Sagittal Balance Parameters Correlate with Resorption of the Lumbar Disc Extrusion: Results of a Retrospective Study

  Objective  A retrospective study was designed to explore the relationship between the satittal spinopelvic alignment in patients with lumbar disc extrusion and spontaneous resorption.

  Methods  From May 2010 to March 2019, referring to NASS evidence-based clinical guidelines, patients with lumbar disc extrusion were enrolled in this retrospective study, according to the degree of herniation size during the follow-up, the patients were divided into two groups: resorption (group R: the herniated disc completely disappeared or the herniation size was grade 1 according to Michgan State University (MSU) classification) and nonresorption (group N: the herniated disc remain unchanged or the herniation size overpass grade 1), spinopelvic parameters (including the pelvic incidence (PI), sacral slope (SS), pelvic tilt (PT), lumbar lordosis (LL)) were determined on standing profile radiographs of the lumbar spine and pelvis, and mean values were compared using the multi-factor analysis of variance.

  Results  This study included 67 patients with lumbar disc extrusion. There were 37 in group R (the average age was 42.6 years), 21 males and 16 females, 13 cases at L_4-5 level and 24 cases at L₅-S₁ level, follow-up 22 months, and 30 in group N (the average age was 40.8 years), 19 males and 11 females, 12 cases at L_4-5 level and 18 cases at L₅-S₁ level, follow-up 21 months, at the follow up time, there symptoms were all satisfactorily relieved. There were no signifcant differences in age, gender, smoking history, chronic medical history, prominent segmnet, MSU classification, follow up time and other baseline conditions between two groups (P>0.05). At the follow-up, in group R, all 30 cases of sagittal displaced disc disappeared, the herniated disc changed from the initial MSU classification of grade 2 in 19 cases and grade 3 in 18 cases to the post-absorption residual disc, which were limited to grade 1; in group N, 20 cases of sagittal displaced disc reduced to 14 cases, the herniated disc changed from the initial MSU classification of grade 2 in 21 cases and grade 3 in 9 cases to grade 2 in 27 cases and grade 3 in 3 cases. There was no significant difference in spinopelvic parameters between the two groups before the treatment (P>0.05). At the follow-up, there was no significant difference in PI between the two groups (P>0.05); the SS and LL in group R were bigger than those in group N, the PT in group R was smaller than that in group N, and the difference was statistically significant (P<0.05). Compared within the same group, before treatment and follow-up, there were no significant differences in PI, SS and PT in group R, but a bigger LL (P<0.05); no significant differences in all the parameters in group N were found.

  Conclusion  Resorption may result in pinopelvic parameter changes, which suggest that the lumbar spine is better at cushioning against load, reducing the disc pressure, and leading to resorption of the herniated disc.