An instrumented tissue tester for measuring soft tissue property under the metatarsal heads in relation to metatarsophalangeal joint angle

Wen Ming Chen, Victor Phyau-Wui Shim, Seung Bum Park, Taeyong Lee

Research output: Contribution to journalArticlepeer-review

16 Scopus citations

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.

Original languageEnglish
Pages (from-to)1801-1804
Number of pages4
JournalJournal of Biomechanics
Volume44
Issue number9
DOIs
StatePublished - 3 Jun 2011

Keywords

  • Foot
  • Localized mechanical response
  • Metatarsal head
  • Metatarsophalangeal joint
  • Soft-tissue pad

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