Most studies that considered the sagittal balance and spinopelvic parameters in literature are retrospective analyses of collected data from follow-up records of registered patients who already have done their surgery without considering these parameters in preoperative planning.
The prevalence of spondylolisthesis in population-based studies have suggested that lumbar spondylolysis have a prevalence of 6% in adult [12, 13]. and that 25% of these populations with spondylolysis experience at least a period of significant back pain in their lifetime.
Isthmic spondylolisthesis appears in a majority of individuals with spondylolysis. Sixty-eight percent of first graders of spondylolysis have been shown to have associated isthmic spondylolisthesis . And this is matching our results as we had 26 patients of isthmic type and 16 of degenerative type, which involved the L3 L4 level in 3 patients, L4 L5 level in 12 patients, the L5S1 level in 18 patients, and multiple levels in 7 patients, with a prevalence of level L5, S1 in the isthmic type and L4,5 in the degenerative type.
So far, there are no definite methods except radiological images to evaluate the instability. So assessment of instability of the spine is a radiological term. Accordingly, the definition of instability is the motion of the above vertebra over expected normal values in the normal spine. In the definition of White and Panjabi, it is the displacement in the sagittal plane of more than 4.5 mm or angulation of more than 22° . Nachemson defined it as translational motion of more than 3 mm and angular motion of more than 10° between L1 and L5 and (more than 4 mm translational motion and 20° angular motion at L5, S1) . In this study, we have considered the Panjabi definition.
Many studies support the improvement of functional outcomes in the different surgical managements of a low-grade spondylolisthesis after the failure of adequate medical treatment and their pain relive either radicular or lower back pain compared to the present study with the same result [16,17,18]. Recent NASS guidelines have recommended surgical decompression with fusion in cases of degenerative lumbar spondylolisthesis over decompression only or nonsurgical options with better clinical outcomes .
Different types of surgery for the management of a low-grade spondylolisthesis have been described in the literature including laminectomy, posterior lumbar intervertebral body fusion (PLIF), transforaminal lumbar interbody fusion (TLIF), anterior lumbar intervertebral body (ALIF), oblique lumbar interbody fusion/anterior to psoas (OLIF/ATP), lateral lumbar interbody fusion (LLIF), and extreme lateral interbody fusion (XLIF). There is no evidence that one surgical approach is clinically superior to another. There is an increasing trend toward MIS approaches due to less intraoperative blood loss; however, long-term data is lacking [20,21,22].
It is now well accepted that with surgical correction, some spinopelvic parameters of spondylolisthesis such as slip reduction, segmental, and global lumbar lordosis, and some reduction can improve spinopelvic balance and the shape of the lumbar spine but most studies focused on high-grade spondylolisthesis [23,24,25,26].
In this study, the preoperative analysis of spinopelvic parameters and the global sagittal balance shows that low PI patients were a small group compared to high PI patients. Low PI reduction of their spondylolisthesis was more correctable than high PI patients, but this was not analyzed in this study because low PI was a small group of patients. Too high pelvic tilt angles showed a postoperative decrease in values of these angles with reduction and fusion, and this provided more physiological value that decreased muscle strain and gave a more favorable outcome. Surgery increased PT to higher values than preoperative which is compatible with the high PI of most of the patients in this study. Although these changes are not statistically significant, mostly due to that there is no major sagittal imbalance noticed in most of our cases as this study included mid and low-grade spondylolisthesis .
We have used bending rods± fusion by harvesting bone grafts from the bone that we removed by decompression of theca and nerve roots this gave us the correction of lumbar lordosis with a range of 5–8° in postoperative images. When we need more, we add a PLIF cage which increases our correction to 10–15° in postoperative images. We did not use hyperlordotic cages as it is not available, and our patients did not need more correction than 15°. And this is matching Bourghli et al.’s and Harimaya et al.’s studies [28, 29].
Several studies demonstrated a single pedicle subtraction osteotomy (PSO) can generate 20 to 40° of LL and an approximate 10 to 12 cm change in SVA, depending on the wedge of bone removed [30,31,32,33,34]. Vertebral column resection (VCR) is a procedure of last resort and only considered when more conservative osteotomy will not suffice. Posterior VCR (PVCR) involves resection of all posterior elements, facet joints above/below, pedicles, entire vertebral body, and discs above/below. VCR allows for the tremendous ability to correct the deformity as the entire spine is disarticulated and shortened. In this study, there was no need for osteotomies to increase the degree of sagittal balance correction as bending rods ± TLIF were enough.
Using a short-segment fixation with fusion is the main concept of spine surgeons apart from scoliosis surgeons who prefer long-segment fixation which increases the risk of the flat back syndrome . Unless needed, it is enough for a low-grade lumbar spondylolisthesis to use a short segment of spinal fusion as reported by Cho et al. , with great stress on the importance of considering spinal alignment by the restoration of LL in the treatment of a low-grade spondylolisthesis as reported by Lee et al. , and loss of LL is postoperatively being associated with increased incidence of low back pain and adjacent segment disease, which was reported in many studies [38,39,40,41,42]. In this study, a short-segment fixation was done in all patients without the need for a long segment which may be because we were working on a low-grade spondylolisthesis.
Our results are matching the results of Jackson et al. who had found the difference in the C7 plumb line to S1 offset between patients with spondylolisthesis and normal individuals . Harroud et al. found a major difference in the sagittal vertical axis between high-grade and low-grade spondylolisthesis .
Hresko et al. recommended that partial reduction and instrumentation may be the most important determinant of outcomes, as no correlation was found in his series between the amount of reduction of spondylolisthesis and the improvement in the pelvic tilt .
Bourghli et al. suggested that the most important point to increase the functional outcome postoperatively is to reposition L5 over S1 as measured by L5 incidence and lumbosacral angle (LSA), rather than reduction of the spondylolisthesis grade. In our study, LSA improved after surgery, moving toward a more normal value, without a statistical significance, but the moderate improvement in LSA showed that L5 repositioning occurred. And this is similar to our results .
In this series, the functional outcome is satisfactory with high statistical significance either in pain relief which had tested by VAS scale or gain more improvement in function as tested by ODI score, and this is also the same results in the series of Bourghli et al.  and Korovessis et al. , but the later one is a retrospective study.
Our results are similar to the results of a meta-analysis done by Kwon et al. in which a better outcome for the treatment of spondylolisthesis is by using instrumented posterior spinal fusion in combination with an interbody graft as opposed to either PSF treatment alone or interbody graft alone . The positive impact of interbody support in the surgical treatment of spondylolisthesis on radiographic and clinical outcomes which has been confirmed by Molinari . This is contrary to the results of Hsu et al. who founded that surgical outcomes in the treatment of a low-grade lumbar degenerative spondylolisthesis with spinal fusion are not correlated with restoration of the LL. And they explained that in their retrospective study, the sagittal balance of patients was in the normal range, preoperatively .
The limitations of this study is that it is not a long-term follow-up, and no randomization and there is no control group.