The extent of matrix damage and chondrocyte death

in mechanically traumatized cartilage explants

depends on rate of loading.

J. Orthopaedic Research. 19(5):779-784, 2001.

Ewers, BJ, Devoracek-Disksna, D, Orth, MW, Haut, RC.

ABSTRACT:

Excessive mechanical loading of articular cartilage can lead to matrix damage and chondrocyte death. The relationship between this damage and secondary osteoarthritis is still unknown. In vitro studies of explants have suggested that matrix damage and cell death correlate with the state of stress and strain produced by applied boundary tractions. Recently, however, confocal microscopy has shown that local matrix strains differ from the strains produced in adjacent cells under physiological loading. The current study documents mechanically induced matrix damage and cell death in explants, and then attempts to correlate the mechanical damage with the state of stress and strain in the matrix and embedded cells. Thirty bovine cartilage explants were equilibrated for two days. Ten served as controls and the remaining randomly underwent unconfined compression to 30 MPa at either a high (~667 MPa/s) or low rate of loading (30 MPa/s). Matrix damage and cell viability were documented for each group. The experimentally determined displacements for both the high and low rate experiments were then applied to isotropic and transversely isotropic computational models of the explant, with or without depth-dependent, matrix material properties. The amount of displacement on a cell was then linearly interpolated and applied to a computational model of the cell. The isotropic model with depth-dependent material properties best associated areas of high stress with matrix damage and predicted the lateral expansion profiles documented in the recent literature. The current study also suggested that the extent of cell strain in each layer was most influenced by the shape of the cell, not the depth-dependent material properties of the matrix.

Orthopaedic Biomechanics Laboratories,

College of Osteopathic Medicine,

Michigan State University,

East Lansing, Michigan 48824

Please address correspondence to:

Roger C. Haut, Ph.D.,

Orthopaedic Biomechanics Laboratory,

College of Osteopathic Medicine,

A414 East Fee Hall,

Michigan State University,

East Lansing, MI 48824,

Tel: (517)355-0320,

Fax: (517)353-0789,

E-mail: haut@msu.edu