The Development and Application of a Custom Robotic Biomechanical Testing Platform Employing Real-time Load-control to Compare Spinal Biomechanical Testing Protocols: Pure Moment, Ideal Follower Load, and a Novel Trunk Weight Protocol
Date of Award
Master of Science (MS)
Biomedical Engineering and Imaging
Brian P. Kelly, Ph.D.
Denis J. DiAngelo, Ph.D. Richard J. Kasser, Ph.D.
The human lumbar spine has been the subject of biomechanical study for many decades owing to the numerous medical cases resulting in the development of various corrective surgical procedures and medical devices intended to relieve patient discomfort. Spinal biomechanics is a broad field containing but not limited to the in vitro study of cadaveric tissue utilizing testing platforms used to apply motion- or load-profiles to tissue in the investigation of the various kinetic or kinematic responses, respectively. The particular arena field of this research concerns the field of robotics as it applies to testing platforms and how they are applied to lumbar spine biomechanical testing.
The in vivo spine is subject to six degrees of freedom (DOF) of motion as a consequence of the applied loads of surrounding musculature which apply component loads in 6 DOF. However current in vitro standard protocols apply isolated loads primarily in the anatomical planes. Although the primary goal of in vitro testing may not be the simulation of in vivo circumstances, the accurate recreation of the in vivo loading environment would reveal much regarding the passive biomechanics of the spine. To accomplish such a goal, it would be ideal to utilize a platform capable of providing 6 DOF of controlled mobility as well as capable of apply controlled load in those 6 DOF.
The Musculoskeletal Research Laboratory has developed such a system. The system’s load-control capabilities were validated by simulating two standard biomechanical protocols, the pure moment and the ideal follower load on 6 L4-L5 single motion segment units. The robotic performance of the system was evaluated by measuring the tracking errors during testing, or the difference between experimental forces being applied and the forces commanded by the custom motion programs executed during protocol simulation. The biomechanical data that was recorded and compared to the literature for validation was rotational range of motion in the sagittal plane and anatomical point translation. Translation data proved to be difficult to compare effectively to the literature due to the sparseness of comparable numbers. There was also interest in the platform’s ability to control protocols. To test this hypothesis, three different biomechanical protocols were simulated and there biomechanical results were compared: pure moment, ideal follower load, and trunk weight.
The system provided stable, good load-control in during combined motions involving all 6 DOF. The tracking errors observed were low compared to other published robotic biomechanical platforms. The mean combined flexion-extension rotational range of motion in the sagittal plane for the pure moment protocol, the ideal follower load, and the trunk weight protocols were 8.2°(±2.5°), 7.6°(±2.9°), and 7.4°(±2.8°), respectively. There were statistically significant differences in the absolute translational data across the protocols but when comparing relative changes due to flexion and extension only, there are no significant differences across protocols.
In conclusion to this research the platform developed and validated in the current study adequately provides the capabilities of 6 DOF coordinated motion and 5 DOF coordinated load-control. It is sufficient to simulate the standard spine biomechanical test protocols of pure moment and ideal follower load on single segments. It is also a good tool for comparing the effects of particular protocols on the passive biomechanics of human cadaveric tissue. To the author’s knowledge, this is the first publication of a fully robotic system adequately controlling a non-zero dynamic force vector while a bending protocol was being applied to a human spinal segment. This research is limited to the sagittal plane and single lumbar spine motion segment units.
Bennett, Charles Ramsey , "The Development and Application of a Custom Robotic Biomechanical Testing Platform Employing Real-time Load-control to Compare Spinal Biomechanical Testing Protocols: Pure Moment, Ideal Follower Load, and a Novel Trunk Weight Protocol" (2013). Theses and Dissertations (ETD). Paper 331. http://dx.doi.org/10.21007/etd.cghs.2013.0026.