title: Intradiscal pressure depends on recent loading and correlates with disc height and compressive stiffness.
abstract: OBJECTIVE
  Intervertebral discs exhibit time-dependent deformation (creep), which could influence the relation between applied stress and intradiscal pressure. This study investigates the effect of prolonged dynamic loading on intradiscal pressure, disc height and compressive stiffness, and examines their mutual relationships.
  
  
  METHODS
  Fifteen caprine lumbar discs with 5 mm of vertebral bone on either side were compressed by 1 Hz sinusoidal load for 4.5 h. After preload, 'High' (130 ± 20 N) or 'Low' (50 ± 10 N) loads were alternated every half hour. Continuous intradiscal pressure measurement was performed with a pressure transducer needle.
  
  
  RESULTS
  Each disc showed a linear relationship between axial compression and intradiscal pressure (R (2) > 0.91). The intercept of linear regression analysis declined over time, but the gradient remained constant. Disc height changes were correlated to intradiscal pressure changes (R (2) > 0.98): both decreased during High loading, and increased during Low loading. In contrast, compressive stiffness increased during High loading, and was inversely related to intradiscal pressure and disc height.
  
  
  CONCLUSIONS
  Intradiscal pressure is influenced by recent loading due to fluid flow. The correlations found in this study suggest that intradiscal pressure is important for disc height and axial compliance. These findings are relevant for mechanobiology studies, nucleus replacements, finite element models, and ex vivo organ culture systems.
authors.affiliation: Department of Orthopaedic Surgery, MOVE Research Institute Amsterdam, VU University Medical Center, De Boelelaan 1117, PO box 7057, 1007 MB, Amsterdam, The Netherlands, pp.vergroesen@vumc.nl.
authors.forename: Pieter-Paul A
authors.initials: PP
authors.lastname: Vergroesen
authors.forename: Albert J
authors.initials: AJ
authors.lastname: van der Veen
authors.forename: Barend J
authors.initials: BJ
authors.lastname: van Royen
authors.forename: Idsart
authors.initials: I
authors.lastname: Kingma
authors.forename: Theo H
authors.initials: TH
authors.lastname: Smit
mesh_terms: D000818:Animals; D006041:Goats; D007403:Intervertebral Disc / Q000473:pathology* / Q000503:physiopathology*; D016014:Linear Models; D008159:Lumbar Vertebrae / Q000473:pathology* / Q000503:physiopathology*; D023421:Models, Animal; D014160:Transducers, Pressure; D016474:Weight-Bearing / Q000502:physiology*