title: A linear-actuated torsional device to replicate clinically relevant spiral fractures in long bones.
abstract: To better understand the mechanisms underlying spiral fracture we would like to carry out biomechanical tests of long bones loaded in torsion to failure. A device was fabricated to perform torsional tests of long bones using a single-axis linear actuator. The principal operation of the device was to transform the vertical displacement of a material testing machine's linear actuator into rotational movement using a spur gear and rack system. Accuracy and precision of the device were quantified using cast-acrylic rods with known torque-rotation behavior. Cadaveric experimentation was used to replicate a clinically relevant spiral fracture in eleven human proximal tibiae; strain-gage data were recorded for a single specimen. The device had an experimental error of less than 0.2 Nm and was repeatable to within 0.3%. Strain gage data were in line with those expected from pure torsion and the cadaveric tibiae illustrated spiral fractures at ultimate torque and rotation values of 130.6 +/- 53.2 Nm and 8.3 +/- 1.5 degrees, respectively. Ultimate torque was highly correlated with DXA assessed bone mineral density (r = 0.87; p < 0.00 1). The device presented is applicable to any torsional testing of long bone when only a single-axis linear actuator is available.
authors.affiliation: Department of Kinesiology and Nutrition, University of Illinois at Chicago, IL 60612 USA. edwardsb@uic.edu
authors.forename: W Brent
authors.initials: WB
authors.lastname: Edwards
authors.forename: Karen L
authors.initials: KL
authors.lastname: Troy
mesh_terms: D004867:Equipment Design; D019544:Equipment Failure Analysis; D005596:Fractures, Closed / Q000503:physiopathology*; D006801:Humans; D010812:Physical Stimulation / Q000295:instrumentation*; D012371:Robotics / Q000295:instrumentation*; D013978:Tibial Fractures / Q000503:physiopathology*; D019415:Torque