Abstract
Study Design. Mechanical testing of cadaveric spines.
Objective. To determine whether vertebral body osteophytes act
primarily to reduce compressive stress on the intervertebral discs, or
to stabilize the spine in bending.
Summary of Background Data. The mechanical signifi cance of
vertebral osteophytes is unclear.
Methods. Thoracolumbar spines were obtained from cadavers,
aged 51 to 92 years, with vertebral body osteophytes, mostly
anterolateral. Twenty motion segments, from T5–T6 to L3–L4, were
loaded in compression to 1.5 kN, and then in fl exion, extension,
and lateral bending to 10 to 25 Nm (depending on specimen size)
with a compressive preload. Vertebral movements were tracked
us- ing an optical 2-dimensional MacRefl ex system. Tests were
performed in random order, and were repeated after excision of all
osteophytes. Osteophyte function was inferred from (a) changes in
the force or moment resisted and (b) changes in tangent stiffness,
measured at maximum displacement or rotation angle. Volumetric
bone mineral density (BMD) was measured using dual photon x-ray
absorptiometry and water immersion. Results were analyzed using
repeated measures analysis of variance.
Results. Resistance to compression was reduced by an average
of 17% after osteophyte removal (P 0.05), and resistance to
bending moment in fl exion, extension, and left and right lateral
bending was reduced by 49%, 36%, 36%, and 35%, respectively
(all P 0.01). Changes in tangent stiffness were similar. Osteophyte
removal increased the neutral zone in bending (P 0.05) and, on
average, reduced motion segment BMD by 7% to 9%. Results were
insensitive to applied loads and moments, but several changes were
proportional to osteophyte size.
Conclusion. Vertebral body osteophytes resist bending movements more
than compression. Because they reverse the instability in bending that can
stimulate their formation, these osteophytes seem to be adaptive rather
than degenerative. Results suggest that osteophytes could cause clinical
BMD measurements to underestimate vertebral compressive strength.
Translated title of the contribution | Mechanical function of vertebral body osteophytes, as revealed by experiments on cadaveric spines |
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Original language | English |
Pages (from-to) | 770 - 777 |
Number of pages | 8 |
Journal | Spine |
Volume | 36 |
DOIs | |
Publication status | Published - May 2011 |