Advisor: Michele Marcolongo, Ph.D.
The lifetime prevalence of lower back pain is 65-80%, and on average 50-90% of adults endures Lower Back Pain (LBP). Lumbar degenerated discs are thought to affect about 75% of cases with LBP. Degenerated discs are not able to withstand the forces distributed on the spine properly and they can adversely affect other spine levels as well by inducing more loads on them, due to inefficiency of the degenerated disc to absorb its portion of the total load on the spine. In a healthy intervertebral disc (IVD), forces generated are absorbed and transmitted appropriately from the nucleus pulposus (NP) to the annulus fibrosus (AF), however in a degenerated disc force transmission is from endplate to endplate thus, there is no communication between the NP and AF due to a lack of hydrostatic pressure inside the NP. Hydrostatic pressure produced within the NP, decreases with increasing disc degeneration grade. Specifically, the hydrostatic pressure in moderately degenerated discs has been shown to be 30% less than in a healthy disc. This hydrostatic pressure therefore is responsible for proper load transmission in the IVD and therefore lack of this pressure further creates a decrease in disc height, stress concentrations in AF and increases the chance for IVD herniation.
A total of seven cadaver lumbar specimens (L1L5) were loaded in compression. We proposed firstly a method of measuring the hydrostatic pressure in the NP through the use of a pressure transducer (PT) to monitor the change in pressure during a variety of loading conditions. Then we proposed to place a polymeric implant into the NP. Original specimen disc height was measured by use of a fluoroscan x-ray machine before testing. We proposed to increase the volume of implantation to values of 2.5%, 5.0%, 7.5%, 9%, 11.5%, and 13.0% of the original disc height. Our hypothesis was that augmenting the NP with a polymeric implant will increase disc height and hydrostatic pressure in proportion to the volume of material implanted. Hydrostatic pressure, disc height, and stiffness measurements were analyzed between different implant percentages. Neutral zone measurements were also measured to analyze significant differences between the stiffness values in the compressive and tensile neutral zone regions.
Our results concluded that pressure in the NP increased significantly, by up to 60% of initial pressure measured at the highest load observed, due to volume of implant. The disc height increased by up to 14% of original disc height, upon implantation. Stiffness of the disc remained unchanged after a load of 400 N despite the increase in pressure and disc height due to implantation. The polymeric implant used in this study improved mechanical properties essential for proper load bearing of the human intervertebral disc.
The LeBow Engineering Center is located at the corner of 32nd and Market Streets.