Correlations between the sagittal plane parameters of the spine and pelvis and lumbar disc degeneration

BACKGROUND: Studies have shown that lumbar disc herniation, degenerative lumbar instability, and other degenerative lumbar spinal diseases are often secondary to disc degeneration. By studying the intervertebral disc, researchers have clarified the pathological changes involved in intervertebral disc degeneration but have ignored the roles of biomechanical factors in the development of disc degeneration. This study aims to investigate the relationships among the location, scope, and extent of lumbar disc degeneration and sagittal spinal-pelvic parameters. METHODS: A retrospective analysis was performed on the clinical data of 284 patients with lumbar degenerative disc diseases (lumbar disc herniation and degenerative lumbar instability) from January 2013 to December 2016. Statistics were calculated for the following: (1.) patients’ general information: name, sex, age, height, and weight. (2.) Measurements of sagittal parameters from total spinal radiographs: thoracic kyphosis (TK), Lumbar lordosis (LL), sacral slope (SS), pelvic tilt (PT), pelvic incidence (PI), sagittal vertical axis (SVA), T1 tilt angle (TA), and T1 pelvic angle (TPA). (3.) Location, scope, extent, and overall degree of lumbar disc degeneration. Parameters were analyzed in groups by sex, PI, and SVA, and a correlation analysis was performed for the location, scope, extent, and overall degree of lumbar intervertebral disc degeneration with 8 spinal-pelvic sagittal parameters. RESULTS: The mean ages of the male and female patient groups were 59.00 and 53.28 years old, respectively (P < 0.05). The PT, location, scope, and overall degree of degradation were significantly different between the sexes (P < 0.05). Linear correlation analysis results showed that the overall degree and extent of degradation (r = 0.788, P < 0.01), LL and SS (r = 0.737, P < 0.01), PI and PT (r = 0.607, P < 0.01), and TPA and PT (r = 0.899, P < 0.01) were strongly correlated. The location values were 4.08 ± 0.72 in patients with PI≤50° and 3.62 ± 0.94 in patients with PI> 50° (P = 0.018). Different SVASVA groups differed in their overall degree of degeneration (P = 0.002). CONCLUSIONS: The location of lumbar intervertebral disc degeneration is affected by spinal-pelvic sagittal morphology. Populations with small PI values tend to exhibit degeneration at the L4/5 and L5/S1 discs, and populations with large PI values tend to exhibit degeneration at the L3/4 and L4/5 discs. The SVA value and the overall degree of lumbar disc degeneration are positively correlated.