Time-dependent compressive deformation of the ageing spine relevance to spinal stenosis

P Pollintine, M S L M van Tunen, J Luo, M D Brown, P Dolan, M A Adams

Research output: Contribution to journalArticle

31 Citations (Scopus)

Abstract

Study Design. Mechanical testing of cadaveric spines. Objective. To test the hypothesis that, in the ageing spine, vertebrae deform more than discs, and contribute to time-dependent creep. Summary of Background Data. Intervertebral discs and vertebrae deform under load, narrowing the intervertebral foramen and increasing the risk of nerve root entrapment. Little is known about compressive deformations when elderly spines are subjected to sustained physiologic loading. Methods. A total of 117 thoracolumbar motion segments, aged 19 to 96 yrs (mean, 69), were subjected to 1kN compressive loading for 0.5, 1, or 2 hours. Deformations during the first 7 seconds were designated "elastic" and subsequent deformations as "creep". A 3-parameter model was fitted to experimental data in order to characterize their viscous modulus E-1, elastic modulus E-2 (initial stiffness), and viscosity eta (resistance to fluid flow). Intradiscal pressure (IDP) was measured using a miniature needle-mounted transducer. In 17 specimens loaded for 0.5 hours, an optical MacReflex system measured compressive deformations separately in the disc and each vertebral body. Results. On average, the disc contributed 28% of the spine's elastic deformation, 51% of the creep deformation, and 38% of total deformation. Elastic, creep, and total deformations of 84 motion segments in 2-hour tests averaged 0.87, 1.37, and 2.24 mm respectively. Measured deformations were predicted accurately by the model (average r(2) = 0.97), but E-1, E-2, and eta depended on the duration of loading. E-1 and eta decreased with advancing age and disc degeneration, in proportion to falling IDP (P < 0.001). Total compressive deformation increased with age, but rarely exceeded 3 mm. Conclusion. When the ageing spine is compressed, vertebral bodies show greater elastic deformations than intervertebral discs, and creep by a similar amount. Responses to axial compression depend largely on IDP, but deformations appear to be limited by impaction of adjacent neural arches. Total compressive deformations are sufficient to cause foraminal stenosis in some individuals.
Original languageEnglish
Pages (from-to)386-394
Number of pages9
JournalSpine
Volume35
Issue number4
DOIs
Publication statusPublished - Feb 2010

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Spinal Stenosis
Spine
Intervertebral Disc
Pressure
Accidental Falls
Nerve Compression Syndromes
Intervertebral Disc Degeneration
Optical Devices
Elastic Modulus
Transducers
Viscosity
Needles
Pathologic Constriction

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Pollintine, P., van Tunen, M. S. L. M., Luo, J., Brown, M. D., Dolan, P., & Adams, M. A. (2010). Time-dependent compressive deformation of the ageing spine relevance to spinal stenosis. Spine, 35(4), 386-394. https://doi.org/10.1097/BRS.0b013e3181b0ef26

Time-dependent compressive deformation of the ageing spine relevance to spinal stenosis. / Pollintine, P; van Tunen, M S L M; Luo, J; Brown, M D; Dolan, P; Adams, M A.

In: Spine, Vol. 35, No. 4, 02.2010, p. 386-394.

Research output: Contribution to journalArticle

Pollintine, P, van Tunen, MSLM, Luo, J, Brown, MD, Dolan, P & Adams, MA 2010, 'Time-dependent compressive deformation of the ageing spine relevance to spinal stenosis', Spine, vol. 35, no. 4, pp. 386-394. https://doi.org/10.1097/BRS.0b013e3181b0ef26
Pollintine P, van Tunen MSLM, Luo J, Brown MD, Dolan P, Adams MA. Time-dependent compressive deformation of the ageing spine relevance to spinal stenosis. Spine. 2010 Feb;35(4):386-394. https://doi.org/10.1097/BRS.0b013e3181b0ef26
Pollintine, P ; van Tunen, M S L M ; Luo, J ; Brown, M D ; Dolan, P ; Adams, M A. / Time-dependent compressive deformation of the ageing spine relevance to spinal stenosis. In: Spine. 2010 ; Vol. 35, No. 4. pp. 386-394.
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N2 - Study Design. Mechanical testing of cadaveric spines. Objective. To test the hypothesis that, in the ageing spine, vertebrae deform more than discs, and contribute to time-dependent creep. Summary of Background Data. Intervertebral discs and vertebrae deform under load, narrowing the intervertebral foramen and increasing the risk of nerve root entrapment. Little is known about compressive deformations when elderly spines are subjected to sustained physiologic loading. Methods. A total of 117 thoracolumbar motion segments, aged 19 to 96 yrs (mean, 69), were subjected to 1kN compressive loading for 0.5, 1, or 2 hours. Deformations during the first 7 seconds were designated "elastic" and subsequent deformations as "creep". A 3-parameter model was fitted to experimental data in order to characterize their viscous modulus E-1, elastic modulus E-2 (initial stiffness), and viscosity eta (resistance to fluid flow). Intradiscal pressure (IDP) was measured using a miniature needle-mounted transducer. In 17 specimens loaded for 0.5 hours, an optical MacReflex system measured compressive deformations separately in the disc and each vertebral body. Results. On average, the disc contributed 28% of the spine's elastic deformation, 51% of the creep deformation, and 38% of total deformation. Elastic, creep, and total deformations of 84 motion segments in 2-hour tests averaged 0.87, 1.37, and 2.24 mm respectively. Measured deformations were predicted accurately by the model (average r(2) = 0.97), but E-1, E-2, and eta depended on the duration of loading. E-1 and eta decreased with advancing age and disc degeneration, in proportion to falling IDP (P < 0.001). Total compressive deformation increased with age, but rarely exceeded 3 mm. Conclusion. When the ageing spine is compressed, vertebral bodies show greater elastic deformations than intervertebral discs, and creep by a similar amount. Responses to axial compression depend largely on IDP, but deformations appear to be limited by impaction of adjacent neural arches. Total compressive deformations are sufficient to cause foraminal stenosis in some individuals.

AB - Study Design. Mechanical testing of cadaveric spines. Objective. To test the hypothesis that, in the ageing spine, vertebrae deform more than discs, and contribute to time-dependent creep. Summary of Background Data. Intervertebral discs and vertebrae deform under load, narrowing the intervertebral foramen and increasing the risk of nerve root entrapment. Little is known about compressive deformations when elderly spines are subjected to sustained physiologic loading. Methods. A total of 117 thoracolumbar motion segments, aged 19 to 96 yrs (mean, 69), were subjected to 1kN compressive loading for 0.5, 1, or 2 hours. Deformations during the first 7 seconds were designated "elastic" and subsequent deformations as "creep". A 3-parameter model was fitted to experimental data in order to characterize their viscous modulus E-1, elastic modulus E-2 (initial stiffness), and viscosity eta (resistance to fluid flow). Intradiscal pressure (IDP) was measured using a miniature needle-mounted transducer. In 17 specimens loaded for 0.5 hours, an optical MacReflex system measured compressive deformations separately in the disc and each vertebral body. Results. On average, the disc contributed 28% of the spine's elastic deformation, 51% of the creep deformation, and 38% of total deformation. Elastic, creep, and total deformations of 84 motion segments in 2-hour tests averaged 0.87, 1.37, and 2.24 mm respectively. Measured deformations were predicted accurately by the model (average r(2) = 0.97), but E-1, E-2, and eta depended on the duration of loading. E-1 and eta decreased with advancing age and disc degeneration, in proportion to falling IDP (P < 0.001). Total compressive deformation increased with age, but rarely exceeded 3 mm. Conclusion. When the ageing spine is compressed, vertebral bodies show greater elastic deformations than intervertebral discs, and creep by a similar amount. Responses to axial compression depend largely on IDP, but deformations appear to be limited by impaction of adjacent neural arches. Total compressive deformations are sufficient to cause foraminal stenosis in some individuals.

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