title: Compliance of the L5-S1 spinal unit: a comparative study between an unconstrained and a partially constrained system.
abstract: A comparison between an unconstrained and a partially constrained system for in vitro biomechanical testing of the L5-S1 spinal unit was conducted. The objective was to compare the compliance and the coupling of the L5-S1 unit measured with an unconstrained and a partially constrained test for the three major physiological motions of the human spine. Very few studies have compared unconstrained and partially constrained testing systems using the same cadaveric functional spinal units (FSUs). Seven human L5-S1 units were therefore tested on both a pneumatic, unconstrained, and a servohydraulic, partially constrained system. Each FSU was tested along three motions: flexion-extension (FE), lateral bending (LB) and axial rotation (AR). The obtained kinematics on both systems is not equivalent, except for the FE case, where both motions are similar. The directions of coupled motions were similar for both tests, but their magnitudes were smaller in the partially constrained configuration. The use of a partially constrained system to characterize LB and AR of the lumbosacral FSU decreased significantly the measured stiffness of the segment. The unconstrained system is today's "gold standard" for the characterization of FSUs. The selected partially constrained method seems also to be an appropriate way to characterize FSUs for specific applications. Care should be taken using the latter method when the coupled motions are important.
authors.affiliation: Mechanical Engineering Department, Laboratory of Applied Mechanics and Reliability Analysis, Swiss Federal Institute of Technology, Lausanne, Switzerland. eric.charriere@hispeed.ch
authors.forename: E A
authors.initials: EA
authors.lastname: Charriere
authors.forename: T
authors.initials: T
authors.lastname: Beutler
authors.forename: M
authors.initials: M
authors.lastname: Caride
authors.forename: P
authors.initials: P
authors.lastname: Mordasini
authors.forename: T E
authors.initials: TE
authors.lastname: Orr
authors.forename: P K
authors.initials: PK
authors.lastname: Zysset
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D002102:Cadaver; D003187:Compliance; D004867:Equipment Design; D004869:Equipment Safety; D005260:Female; D049671:History, 18th Century; D006801:Humans; D008159:Lumbar Vertebrae / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D009985:Orthopedics / Q000379:methods; D016059:Range of Motion, Articular / Q000502:physiology*; D012399:Rotation; D012447:Sacrum / Q000502:physiology*; D012680:Sensitivity and Specificity; D013314:Stress, Mechanical