title: Ex vivo measurement of lumbar intervertebral disc pressure using fibre-Bragg gratings.
abstract: Methods were developed to measure intervertebral disc pressure using optical fibre-Bragg gratings (FBGs). The FBG sensor was calibrated for hydrostatic pressure in a purpose-built apparatus and the average sensitivity was determined to be -5.7 +/- 0.085 pm/MPa (mean +/- SD). The average coefficient of determination (r(2)) for the calibration data was 0.99, and the average hysteresis of the sensor was 2.13% of full scale. The FBG was used to measure intradiscal pressure response to compressive load in five lumbar functional spine units. The pressure measured by the FBG sensor varied linearly with applied compressive load with coefficients of determination ranging from 0.84 to 0.97. The FBG sensor's sensitivity to compressive load ranged from 0.702 +/- 0.043 kPa/N (mean +/- SD) in a L1-L2 specimen, to 1.07 +/- 0.069 kPa/N in a L4-L5 specimen. These measurements agree with those of previous studies in lumbar spines. Two strain gauge pressure sensors were also used to measure intradiscal pressure response to compressive load. The measured pressure sensitivity to load ranged from 0.251 kPa/N (L4-L5) to 0.850 kPa/N (L2-L3). The average difference in pressure sensitivity to load between Sensors 1 and 2 was 12.9% of the value for Sensor 1, with a range from 1.1% to 20.4%, which suggests that disc pressure was not purely hydrostatic. This may have contributed to the difference between the responses of the FBG and strain gauge sensors.
authors.affiliation: Department of Mechanical Engineering, University of Victoria, P.O. Box 3055, Victoria, B.C., Canada V8W 3P6. dennison@uvic.ca
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Dennison
authors.forename: Peter M
authors.initials: PM
authors.lastname: Wild
authors.forename: Peter W G
authors.initials: PW
authors.lastname: Byrnes
authors.forename: Amy
authors.initials: A
authors.lastname: Saari
authors.forename: Eyal
authors.initials: E
authors.lastname: Itshayek
authors.forename: Derek C
authors.initials: DC
authors.lastname: Wilson
authors.forename: Qingan A
authors.initials: QA
authors.lastname: Zhu
authors.forename: Marcel F S
authors.initials: MF
authors.lastname: Dvorak
authors.forename: Peter A
authors.initials: PA
authors.lastname: Cripton
authors.forename: David R
authors.initials: DR
authors.lastname: Wilson
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena / Q000295:instrumentation / Q000379:methods; D002138:Calibration; D005260:Female; D005336:Fiber Optic Technology / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D006874:Hydrostatic Pressure; D007403:Intervertebral Disc / Q000502:physiology*; D008159:Lumbar Vertebrae / Q000502:physiology; D008297:Male; D008875:Middle Aged; D016474:Weight-Bearing / Q000502:physiology*