Title: Finite element simulation of intra-carpal tunnel pressure: the effects of individual finger flexion and histological changes

Authors: Kyrin Liong; Amitabha Lahiri; Shujin Lee; Dawn Chia; Arijit Biswas; Heow Pueh Lee

Addresses: Department of Mechanical Engineering, National University of Singapore, 9 Engineering Drive 1, Block EA, 07-08, Singapore ' Department of Hand and Reconstructive Microsurgery, National University Hospital, 5 Lower Kent Ridge Road, Main Building 1, Level 2, Singapore ' Department of Surgery, Yong Loo Lin School of Medicine, National University of Singapore, C/O NUHS Tower Block, Level 8, 1E Kent Ridge Road, Singapore ' Department of Obstetrics and Gynecology, National University Hospital, 5 Lower Kent Ridge Road, Kent Ridge Wing 2, Level 3, Singapore ' Department of Obstetrics and Gynecology, National University Hospital, 5 Lower Kent Ridge Road, Kent Ridge Wing 2, Level 3, Singapore ' Department of Mechanical Engineering, National University of Singapore, 9 Engineering Drive 1, Block EA, 07-08, Singapore

Abstract: Carpal tunnel syndrome (CTS) is a common neuropathy, yet its etiology is unknown. While repetitive finger flexion and interstitial subsynovial connective tissue (SSCT) thickening are commonly associated with idiopathic CTS development, the stress that the nerve experiences remain unexamined. In this study, a patient-specific computational model of the carpal tunnel was developed. Tendon displacements corresponding to thumb, index finger (IF) and middle finger (MF) flexion were prescribed. To replicate a CTS candidate, the most common physiological finding - fibrosis of the SSCT - was modelled. Heightened nerve coefficients were also prescribed to simulate nerve stiffening. This revealed that volarly-moving tendons, as in IF and thumb flexion, elicit greater nerve stresses than those dorsally-moving tendons, as in MF flexion. The stress encountered in CTS candidates significantly exceeded those in normal candidates, demonstrating that tendon path, and the in-vivo conditions of an individual's SSCT and median nerve stiffness predominantly affect nerve stress.

Keywords: carpal tunnel syndrome; intra-carpal tunnel pressure; individual finger flexion; median nerve; finite element method; FEM; modelling; simulation; histological changes; nerve stress; tendon displacements; interstitial subsynovial connective tissue; SSCT; fibrosis; nerve stiffening; volarly-moving tendons; thumb flexion; index finger flexion; middle finger flexion; dorsally-moving tendons.

DOI: 10.1504/IJECB.2015.073929

International Journal of Experimental and Computational Biomechanics, 2015 Vol.3 No.3, pp.250 - 266

Received: 09 Jan 2015
Accepted: 30 Apr 2015
Published online: 30 Dec 2015 *

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