CLINICAL STUDIES INDICATE variations in intravertebral pressures in pa
tients with and without low back pain. It is known that not all patien
ts with back pain have abnormal lumbar radiographs and, furthermore, m
icrofractures of the endplate may be one of the causes in the origin o
f low back pain. Consequently, this study was conducted to determine t
he interrelationship between microtrauma and intraosseous pressures in
the lumbar spine. Miniature pressure transducers were inserted into t
he vertebral bodies and spinous processes of human cadaver spinal unit
s. Radio-opaque medium was injected into the nucleus to fluoroscopical
ly monitor the movement of the fluid from the disc as the preparation
was loaded up to the initiation of microtrauma (before reaching the ul
timate load-carrying capacity). The onset of injury was evidenced by t
he microfracture of one of the two endplates and impregnation of the c
ontrast medium into the spongiosa. After relaxation, another cycle of
loading was applied by limiting the deflections to the maximum compres
sion sustained under the intact configuration, The load, stiffness, an
d energy-absorbing capacities were lower (P < 0.05) for the injured sp
ecimen compared with the intact configuration. The intraosseous pressu
res were higher (P < 0.05) in the vertebral body and the spinous proce
ss of the vertebra where the endplate exhibited microtrauma in the inj
ured cycle compared with the intact cycle. In contrast, the intraosseo
us pressures in the vertebral body and the spinous process at the leve
l where the endplate remained intact were not significantly different
between the two cycles of loading. These findings suggest that the pre
ssures at one level are not affected by the pressures caused by the on
set of microtrauma at the other spinal level. Furthermore, because the
pressures in the spinous process and vertebral bodies demonstrated si
milar tendencies before and after microtrauma, it should be possible t
o monitor the pressures in either component of the vertebra. This find
ing may be clinically applicable, because it is a relatively simple pr
ocedure to monitor spinous process pressures as opposed to vertebral b
ody pressures in vivo.