement, nerves that moved vastly with surrounding tendons in the longitudinal direction had 0.1 mm greater vertical displacement in the cross-sectional plane (p < 0.01).
CONCLUSION: Results of this study demonstrated daily hand use can cause compression of the MN, which may have some influence on the pathogenic process of CTS. Furthermore, this study showed that the effect of functional hand use on the MN varies from person to person: individuals whose nerve exhibited shape change and underwent compression during gripping may be at higher risk for developing CTS due to this higher compression. Similarly, individuals with greater longitudinal and transverse nerve displacement could be at higher risk for friction against the nerve, which may lead to the pathogenesis. Understanding the individual effects of daily functional hand use on the MN may help develop individualized treatment in hand therapy (Roll & Hardison, 2017). Future longitudinal studies should investigate the long-term effects of functional hand use to develop a more robust understanding of the development of CTS.
References
Abichandani, S., Shaikh, S., & Nadiger, R. (2013). Carpal tunnel syndrome - an occupational hazard facing dentistry. Int Dent J, 63(5), 230-236. https://doi.org/10.1111/idj.12037
Calandruccio, J. H., & Thompson, N. B. (2018). Carpal Tunnel Syndrome: Making Evidence-Based Treatment Decisions. Orthop Clin North Am, 49(2), 223-229. https://www.sciencedirect.com/science/article/abs/pii/S0030589817302067?via%3Dihub. https://doi.org/10.1016/j.ocl.2017.11.009
Roll, S. C., & Hardison, M. E. (2017). Effectiveness of Occupational Therapy Interventions for Adults With Musculoskeletal Conditions of the Forearm, Wrist, and Hand: A Systematic Review. Am J Occup Ther, 71(1), 7101180010. https://doi.org/10.5014/ajot.2017.023234
