title: Modeling of time-dependent force response of fingertip to dynamic loading.
abstract: An extended exposure to repeated loading on fingertip has been associated to many vascular, sensorineural, and musculoskeletal disorders in the fingers, such as carpal tunnel syndrome, hand-arm vibration syndrome, and flexor tenosynovitis. A better understanding of the pathomechanics of these sensorineural and vascular diseases in fingers requires a formulation of a biomechanical model of the fingertips and analyses to predict the mechanical responses of the soft tissues to dynamic loading. In the present study, a model based on finite element techniques has been developed to simulate the mechanical responses of the fingertips to dynamic loading. The proposed model is two-dimensional and incorporates the essential anatomical structures of a finger: skin, subcutaneous tissue, bone, and nail. The skin tissue is assumed to be hyperelastic and viscoelastic. The subcutaneous tissue was considered to be a nonlinear, biphasic material composed of a hyperelastic solid and an invicid fluid, while its hydraulic permeability was considered to be deformation dependent. Two series of numerical tests were performed using the proposed finger tip model to: (a) simulate the responses of the fingertip to repeated loading, where the contact plate was assumed to be fixed, and the bone within the fingertip was subjected to a prescribed sinusoidal displacement in vertical direction; (b) simulate the force response of the fingertip in a single keystroke, where the keyboard was composed of a hard plastic keycap, a rigid support block, and a nonlinear spring. The time-dependent behavior of the fingertip under dynamic loading was derived. The model predictions of the time-histories of force response of the fingertip and the phenomenon of fingertip separation from the contacting plate during cyclic loading agree well with the reported experimental observations.
authors.affiliation: E&CTB/HELD, National Institute for Occupational Safety and Health, Center for Disease Control and Prevention, 1095 Willowdale Road, Morgantown, WV 26505, USA. jwu@dcd.gov
authors.forename: J Z
authors.initials: JZ
authors.lastname: Wu
authors.forename: R G
authors.initials: RG
authors.lastname: Dong
authors.forename: W P
authors.initials: WP
authors.lastname: Smutz
authors.forename: A W
authors.initials: AW
authors.lastname: Schopper
mesh_terms: D001842:Bone and Bones / Q000502:physiology; D003198:Computer Simulation; D004548:Elasticity; D005385:Fingers / Q000502:physiology*; D020342:Finite Element Analysis; D006801:Humans; D008954:Models, Biological; D009038:Motion; D017711:Nonlinear Dynamics; D010812:Physical Stimulation; D011312:Pressure; D012680:Sensitivity and Specificity; D012879:Skin Physiological Phenomena; D013314:Stress, Mechanical; D014584:User-Computer Interface; D014783:Viscosity; D016474:Weight-Bearing / Q000502:physiology*; D015443:Word Processing