A very recent study from 2019, 1 in the Journal of Biomechanics offered some interesting results. It set out to analyze the relationship between IVD intervertebral disc (IVD) and facet joint (FJ) degeneration with regards to chronic low back pain. The results suggested that FJ loading is significantly impacted by the early mechanical changes linked to IVD degeneration. However, the said impact decreased as the degeneration progressed.
What Was the Context?
LBP or low back pain has been researched to be the most common condition (musculoskeletal), negatively affecting humans around the world. The impact of LBP is psychological, physical, economic, and sociological. While a majority of LBP cases are non-specific or generalized (which at our company does not exist), individual research studies have identified several specific causes behind LBP. The most common of these causes are IVD degeneration as well as FJ degeneration. Even though genetics is considered to be a contributor to degeneration, an important role is played by the mechanical environment with regards to pathogenesis. Furthermore, as degenerative changes occur, so can the load transfer from the disc to facets and vice-versa. The present study decided to look deeper into this relationship.
The current research effort developed a parametric finite element (FE) model using ANSYS APDL of an L4-L5 human motion segment. A total of five loading scenarios were considered for this experiment. The degree of disc degeneration was analyzed for each model based on the ratio of the intact disc height to the actual disc height. A similar method was used for FJ degeneration. Four groups were made to cover grades 0 to 3; Grade 0 = non-degenerated disc, Grade 1 = mild degeneration, Grade 2 = moderately degenerated, and Grade 3 = severely degenerated.
The analysis was conducted using a custom Python code. Volumetric operations and imaging were done using the vtk module v6.3. The statistical module of the SciPy library was used for data analysis. (To understand more we advise getting a hold of the full text)
What Were the Results?
Of the total of 1000 models, 14 of them were excluded from further evaluation. This was because they didn’t converge in a single loading scenario. The remaining models showed some interesting results. In the four groups made for disc degeneration (from grade 0 to 3), the said groups, respectively, had 248, 245, 246, and 247 models. In the FJ group, it was 178, 427, 330, and 51.
In Grade 0, 141 showed non-degenerated FJ. Grade 1 had 106 mild degeneration of FJ. The FJ was moderately degenerated in only one sample in Grade 2. Coming to the mildly degenerated disc group, there was an affinity toward higher FJ degeneration grades. The moderately degenerated disc group showed four instances of non-degenerated faces, with 111 being Grade 1, 126 being Grade 2, and 5 being Grade 3. In the severely degenerated disc group, the results showed FJ degeneration in 27 instances in Grade 1, 174 in Grade 2, and 64 models in Grade 3. A strong association between intervertebral disc and facet joint degeneration was observed. A strong positive correlation was analyzed between the FJ gap as well as both the strain in the anterior annulus and the force acting on the IVD.
What was Concluded?
The results of the current study put forth a strong association between IVD degeneration and FJ. The results were backed by previous literature. The gap width of the FJ showed the strongest correlation with disc load (the load which comes through the IVD). The research team of this study agreed that FJ degeneration causes loading and abnormal motion of the IVD, leading to the latter’s degeneration.
Furthermore, the team observed a strong negative correlation existing between FJ capsule tension and disc degeneration. The results of the study suggested that early mechanical changes linked to IVD degeneration had a significant effect on FJ loading. Also, as the degeneration progressed, the said impact is decreased. FJ degeneration also continued to affect disc loading, pointing toward a possible increase in support of disc degeneration.
The results of the current research study tend to suggest that early mechanical changes linked to IVD degeneration have the highest effect on the FJ loading. And as the degeneration continues, the said effect is lowered, whereas FJ degeneration seems to increasingly influence the disc loading, which might indicate increasing support of the disc degeneration.
The research team hopes their efforts help others in further understanding the existing link between FJ and IVD degeneration.