Introduction: Low back pain (LBP) patients often experience aggravated pain in positions of spinal loading. Quantitative MRI studies have found load-induced differences in posterior part of intervertebral discs (IVDs) between LBP patients and controls. MRI during axial loading has been reported to induce concordant pain in some LBP patients. The effect of axial loading, captured with quantitative sequences, may help identify IVD characteristics linked to load-induced pain, potentially aiding the discovery of imaging biomarkers for LBP. The aim of this study was to investigate if there are any load-induced differences, between IVDs in LBP patients experiencing aggravated pain during loading and those who do not.
Method: 178 LBP patients, recruited for another study, were investigated. They had been imaged with quantitative (T2 mapping) MRI with and without axial loading in the supine position and had reported intensity and character of daily pain and pain during the investigation on a numerical rating scale (NRS) from 0 to 10. As part of the current study the patients were stratified according to whether or not they experienced aggravated pain during the MRI. Load-induced T2-value behavior in entire IVDs, and in central/posterior IVD-parts on levels L3/L4 to L5/S1 was compared between the two groups. Sub analyses, within each group, were performed on IVDs with Pfirrmann grade 3 to 4 and high intensity zones (HIZs).
Results: In total 120 patients stated aggravated pain during the investigation with axial load (mean intensity of pain during the examination of 5.8 on the NRS, compared with 5.7 as their daily level) and 58 patients stated no aggravated pain (mean 2.3 compared with 5.4). Among the patients with aggravated pain, 84% stated it to be concordant with their daily pain. Higher load-induced T2-value increases were found in entire IVDs on level L5/S1 (relative difference of 2% [95% CI; 0-5%]; p = 0.038) and in posterior part of IVDs on level L3/L4 (relative difference of 4% [95% CI; 0-7%]; p = 0.033) in patients with aggravated pain compared to those without. No differences between the groups were found stratifying for IVDs with Pfirrmann grade 3 and 4 or with HIZs. The percentage of HIZs were similar in both groups. HIZ IVDs in patients with aggravated pain exhibited load-indued increase of T2 values in posterior part on levels L4/L5 (4% [95% CI; 1-7%]; p = 0.015) and L5/S1 (6% [95% CI; 1-11%]; p = 0.031) that was not found in IVDs in patients without aggravated pain.
Discussion: Higher load-induced global and posterior T2-value increments in IVDs in LBP-patients with aggravated pain during the MRI examination, compared to the group without aggravated pain, was shown. This suggest different biomechanical IVD-phenotypes between the two groups and strengthening the theory that load induced pain in LBP-patients is associated to deviant behavior in posterior IVD-parts. Different behavior within the groups remained when analyzing only HIZ IVDs, suggesting that other features are responsible for the deviant load-induced behavior and that HIZ is insufficient to use as a stand-alone marker for load induced pain.