Discography is commonly used in the workup of back disorders. The clinical
utility of the test is controversial, and little is known about mechanical
changes that may occur in the disc during this exam. To quantify three-dime
nsional deformations of the posterior annulus during discography. and to ex
amine some of the covariates that influence the deformations, displacements
of the lumbar posterior annulus were measured during discographic injectio
n for three different spinal positions. Disc bulge and annular strains were
calculated from the displacements. The combined effect of disc pressurizat
ion, spine position, and location on the disc (lateral versus midline) expl
ained much of the variation in the measured bulges and strains (r(2) = 0.56
). Disc pressurization or spine position alone did not always have a signif
icant effect on strains, and the strains and bulges were often influenced b
y the interactions between position of the spine, location of the disc, and
pressurization, In clinical studies of discography, these results suggest
that patient position during the examination should be standardized.