Goal of the Study?
In this study 1, the authors attempt to build a three-dimensional finite element (FE) model to investigate how changes to the nucleus pulposus (NP) under axial compression loads influences bulging in the lumbar disc.
Why are they doing this study?
The intervertebral disc provides cushioning between vertebrae and absorbs pressure on the spine. A disc herniation happens when the annulus fibers are weakened or torn, and the NP pushes through the annulus fibrosus (AF). This bulging can generate pressure on the adjacent nerve roots causing lower back pain (LBP) and may even lead to paralysis.
Existing research suggests that under the same compression the extent of the bulging differs by area, with the posterior region experiencing the least amount of bulging. Taking this knowledge into consideration, the authors argue that it is important to understand the behaviour of bulging in the disc to prevent severe damage and provide a path to more effective treatment.
What was done?
The researchers created a 3D FEA model that simulates a functional human spinal unit of the lumbar region under axial compression loads. The material properties of the AN and NP are assumed to be linear elastic and the structure of the AF is modeled as a homogeneous material without fibrin.
To validate the model, the authors looked at the axial and bulging displacements under axial compression load and compared that to existing data. They further validated their model by comparing the distribution of stress in the AF with and without the NP.
What did they find?
The researchers found that the condition of the disc (partial removal, full removal or intact) significantly affects how the disc bulges and where. For example, they found that for a disc without an NP the posterior region bulges inward. In contrast, for both an intact NP and with partial removal of the NP, the bulging occurs outward due to increasing pressure at the central part of the AF.
Why do these findings matter?
The findings can help to improve treatment decisions of the degenerative disc and nucleus pulposus.