De. Harrison et al., Comparison of axial and flexural stresses in lordosis and three buckled configurations of the cervical spine, CLIN BIOMEC, 16(4), 2001, pp. 276-284
Objective. To calculate and compare combined axial and flexural stresses in
lordosis Versus buckled configurations of the sagittal cervical curve.
Design. Digitized measurements from lateral cervical radiographs of four di
fferent shapes were used to calculate axial loads and bending moments on th
e vertebral bodies of C2-C7.
Background. Osteoarthritis and spinal degeneration are factors in neck and
back pain. Calculations of stress in clinically occurring configurations of
the sagittal cervical spine are rare.
Methods, Center of gravity of the head (inferior-posterior sella turcica) a
nd vertebral body margins were digitized on four different lateral cervical
radiographs: lordosis, kyphosis, and two "S"-shapes. Polynomials (seventh
degree) and stress concentrations on the concave and convex margins were de
rived for the shape of the sagittal cervical curvatures from C1 to T1. Mome
nts of inertia were determined from digitizing and the use of an elliptical
shell model of cross-section. Moment arms from a vertical line through the
center of gravity of the head to the atlas and scaled neck extensor moment
arms from the literature were used to compute the Vertical component of ex
tensor muscle effort. Segmental lever arms were calculated from a vertical
line through C1 to each vertebra.
Results. In lordosis, anterior and posterior stresses in the vertebral body
are nearly uniform and minimal. In kyphotic areas, combined stresses chang
ed from tension to compression at the anterior vertebral margins and were v
ery large (6-10 times as large in magnitude) compared to lordosis. In kypho
tic areas at the posterior vertebral body, the combined stresses changed fr
om compression (in lordosis) to tension,
Conclusions. The stresses in kyphotic areas are very large and opposite in
direction compared to a normal lordosis. This analysis provides the basis f
or the formation of osteophytes (Wolffs Law) on the anterior margins of ver
tebrae in kyphotic regions of the sagittal cervical curve. This indicates t
hat any kyphosis is an undesirable configuration in the cervical spine.