Accurate in vitro identification of fracture onset in bones: Failure mechanism of the proximal human femur

Mateusz Maria Juszczyk, Luca Cristofolini, Marco Salvà, Lorenzo Zani, Enrico Schileo, Marco Viceconti

Research output: Contribution to journalArticle

Abstract

Bone fractures have extensively been investigated, especially for the proximal femur. While failure load can easily be recorded, and the fracture surface is readily accessible, identification of the point of fracture initiation is difficult. Accurate location of fracture initiation is extremely important to understand the multi-scale determinants of bone fracture. In this study, a recently developed technique based on electro-conductive lines was applied to the proximal femoral metaphysis to elucidate the fracture mechanism. Eight cadaveric femurs were prepared with 15-20 electro-conductive lines (crack-grid) covering the proximal region. The crack-grid was connected to a dedicated data-logger that monitored electrical continuity of each line at 700. kHz. High-speed videos (12,000 frames/s, 0.1-0.2. mm pixel size) of the destructive tests were acquired. Most crack-grid-lines failed in a time-span of 0.08-0.50. ms, which was comparable to that identified in the high-speed videos, and consistent with previous video recordings. However, on all specimens 1-3 crack-grid-lines failed significantly earlier (2-200. ms) than the majority of the crack-grid-lines. The first crack-grid-line to fail was always the closest one to the point of fracture initiation identified in the high-speed videos (superior-lateral neck region). Then the crack propagated simultaneously, at comparable velocity on the anterior and posterior sides of the neck. Such a failure pattern has never been observed before, as spatial resolution of the high-speed videos prevented from observing the initial opening of a crack. This mechanism (fracture onset, time-lag, followed by catastrophic failure) can be explained with a transfer of load to the internal trabecular structure caused by the initial fracture of the thin cortical shell. This study proves the suitability of the crack-grid method to investigate bone fractures associated to tensile stress. The crack-grid method enables significantly faster sampling than high-speed cameras. The present findings elucidate some aspects of the failure mechanism of the proximal human femoral metaphysis.

Original languageEnglish
Pages (from-to)158-164
Number of pages7
JournalJournal of Biomechanics
Volume46
Issue number1
DOIs
Publication statusPublished - Jan 4 2013

Keywords

  • Biomechanical destructive test
  • Bone fracture
  • Crack gauge
  • Crack initiation point
  • Fracture propagation velocity
  • In vitro testing
  • Proximal femoral diaphysis
  • Proximal human femur

ASJC Scopus subject areas

  • Orthopedics and Sports Medicine
  • Rehabilitation
  • Biophysics
  • Biomedical Engineering

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