J. Mizrahi et al., FINITE-ELEMENT STRESS-ANALYSIS OF THE NORMAL AND OSTEOPOROTIC LUMBAR VERTEBRAL BODY, Spine (Philadelphia, Pa. 1976), 18(14), 1993, pp. 2088-2096
A finite-element model of an isolated elderly human L3 vertebral body
was developed to study how material properties and loading conditions
influence end-plate and cortical-shell displacements and stresses. The
model consisted of an idealized geometric representation of an isolat
ed vertebral body, with a 1-mm-thick end plate and cortical shell. For
uniform compression, large tensile stresses occurred all around the c
ortical shell just below the end plate as a result of bending of the c
ortical shell as it supported the end plate. Large tensile bending str
esses also developed in the inferior surface of the end plate. Equal r
eductions in both trabecular and cortical bone moduli increased displa
cements but did not affect peak stresses. A 50% reduction in trabecula
r bone modulus alone increased peak stresses in the end plate by 74%.
Elimination of the cortical shell reduced peak stresses in the end pla
te by approximately 20%. For nonuniform, anteriorly eccentric compress
ion, peak stresses everywhere changed by less than 11% but moved to th
e anterior aspect. When material properties were adjusted to represent
osteoporosis with disproportionate reductions in trabecular (50% decr
ease) and cortical (25% decrease) bone moduli, anterior compression in
creased peak stresses by up to 250% compared to uniform compression. I
f fractures are initiated in regions of large tensile stresses, the re
sults from this relatively simple model may explain how central end-pl
ate and transverse fractures initiate from uniform compression of the
end plate. Furthermore, for anterior compression, disproportionate mod
ulus reductions in trabecular and cortical bone may substantially incr
ease end plate and cortical shell stresses, suggesting a cause of age-
related spine fractures.