Spinopelvic Alignment and Functional Outcome after Circumferential Fusion for Low-grade Isthmic Spondylolisthesis

Abstract

IntroductionFunctional outcomes after surgery for low-grade isthmic spondylolisthesis(LGIS) is reported limitedly for combined posterior and anterior approach procedures. Imbalances in the sagittal alignment of spine and pelvis are increasingly seen as the reason for the development and progression of LGIS. Aims of this study: 1) functional outcome, 2) the effects on spinopelvic alignment, after circumferential fusion. Surgical treatment goals are restoration of stability, reduction of slippage, restoration of disc height and angulation, correction of spinopelvic parameters toward neutral values, and improve functional status. We hypothesized 1) a significant improvement on clinical outcome at 2-year follow-up and 2) a stable post-operative situation around the targeted vertebrae and restoration of the spinopelvic parameters to values seen in healthy subjects. Materials and Methods43 subjects enrolled with LGIS at L5-S1. Each subject received a posterior decompression and pedicle screw instrumentation followed by an instrumented anterior lumbar interbody fusion in two separate procedures. (1) Outcome measures were registered pre-operative and after 12 and 24 months. Primary outcome was functional status (ODI). Secondary outcomes: Quality of Life (SF-36 subdomains, EQ-5D subscales), and pain intensity (VAS back and leg pain). (2) Full spine radiographs were taken pre-operative and after 3, 12, and 24 months postoperative. Obtained spinopelvic parameters are: sacral slope, pelvic tilt, pelvic incidence, thoracic kyphosis, L5-S1 lordosis, L1-S1 lordosis and sagittal vertical axis. The degree of slippage reduction and L5-S1 angular motion was measured. To evaluate both study aims a repeated measures ANOVA was used to indicate differences over time. Results42 patients (25 female), average age 39,0 (25–51) with an average BMI 25,8 (21,5–30,4) participated in the study. Functional results are given as means with (standard deviation) pre-operative, at 12 months and 24 months postoperative for ODI: 35,0 (14,4); 10,0 (15,0); 9,5 (15,3); for SF-36 PCS: 42,0 (12,7); 70,5 (21,0); 71,5 (21,5); for SF-36 MCS: 64,0 (16,6); 81 (19,4); 81,5 (19,5); for EQ-5D: 0,56 (0,29); 0,84 (0,28); 0,83 (0,240); for VAS (back pain): 64,5 (26,2); 16,0 (32,2); 22,0 (23,9). Degree of slip decreased significantly from 27,0% (11,9%) to 7,4% (11,7%) postoperatively. Angular motion decreased statistically significant immediately postoperative and remained stable thereafter. L5-S1 and L1-S1 lordosis and sacral slope showed a significant increase postoperatively, whereas the pelvic tilt and sagittal vertical axis significantly decreased. ConclusionCircumferential instrumented fusion for LGIS via combined approach improves functional outcome at short term follow-up. After careful patient selection and unsuccessful conservative management surgical treatment is a suitable alternative with predictable short term outcome. Circumferential fusion corrects deformity and creates a stable situation in LGIS. We find that sagittal alignment is probably influenced positively, by bringing the SVA in a more neutral position.