3+ 4/2002 - Společnost pro pojivové tkáně

Acknowledgments This research has
been supported bv the grant of GACIZ No.
106/00/1464 and the grant of MSMT
No.240000012.
OSTEOPOROTIC VERTEBRAL
FRACTURES IN THE ELDERLY:
DOES THE ANTERIOR VERTEBRAL
BODY LOSE STRENGTH FOLLOWING
STRESS SHIELDING BY THE NEURAL
ARCH
P. Pollintine, S. J. Garbutt, J. H.Tobias1, D. S. MeNally2,
G. K. Wakely, P. Dolan, M. A. Adams
Department of Anatomy, and 1Rheumatology Unit,
University of Bristol, U.K. 2University of Nottingham,
U.K.
Introduction: Osteoporotic vertebral
fractures are normally attributed to systemic
bone loss caused by age-related hormonal
changes and reduced physical activity.
However, regional vertebral bone mass
and density will also depend on the manner
in which the intervertebral disc presses on
the vertebral body, and on load-bearing by
the neural arch. We hypothesise that agerelated
degeneration of intervertebral discs
increases neural arch compressive loadbearing,
and influences the distribution of
compressive load on the vertebral body,
causing anterior vertebral body bone loss
and weakening in the elderly spine.
Materials and methods: Fifteen
cadaveric motion segments (aged 72–92
yrs),comprising 2 adjacent vertebral bodies
and the intervening disc and ligaments,
were compressed to 1.5kN while positioned
to simulate erect standing posture
and a simulated forward stooped posture.
The distribution of intradiscal stress, measured
by pulling a miniature pressure transducer
along the mid-sagittal diameter of the
disc, was integrated over area to give the
force acting on the anterior and posterior
halves of the vertebral body (1).These were
subtracted from the 1.5 kN to determine
the force on the neural arch. Compressive
strength of each motion segment was measured
in the stooped posture. Bone mineral
density (BMD) of the anterior and whole
vertebral body was measured by dual energy
x-ray absorptiometry.
Results: In erect posture, the neural
arch resisted 48 % (STD 26˚10) of the
applied 1,5 kN, while the anterior vertebral
body resisted only 15 % (STD 19 %). However,
in the stooped posture these values
changed to 14 % (STD 7 %) and 57 % (STD
22 %) respectively. Compressive strength in
flexion correlated negatively with neural
arch load-bearing in erect posture (r2=0.51,
p=0.006). Compressive strength correlated
with whole vertebral body BMD (r2 = 0.55,
p