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The impact of sagittal balance on clinical results after posterior interbody fusion for patients with degenerative spondylolisthesis: A Pilot study
© Kim et al; licensee BioMed Central Ltd. 2011
Received: 28 September 2010
Accepted: 5 April 2011
Published: 5 April 2011
Comparatively little is known about the relation between the sagittal vertical axis and clinical outcome in cases of degenerative lumbar spondylolisthesis. The objective of this study was to determine whether lumbar sagittal balance affects clinical outcomes after posterior interbody fusion. This series suggests that consideration of sagittal balance during posterior interbody fusion for degenerative spondylolisthesis can yield high levels of patient satisfaction and restore spinal balance
A retrospective study of clinical outcomes and a radiological review was performed on 18 patients with one or two level degenerative spondylolisthesis. Patients were divided into two groups: the patients without improvement in pelvic tilt, postoperatively (Group A; n = 10) and the patients with improvement in pelvic tilt postoperatively (Group B; n = 8). Pre- and postoperative clinical outcome surveys were administered to determine Visual Analogue Pain Scores (VAS) and Oswestry disability index (ODI). In addition, we evaluated full spine radiographic films for pelvic tilt (PT), sacral slope (SS), pelvic incidence (PI), thoracic kyphosis (TK), lumbar lordosis (LL), sacrofemoral distance (SFD), and sacro C7 plumb line distance (SC7D)
All 18 patients underwent surgery principally for the relief of radicular leg pain and back pain. In groups A and B, mean preoperative VAS were 6.85 and 6.81, respectively, and these improved to 3.20 and 1.63 at last follow-up. Mean preoperative ODI were 43.2 and 50.4, respectively, and these improved to 23.6 and 18.9 at last follow-up. In spinopelvic parameters, no significant difference was found between preoperative and follow up variables except PT in Group A. However, significant difference was found between the preoperative and follows up values of PT, SS, TK, LL, and SFD/SC7D in Group B. Between parameters of group A and B, there is borderline significance on preoperative PT, preoperative LL and last follow up SS.
Correlation analysis revealed the VAS improvements in Group A were significantly related to postoperative lumbar lordosis (Pearson's coefficient = -0.829; p = 0.003). Similarly, ODI improvements were also associated with postoperative lumbar lordosis (Pearson's coefficient = -0.700; p = 0.024). However, in Group B, VAS and ODI improvements were not found to be related to postoperative lumbar lordosis and to spinopelvic parameters.
In the current series, patients improving PT after fusion were found to achieve good clinical outcomes in degenerative spondylolisthesis. Overall, our findings show that it is important to quantify sagittal spinopelvic parameters and promote sagittal balance when performing lumbar fusion for degenerative spondylolisthesis.
The clinical outcomes of spinal fusion in degenerative spondylolisthesis are influenced by a variety of pathophysiologic factors, such as, the recurrence of spinal canal stenosis, instability, lumbar kyphosis, nonunion, and the disturbance of adjacent segments [1, 2]. Although satisfactory clinical outcomes have been reported for a variety of surgical techniques, the optimal management of degenerative spondylolisthesis remains controversial. Recently, laboratory and clinical evidence has indicated that if fusion surgery is undertaken, improved short- and long-term outcomes can be achieved by correcting any sagittal deformity present [3–5].
Some studies have attempted to correlate spinopelvic parameters with health related quality of life (HRQOL) or pain measures in order to provide some insight during surgical planning for isthmic spondylolisthesis [6, 7]. These studies identified key radiographic parameters that are correlated with patient pain and disability, and found that pelvic tilt (PT) is related to HRQOL. However, these studies were not without limitations, and evidence supporting this relationship remains limited and it has not been determined whether sagittal vertical axis influences clinical outcomes in degenerative spondylolisthesis [9–11].
The purpose of this study was to explore the relationships between pelvic tilt and other spinopelvic parameters and with clinical outcomes after spinal fusion for degenerative spondylolisthesis. In addition, we attempted to determine whether specific critical values of spinopelvic parameters can predict poor HRQOL, and thus, aid surgical planning.
We retrospectively reviewed 220 patients who underwent surgery for degenerative spondylolisthesis from July 2003 to June 2008 at our institute. All patients were operated on by four senior surgeons (KES, WE, CSS and LJS). Eighteen of these patients were selected for this study by applying the following criteria: 1) one or two-level degenerative lumbar spondylolisthesis; 2) treatment by posterior interbody fusion; 3) patients showing radiological solid fusion on follow up computed tomography (CT); and 4) a minimum clinical and radiologic follow-up of 24 months. The following exclusion criteria were applied: 1) more than three-level fusion; 2) a history of a previous spinal operation; and 3) the presence of severe systemic disease, a vertebral fracture, or osteoporosis. All patients visited our outpatient department in June 2010, and a trained nurse collected follow-up clinical data. The medical records of patients were reviewed, along radiographic studies that included preoperative and postoperative radiographs, computed tomography (CT) scans, and magnetic resonance images.
Summary of patient demographic and preoperative clinical characteristics
Group A (n = 10)
Group B (n = 8)
Mean age in yrs (range)
Clinical and radiological evaluations
All patients were examined clinically and radiographically before and after surgery at the following times: immediately after surgery and at 3, 6, and 12 months and annually thereafter. At clinical evaluations, all patients completed the Visual Analogue Pain Score (VAS) for back pain and the Oswestry disability index (ODI) questionnaire in order to assess HRQOLs . Clinical outcome was evaluated with improvement in VAS and in ODI. Preoperative and final follow up data were assessed using clinical charts and operative reports.
Patients were divided into two groups using improvement of PT at last follow up: group A showed a tendency towards increased and unchanged PT; and group B showed a tendency towards decreased PT to normal range. Radiologic factors and clinical outcomes were compared statistically between two groups.
Statistical analysis was performed using PASW statistical software ver. 18.0 (SPSS Inc., Chicago, IL). The Mann-Whitney U-test was used to compare group clinical and radiological outcomes. Wilcoxon's rank sum test was used to compare differences between pre-, postoperative and final follow-up parameters of clinical and radiological outcomes. Correlation studies were performed using Pearson's coefficients to investigate relations between all radiologic parameters and VAS and ODI improvements.
Result of clinical outcomes and spinopelvic parameter of 18 patients
Comparison of clinical outcomes in the two study groups based on changes in pelvic tilt after spinal fusion.
Improvement rate of VAS
Improvement rate of ODI
A (n = 10)
6.85 ± 2.53
3.20 ± 2.35
43.2 ± 19.0
23.6 ± 13.4
B (n = 8)
6.81 ± 1.81
1.63 ± 0.52
50.4 ± 20.8
18.9 ± 13.8
Mean values ( ± standard deviation) of Spinopelvic parameters in the two study groups based on changes in pelvic tilt after spinal fusion
Sacral slope (°)
(n = 10)
21.5 ± 5.0
24.3 ± 5.1
25.1 ± 6.2†
31.2 ± 8.8
27.9 ± 8.7
28.9 ± 9.8
52.7 ± 7.9
52.2 ± 6.7
53.7 ± 7.0
(n = 8)
26.4 ± 4.2
24.5 ± 4.7
18.4 ± 3.6†
29.1 ± 62
29.2 ± 7.1
36.7 ± 6.5†
55.5 ± 6.3
55.0 ± 8.0
55.1 ± 7.7
(n = 10)
38.4 ± 9.7
36.4 ± 8.8
33.7 ± 10.0
46.5 ± 9.3
45.0 ± 9.9
48.1 ± 10.9
0.81 ± 0.9
0.82 ± 0.4
0.50 ± 0.6
(n = 8)
35.2 ± 8.9
37.1 ± 8.9
41.3 ± 9.6†
38.4 ± 8.1
39.9 ± 10.8
47.4 ± 7.5†
0.74 ± 0.4
0.11 ± 0.4
0.27 ± 0.4†
Pearson's correlation coefficients between spinopelvic and clinical parameters in the two study groups
(n = 10)
(n = 8)
Sacral slope (°)
The optimal surgical approach to the management of lumbar degenerative spondylolisthesis has yet to be determined. Although gross spinal imbalance in association with degenerative lumbar spondylolisthesis is rare, more subtle forms of segmental imbalance may influence early surgical outcome and the later development of adjacent segment disease [3, 13, 14]. Furthermore, although slippage and lordosis at the level of spondylolisthesis have been evaluated radiologically, few reports have discussed lumbar sagittal balance in patients with degenerative lumbar spondylolisthesis
In an early study on 95 patients, Schwab et al identified radiologic parameters correlated with self-perceived pain (measured using a VAS scale), namely, intervertebral subluxation (olisthesis), L3 and L4 coronal vertebral obliquity, and loss of lumbar lordosis . In addition, in a later report, loss of lordosis was also found to be correlated with lower Short Form 36 (SF-36) scores . More recently, Glassman et al investigated the relationship between global alignment and measures of HRQOL, and found that sagittal vertical axis (measured as the offset between C7 plumb line and the posterosuperior corner of S1) was correlated with pain and a decrease in function as measured using ODI and SF-12 [3, 4]. Considerable work is now directed at improving our understanding of not only ideal spinal alignment but also of spinopelvic relationships. Lazennec et al found that PT was correlated with increased pain in patients that underwent a lumbosacral fusion and demonstrated that patients with a larger postoperative PT were more likely to demonstrate residual pain .
Clinical and radiological outcomes based on postoperative PT
We noted that a change of pelvic tilt after spinal fusion was associated with improvements in VAS and ODI, and a statistically significant association was observed between lumbar lordosis and improvements in VAS and ODI in patients whose postoperative pelvic tilt was not improved. By classifying patients according to an in improvement in pelvic tilt after operation demonstrated that pain and disability were greater in Group A than in Group B. Furthermore, patients in Group A had higher levels of self-reported pain and disability. In other words, patients with a non-improved PT postoperatively also had lower HRQOLs. In Group A, patients showed a tendency toward a poor clinical outcome. However, interestingly patients who presented with lower LL showed a better clinical outcome, and patients without lower LL in Group A experienced the highest levels of self reported pain and disability. On the other hand, in Group B, patients had better clinical outcomes regardless of LL values and the other parameters.
Actually, it would seem that there is the morphological difference between both groups preoperatively although this difference is not significant statistically. In group B with lumbar hypolordosis, operation could improve the lumbar lordosis into normal range by compression following decreasing PT. In group A with well compensated spondylolisthesis showing normal lumbar lordosis, however, operation could not improve any spinopelvic parameter including lumbar lordosis and pelvic tilt. Finally, the surgical result of group with lumbar hypolordosis was better than those of group with normal lumbar lordosis.
Importance of PT and lumbar lordosis
Improvements in PT postoperatively played a significant role in the achievement of a good clinical outcome, as determined by VAS and ODI. Although postoperative PT was not improved, LL also contributed to a good clinical outcome. It is becoming increasingly recognized that studies of spinal alignment should include pelvic position. Although PI determines LL, PT is a positional parameter that reflects compensation to spinal deformity. This study confirms that pelvic position, as measured by PT, is correlated with HRQOL in the setting of adult deformity, and that high PT values reflect compensatory pelvic retroversion due to sagittal spinal malalignment. Furthermore, the significant correlation found between postoperative PT improvement and clinical outcome appears to indicate that resetting PT to a normal value is important for restoring ambulatory function by improving the range of hip extension.
However, Increasing PT is not the only way to compensate a local loss of lordosis. The primary compensation is obtained by hyper extension of the segment above or below the hypolordosis area. This study also confirms the presence of relationships between LL and clinical outcomes, which is consistent with published reports [18, 19]. LL is a key consideration when analyzing radiographic alignment, and is thought to cause chronic lower back pain by increasing traction loadings on posterior elements of the spine, including the paravertebral muscles .
Other Radiographic Parameters of Importance
The issue of spinal balance is attracting attention in the literature. However, conflicting results have been reported about the relationship between radiological factors related to sagittal balance and clinical outcomes after lumbar arthrodesis [10, 21]. With regard to early clinical outcomes, Kawakami et al. noted improved clinical recovery rates in patients that underwent fusion for degenerative spondylolisthesis when the L1 axis S1 interval (their measure of the position of the plumb line in front of the sacrum) was less than 35 mm and when lordosis of the fused segments was achieved . However, although the correction of sagittal plane deformity may be achieved by a number of means, there appears to be relatively little information in the literature regarding degenerative spondylolisthesis. In the present study, no significant relationship was found between radiological factors related to sagittal balance and clinical success except PT and LL.
This is the first study to evaluate the impact of sagittal balance in patients with degenerative spondylolisthesis that underwent fusion surgery. Thus, clinically, analyses of spinopelvic parameters, such as, pelvic tilt and lumbar lordosis, appear to be essential to the understanding of the impact of spinal deformity and the treatment choice in degenerative lumbar spondylolisthesis. Nevertheless, the retrospective study design of the present study and the small number of patients included should be considered when interpreting our results.
The authors wish to thank Dr. John Roberts for editing the manuscript and help with the English language.
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