Viscoelastic Characterization of Mesenchymal Gap Tissue and Consequences for Tension Accumulation During Distraction

[+] Author and Article Information
M. Richards, A. S. Wineman, E. Alsberg, J. A. Goulet, S. A. Goldstein

Orthopædic Research Labs, G-0161, 400 NIB, University of Michigan, Ann Arbor, MI 48109-0486

J Biomech Eng 121(1), 116-123 (Feb 01, 1999) (8 pages) doi:10.1115/1.2798032 History: Received November 10, 1997; Revised August 20, 1998; Online October 30, 2007


Nonlinear viscoelastic analysis was used to characterize the time-dependent behavior of mesenchymal gap tissue generated during distraction osteogenesis. Six (n = 6) lengthened tibiae were harvested from New Zealand white rabbits at 18 days. This gap tissue was subjected to a series of step displacement tests of increasing magnitude, and force relaxation behavior was monitored. Isochrones in stress-strain space were fit to odd cubic functions of strain. An analytic expression, linear in both e and e3, was developed to predict stress accumulation within the gap tissue as a function of time during distraction. Stress relaxation functions were described well by two-term Prony series. The two time constants determined from mechanical testing results were consistent, suggesting the presence of two fundamental physiologic relaxation processes. Gap tissue stresses were predicted to rise considerably during early stages of lengthening when distraction magnitudes exceeded the clinical norm of 0.25 mm. These differences in tension accumulation were less pronounced by the time lengthening was completed. Specifically, these results may in part explain clinical observations of decreased bone regeneration and altered tissue proliferation and differentiation at higher distraction rates. More generally, this work provides a framework for the rigorous characterization of the viscoelastic properties of biologic tissues ordinarily exposed to step strains.

Copyright © 1999 by The American Society of Mechanical Engineers
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