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Health and Safety at Work
Published in Stephen Pheasant, Christine M. Haslegrave, Bodyspace, 2018
Stephen Pheasant, Christine M. Haslegrave
The probability also is that these factors act cumulatively over a period of time (although the process of cumulative injury will doubtless be offset to some extent by the body’s natural mechanisms of repair). There is some striking epidemiological evidence for this — at least over the very long time scale. Degenerative disc disease is generally thought of as being part of the natural ageing process. The physiological changes in the properties of the disc which underlie the process of degeneration commence at around age 25; past middle age we are all affected to a greater or lesser extent. Superimposed over these physiological changes are the effects on the discs of normal wear and tear. A constitutional predisposition is also thought to be involved, although the principal evidence cited for this proposition is that people who show severe signs of degenerative changes in one part of the spine are likely to show them in other parts as well, and this evidence could be interpreted in other ways.
Understanding Musculoskeletal Disorders (MSDs)
Published in Dan MacLeod, The Ergonomics Kit, 2006
The discs provide cushioning between the vertebrae. They enable us to bend and twist, and have the incredible range of motion that our backs have. Unfortunately, with enough bending and twisting, especially while carrying a load, the discs can suffer wear and tear. After a time the discs can narrow, harden, and the surfaces fissure and crack; what we call “degenerative disc disease.” Once weakened, the discs can bulge out, strain, or herniate.
Finite element study on the influence of pore size and structure on stress shielding effect of additive manufactured spinal cage
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2022
Vijay Kumar Meena, Parveen Kalra, Ravindra Kumar Sinha
Spinal injuries and spinal disorders are becoming increasingly common ailments in modern life. One of the most common diseases/ailments is Degenerative Disc Disease, popularly known as DDD (Pannell et al. 2015). The cure involves surgical procedures of degenerated disc and insertion of appropriate implants, namely spinal cages between the vertebrae. Titanium alloy (Ti6Al4V) is the preferred choice for spinal cages due to its high tensile strength, good biocompatibility, good fatigue strength, and corrosion resistance (Ramakrishna et al. 2001). These spinal cages are generally made of solid dense metals/polymers e.g. titanium, Carbon Fiber Reinforced PEEK, etc. Young’s modulus of these materials is much higher than human bone Young’s modulus. The elastic modulus of bone varies between 1 and 20 GPa whereas the elastic modulus of titanium is 110 GPa. Due to this vast difference in elastic modulus, the loads are not transferred from the implant to adjacent bone tissue, resulting in stress shielding between the host bone and the implant. This leads to adaptive resorption of bone tissue and a decrease in mechanical rigidity of the bone as per Wolff’s law (Chen et al. 2010). Similarly, with reduced stress shielding, bone tissues are known to generate deposition of new bone, which increases mechanical rigidity (Stock 2018). Also, the smooth and shiny surface of solid metal implants makes it difficult to integrate with the host bone. This causes amyotrophy and osteonecrosis of bones around the implants, loosening of the implant, distortion of bones, etc (Haibo et al. 2012).