The effects of axial loading on the morphometric and T₂ characteristics of lumbar discs in relation to disc degeneration

Background: Intervertebral disc degeneration affects the morphology, biomechanics and biochemistry of the disc. The study aimed to compare the effects of compression and traction on lumbar discs measurements in relation to degeneration.

Methods: Thirty-five volunteers (30 (SD 11) yrs.) with and without chronic back pain rested supine 15 min before an unloaded T₂-mapping MRI, were then loaded 20 min with 50% body weight with imaging during the last 5 min, and then repeated this process under traction. For lumbar discs, height, angle, width, mean-T₂, and T₂-weighted centroid locations were calculated. A repeated measure ANCOVA and Cohen's d compared loading conditions. Relations between measurement changes between conditions and degeneration assessed by Pfirrmann ratings were examined graphically.

Findings: From compression to traction, we observed significant: decrease in L1-2 mean-T₂ (Effect size = -0.35); inferior and posterior shift in L4-5 (0.4, 0.14) and L5-S1 (0.25, 0.33) T₂-weighted centroid. From unloaded to compression, we observed a significant: increase in L5-S1 width (Effect Size = 0.22); anterior shift in L1-2 T₂-weighted centroid (0.39); and L3-4 (mean 2.1°) and L4-5 (1.8°) extension angle. More degeneration was graphically related with larger changes from Compression to Traction (more superior and, anterior position of the T₂-weighted centroid, increased height, reduced extension of segmental angle) and from Unloaded to Compression larger changes in inferior displacement of the T_2-weighted centroid, decrease in height) but less anterior displacement of the centroid and less change in segmental angles.

Interpretation: The largest loading responses were at lower levels, generally with more degeneration. T₂-weighted centroid locations, angle and disc height detected the largest loading response.