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

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.