Disc height discrepancy between supine and standing positions as a screening metric for discogenic back pain in patients with disc degeneration

Background context: The diagnosis of discogenic low back pain (LBP) from disc degeneration of the lumbar spine is often evaluated with discography. Non-invasive, simple screening methods other than invasive discography are useful, as evidence supporting clinical findings and magnetic resonance imaging (MRI) have come to the forefront.

Purpose: To investigate disc height (DH) discrepancy between supine and standing positions on simple radiography to clarify its clinical screening value in individuals with discogenic LBP.

Study design/settings: Retrospective matched cohort design.

Patient sample: Ninety-two patients with early to middle stage disc degeneration (Pfirrmann grade II, III, IV).

Outcome measures: Each subject underwent simple radiographs and MRI. Baseline characteristics, including demographic data and MRI findings, and radiological findings, including DH discrepancy, segmental angle, and sagittal balance, were analyzed. DH discrepancy ratio was calculated as (1 - [calibrated DH on standing radiography/calibrated DH on supine radiography]) × 100%.

Methods: We matched LBP group of 46 patients with intractable discogenic pain (≥7 of visual analog scale scores) confirmed by discography with control group of 46 patients with similar stage disc degeneration with mild LBP (≤4 of visual analog scale scores). Binary regression analysis, receiver operating characteristic (ROC) curve analysis, and cut-off value for diagnosis were used to evaluate and clarify diagnostic value of various factors.

Results: There was no significant difference between the two groups in terms of baseline characteristics, including age, sex, body mass index, pathological level, and magnetic resonance findings such as disc degeneration, high intensity zone, and para-spinal muscle volume. Among the various radiological findings, the calibrated mean DH in the standing position (20.87±5.65 [LBP group] versus 26.95±3.02 [control group], p<0.001) and the DH discrepancy ratio (14.55±6.13% [LBP group] versus 1.47±0.75% [control group], p=0.007) were significantly different between the two groups. The cut-off value for DH discrepancy ratio to screen discogenic LBP was ≥6.04%. Additionally, as a compensation for pain, sagittal vertical axis (3.43±2.03 cm [LBP group] versus -0.54±3.05cm [control group], p=0.002) and pelvic incidence (54.74±6.76° [LBP group] versus 43.98±8.67° [control group]; p=0.006) were different between the two groups.

Conclusions: The results suggest that DH discrepancy between the supine and standing positions could be a screening metric for discogenic LBP in early to middle stage disc degeneration of the lumbar spine.

Keywords: disc degeneration; disc height; intervertebral disc; low back pain.