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Title: An instrumented tissue tester for measuring soft tissue property under the metatarsal heads in relation to metatarsophalangeal joint angle
Authors: Chen, W.-M.
Phyau-Wui Shim, V. 
Park, S.-B.
Lee, T. 
Keywords: Foot
Localized mechanical response
Metatarsal head
Metatarsophalangeal joint
Soft-tissue pad
Issue Date: 3-Jun-2011
Citation: Chen, W.-M., Phyau-Wui Shim, V., Park, S.-B., Lee, T. (2011-06-03). An instrumented tissue tester for measuring soft tissue property under the metatarsal heads in relation to metatarsophalangeal joint angle. Journal of Biomechanics 44 (9) : 1801-1804. ScholarBank@NUS Repository.
Abstract: Identification of the localized mechanical response of the plantar soft tissue pads underneath the metatarsal heads (i.e., sub-MTH pad) to external loading is key to understand and predict how it functions in a gait cycle. The mechanical response depends on various parameters, such as the external load (direction and rate), the sub-MTH tissue properties (anisotropy and viscoelasticity), and the configuration of the metatarsophalangeal (MTP) joint overlying the tissue. In this study, an instrument-driven tissue tester that incorporates a portable motorized indentor within a special foot positioning apparatus was developed for realistic in vivo mechanical characterization (i.e. tissue stiffness and force relaxation behavior) of the local sub-MTH pad with the MTP joint configured at various dorsiflexion angles associated with gait. The tester yields consistent results for tests on the 2nd sub-MTH pad. Measurement errors for the initial stiffness (for indentation depths ≤1. mm), end-point stiffness, and percentage force relaxation were less than 0.084. N/mm, 0.133. N/mm, and 0.127%, respectively, across all test configurations. The end-point tissue stiffness, which increased by 104.2% due to a 50° MTP joint dorsiflexion, also agreed with a previous investigation. In vivo tissue's force relaxation was shown to be pronounced (avg.=8.1%), even for a short holding-time interval. The proposed technique to facilitate study of the dependence of the local sub-MTH pad and tissue response on the MTP joint angle might be preferable to methods that focus solely on measurement of tissue property because under physiologic conditions the sub-MTH pad elasticity may vary in gait, to adapt to drastically changing mechanical demands in the sub-MTH region of the terminal stance-phase, where MTP joint dorsiflexion occurs. © 2011 Elsevier Ltd.
Source Title: Journal of Biomechanics
ISSN: 00219290
DOI: 10.1016/j.jbiomech.2011.03.031
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