title: Influence of varying muscle forces on lumbar intradiscal pressure: an in vitro study.
abstract: The purposes of this study were to determine the effect of including muscle forces in the experimental loading of the spine on the intradiscal pressure and to determine whether this effect correlates with previously established in vivo data. We modeled the spine muscles as of five distinct groups and isolated the effect of each group on the intradiscal pressure (L4-L5). Seven human lumbosacral spines were tested in pure flexion/extension, right/left lateral bending, and left/right axial rotation moments. Stimulated muscle activity strongly influenced load-pressure characteristics, especially for the multifidus. Without muscle forces active, pressure increased proportionately with increasing moment. With five pairs of symmetrical constant muscle forces active (80 N per pair) the pressure increased more than 200% in neutral position and did not increase with increasing moment. The pressure without muscle forces and without axial preload was 0.12 MPa, which is about the same found by earlier in vivo studies of anesthetized subjects in prone position. With simulated muscle forces, the pressure was 0.39 MPa and in the range found for non-anesthetized subjects. We conclude that simulating muscle forces substantially affects intradiscal pressure.
authors.affiliation: Department Unfallchirurgische Forschung und Biomechanik, Universität Ulm, Germany.
authors.forename: H J
authors.initials: HJ
authors.lastname: Wilke
authors.forename: S
authors.initials: S
authors.lastname: Wolf
authors.forename: L E
authors.initials: LE
authors.lastname: Claes
authors.forename: M
authors.initials: M
authors.lastname: Arand
authors.forename: A
authors.initials: A
authors.lastname: Wiesend
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D002102:Cadaver; D006801:Humans; D007403:Intervertebral Disc / Q000502:physiology*; D008161:Lumbosacral Region; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000502:physiology*; D010827:Physiology / Q000295:instrumentation; D011312:Pressure; D012399:Rotation