Mechanical function of vertebral body osteophytes, as revealed by experiments on cadaveric spines.
METHODS
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.


BACKGROUND
The mechanical significance 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 flexion, extension, and lateral bending to 10 to 25 Nm (depending on specimen size) with a compressive preload. Vertebral movements were tracked using an optical 2-dimensional MacReflex 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 flexion, 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.


CONCLUSIONS
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.
Al-Rawahi
Maimouna
M
Sultan Qaboos University Hospital, Sultanate of Oman.
Luo
Jin
J
Pollintine
Phillip
P
Dolan
Patricia
P
Adams
Michael A
MA
D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D015519:Bone Density; D002102:Cadaver; D019245:Compressive Strength; D005260:Female; D006801:Humans; D007403:Intervertebral Disc / Q000503:physiopathology*; D008159:Lumbar Vertebrae / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D054850:Osteophyte / Q000503:physiopathology*; D016059:Range of Motion, Articular; D013128:Spinal Osteophytosis / Q000503:physiopathology*; D013314:Stress, Mechanical; D013904:Thoracic Vertebrae / Q000503:physiopathology*