The Concavity Index

Abstract

Low back pain (LBP) is one of the most common musculoskeletal disorders facing the working world. Most LBP studies focus on exposure to physical risk factors in the workplace such as lifting, pushing, pulling and awkward postures. Unfortunately, many of these studies do not consider personal risk factors. Several studies have observed that personal characteristics ssuch as age and gender are predictive of LBP. However, studies that focus on MRI characteristics of the disc structure and the relationship between lumbar discs and personal characteristics are very rare. For this study, T2-weighted MRI scans were obtained from 50 subjects (25 females & 25 males) whose age ranged from 20-40 years (mean 31.12 years, SD ± 5.4) without any self-reported chronic episodes of low back pain. The MRI scans contain the sagittal profile of lumbar endplates (L2-S1). Each examiner measured the height and the concavity levels of the lumbar discs. These measures were used to calculate a Concavity Index (CI; concavity level divided by vertebral body height). CIs were compared to Pfirrmann IVD grading scores to evaluate their agreement and compare their respective inter-observer reliabilities. A higher CI is hypothesized to be indicative of spinal degradation and subsequent low back pain. Gender differences were observed for CIs at all levels, particularly for the L5-S1. A linear relationship between average CI and corresponding Pfirrmann classification was observed. While overall agreement among Pfirrmaann raters was high, 10% of ratings disagreed by two or more categories. CIs had an average coefficient of variation of just 0.95% across all participants and lumbar regions. This work presents an alternative method for quantifying intervertebral disc degeneration that appears to have advantages over the traditional Pfirrmann grading scale.