The role of the nucleus pulposus in neutral zone human lumbar intervertebral disc mechanics
ABSTRACT To study the effect of denucleation on the mechanical behavior of the human lumbar intervertebral disc through a 2mm incision, two groups of six human cadaver lumbar spinal units were tested in axial compression, axial rotation, lateral bending and flexion/extension after incremental steps of "partial" denucleation. Neutral zone, range of motion, stiffness, intradiscal pressure and energy dissipation were measured; the results showed that the contribution of the nucleus pulposus to the mechanical behavior of the intervertebral disc was more dominant through the neutral zone than at the farther limits of applied loads and moments.
Full-textDOI: · Available from: Marco Cannella, Sep 29, 2015
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- "The applied compressive loads were selected to represent moderate levels of physiological stress (0.58MPa and 1.16MPa) experienced during walking or while standing and carrying an object (Wilke, Neef et al. 1999). The measured linear-region stiffness (1500 N/mm) was within the range previously reported (Brinckmann and Grootenboer 1991; Shea, Takeuchi et al. 1994; Okawa, Shinomiya et al. 1996; Beckstein, Sen et al. 2008; Cannella, Arthur et al. 2008), suggesting that our protocol and population was representative of established standards. In addition, the correlations with degeneration in this study were consistent with established literature, which has demonstrated that the disc creep rate is faster in degenerated discs (Kazarian 1975; Keller, Spengler et al. 1987; Li, Patwardhan et al. 1995; Pollintine, van Tunen et al. 2010). "
ABSTRACT: The intervertebral disc maintains a balance between externally applied loads and internal osmotic pressure. Fluid flow plays a key role in this process, causing fluctuations in disc hydration and height. The objectives of this study were to quantify and model the axial creep and recovery responses of nondegenerate and degenerate human lumbar discs. Two experiments were performed. First, a slow compressive ramp was applied to 2000 N, unloaded to allow recovery for up to 24 h, and re-applied. The linear-region stiffness and disc height were within 5% of the initial condition for recovery times greater than 8 h. In the second experiment, a 1000 N creep load was applied for four hours, unloaded recovery monitored for 24 h, and the creep load repeated. A viscoelastic model comprised of a "fast" and "slow" exponential response was used to describe the creep and recovery, where the fast response is associated with flow in the nucleus pulposus (NP) and endplate, while the slow response is associated with the annulus fibrosus (AF). The study demonstrated that recovery is 3-4X slower than loading. The fast response was correlated with degeneration, suggesting larger changes in the NP with degeneration compared to the AF. However, the fast response comprised only 10%-15% of the total equilibrium displacement, with the AF-dominated slow response comprising 40%-70%. Finally, the physiological loads and deformations and their associated long equilibrium times confirm that diurnal loading does not represent "equilibrium" in the disc, but that over time the disc is in steady-state.10/2011; 4(7):933-42. DOI:10.1016/j.jmbbm.2011.02.002
Conference Paper: Automation segmentation of PET image for brain tumors[Show abstract] [Hide abstract]
ABSTRACT: The paper presents an improved fuzzy c-means (FCM) algorithm for obtaining segmentation results of PET image. The segmentation of images with low resolution is usually more difficult than images with high resolution on account of boundary definition difficulties. In order to extract tumor from a PET image, we have to specify the numbers of clusters and which may vary from one image to another when we apply FCM algorithm. However we can divide all contents of image into two parts: background and foreground. Then iterative fuzzy clustering was used and we can get desired results via parameters assessment. The advantage of the algorithm is completely automatic and simple. It is shown that the algorithm is robust for a lot of different datum by experiment.Nuclear Science Symposium Conference Record, 2003 IEEE; 11/2003
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ABSTRACT: In vivo experiments to examine physiologic consequences and in vitro tests to determine immediate biomechanical effects of anular injury by needle puncture. To determine whether a relationship exists between induction of degenerative changes in anulus fibrosus (AF) and compromised disc biomechanical function according to injury size. Various studies in intervertebral disc mechanics, degeneration, and regeneration involve the creation of a defect in the anulus fibrosus (AF). However, the impact of the puncture, itself, on biomechanical function and disc health are not understood. For in vivo experiments, rat caudal discs subjected to percutaneous anular punctures using different gauge size hypodermic needles (18, 22, 26 g) and nonpunctured controls were examined histologically up to 4 weeks postsurgery. For in vitro biomechanical testing, healthy motion segments were isolated and their creep compression response assessed immediately after needle puncture. We found that needle size-dependence of creep compression behavior paralleled the size-dependence of degenerative changes in the AF. Specifically, 18-g punctures resulted in inward bulging of the AF, lamellar disorganization, and cellular changes. These changes were not seen in 22- and 26-g punctured discs. Biomechanical tests showed that only 18-g needle punctures led to significant changes in disc mechanics. Importantly, a statistically significant association was found between needle sizes that caused biomechanical changes and induction of degenerative changes in the AF. Our findings suggest that injury sizes large enough to disrupt biomechanical function are needed to drive degenerative changes in rat caudal disc AF. Based on the data, we believe that small anular defects become sealed, allowing the disc to function normally and the AF to heal. Larger defects appear to require longer wound closure times, and may prolong the duration of impaired disc function.Spine 06/2009; 34(10):998-1005. DOI:10.1097/BRS.0b013e31819c09c4 · 2.30 Impact Factor