The Study: Numerical Prediction of the Mechanical Failure of the Intervertebral Disc under Complex Loading Conditions
a. Finite element modeling has been used to study the disc.
b. Usually these are used to model simple loading conditions of the disc.
c. “The aim of this study was to generate a finite element model of the ovine lumbar intervertebral disc, in which the annulus was characterized by an anisotropic hyperelastic formulation, and to use it to define which mechanical condition was unsafe for the disc.”
d. They modeled the L3-4 disc.
e. “Flexion was considered as the main load responsible for the disc failure. Indeed, when it was combined with lateral bending or with axial rotation only, or when it was applied as a pure load, the predicted stresses were higher than the threshold values determining a high risk of failure.”
f. “The application of flexion with other loads (i.e. lateral bending or axial rotation) always generated the highest state of stress in all directions.” Parenthesis ours.
g. “The major influence of flexion was demonstrated by the fact that it generated stress up to 7 MPa by itself, whereas with the other loads the stress was lower than 4 MPa in all directions (Figure 9).”
h. “…flexion is the load that leads the disc to the most unsafe condition.”
Flexion is not the only load that affects the disc but it is “the load that leads the disc to the most unsafe condition.”
First of all, the authors were careful to note that modeling in this study had a lot of limitations. In addition, different loads have different effects. This is a very complex article and those of you with an interest in the effects of loading on the disc may want to read the full text. I know some of you incorporate the study of rheology into your care and for those people looking at where and how various movements affect the disc this article might be especially appealing. But once again this shows that the body is complex and an understanding of its structure is important.
Reviewer: Roger Coleman DC
Editor: Mark R. Payne DC
Reference: Casaroli G, Villa T, Bassani T, Berger-Roscher N, Wilke HJ, Galbusera F. Numerical Prediction of the Mechanical Failure of the Intervertebral Disc under Complex Loading Conditions. Materials (Basel) 2017 Jan 3;10(1). pii: E31. doi: 10.3390/ma10010031.
Link to Abstract: https://www.ncbi.nlm.nih.gov/pubmed/28772392