Disc degeneration implies low back pain

Abstract

Background: Low back pain exerts a tremendous burden on individual patients and society due to its prevalence and ability to cause long-term disability. Contemporary treatment and prevention efforts are stymied by the absence of a confirmed cause for the majority of low back pain patients.

Methods: A system dynamics approach is used to build a physiologically-based model investigating the relationship between disc degeneration and low back pain. The model's predictions are evaluated under two different types of study designs and compared with established observations on low back pain.

Results: A three-compartment model (no disc degeneration, disc degeneration with pain remission, disc degeneration with pain recurrence) accurately predicts the age-specific prevalence observed in one of the largest population-based surveys (R (2) = 0.998). The estimated transition age at which intervertebral discs lose the growth potential and begin degenerating is 13.3 years. The estimated disc degeneration rate is 0.0344/year. Without any additional change being made to parameter's values, the model also fully accounts for the age-specific prevalence of disc degeneration detected with a lumbar MRI among asymptomatic individuals (R (2) = 0.978).

Conclusions: Dual testing of the proposed mechanistic model with two independent data sources (one with lumbar MRI and the other without) confirm that disc degeneration is the driving force behind and cause of age dependence in low back pain. Observed complexity of low back pain epidemiology arises from the slow dynamics of disc degeneration coupled with the fast dynamics of disease recurrence.

Fig. 1

A three-compartment flow chart for the dynamic back-pain model. Individuals without disc degeneration initially reside in compartment N. Once having disc degeneration, they are moved to compartment D ₀. This is then followed by frequent interchange between compartments D ₀ and D ₁

Fig. 2

Changing prevalence of low back pain (filled squares and dotted line) and asymptomatic disc degeneration (filled diamonds and dashed line) with age. The filled squares represent the observed prevalence of low back pain among the Hungarian population (Horváth et al. 2010). The dotted line represents the result of curve fitting with the prevalence function $z^{*}\left(t\right)=\alpha +\beta \left(1-e^{-{\lambda }_1\left(t-t_0\right)}\right)$ (α = 0.031, β = 0.698, λ₁ = 0.0344, t ₀ = 13.3; R ² = 0.998). Filled diamonds are based on the graph (percentage of disc degeneration among asymptomatic women) of Powell et al. (1986). The prediction (dashed line) is based on the function $y^{*}\left(t\right)=\frac{\left(1-\beta \right)\left(1-e^{-{\lambda }_1\left(t-t_0\right)}\right)}{e^{-{\lambda }_1\left(t-t_0\right)}+\left(1-\beta \right)\left(1-e^{-{\lambda }_1\left(t-t_0\right)}\right)}$ (R ² = 0.978). Note that the parameter values of y ^*(t) are taken from z ^*(t). The only adjustment made is to the symptom expression fraction β (normalized for a predefined duration factor μ; see main text for more details)