[Correlation of lumbar disc degeneration and spinal-pelvic sagittal balance]

To elucidate the relationship between spino-pelvic sagittal balance parameters and lumbar intervertebral disc degeneration of each segment through retrospective analysis in lumbar degeneration patients.

Retrospective analysis was conducted for the follow-up data in 126 patients with lumbar degenerative disease from July 2009 to June 2012. There were 38 cases with whole spine plates and 88 cases with lumbar plates. All of them received magnetic resonance imaging (MRI) scans. Through software Image J, the following spino-pelvic sagittal balance parameters were measured: sagittal vertical axis (SVA, distance between C7 plumb line and posterior upper corner of S1 endplate), thoracic kyphosis (TK, T5-T12 Cobb angle), thoracolumbar kyphosis (TLK, T10-L2 Cobb angle), lumbar lordosis (LL, L1-L5 Cobb angle), pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), T1 spino-pelvic inclination (T1-SPI), T9 spino-pelvic inclination (T9-SPI), spino-sacral angle (SSA), spino-pelvic angle (SPA) and C7 tilt (C7T). Based on the grading system of Pfirrmann et al, the intervertebral disc degeneration grades were acquired for each lumbar segment. According to the normal range of previous studies, each spino-pelvic sagittal balance parameter was classified into 3 groups, i.e. Group A (less than normal), Group B (normal) and Group C (more than normal). All statistical analyses were performed to compare the differences of each lumbar segment/intervertebral disc degeneration among groups by one-way ANOVA test via SPSS 18.0. And P-value < 0.05 was deemed significant.

PI had a significant impact on the L5/S1 disc degeneration. And L5/S1 disc degeneration had a significant impact on sagittal balance. Among 57 cases of large PI, LL, PT, SS, SVA, C7T, SPA in L5/S1 of mild-to-moderate and severe degeneration groups was 36.91 ± 14.93 and 29.71 ± 11.30 (P = 0.045), 18.82 ± 8.27 and 25.18 ± 10.19 (P = 0.012), 39.45 ± 8.82 and 34.57 ± 8.88 (P = 0.042), 23.04 ± 26.63 and 62.15 ± 33.82 (P = 0.002), 88.85 ± 3.13 and 83.98 ± 4.62 (P = 0.003), 157.88 ± 11.20 and 147.75 ± 13.98 (P = 0.043) respectively. TLK in L1/L2 with mild-to-moderate and severe degeneration groups was 4.59 ± 7.81 and 14.91 ± 14.75 (P = 0.026). All of L1/L2, L2/L3 and L3/L4 disc degeneration had a significant impact on SPA. SPA in L1/L2, L2/L3, and L3/L4 with mild-to-moderate and severe degeneration groups was 158.47 ± 11.97 and 147.84 ± 12.72 (P = 0.031), 159.91 ± 10.78 and 148.75 ± 13.17 (P = 0.024), 158.46 ± 10.86 and 148.61 ± 13.93 (P = 0.047) respectively.

With an important impact on lumbar disc degeneration, PI, either too big or too small, may predispose to the occurrences of lumbar disc degeneration. L5/S1 disc degeneration has a significant impact on pelvis postural parameters (PT, SS). L5/S1 degeneration is a key causative factor of pelvic posterior rotation and compensatory process. L5/S1 disc degeneration has an important impact on pelvis overall parameters (SVA, SPA, C7T). And the degeneration of L5/S1 is a key cause of trunk imbalance.