The Journal of Bone and Joint Surgery, Vol 73, Issue 6 914-923, Copyright © 1991 by Journal of Bone and Joint Surgery, Inc
Formation of bone in tibial defects in a canine model. Histomorphometric and biomechanical studies
MD Markel, MA Wikenheiser and EY Chao
Department of Orthopedics, Mayo Clinic, Rochester, Minnesota.
The histomorphometric, material, and structural properties of the
reparative tissue and bone that formed in a two-millimeter tibial defect in
dogs were determined at two, four, eight, and twelve weeks after the
operation. At two weeks, the tibial defect was filled mainly with
undifferentiated connective tissue. After two weeks, the relative
proportion of undifferentiated connective tissue decreased and the amount
of bone progressively increased throughout the twelve weeks. New bone
formed primarily by intramembranous ossification, with a small degree of
endochondral ossification. At twelve weeks, bone occupied 62 per cent of
the defect. The calcium content of the reparative tissue increased between
four and eight weeks and then, at twelve weeks, reached a plateau of 77 per
cent that of normal cortical bone. Anisotropy of the new bone that formed
in the defect increased from 13.8 per cent to 26 per cent, and the mean
width of the trabecular bone increased 27 per cent between the eighth and
twelfth weeks. Maximum torque and torsional stiffness increased between two
and eight weeks and then, by twelve weeks, the values leveled off at 44 and
29 per cent of the values for intact bone. Indentation stiffness increased
between the fourth and twelfth weeks; at twelve weeks, it was 22 per cent
of the stiffness of normal cortical bone. Indentation stiffness increased
283 per cent between eight and twelve weeks, despite insignificant changes
in calcium content, amount of new bone, non-osseous space, water content,
or volume of trabecular bone during this time. This change in indentation
stiffness did correlate with increases in anisotropy of the new bone
between eight and twelve weeks.