A preliminary study of mechanically stress-induced changes in the extracellular matrix of the canine intervertebral disc.

The intervertebral discs of a young (age, 3 years) and an old (age, 8 years) dog were isolated as motion segments and cyclically stressed in physiologic nondestructive axial compression loads. Chemical analysis of the matrix of the annulus fibrosus revealed a shift in proteoglycan molecular size from larger to smaller moieties for the older dog but not for the younger. These preliminary results may indicate an age-related inability of the disc to tolerate cyclic stress.