Delineation of in-vitro lumbar spine structural properties using a robotic/UFS testing system with hybrid control: Experiments and analytical simulation

Spine disorders are one of the most prevalent and costly problems facing modern medicine, with an estimated annual cost of over ;The primary objective of this research was to apply robotics technology and control methods to the measurement of lumbar spine structural properties, and to develop an analytical simulation of both the robot and the specimen. An existing robotic/UFS (universal force sensor) testing system using a hybrid (stiffness-based) control method was adapted to measurement of flexion/extension kinetics of 15 lumbar functional spinal units (FSUs). Results demonstrated characteristic kinetic features of the lumbar spine---including typical neutral and elastic zones as described in previous studies. It was found that hybrid control methods combining both load and displacement feedback provided improved delineation and control of the specimen within the neutral zone. For each specimen, sequential sectioning of the ligaments, facets, and disc was performed. hi-situ loads carried by each of the FSU component structures during flexion/extension was measured. These studies provided valuable data necessary for the development of analytical specimen models.;Analytical models of both the specimen and the robotic/UFS testing system were developed using kinetic theory derived from classical robotics literature. These models were combined into a simulation, or "virtual testing system," enabling a wide variety of control algorithms, testing procedures, and specimen variables to be developed and visualized. Further developments of hybrid and other control theories could help to elucidate the interactions that occur among the passive, active, and neural control subsystems of the spine.