title: An instrumented tissue tester for measuring soft tissue property under the metatarsal heads in relation to metatarsophalangeal joint angle.
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.
authors.affiliation: Division of Bioengineering, National University of Singapore, Block E3A #07-15, 7 Engineering Drive 1, Singapore 117574, Singapore.
authors.forename: Wen-Ming
authors.initials: WM
authors.lastname: Chen
authors.forename: Victor
authors.initials: V
authors.lastname: Phyau-Wui Shim
authors.forename: Seung-Bum
authors.initials: SB
authors.lastname: Park
authors.forename: Taeyong
authors.initials: T
authors.lastname: Lee
mesh_terms: D016880:Anisotropy; D001696:Biomechanical Phenomena; D004548:Elasticity; D004867:Equipment Design; D005528:Foot / Q000502:physiology; D005684:Gait; D006801:Humans; D007596:Joints / Q000502:physiology*; D008682:Metatarsal Bones / Q000503:physiopathology*; D008683:Metatarsophalangeal Joint / Q000502:physiology*; D008954:Models, Biological; D015203:Reproducibility of Results; D013314:Stress, Mechanical; D014783:Viscosity