title: An apparatus for applying pure nonconstraining moments to spine segments in vitro.
abstract: METHODS
  This article reports on the design and use of a new apparatus for creating and monitoring pure, relatively nonconstraining moments to induce flexion/extension, lateral bending, and axial rotation in cadaveric spine segments of two or more vertebrae.
  
  
  OBJECTIVE
  The apparatus was designed to take advantage of the precision and control available in a servo-hydraulic testing frame to efficiently create and monitor testing moments.
  
  
  BACKGROUND
  Other laboratories have reported methods of flexibility testing that also use cables and pulleys. However, instead of loading the cables and pulleys using a mechanical testing frame, previous systems have used pneumatic actuators or dead weights.
  
  
  METHODS
  Force from a uniaxial mechanical testing frame is converted to torque applied to the specimen through a system of cables and pulleys. The cable orientation is monitored to ensure that pure moments are created. Applied moments are recorded using one or two load cells.
  
  
  RESULTS
  Sketches of the apparatus are presented and its operation is described.
  
  
  CONCLUSIONS
  Because the materials required to build this apparatus are inexpensive and the equipment needed for its operation is common in mechanical testing labs, this design may be useful for researchers interested in beginning in vitro spine flexibility testing with minimal expenditure.
authors.affiliation: Spinal Biomechanics Research Laboratory, Phoenix, Arizona, USA.
authors.forename: N R
authors.initials: NR
authors.lastname: Crawford
authors.forename: A G
authors.initials: AG
authors.lastname: Brantley
authors.forename: C A
authors.initials: CA
authors.lastname: Dickman
authors.forename: E J
authors.initials: EJ
authors.lastname: Koeneman
mesh_terms: D001696:Biomechanical Phenomena; D002102:Cadaver; D004867:Equipment Design; D006801:Humans; D013131:Spine / Q000502:physiology*; D013314:Stress, Mechanical