MRI-based grading systems for assessing lumbar disc degeneration

Despite low back pain (LBP) being the leading cause of global disability, identifying a specific pain-generating structure remains difficult. Identifying pathoanatomic structures in LBP may help inform appropriate treatment, improve patient outcomes and reduce healthcare costs. Although structures like the intervertebral disc are thought to be pain producing, their clinical relevance in LBP remains uncertain. This may be partly due to the way changes to the intervertebral disc are measured on magnetic resonance imaging (MRI). The aim of this thesis is to identify and describe grading systems for lumbar disc degeneration (DD) and to assess whether different grading systems have stronger associations with clinical outcomes of LBP. In Chapter 2 a scoping review was performed to identify and describe different grading systems for DD. A substantial number of grading systems were identified. There was also heterogeneity in the components used in the systems, and in the methods of synthesis across the studies. This variability likely hinders the ability to draw clear associations with LBP. In Chapter 3 a secondary analysis was performed that assessed the predictive validity of five different grading systems of DD to predict a recurrence of LBP, including new normalised measures. The normalised measures were used as they showed preliminary evidence in a previous study of being more valid than existing systems. No differences in predictive value were identified between the systems; however, the magnitude and direction of effect was influenced by the components used, normalisation and the way the grading system was summarised for analysis. Future research should explore how to standardise which grading systems are used to measure DD and the way grading systems are summarised for analysis as this likely influences the measured association. Normalised measures must be further tested in bigger cohorts to determine if they are more valid when measuring LBP outcomes.