John Sessions and Dr. Anton Bowden, Mechanical Engineering
Background
It is reported by the American Academy of Orthopeadic Surgeons that in 2005, 24% of the population sought treatment for back pain [1]. Additionally, Americans spent over $85.9 billion (2005) on health treatment costs related to back problems with the vast majority being connected to disc degeneration [1]. Despite the vast sum of money being spent on treatment of disc degeneration, the leading surgical treatments for disc degeneration (spinal fusion, total disc replacement) have been shown to increase degeneration at the discs in adjacent levels to the surgery [2].
One limitation of current research into improved surgical treatments for low back pain is that cadaver specimens are typically used for studying the efficacy of these treatments. Cadaver spinal discs are not living tissue and do not degenerate. In vivo disc degradation degrades the quality of the collagen in the circumferential regions of the disc (the annulus fibrosus) resulting in increased compliance of that region. Conversely, the central region of the disc (the nucleus pulposus), increases in stiffness due to the loss of fluid [3]. A critical component of creating better treatment options requires researchers to develop a model of the mechanical effects of a progressively degenerating lumbar disc. Accelerated Human Lumbar Disc Degeneration is the first human model by which enzymatic injections into Functional Spinal Units (FSU) allow researchers to artificially create the same mechanical effects as physiologically degenerated discs and this characterization occurs as the disc degrades.
Project Context
The work for which the ORCA grant was obtained was based upon the hypothesis that human cadaveric lumbar discs can be enzymatically degenerated to match the observed mechanical behavior of living tissue undergoing degeneration. By being able to artificially match the mechanical behavior of the spine in vivo during degeneration, researchers will then be able to better treat disc degeneration and conditions that contribute to its development.
Project Progress
In preparation for this study, I have worked with Dr. Bowden’s lab to examine the degeneration of bovine tail segments using a similar protocol to the human cadaver study. Our lab has chosen to do it this way in order to address unforeseen experimental issues before plunging in and finding these issues while using precious human spine specimens. Project successes include: hypothesis validation, methodology improvements, analysis enhancements, and human FSU dissection.
i. Hypothesis Validation
The bovine study has confirmed that trypsin induces changes in the annulus fibrosus similar to those seen in vivo degeneration. In contrast to earlier work, this research more directly demonstrates that artificial degeneration of a disc more accurately matches observed physiological behaviors when the annulus fibrosus is degenerated rather than the nucleus pulposus [3,5,6]. The results of this preliminary study have been submitted as an abstract to the Orthopedic Research Society [6]. Additionally, the completed version of the work is currently going through its final stages before being published in Clinical Biomechanics.
ii. Methodology Improvements
While the bovine disc study was a great stepping stone for the human study, it did expose experimental issues. The modifications have centered on creating a testing environment which is completely temperature and humidity controlled. Additionally, the lab decided to create an all-in-one machine that would test the specimens without requiring removal of the specimen between tests.
After several months of design and testing, the result is a multi-axis environmentally controlled mechanical spine tester. While many of the design features are similar to existing testers, this spine tester is actually the first of it kind. (The machine itself is currently not being shown due to intellectual property constraints.)
iii. Analysis Enhancements
While constructing a computer algorithm for the data analysis, it was discovered the using natural logarithmic best-fit models were best suited for projecting specimen behavior during degeneration. Using this knowledge, programs have been written to analysis the data automatically following experimentation. This enhancement allows a tremendous advantage over the multi-week effort previously required for data analysis.
iv. Human FSU Dissection
In preparation for the human spine study, seven human spines T12 to S5 have been completely dissected.
Future Work
While a great deal of groundwork has been laid, the human disc degeneration study is not fully completed. Unfortunately, both time and resources limit my involvement in the study. However, the lab has assigned two master students to the project and will complete the testing and submit the research paper for publication.
May I submit my personal gratitude to ORCA for the opportunity to be able to work on the project.
References
- Springen, Karen. “The Price of Pain.” Newsweek 12 Feb. 2008.
- Chosa, E., et al. “Analysis of the effect of lumbar spine fusion on the superior adjacent intervertebral disk in the presence of disk degeneration, using the three-dimensional finite element method. J Spinal Disord Tech, 17(2): p. 134-9, 2004.
- Mwale, Fackson, et.al. “Evaluation of Quantitative Magnetic Resonance Imaging, Biochemical and Mechanical Properties of Trypsin-Treated Intervertebral Discs under Physiological Compression Loading.” Journal of Magnetic Resonance Imaging, 27:563-573, 2008.
- Goertzen. D.J., et al. “Neutral zone and range of motion in the spine are greater with stepwise loading than with a continuous loading protocol. An in vitro porcine investigation.” J Biomechanics, 37, p. 257-261, 2004.
- Roberts, Sally, et.al. “Bovine Explant Model of Degeneration of the Intervertebral Disc.” BioMed Central Musculoskeletal Discord, 9:24, 2008.
- Sessions, John, Tim Bishop, Allyson Sessions, and Dr. Anton Bowden. “Mechanical Characterization of a Bovine Tail for Enzymatic Degeneration.” Brigham Young University, Aug. 2008, abstract submitted to Orthopedic Research Society.