Abstract
Study Design
retrospective case-control study.
Objectives
The objective is to investigate how preoperative sagittal malalignment affects clinical outcomes in short-segment lumbar interbody fusion.
Methods
A total of 684 patients who underwent short-segment lumbar interbody fusion were reviewed with a minimum follow-up of 2 years. According to the SRS-Schwab Adult Spinal Deformity Classification, preoperative sagittal malalignment was defined as a sagittal vertical axis (SVA) ≥ 95 mm or pelvic tilt (PT) ≥ 30 degrees or Pelvic incidence (PI) – Lumbar lordosis (LL) ≥ 20 degrees in this study. Patients were divided into a well-alignment group and a malalignment group. Spinopelvic parameters such as thoracic kyphosis (TK), LL, lower LL (LLL), sacral slope (SS), PT, PI, SVA, T1 pelvic angle (TPA), and segmental lordosis (SL), as well as Visual Analog Scale (VAS) of low back pain and leg pain, Oswestry Disability Index (ODI), and Roland-Morris Disability Questionnaire (RDQ) were measured preoperatively and at the final follow-up.
Results
The well-alignment group included 443 patients, and the malalignment group included 241 patients. In the malalignment group, PT, PI, SVA, and TPA were higher, whereas TK, LL, LLL, and SL were lower than in the well-alignment group. There were no significant differences between the groups regarding ΔVAS of low back pain, ΔVAS of leg pain, ΔODI, and ΔRDQ. The satisfaction rate was lower in the malalignment group.
Conclusion
This study demonstrated that preoperative sagittal malalignment and spinopelvic parameters were not associated with clinical outcomes except for the satisfaction rate in short-segment lumbar interbody fusion.
Keywords: Preoperative sagittal malalignment, Spinopelvic parameters, Lumbar interbody fusion, Short-segment fusion, Clinical outcomes
Introduction
Sagittal alignment has been reported as an important factor affecting surgical outcomes after spinal fusion surgeries.1,2 In particular, it is recommended to achieve well-balanced sagittal alignment using long-fusion and various types of osteotomy techniques in corrective surgery for adult spinal deformity. 3
Corrective surgery is essential for patients whose chief complaints are due to spinopelvic malalignment, such as back muscle fatigue, difficulty in forward gaze, and gastroesophageal reflux. However, this procedure is invasive, and complication rates are high. 4 Therefore, in cases where neurological symptoms caused by focal stenosis are predominant, short-segment fusion is frequently indicated regardless of sagittal alignment.
The relationship between postoperative sagittal alignment and surgical outcomes after short-segment fusion has received increasing attention in recent years. However, few studies have investigated whether preoperative sagittal alignment affects clinical outcomes.5,6 This point is important because, if patients with preoperative sagittal malalignment experience worse surgical outcomes than those without sagittal malalignment, additional corrective maneuvers during surgery may need to be considered.
We hypothesized that clinical outcomes after short-segment fusion in patients with preoperative sagittal malalignment are similar to those without sagittal malalignment. This is because we consider that not sagittal malalignment but neurological deficits mainly affect pain and activities of daily living, if they do not have symptoms related to sagittal imbalance. The purpose of this study was to investigate the effect of preoperative sagittal malalignment on clinical outcomes after short-segment lumbar interbody fusion.
Methods
Ethics Statement
We conducted this study in compliance with the principles of the Declaration of Helsinki. The study’s protocol was reviewed and approved by the Institutional Review Board of our hospital (approval number:2023-37). Informed consent was waived because of the retrospective nature of the study.
Study Design and Patients Data
This is a single-center retrospective case-control study. We investigated medical records and radiographic data from patients who had undergone short-segment (1-2 segments) lumbar interbody fusion at a single institution in Japan from September 2011 to May 2023. In our institution, short-segment fusion is the first choice for patients with sagittal malalignment when neurological symptoms, rather than symptoms related to sagittal imbalance, are the primary complaint or have a greater impact on daily life, and after consultation with the patients, short-segment fusion is generally recommended as the initial procedure in such cases. In a rare case only two cases), lower lumbar interbody fusion (L4-S1 fusion) was initially performed in patients with spinal kyphosis. The surgical method, whether short-segment fusion, corrective long fusion, decompression alone, or other approaches was decided at a preoperative spinal conference by consensus among the spine surgeons at our institution. A total of 684 patients met the following inclusion criteria: (1) their chief complaint was a neurological symptom caused by focal stenosis; (2) the fusion procedure was posterior lumbar interbody fusion (PLIF) or transforaminal lumbar interbody fusion (TLIF); (3) the fusion segment was one or two segments; and (4) whole spine radiographs were obtained preoperatively and postoperatively. Exclusion criteria were as follows: (1) less than 2 years of follow-up; (2) previous spinal fusion surgery; (3) surgeries for traumas or tumors; and (4) under 18 years of age.
Clinical data including age, gender, body mass index (BMI), surgical procedure (PLIF or TLIF, or PLIF and TLIF), number of fusion segments, fusion level, and diagnosis of lumbar degenerative diseases were obtained from medical records. Lumbar bone mineral density (BMD) was measured in 672 patients, and femoral BMD was measured in 673 patients preoperatively. The study population consisted of 260 men and 424 women with a mean age of 68.6 years at the time of initial surgery (range; 22-89 years). The mean BMI was 25 kg/m2. The mean follow-up period was 52.5 months (range; 24-154months). Surgical procedures were PLIF in 253 patients, TLIF in 428, and both PLIF and TLIF in 3. One-segment fusion was performed in 471 patients, and two-segment fusion was performed in 213 patients. The most common fused segment was L4/5. Diagnoses of lumbar degenerative diseases were as follows: lumbar degenerative spondylolisthesis in 371 patients, lumbar foraminal stenosis in 151, lumbar spinal stenosis in 70, lumbar isthmic spondylolisthesis in 35, lumbar degenerative scoliosis in 33, recurrent lumbar disc herniation in 10, lateral lumbar disc herniation in 6, central lumbar disc herniation in 5, spinal kyphosis in 2, and, lumbar facet cyst in 1. Mean lumbar BMD (T-score) was 0.2 and mean femoral BMD was -1.1 (Table 1).
Table 1.
Patient characteristics
| patients | 684 |
|---|---|
| age (years) | 68.6 ± 10.4 |
| Sex | |
| Men | 38.0% (260) |
| women | 62.0% (424) |
| BMI (kg/m2) | 25.0 ± 3.9 |
| Surgical procedure | |
| PLIF | 253 |
| TLIF | 428 |
| PLIF and TLIF | 3 |
| number of fusion segment | |
| one segment | 68.9% (471) |
| two segments | 31.1% (213) |
| fusion level | |
| L1/2 | 0.7% (5) |
| L2/3 | 0.7% (5) |
| L2-4 | 1.3% (9) |
| L3/4 | 10.8% (74) |
| L3-5 | 14.5% (99) |
| L3-S1 | 0.7% (5) |
| L4/5 | 40.1% (274) |
| L4/S1 | 1.2% (8) |
| L4-6 | 0.7% (5) |
| L4-S1 | 13.7% (94) |
| L5/6 | 1.6% (11) |
| L5/S1 | 13.6% (93) |
| L6/S1 | 0.3% (2) |
| Diagnosis | |
| lumbar degenerative spondylolisthesis | 54.2% (371) |
| lumbar foraminal stenosis | 22.1% (151) |
| lumbar spinal stenosis | 10.2% (70) |
| lumbar isthmic spondylolisthesis | 5.1% (35) |
| lumbar degenerative scoliosis | 4.8% (33) |
| recurrent lumbar disc herniation | 1.5% (10) |
| lateral lumbar disc herniation | 0.9% (6) |
| central lumbar disc herniation | 0.7% (5) |
| spinal kyphosis | 0.3% (2) |
| lumbar facet cyst | 0.1% (1) |
| BMD (T-score) | |
| Lumbar | 0.2 ± 1.7 |
| Femoral | -1.1 ± 1.1 |
| follow-up period (month) | 52.5 ± 28.1 |
Data are shown as means ± standard deviations or percentages (numbers).
BMI; body mass index, PLIF; posterior lumbar interbody fusion, TLIF; transforaminal lumbar interbody fusion, BMD; bone mineral density.
Radiographic Parameters.
Standing anteroposterior and lateral whole spine radiographs were obtained preoperatively and at the latest follow-up. In non-revision cases, the latest radiograph obtained within 3 months of the final clinical outcome assessment was used as the final radiograph. In revision cases, the last radiograph obtained before revision surgery was used as the final radiograph. Measured parameters were: thoracic kyphosis (TK: sagittal Cobb angle from the superior endplate of T5 to the inferior endplate of T12), lumbar lordosis (LL: sagittal Cobb angle of the superior endplate of L1 to the superior endplate of S1), lower lumbar lordosis (LLL: sagittal Cobb angle of the superior endplate of L4 to the superior endplate of S1), sacral slope (SS: angle between the superior endplate of S1 and the horizontal line), pelvic tilt (PT: angle made between lines originating at the bicoxofemoral axis and extending vertically and to the midline of the superior endplate of S1), pelvic incidence (PI: angle between a line perpendicular to the superior endplate of S1 and the line connecting the superior endplate of S1 to the bicoxofemoral axis), anterior deviation of sagittal vertical axis (SVA: plum line from the center of C7 vertebral body to the posterior sagittal prominence on the lateral radiograph), T1 pelvic angle (TPA: angle from T1 to bicoxofemoral axis and a line from bicoxofemoral axis to the center of S1 endplate), and segmental lordosis (SL: sagittal Cobb angle between the upper and lower endplates of each fused segment) (Figure 1).5,7
Figure 1A.
Measurement of radiographic parameters. TK, thoracic kyphosis (sagittal Cobb angle from the superior endplate of T5 to the inferior endplate of T12); LL, lumbar lordosis (sagittal Cobb angle of the superior endplate of L1 to the superior endplate of S1); SS, sacral slope (angle between the superior endplate of S1 and the horizontal line); PT, pelvic tilt (angle made between lines originating at the bicoxofemoral axis and extending vertically and to the midline of the superior endplate of S1); SL, segmental lordosis (sagittal Cobb angle between the upper and lower endplates of each fused segment). Fig.1B Measurement of radiographic parameters. LLL, lower lumbar lordosis (sagittal Cobb angle of the superior endplate of L4 to the superior endplate of S1); PI, pelvic incidence (angle between a line perpendicular to the superior endplate of S1 and the line connecting the superior endplate of S1 to the bicoxofemoral axis). Fig.1C Measurement of radiographic parameters. SVA, sagittal vertical axis (plum line from the center of C7 vertebral body to the posterior sagittal prominence on the lateral radiograph); TPA, T1 pelvic angle (angle from T1 to bicoxofemoral axis and a line from bicoxofemoral axis to the center of S1 endplate)
Clinical Outcomes
Clinical outcomes were assessed using the visual analog scale (VAS) of low back pain, VAS of leg pain, Oswestry Disability Index (ODI), and Roland-Morris Disability Questionnaire (RDQ) preoperatively and at the final follow-up.8-10 Because most patients were elderly, ODI question No.8 was omitted, and ODI scores were converted to percentages. We also measured ΔVAS of low back pain (preoperative low back pain – final low back pain), ΔVAS of leg pain, ΔODI, and ΔRDQ. Satisfaction rate for surgery was assessed at the final follow-up. Satisfaction rate measured how satisfied the patients are with the result of their surgery. It ranges from 0 to 100, with 0 indicating no satisfaction and 100 indicating complete satisfaction. Pathologies of additional surgery were also reviewed.
Statistical Analysis
According to the SRS-Schwab Adult Spinal Deformity Classification, 11 preoperative sagittal imbalance was defined as an SVA > 95 mm, PT > 30 degrees, or PI-LL > 20 degrees in this study. Based on this benchmark, patients were divided into two groups: a well-alignment group (preoperative SVA ≤ 95 mm, preoperative PT ≤ 30 degrees, and preoperative PI-LL ≤ 20 degrees) and a malalignment group (preoperative SVA > 95 mm, preoperative PT > 30 degrees, or preoperative PI-LL > 20 degrees).
To exclude diagnostic heterogeneity, a subgroup analysis of patients with lumbar degenerative spondylolisthesis, the most common pathology, was performed.
As another subgroup analysis, we subdivided the malalignment group into the MW group, which achieved improvement in sagittal parameters at the final follow-up (SVA ≤ 95 mm, PI ≤ 30 degrees, and PI-LL ≤ 20 degrees at the final follow-up period) and the MM group, which did not, to investigate whether improvement in sagittal malalignment affected clinical outcomes. Furthermore, we investigated the difference between the MW group and the MM group when lower lumbar interbody fusion was performed to evaluate whether restoration of lower lumbar lordosis is related to restoration of global sagittal alignment. Lower lumbar interbody fusion involved the fusion levels as follows: one-segment fusion (L4/5, L5/S1, L4/S1 [sacralization], L5/6 [lumbarization], L6/S1 [lumbarization]), two-segment fusion (L3-5, L4-S1, L4-6 [lumbarization], L5-S1 [lumbarization]). In addition, comparisons were conducted between the well-alignment group and the MW group and between the well-alignment group and the MM group. Regarding the correction surgery for sagittal malalignment, demographic data and preoperative sagittal alignment were compared between the patients who required correction surgery and those who did not need to investigate the characteristics and predictors of the need for correction surgery.
All analyses were performed using Bellcurve for Excel ver. 4.05 (Social Survey Research Information Co., Ltd. Japan), with a p-value < 0.05 considered statistically significant. Pearson chi-square analysis was performed to assess the statistical significance of sex, surgical procedure, number of fusion segments, level of fusion segment and diagnosis of lumbar degenerative disease. The normality of the data distribution was assessed using the Shapiro-Wilk test. Differences in continuous variables between the groups were assessed using Weich’s t-test (for normally distributed data) and the Mann-Witney U test (for non-normally distributed data). A multiple linear regression was performed to predict ΔVAS of back pain, ΔODI, and ΔRDQ respectively based on age, sex, the number of fusion segments, BMI, and sagittal alignment (well-alignment or malalignment). The sample size calculation was performed using G*Power 3.1.9.7 (Faul 2007, Faul 2009).
Results
There were 443 patients in the well-alignment group and 241 patients in the malalignment group. One third of the current cohort (35.2%) had preoperative sagittal malalignment. Age was significantly higher in the malalignment group than in the well-alignment group (p < 0.001). Preoperative sagittal malalignment was observed more frequently in women than in men (p < 0.001). BMI was significantly higher in the malalignment group than in the well-alignment group (p = 0.035). The rate of two-segment fusion was significantly higher in the malalignment group than in the well-alignment group (p = 0.039). There was significant difference between the two groups in the fusion level. The rate of degenerative lumbar scoliosis was significantly higher in the malalignment group than in the well-alignment group (p = 0.045). There was no significant difference between the two groups in surgical procedure, BMD, and follow-up period (Table 2). Assuming a two-tailed paired t-test with an effect size of 0.2, a significance level of 5%, and a power of 80%, the required sample size was calculated to be 191 cases, indicating that the sample size of this study (684 patients) provided adequate statistical power.
Table 2.
Patient characteristics between the well-alignment group and the malalignment group
| | well-alignment group | malalignment group | p-value |
|---|---|---|---|
| patients | 443 | 241 | |
| age (years) | 67.5 ± 10.6 | 70.4 ± 9.8 | < 0.001 |
| sex | | | |
| men | 196 | 64 | < 0.001 |
| women | 247 | 177 | |
| BMI (kg/m2) | 24.7 ± 3.6 | 25.5 ± 4.4 | 0.035 |
| surgical procedure | | | 0.1 |
| PLIF | 174 | 79 | |
| TLIF | 266 | 162 | |
| PLIF and TLIF | 3 | 0 | |
| number of fusion segments | | | 0.039 |
| one | 71.6% (317) | 63.9% (154) | |
| two | 28.4% (126) | 36.1% (87) | |
| fusion level | | | 0.002 |
| L1/2 | 0.4% (2) | 1.2% (3) | |
| L2/3 | 0.9% (4) | 0.4% (1) | |
| L2-4 | 1.3% (6) | 1.2% (3) | |
| L3/4 | 8.8% (39) | 14.5% (35) | |
| L3-5 | 12.4% (55) | 18.3% (44) | |
| L3-S1 | 1.1% (5) | 0% (0) | |
| L4/5 | 42.7% (189) | 35.3% (85) | |
| L4/S1 | 1.1% (5) | 1.2% (3) | |
| L4-6 | 0% (0) | 2.1% (5) | |
| L4-S1 | 13.5% (60) | 14.1% (34) | |
| L5/6 | 1.3% (6) | 2.1% (5) | |
| L5/S1 | 16% (71) | 9.1% (22) | |
| L6/S1 | 0.2% (1) | 0.4% (1) | |
| diagnosis | | | 0.045 |
| lumbar degenerative spondylolisthesis | 54.4% (241) | 53.9% (130) | |
| lumbar foraminal stenosis | 24.8% (108) | 17.8% (43) | |
| lumbar spinal stenosis | 9.7% (43) | 11.2% (27) | |
| lumbar isthmic spondylolisthesis | 5.6% (25) | 4.1% (10) | |
| lumbar degenerative scoliosis | 3.4% (15) | 7.5% (18) | |
| recurrent lumbar disc herniation | 1.1% (5) | 2.1% (5) | |
| lateral lumbar disc herniation | 0.5% (2) | 1.7% (4) | |
| central lumbar disc herniation | 0.7% (3) | 0.8% (2) | |
| spinal kyphosis | 0% (0) | 0.8% (2) | |
| lumbar facet cyst | 0.2% (1) | 0% (0) | |
| BMD (T-score) | |||
| Lumbar | 0.1 ± 1.8 | 0.3 ± 1.7 | 0.166 |
| Femoral | -1.1 ± 1.1 | -1.2 ± 1.1 | 0.321 |
| follow-up period (month) | 53.5 ± 28.6 | 50.9 ± 27.1 | 0.24 |
Data are shown as means ± standard deviations or percentages (numbers).
BMI; body mass index, PLIF; posterior lumbar interbody fusion, TLIF; transforaminal lumbar interbody fusion, BMD; bone mineral density.
Radiographic Parameters
Regarding radiographic parameters, significant differences were observed in all measured sagittal parameters between the two groups. TK was lower in the malalignment group: 29 degrees vs 24.2 degrees preoperatively (well-alignment group vs malalignment group), and 30.2 degrees vs 25.5 degrees at the final follow-up. LL was also lower in the malalignment group: 42.2 degrees vs 27.1 degrees preoperatively and 41.1 degrees vs 28.6 degrees at the final follow-up. LLL was lower in the malalignment group: 26.7 degrees vs 16.9 degrees preoperatively and 26.5 degrees vs 19 degrees at the final follow-up. SS was lower in the malalignment group: 30.9 degrees vs 26.3 degrees preoperatively and 31.2 degrees vs 27 degrees at the final follow-up. SL was lower in the malalignment group as well: 16.7 degrees vs 11 degrees preoperatively and 17.4 degrees vs 14.3 degrees at the final follow-up. In contrast, PT was higher in the malalignment group: 18 degrees vs 29.1 degrees preoperatively and 19 degrees vs 29.7 degrees at the final follow-up. PI was also higher in the malalignment group: 48.9 degrees vs 55.3 degrees preoperatively, and 50.1 degrees versus 56.7 degrees at the final follow-up. SVA was higher in the malalignment group: 31.5 mm vs 86.4 mm preoperatively and 44.9 mm vs 83.7 mm at the final follow-up. TPA was higher in the malalignment group: 15.5 degrees vs 29.9 degrees preoperatively, and 17.4 degrees versus 30.2 degrees at the final follow-up (Table 3).
Table 3.
Radiographic parameters between the well-alignment group and the malalignment group
| | well-alignment group | malalignment group | p-value |
|---|---|---|---|
| TK (degree) | |||
| Pre | 29 ± 9.8 | 24.2 ± 11.7 | < 0.001 |
| final | 30.2 ± 11 | 25.5 ± 12.7 | < 0.001 |
| LL (degree) | |||
| Pre | 42.2 ± 11.4 | 27.1 ± 14.6 | < 0.001 |
| final | 41.1 ± 14.3 | 28.6 ± 17.8 | < 0.001 |
| LLL (degree) | |||
| Pre | 26.7 ± 9.1 | 16.9 ± 9.1 | < 0.001 |
| final | 26.5 ± 10.3 | 19 ± 13.5 | < 0.001 |
| SS (degree) | |||
| Pre | 31.1 ± 9 | 26.3 ± 9.5 | < 0.001 |
| final | 31.2 ± 9 | 27 ± 10.3 | < 0.001 |
| PT (degree) | |||
| Pre | 18 ± 6 | 29.1 ± 8.7 | < 0.001 |
| final | 19 ± 6.9 | 29.7 ± 9.7 | < 0.001 |
| PI (degree) | |||
| Pre | 48.9 ± 9.4 | 55.3 ± 11.4 | < 0.001 |
| final | 50.1 ± 9.4 | 56.7 ± 12.2 | < 0.001 |
| SVA (mm) | |||
| Pre | 31.5 ± 32.7 | 86.4 ± 48.1 | < 0.001 |
| final | 44.9 ± 43.9 | 83.7 ± 53.8 | < 0.001 |
| TPA (degree) | |||
| Pre | 15.5 ± 6.8 | 29.9 ± 8.1 | < 0.001 |
| Final | 17.4 ± 8 | 30.2 ± 11 | < 0.001 |
| SL (degree) | |||
| Pre | 16.7 ± 8 | 11 ± 9.7 | < 0.001 |
| Final | 17.4 ± 8 | 14.3 ± 9.9 | < 0.001 |
Data are shown as means ± standard deviations.
TK; thoracic kyphosis, LL; lumbar lordosis, LLL; lower lumbar lordosis, SS; sacral slope, PT; pelvic tilt, PI; pelvic incidence, SVA; sagittal vertebral axis, TPA; T1 pelvic angle, SL; segmental lordosis.
Clinical Outcomes
Preoperative ODI and RDQ were significantly higher in the malalignment group than in the well-alignment group: 43.7% vs 47.7% for ODI and 11.6 vs 13.3 for RDQ respectively. Preoperative VAS of low back pain and leg pain showed no significant differences: 52.8 vs 57.3 for low back pain and 66 vs 65.6 for leg pain. Both groups showed significant improvement after surgery. At the final follow-up, ODI was significantly higher in the malalignment group than in the well-alignment group (22.7% vs 25.8%). In contrast, no statistically significant differences were obtained in other outcomes: 24.7 vs 27.1 for VAS of low back pain, 22.9 vs 22.7 for VAS of leg pain, and 5.6 vs 6.2 for RDQ. No significant differences were observed in ΔVAS of low back pain (28.1 vs 30.2), ΔVAS of leg pain (43.2 vs 42.9), ΔODI (21.3% vs 21.9%), and ΔRDQ (6 vs 7.2). The satisfaction rate was significantly higher in the well-alignment group (76.6 vs 71.5) (Table 4).
Table 4.
Clinical outcomes between the well-alignment group and the malalignment group
| | well-alignment group | malalignment group | p-value |
|---|---|---|---|
| VAS low back pain | | | |
| Pre | 52.8 ± 33.3 | 57.3 ± 29.2 | 0.169 |
| final | 24.7 ± 28.1 | 27.1 ± 29.6 | 0.375 |
| ΔVAS low back pain | 28.1 ± 39.5 | 30.2 ± 40.2 | 0.298 |
| VAS leg pain | | | |
| Pre | 66 ± 30.6 | 65.6 ± 32.2 | 0.874 |
| Final | 22.9 ± 29.3 | 22.7 ± 28.1 | 0.775 |
| ΔVAS leg pain | 43.2 ± 41.9 | 42.9 ± 39.6 | 0.724 |
| ODI (%) | | | |
| Pre | 43.7 ± 18.2 | 47.7 ± 17.8 | 0.01 |
| Final | 22.7 ± 19.1 | 25.8 ± 19.9 | 0.041 |
| ΔODI | 21.3 ± 24.3 | 21.9 ± 25.4 | 0.753 |
| RDQ | | | |
| Pre | 11.6 ± 5.8 | 13.3 ± 4.9 | < 0.001 |
| Final | 5.6 ± 6.2 | 6.2 ± 6.2 | 0.177 |
| ΔRDQ | 6 ± 7.6 | 7.2 ± 7.3 | 0.07 |
| Satisfaction rate | 76.6 ± 23.2 | 71.5 ± 26.4 | 0.023 |
Data are shown as means ± standard deviations.
VAS; visual analog scale, ODI; Oswestry Disability Index, RDQ; Roland-Morris Disability Questionnaire.
Pathologies of Additional Surgery
Overall, 82 of 684 patients (12.0%) underwent additional surgery. The rate was 12.2% in the well-alignment group (54 of 443 patients) and 11.6% in the malalignment group (28 of 241 patients), with no statistically significant difference between the two groups. Pathologies of additional surgery are shown in Table 5. The most common pathology was adjacent segment disease in both groups. Correction surgery for sagittal malalignment was required in six patients (0.9%): one in the well-alignment group, and five in the malalignment group, and there was a significant difference between the two groups (p=0.013) (Figure 2).
Table 5.
Pathologies of additional surgery in well-alignment group and malalignment group
| | well-alignment group (n=443) | malalignment group (n=241) | p-value |
|---|---|---|---|
| Total | 54 (12.2%) | 28 (11.6%) | 0.826 |
| ASD | 41 (9.3%) | 12 (5%) | 0.046 |
| pseudoarthrosis | 3 (0.7%) | 3 (1.3%) | 0.447 |
| sagittal imbalance | 1 (0.2%) | 5 (2.1%) | 0.013 |
| canal stenosis (not adjacent) | 1 (0.2%) | 3 (1.3%) | 0.095 |
| instrumentation failure | 1 (0.2%) | 2 (0.8%) | 0.253 |
| infection | 4 (0.9%) | 1 (0.4%) | 0.474 |
| vertebral fracture | 1 (0.2%) | 1 (0.4%) | 0.662 |
| leak of grafted bone | 2 (0.5%) | 0 | 0.296 |
| dehiscence | 1 (0.2%) | 0 | 0.46 |
| hematoma | 0 | 1 (0.4%) | 0.175 |
| progression of DSA | 0 | 1 (0.4%) | 0.175 |
Data are shown as numbers (percentages).
ASD; adjacent segmental disease, DSA; destructive spondyloarthropathy.
Figure 2.
A 68-year-old woman with neurological deficits and sagittal malalignment (sagittal vertical axis [SVA], 72.4mm; lumbar lordosis [LL] 18 degrees; pelvic tilt [PT], 28 degrees; pelvic incidence [PI], 51 degrees; segmental lordosis [SL], 0.6 degrees; PI-LL, 33 degrees) (Fig.2A). She underwent short-segment lumbar interbody fusion for neurological deficits (Fig.2B). She developed symptoms of sagittal imbalance after the initial surgery (SVA, 122 mm; LL, -4 degrees; PT, 32 degrees; PI, 52 degrees; SL, 3.7 degrees; PI-LL, 56 degrees) (Fig.2C). Corrective surgery was performed nine months after the initial surgery (Fig.2D)
Clinical outcomes focusing on lumbar degenerative spondylolisthesis
There were 371 patients with lumbar degenerative spondylolisthesis, including 241 in the well-alignment group and 130 in the malalignment group. Preoperative RDQ was significantly higher in the malalignment group than in the well-alignment group: 11 vs 13. Although ODI at the final follow-up was significantly higher in the malalignment group (22.3% vs 26.3%), there were no significant differences observed in ΔVAS of low back pain (25.2 vs 27.8), ΔVAS of leg pain (41.7 vs 40), ΔODI (20.1% vs 18.8%), and ΔRDQ (5.6 vs 6.7). Satisfaction rate was significantly lower in the malalignment group than in the well-alignment group (77.6 vs 72.5) (Supplemental Table 1).
Clinical outcomes between the MW group and the MM group
There were 60 patients in the MW group and 181 patients in the MM group. One quarter (24.9%) of the malalignment group improved their sagittal alignment at the final follow-up. VAS of low back pain (the MW group vs the MM group: 15.6 vs 30.9), VAS of leg pain (17.1 vs 24.6), ODI (15.9% vs 29.1%), and RDQ (3.7 vs 7) at the final follow-up were significantly lower in the MW group than in the MM group. ΔVAS of leg pain (51.6 vs 40), ΔODI (35.1% vs 17.5%), and ΔRDQ (10 vs 6.3) were higher in the MW group than in the MM group (Table 7). The MW group had significantly lower VAS of low back pain (well-alignment group vs MW group: 24.7 vs 15.7), ODI (22.7% vs 15.9%), and RDQ (5.6 vs 3.7) than the well-alignment group at the final follow-up. On the other hand, the MM group had significantly higher VAS of low back pain (well-alignment group vs MM group: 24.7 vs 30.9), ODI (22.7% vs 29.1%), RDQ (5.6 vs 7), and lower satisfaction rate (76.6 vs 67.8) than the well-alignment group at the final follow-up (Supplemental Table 2).
Table 7.
Results of Multiple Regression Analysis for Variables Predicting ΔODI
| variables | B | SE | β | t-value | p-value |
|---|---|---|---|---|---|
| age (+1 year) | -0.2483 | 0.0957 | -0.1048 | -2.5935 | 0.0097 |
| sex (man vs woman) | -2.7202 | 1.9971 | -0.0536 | -1.3621 | 0.1736 |
| the number of fusion segments (one vs two) | -2.4961 | 2.0516 | -0.0469 | -1.2167 | 0.2241 |
| BMI (+1 kg/m2) | -0.249 | 0.2492 | -0.0397 | -0.9992 | 0.318 |
| sagittal alignment (well-alignment vs malalignment) | 2.2281 | 2.0296 | 0.0432 | 1.0978 | 0.2727 |
R = 0.1346, adjusted R = 0.1043, F value = 2.5019.
ODI; Oswestry Disability Index, BMI; body mass index.
Radiographic parameters between the MW group and the MM group
A total of 199 of the 241 malalignment patients (82.6%) underwent lower lumbar interbody fusion. The MW group included 48 patients, while the MM group included 151 patients. Preoperative LLL tended to be higher in the MW group than in the MM group (the MW group vs the MM group: 19.7 degrees vs 15.9 degrees). LLL at the final follow-up was significantly higher in the MW group than in the MM group (26.1 degrees vs 17.9 degrees). ΔLLL was significantly higher in the MW group than in the MM group (6.3 degrees vs 2 degrees) (Supplemental Table 3).
Characteristics and predictors of the need for correction surgery
Regarding demographic data, only diagnosis showed a significant difference between the patients who required correction surgery and who did not. Spinal kyphosis was observed more frequently in the patients who required correction surgery. Regarding preoperative sagittal parameters, there were significant differences except for PI (Supplemental Table 4).
The results of multiple linear regression analysis
No significant regression equation was found in ΔVAS of low back pain (Table 6). A significant regression equation was found in ΔODI (F (5, 678) = 2.5019, p = 0.0294), with an R2 of 0.0181. The predicted ΔODI was calculated as 48.8811 – 0.2483 × age, where age is measured in years. ΔODI decreased by 0.2483 for each one-year increase in age indicating that age was a significant predictor of ΔODI (Table 7). Additionally, a significant regression equation was found (F (5, 678) = 3.1059, p = 0.0088, with an R2 of 0.0224. The predicted ΔRDQ was calculated as 12.1681-0.0623 × age -1.3366 × sex + 1.64 × sagittal alignment, where age is measured in years, sex is coded as 0 = man and 1 = woman, and sagittal alignment is coded as 0 = the well-alignment group and 1 = the malalignment group. ΔRDQ decreased by 0.0623 for each one-year increase in age, ΔRDQ in woman was 1.3366 lower than that in man, ΔRDQ in the malalignment group was 1.64 higher than that in the well-alignment group, indicating that age, sex, and sagittal alignment were significant predictors of ΔRDQ (Table 8).
Table 6.
Results of Multiple Regression Analysis for Variables Predicting ΔVAS of low back pain
| variables | B | SE | β | t-value | p-value |
|---|---|---|---|---|---|
| age (+1 year) | -0.207 | 0.1552 | -0.0542 | -1.3335 | 0.1828 |
| sex (man vs woman) | -1.8759 | 3.2384 | -0.0229 | -0.5793 | 0.5626 |
| the number of fusion segments (one vs two) | 3.348 | 3.3267 | 0.039 | 1.0064 | 0.3146 |
| BMI (+1 kg/m2) | 0.275 | 0.4041 | 0.0272 | 0.6805 | 0.4964 |
| sagittal alignment (well-alignment vs malalignment) | 2.4854 | 3.2911 | 0.0299 | 0.7552 | 0.4504 |
R = 0.0821, F value = 0.9193.
VAS; visual analog scale, BMI; body mass index.
Table 8.
Results of Multiple Regression Analysis for Variables Predicting ΔRDQ
| variables | B | SE | β | t-value | p-value |
|---|---|---|---|---|---|
| age (+1 year) | -0.0623 | 0.0291 | -0.0862 | -2.1377 | 0.0329 |
| sex (man vs woman) | -1.3366 | 0.6081 | -0.0863 | -2.1980 | 0.0283 |
| the number of fusion segments (one vs two) | -0.2329 | 0.6247 | -0.0143 | -0.3728 | 0.7094 |
| BMI (+1 kg/m2) | -0.0365 | 0.0759 | -0.0190 | -0.4809 | 0.6308 |
| sagittal alignment (well-alignment vs malalignment) | 1.64 | 0.6180 | 0.1042 | 7.0427 | 0.0081 |
R = 0.1496, adjusted R = 0.1232, F value = 3.1059.
RDQ; Roland-Morris Disability Questionnaire, BMI; body mass index.
Discussion
This study investigated whether preoperative sagittal malalignment affects clinical outcomes after lumbar short-segment fusion. Although there were significant differences regarding radiographic sagittal parameters, there were no significant differences regarding ΔVAS of low back pain, ΔVAS of leg pain, ΔODI and ΔRDQ between the well-alignment group and the malalignment group. In addition, as a subgroup analysis, the malalignment group was subdivided into the MW group, which achieved improvement in sagittal parameters at the final follow-up and the MM group, which did not, to investigate whether improvement in sagittal malalignment affected clinical outcomes. Clinical outcomes at the final follow-up were significantly better in the MW group than in the MM group.
It is well known that postoperative sagittal alignment influences clinical outcomes and health related quality of life (HRQOL) scores. In particular, achieving well-balanced sagittal alignment using long-fusion and various types of osteotomy techniques is recommended in corrective surgery for adult spinal deformity. 3 In adult spinal deformity, realignment targets have been previously reported, including SVA, which should be reduced to within 50mm postoperatively. 3
Measurement of spinopelvic parameters has now become a routine part of many interventions not only for adult spinal deformity but also for other degenerative spinal diseases.12-15 There are several reports describing the relationship between postoperative sagittal alignment and clinical outcomes in degenerative lumbar surgery.13,16-20
However, it remains unclear whether preoperative sagittal alignment affects postoperative clinical outcomes because of insufficient evidence. For patients with degenerative lumbar disease and sagittal malalignment, some surgeons perform short-segment decompression and fusion,21,22 whereas others recommend simultaneous correction of sagittal malalignment with long fusion.23-25
There are a few studies that have investigated the relationship between preoperative sagittal balance and clinical outcomes. Cho et al reported the effect of one- or two-level posterior lumbar interbody fusion on global sagittal balance. 5 Patients were divided according to preoperative SVA (Group N: SVA ≤ 5 cm; Group I: SVA > 5 cm), and back pain VAS, leg pain VAS, and ODI were compared, with no significant differences observed between the two groups. Maayan et al reported the impact of preoperative age-adjusted sagittal imbalance on radiographic and clinical outcomes following 1-level minimally invasive TLIF. 6 Patients were divided into balanced and imbalanced groups based on preoperative PI-LL mismatch according to age-adjusted alignment goals. The study revealed that although achievement of the minimum clinically important difference (MCID) for VAS back pain was higher in the unbalanced group, achievement of MCID for other clinical outcomes was not significantly different. Despite the findings, the sample sizes were relatively small, and the follow-up periods were short in these studies. Therefore, the influence of preoperative sagittal imbalance on clinical outcomes remains unclear. In this context, our study showed no significant differences between the well-alignment and the malalignment groups in VAS of back pain, leg pain, and RDQ at the final follow-up. ODI at the final follow-up was significantly higher in the malalignment group than in the well-alignment group, yet the difference was only 3.6%. This difference was within the MCID of 12.8 (scale, 0-100) suggested by a previous study, 26 and ΔODI exceeded the MCID in both groups. As our study included a relatively large study population, this small difference in mean ODI at the final follow-up may be statistically significant but not clinically relevant. Overall, the clinical outcomes of short-segment fusion in patients with preoperative sagittal malalignment were almost equivalent to those in patients without preoperative sagittal malalignment.
In this study, a significant difference in the satisfaction rate was observed between the well-alignment and malalignment groups. However, given that the satisfaction rate was over 70 in both groups, it may be reasonable to think that patients in the malalignment group were generally satisfied with short-segment fusion, as were those in the well-alignment group.
ΔRDQ was about to reach statistical significance (p=0.07). In addition, multiple linear regression analysis showed that preoperative sagittal malalignment was a significant favorable predictor of ΔRDQ. This result might be caused by higher preoperative RDQ in the malalignment group. Although it is unclear why ΔRDQ in the malalignment group was higher than in the well-alignment group, it was determined that RDQ in both the malalignment group and the well-alignment group improved at the final follow-up.
Satisfaction rate was significantly lower in the malalignment group than in the well-alignment group, despite similar clinical improvements being obtained. This difference is suspected to be due to little understanding of the effects of surgery. Even after a preoperative explanation that short-segment fusion is primarily intended to relieve neurological symptoms rather than correct sagittal malalignment, the patients in the malalignment group might not have fully understood the preoperative explanation, and might still have expected realignment of their sagittal malalignment. Therefore, more detailed preoperative explanations might be needed for patients, especially those in the malalignment group.
In this study, we adopted the SRS- Schwab Adult Spinal Deformity Classification as the cutoff value between the well-alignment group and the malalignment group, because we considered that this cutoff (SVA > 95 mm, PT > 30 degrees, or PI-LL > 20 degrees) was useful in clinical practice. However, an age-adjusted alignment target has been proposed recently. To estimate each patient’s admissible sagittal alignment, an age-adjusted alignment target might need to be calculated. Further study is needed to clarify this point.
Several studies have examined whether global sagittal alignment changes after short-segment fusion.16,27-29 Cho et al noted that global sagittal balance improved after short-level lumbar fusion in patients having spinal stenosis with spondylolisthesis who had preoperative sagittal imbalance. 5 Lu et al reported that sagittal alignment improved after short fusion in degenerative lumbar spinal disorders with preoperative sagittal imbalance only in patients without sagittal imbalance syndrome. 30 On the other hand, Ould-Slimane et al evaluated 45 patients who underwent single-level TLIF and found that global sagittal balance was not significantly modified after surgery. 31 Nevertheless, few studies have reported the proportion of patients who require corrective surgery for global sagittal imbalance after short-segment fusion. Hori et al investigated 70 patients with degenerative lumbar scoliosis who underwent short-segment fusion (fewer than 3 levels), and reported that 2 patients required additional surgery due to progression of the spinal deformity. 21 In our current study, 6 patients (0.9%) required corrective surgery.
It is notable that corrective surgery for sagittal malalignment was performed more frequently in the malalignment group. This point suggests that some patients in the malalignment group may be more likely to experience worsening symptoms of sagittal imbalance during follow-up. Perhaps, they might have had symptoms of sagittal malalignment preoperatively, but those symptoms may have been masked by predominant neurologic symptoms. At any rate, we should inform patients that spinal corrective surgery may be needed if sagittal alignment worsens after surgery, especially in the patients in the malalignment group.
There were no significant differences between the patients who required correction surgery and those who did not regarding demographic data except for diagnosis. Correction surgery was performed more frequently in the patient diagnosed with spinal kyphosis. This is hardly surprising, considering that L4-S1 fusion was initially performed in patients with spinal kyphosis. They were preoperatively informed that they might require correction surgery if they were not satisfied with the result of short-segment fusion. One patient was satisfied with the results of short-segment fusion alone, but another patient requested correction surgery for the symptoms of sagittal malalignment that had been observed preoperatively. It might be difficult to predict the need for additional correction surgery based only on demographic data. On the other hand, regarding preoperative sagittal parameters, there were significant differences except for PI. Preoperative sagittal malalignment might be a predictor of the need for correction surgery. Therefore, surgeons need to follow those patients more carefully. Nevertheless, the number of patients who required correction surgery was only 6, which was insufficient to draw definitive conclusions. Further large-size studies are needed.
In this study, the MW group obtained better clinical outcomes compared to the MM group. This result suggests that improvement of sagittal malalignment may result in better clinical outcomes even with short-segment fusion. Whether short-segment fusion can correct sagittal malalignment remains controversial. Perhaps, in the MW group, sagittal realignment occurred because neurologic symptoms were alleviated by nerve decompression. It has been reported that lumbar decompression without fusion can induce a reactive improvement in the lumbar and global sagittal alignment even if a sagittal imbalance exists preoperatively. 32 Although it is difficult to predict whether sagittal malalignment improves after surgery, surgeons should make an attempt to create local lordosis to realign the patient’s global alignment even if they perform short-segment fusion. Besides, although there were no significant differences in age, BMI, pathologies, the number of fused segments, or BMD between the MW group and the MM group, this subgroup analysis should be interpreted cautiously because of possible sex differences (The proportion of patients in the MM group was higher among woman than among man, p < 0.001).
ΔLLL was significantly higher in the MW group than in the MM group. LLL at the final follow-up was also significantly higher in the MW group than in the MM group. This finding suggests that restoration of LLL might be related to restoration of global sagittal alignment in the malalignment group. Therefore, even when short-segment lower lumbar interbody fusion is performed, surgeons should pay attention to the restoration of LLL in patients with preoperative sagittal malalignment.
The strengths of this study were a large patient population. However, this study has several limitations. First, it was a single-center study. Therefore, it has a selection bias in choosing short-segment fusion. Second, it was a retrospective study involving patients with different degenerative spinal diseases. Although there was no significant difference in diagnosis between the two groups, it remains unclear whether the pathology of degenerative spinal diseases affects radiographic parameters and clinical outcomes. However, the results focusing on the most common pathology, lumbar degenerative spondylolisthesis, were similar to those including all pathologies. Third, there were significant differences between the two groups regarding some demographic data, such as age, sex, BMI, number of fusion segments, and fusion level. Although these differences were small (for example, the age difference was 2.3 years, and the BMI difference was 0.8 kg/m2), they may affect the results of this study. A background-adjusted study may be needed to clarify this point. Finally, a minimum 2-year follow-up period (average: 52.5 months) may be relatively short for assessing the progression of spinal deformity and late mechanical complication. Since spinal deformity may progress slowly, further follow-up investigation is needed to draw long-term conclusions.
Conclusions
There were no significant differences in clinical outcomes, except for ODI, between the well-alignment and the malalignment groups, and the difference in ODI was smaller than the MCID at the final follow-up. The current large cohort study demonstrated that preoperative sagittal malalignment and spinopelvic parameters did not affect the clinical outcomes except for the satisfaction rate of short-segment fusion.
However, in malignment group, ΔLLL was significantly higher in the MW group than in the MM group. Even when short-segment lower lumbar interbody fusion is performed, surgeons should pay attention to the restoration of LLL in patients with preoperative sagittal malalignment.
Supplemental Material
Supplemental Material for The Effect of Preoperative Sagittal Malalignment on Clinical Outcomes in Short-Segment Lumbar Interbody Fusion by Yukitoshi Shimamura Masahiro Kanayama Fumihiro Oha Michihaya Kono Ryo Fujita Shogo Fukase Kohei Shiota Tsutomu Endo Tomoyuki Hashimoto Norimasa Iwasaki in Global Spine Journa
Supplemental Material for The Effect of Preoperative Sagittal Malalignment on Clinical Outcomes in Short-Segment Lumbar Interbody Fusion by Yukitoshi Shimamura Masahiro Kanayama Fumihiro Oha Michihaya Kono Ryo Fujita Shogo Fukase Kohei Shiota Tsutomu Endo Tomoyuki Hashimoto Norimasa Iwasaki in Global Spine Journa
Supplemental Material for The Effect of Preoperative Sagittal Malalignment on Clinical Outcomes in Short-Segment Lumbar Interbody Fusion by Yukitoshi Shimamura Masahiro Kanayama Fumihiro Oha Michihaya Kono Ryo Fujita Shogo Fukase Kohei Shiota Tsutomu Endo Tomoyuki Hashimoto Norimasa Iwasaki in Global Spine Journa
Supplemental Material for The Effect of Preoperative Sagittal Malalignment on Clinical Outcomes in Short-Segment Lumbar Interbody Fusion by Yukitoshi Shimamura Masahiro Kanayama Fumihiro Oha Michihaya Kono Ryo Fujita Shogo Fukase Kohei Shiota Tsutomu Endo Tomoyuki Hashimoto Norimasa Iwasaki in Global Spine Journa
Author contributions: Yukitoshi Shimamura: Conceptualization, Methodology, Formal analysis, Data curation, Investigation, Writing – Original draft preparation, Visualization. Masahiro Kanayama: Writing – Review & Editing, Supervision. Fumihiro Oha, Michihaya Kono, Ryo Fujita, Shogo Fukase, Kohei Shiota, Tsutomu Endo, Tomoyuki Hashimoto, Norimasa Iwasaki: Writing – Review & Editing.
Funding: The authors received no financial support for the research, authorship, and/or publication of this article.
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Supplemental Material: Supplemental material for this article is available online.
ORCID iDs
Yukitoshi Shimamura https://orcid.org/0000-0002-9491-3198
Michihaya Kono https://orcid.org/0009-0000-8709-5695
Ryo Fujita https://orcid.org/0009-0003-4082-1815
Kohei Shiota https://orcid.org/0009-0002-5103-6487
Tsutomu Endo https://orcid.org/0000-0002-2998-2242
Ethical Consideration
The study was approved by the clinical ethics committee of the Spine Center in Hakodate Central General Hospital (approval number:2023-37) and was conducted according to the 1964 Helsinki Declaration and its later amendments.
Consent to Participate
The requirement for informed consent was waived because of the retrospective nature of the study.
Data Availability Statement
The data underlying this manuscript will be provided by the authors upon reasonable request.*
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Supplemental Material for The Effect of Preoperative Sagittal Malalignment on Clinical Outcomes in Short-Segment Lumbar Interbody Fusion by Yukitoshi Shimamura Masahiro Kanayama Fumihiro Oha Michihaya Kono Ryo Fujita Shogo Fukase Kohei Shiota Tsutomu Endo Tomoyuki Hashimoto Norimasa Iwasaki in Global Spine Journa
Supplemental Material for The Effect of Preoperative Sagittal Malalignment on Clinical Outcomes in Short-Segment Lumbar Interbody Fusion by Yukitoshi Shimamura Masahiro Kanayama Fumihiro Oha Michihaya Kono Ryo Fujita Shogo Fukase Kohei Shiota Tsutomu Endo Tomoyuki Hashimoto Norimasa Iwasaki in Global Spine Journa
Supplemental Material for The Effect of Preoperative Sagittal Malalignment on Clinical Outcomes in Short-Segment Lumbar Interbody Fusion by Yukitoshi Shimamura Masahiro Kanayama Fumihiro Oha Michihaya Kono Ryo Fujita Shogo Fukase Kohei Shiota Tsutomu Endo Tomoyuki Hashimoto Norimasa Iwasaki in Global Spine Journa
Supplemental Material for The Effect of Preoperative Sagittal Malalignment on Clinical Outcomes in Short-Segment Lumbar Interbody Fusion by Yukitoshi Shimamura Masahiro Kanayama Fumihiro Oha Michihaya Kono Ryo Fujita Shogo Fukase Kohei Shiota Tsutomu Endo Tomoyuki Hashimoto Norimasa Iwasaki in Global Spine Journa
Data Availability Statement
The data underlying this manuscript will be provided by the authors upon reasonable request.*