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

M Al-Rawahi, J Luo, Phillip Pollintine, P Dolan, M A Adams

Research output: Contribution to journalArticle

32 Citations (Scopus)

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 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 us- ing 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. 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.
Original languageEnglish
Pages (from-to)770-777
Number of pages8
JournalSpine
Volume36
Issue number10
DOIs
Publication statusPublished - 1 May 2011

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Osteophyte
Spine
Bone Density
Compressive Strength
Intervertebral Disc
Immersion
Photons
Cadaver
Analysis of Variance
X-Rays

Keywords

  • vertebra
  • osteophyte
  • adaptive remodeling
  • mechanics
  • BMD

Cite this

Mechanical function of vertebral body osteophytes, as revealed by experiments on cadaveric spines. / Al-Rawahi, M; Luo, J; Pollintine, Phillip; Dolan, P; Adams, M A.

In: Spine, Vol. 36, No. 10, 01.05.2011, p. 770-777.

Research output: Contribution to journalArticle

Al-Rawahi, M, Luo, J, Pollintine, P, Dolan, P & Adams, MA 2011, 'Mechanical function of vertebral body osteophytes, as revealed by experiments on cadaveric spines', Spine, vol. 36, no. 10, pp. 770-777. https://doi.org/10.1097/BRS.0b013e3181df1a70
Al-Rawahi, M ; Luo, J ; Pollintine, Phillip ; Dolan, P ; Adams, M A. / Mechanical function of vertebral body osteophytes, as revealed by experiments on cadaveric spines. In: Spine. 2011 ; Vol. 36, No. 10. pp. 770-777.
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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 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 us- ing 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. 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.",
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N2 - 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 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 us- ing 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. 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.

AB - 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 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 us- ing 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. 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.

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