Multiaxial spine segment testing: position vs load control and physiological relevance

Author: Daniel Kim

Kim, Daniel, 2021 Multiaxial spine segment testing: position vs load control and physiological relevance, Flinders University, College of Science and Engineering

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The spine moves in a complex way, but it is unknown whether the spine moves in position control or load control. The study investigated the comparison of mechanical properties between load, position, and hybrid control mode. Three pilot tests were conducted to develop the testing protocol and five sheep lumbar spine segments (L4-L5) were tested on the hexapod. The specimens underwent overnight hydration under preload equivalent to a nucleus pressure of 0.1 MPa. Load control was conducted first, ranges of motion were extracted and applied to position and hybrid control. In each control mode, 11 directional loadings were applied in order of shear, axial rotation, bending, flexion/extension, and compression. Two hours of recovery were performed between control modes. The result showed that there were significant overall within-factors interaction effects of control modes and 6DOF loadings in stiffness, phase angle, hysteresis area, hysteresis loss coefficient, and maximum reaction forces/moments. Significant differences between control modes were observed in bending, flexion, extension, and compression movements. In these directional movements, fluid flow of the disc involves causing cumulative creep and this contributed significant differences. Comparison of hybrid control to load and position control was performed to assess physiological relevance. The differences were found in shear, bending, flexion/extension, and compression. However, it is yet insufficient to determine which control mode presents the more-physiological movement of the spine. Further development of the testing protocol is suggested to match the start point of movement in each control mode. The study is continuing with intention of publication in 2022.

Keywords: Spine, Multiaxial, Position Control, Load Control, 6DOF

Subject: Engineering thesis

Thesis type: Masters
Completed: 2021
School: College of Science and Engineering
Supervisor: John Costi