The Journal of Bone and Joint Surgery, Vol 76, Issue 12 1840-1846, Copyright © 1994 by Journal of Bone and Joint Surgery, Inc
The microarchitecture of the axis as the predisposing factor for fracture of the base of the odontoid process. A histomorphometric analysis of twenty-two autopsy specimens
M Amling, M Hahn, VJ Wening, HJ Grote and G Delling
Department of Bone Pathology, Universitats-Krankenhaus Eppendorf, University of Hamburg, Germany.
The axis from twenty-two cadavera was removed at autopsy and was sectioned
in the sagittal plane to a thickness of one millimeter with use of a
surface-stained block-grinding technique. Combined two and
three-dimensional analysis included an evaluation of the volume of the
trabecular bone, the trabecular interconnection, and the cortical thickness
as well as qualitative investigation of the structure of the cancellous
bone. The body of the axis, the base of the odontoid process, and the
odontoid process were analyzed separately. The base of the odontoid process
is a region of least resistance for fractures because of its unique
microarchitecture. The mean volume of trabecular bone of the base of the
odontoid process is 55 per cent less than that of the axis and the odontoid
process. The base also has a markedly poorer trabecular interconnection and
a cortical thickness that is one-third that of the odontoid process. In all
of the specimens, trabeculae that were disconnected from the trabecular
lattice (trabeculae with free ends) were demonstrated in the base of the
odontoid process. The formation of microcallus in six (27 per cent) of the
specimens supports the hypothesis that microfractures occur as a result of
stress peaks, mechanical fatigue, and the relative insufficiency of bone in
the static condition. Therefore, the base of the odontoid process can be
considered as a site of predilection for fractures.