Abstract
Objective
To evaluate the influence of Scoliosis Research Society (SRS)‐Schwab sagittal modifiers of pelvic incidence minus lumbar lordosis mismatch (PI‐LL) on clinical outcomes for adult degenerative scoliosis (ADS) after long posterior instrumentation and fusion.
Methods
This was a single‐institute, retrospective study. From 2012 to 2014, 44 patients with ADS who underwent posterior instrumentation and fusion treatment were reviewed. Radiological evaluations were investigated by standing whole spine (posteroanterior and lateral views) X‐ray and all radiological measurements, including Cobb’s angle, LL, PI, and the grading of vertebral rotation, were performed by two experienced surgeons who were blind to the operations. The patients were divided into three groups based on postoperative PI‐LL and the classification of the SRS‐Schwab: 0 grade PI‐LL (<10°, n = 13); + grade PI‐LL (10°–20°, n = 19); and ++ grade PI‐LL (>20°, n = 12). The clinical outcomes were assessed according to Japanese Orthopaedic Association (JOA) score, Oswestry Disability Index (ODI), Visual Analog Scale (VAS), Lumbar Stiffness Disability Index (LSDI), and complications. Other characteristic data of patients were also collected, including intraoperative blood loss, operative time, length of hospital stay, complications, number of fusion levels, and number of decompressions.
Results
The mean operative time, blood loss, and hospital stay were 284.5 ± 30.2 min, 1040.5 ± 1207.6 mL, and 14.5 ± 1.9 day. At the last follow‐up (2.6 ± 0.6 years), the radiological and functional parameters, except the grading of vertebral rotation, were all significantly improved in comparison with preoperative results (P < 0.05), but it was obvious that an ideal PI‐LL (≤10°) was not achieved in some patients. Significant differences were only observed among the three groups in the ODI and LSDI. Patients with + grade PI‐LL seemed to have the best surgical outcome compared to those with 0 and ++ grade PI‐LL, with the lowest ODI score (+ grade vs 0 grade, 17.3 ± 4.9 vs 26.0 ± 5.4; + grade vs ++ grade, 17.3 ± 4.9 vs 32.4 ± 7.3; P < 0.05) and lower LSDI (+ grade vs 0 grade, 1.6 ± 1.0 vs 3.5 ± 0.5, P < 0.05; + grade vs ++ grade, 1.6 ± 1.0 vs 0.6 ± 0.5, P > 0.05). A Pearson correlation analysis further demonstrated that LSDI was negatively associated with PI‐LL. Furthermore, the incidence rate of postoperative complications was lower in patients with + grade PI‐LL (1/19, 5.26%) than that in patients with 0 (2/13, 15.4%) and ++ grade PI‐LL (3/12, 25%).
Conclusion
Our present study suggest that the ideal PI‐LL may be between 10° and 20° in ADS patients after long posterior instrumentation and fusion.
Keywords: Degenerative scoliosis, Lumbar lordosis, Pelvic incidence, Sagittal balance, SRS‐Schwab classification
Introduction
Adult degenerative scoliosis (ADS) is a frequently encountered spinal deformity in the elderly population, with an estimated prevalence of 6%–68% in those aged >50 years1, 2. Adults with ADS typically present with diverse symptoms, including low back pain, neurologic deficits, functional limitations, or disability, which all influence the quality of life of patients3. Conservative management is recommended initially, but the therapeutic outcomes are commonly unsatisfactory due to the heterogeneous conditions, and surgical treatment strategies are then required.
Currently, various surgical treatments for ADS have been developed, such as decompression alone, the combination of decompression and short fusion, as well as the combination of decompression, long fusion, and correction of deformity4. Selection of a suitable surgical method should be carefully evaluated according to the major symptoms and medical co‐morbidities5. The main aim of the surgery for ADS is to relieve symptoms, while postoperative complications should also be considered to be minimized due to a high occurrence of complications6. Because of the high risk of the recurrence of spinal stenosis, decompression alone is not recommended for ADS, and it is only applied to patients who have a small scoliosis curve but have no lateral subluxation7. The combination of decompression and limited short fusion is recommended for patients with a moderate scoliosis curve and normal sagittal imbalance8. For patients who have a large scoliosis curve and positive sagittal imbalance, the combination of decompression, long fusion, and correction of deformity is required9. Recently, long posterior instrumentation and fusion has been demonstrated to relieve pain, reduce the risks of complications, and improve the quality of life, indicating that long posterior instrumentation and fusion may be effective and safe for the treatment of ADS4, 10.
It is well‐known that ADS is classically defined as a coronal curvature of the spine greater than 10° in a skeletally mature individual who has no previous history of scoliosis. Thus, correction of the coronal Cobb angle is considered the most important goal for corrective surgery. However, recent studies indicate that the sagittal spinal imbalance may be a more critical parameter associated with clinical symptoms than the coronal imbalance and, thus, may be more beneficial to guide decision‐making11, 12, 13. Radiological sagittal parameters that significantly correlate with pain, disability, and the health‐related quality of life include the sagittal vertical axis (SVA), pelvic tilt (PT), and the mismatch between pelvic incidence minus lumbar lordosis (PI‐LL)14, 15. Among them, PI‐LL is especially valuable for planning deformity surgical correction because PI is a constant anatomic parameter for each individual after skeletal maturity and, thus, a surgeon can estimate the required amount of LL to match PI for harmonious balance16, 17.
Schwab et al. suggest that the ideal PI‐LL should be achieved within ±10° for adult spinal deformity18, 19. An excessive PI‐LL mismatch (PI‐LL > 10°) is more likely to lead to the development of adjacent segment disease and the requirement of a revision surgery20. Nevertheless, a recent study of Yamada et al. indicates that an excellent clinical outcome may also be obtained for 23% of patients without sufficient PI‐LL correction, indicating the optimal PI‐LL for corrective surgery remains controversial21, 22. Thus, it is necessary to investigate the effects of different PI‐LL values on the clinical outcomes in ADS patients with corrective surgery and to search for an optimal PI‐LL for corrective surgery.
The goals of this study were: (i) to evaluate the effect of long posterior instrumentation and fusion surgery on the radiological and functional parameters in ADS patients; (ii) to further compare the clinical outcomes of ADS patients who underwent long posterior instrumentation and fusion surgery, but acquired different PI‐LL values according to the classification of the Scoliosis Research Society‐Schwab (SRS‐Schwab) PI‐LL sagittal modifier (<10°, “0”; 10°–20°, “+”; >20°, ++)20. This, to our knowledge, has not been reported. The present study may provide a basis for confirmation of a more appropriate threshold for PI‐LL.
Materials and Methods
Patients
This was a single‐institute, retrospective study of patients with ADS who underwent posterior instrumentation and fusion treatment in the General Hospital of PLA between 2012 and 2014. The inclusion criteria of patients were as follows: (i) Cobb angle of lumbar curves ≥10°; (ii) age > 50 years at time of surgery; (iii) no history of previous lumbar spine surgery; (iv) no history of idiopathic adult scoliosis; (v) long instrumentation from thoracolumbar to L5, the sacrum or the ilium with a minimum of four vertebral segments of fusion; (vi) complete preoperative and postoperative radiographic data and functional evaluation forms; and (vii) a minimum 2‐year follow‐up. This study was approved by the Institutional Review Board in the General Hospital of PLA, and all patients provided written informed consent for the study and surgery.
Data Collection and Outcomes Evaluations
Radiological evaluations were investigated by standing whole spine (posteroanterior and lateral views) X‐ray and all radiological measurements were performed by two experienced surgeons who were not involved with the operations. Radiological parameters included Cobb angle, LL (Cobb angle from the upper endplate of L1 to the upper endplate of S1) and PI (angle subtended by a perpendicular from the upper endplate of S1 and a line connecting the center of the femoral head to the center of the upper endplate of S1), of which PI and LL were used to calculate PI‐LL (PI minus LL). The grading of vertebral rotation was evaluated according to the Nash–Moe method23. Clinical outcomes were assessed by Japanese Orthopaedic Association (JOA) score, Oswestry Disability Index (ODI), Visual Analog Scale (VAS), and Lumbar Stiffness Disability Index (LSDI). Other characteristic data of patients were also collected, including intraoperative blood loss, operative time, length of hospital stay, complications, number of fusion levels, and number of decompressions.
Statistical Analysis
The statistical analysis was performed using SPSS version 11.5 software (SPSS, Chicago, IL, USA). All continuous data were expressed as mean and standard deviation. Normality of continuous data was tested using the Kolmogorov–Smirnov test. Normally distributed values were compared using one‐way analysis of variance (ANOVA) with Bonferroni (homogeneity of variance) or Dunnett T3 tests (heterogeneity of variance) as post‐hoc tests, while values with skew distribution were compared using the Kruskal–Wallis test followed by Bonferroni post‐hoc test. Categorical data were presented as numbers and statistical significance was performed by χ2‐test. A Pearson correlation analysis was performed to investigate the relative influences of postoperative PI‐LL on postoperative clinical and radiographic parameters. P‐values smaller than 0.05 were considered statistically significant.
Results
Patient Baseline Characteristics and Clinical Outcomes
A total of 44 ADS patients were enrolled in this study, including 13 men and 31 women, with an average age of 65.1 ± 2.8 years (range, 58–70 years). They underwent 4–8 (mean, 7.2 ± 1.6)‐level fusion surgery, with T10–L5 (23, 52.3%) as the level most commonly treated, followed by L2–S1 (11, 25.0%), T10–S1 (5, 11.4%), L2–L5 (2, 4.5%), T10‐ilium (2, 4.5%), and L2‐ilium (1, 2.3%). Posterior instrumentation used was pedicle screws in all patients. The mean operative time, blood loss, and hospital stay were 284.5 ± 30.2 min, 1040.5 ± 1207.6 mL, and 14.5 ± 1.9 day, respectively. At the last follow‐up (2.6 ± 0.6 years), the radiological and functional parameters were all significantly improved in comparison with preoperative results. The postoperative Cobb angle was reduced 5.6 times compared to the preoperative result (3.6° ± 1.5° vs 20.3° ± 3.5°, P < 0.05); the postoperative PI‐LL was reduced 2 times compared to the preoperative result (16.5° ± 8.5° vs 35.9° ± 5.2°, P < 0.05); the postoperative JOA increased four times compared to the preoperative result (23.2 ± 1.1 vs 5.6 ± 0.9, P < 0.05); the postoperative ODI was reduced 2.6 times compared to the preoperative result (24.0 ± 8.5 vs 62.8 ± 3.4, P < 0.05); the postoperative VAS was increased 2.3 times compared to the preoperative result (3.1 ± 0.9 vs 7.1 ± 1.1, P < 0.05), but it was obvious that an ideal PI‐LL (≤10°) was not achieved in some patients (Table 1, Figs 1, 2, 3)18. In addition, no significant difference was found between preoperative and postoperative grading of vertebral rotation.
Table 1.
Summary of clinical and radiographic data of 44 adult degenerative scoliosis patients undergoing long posterior instrumentation and fusion
| Variables | Value |
|---|---|
| Age at surgery (year) | 65.1 ± 2.8 |
| Sex (male/female) | 13/31 |
| Number of levels fused (n) | 7.2 ± 1.6 |
| Number of decompressions (n) | 2.3 ± 0.7 |
| Blood loss (mL) | 1040.5 ± 1207.6 |
| Operative time (min) | 284.5 ± 30.2 |
| Length of hospital stay (d) | 14.5 ± 1.9 |
| Preoperative Cobb angle (°) | 20.3 ± 3.5 |
| Cobb angle at follow‐up (°) | 3.6 ± 1.5* |
| Preoperative PI‐LL (°) | 35.9 ± 5.2 |
| Postoperative PI‐LL (°) | 16.5 ± 8.5* |
| Preoperative Nash–Moe grading | 1.2 ± 0.7 |
| Postoperative Nash–Moe grading | 0.8 ± 0.3 |
| Preoperative ODI | 62.8 ± 3.4 |
| ODI at follow‐up | 24.0 ± 8.5* |
| Preoperative JOA (LBP) | 5.6 ± 0.9 |
| JOA at follow‐up (LBP) | 23.2 ± 1.1* |
| Preoperative VAS (LBP) | 7.1 ± 1.1 |
| VAS at follow‐up (LBP) | 3.1 ± 0.9* |
| LSDI | 1.9 ± 1.4 |
Value is expressed as the mean ± standard deviation or number. JOA, Japanese Orthopaedic Association; LBP, low back pain; LL, lumbar lordosis; LSDI, Lumbar Stiffness Disability Index; ODI, Oswestry Disability Index; PI, pelvic incidence; PI‐LL, PI minus LL; VAS, Visual Analog Scale
P < 0.05, compared with preoperative result.
Figure 1.
A 67‐year‐old male patient received a T10–L5 posterior fusion surgery for adult degenerative scoliosis, with the coronal Cobb angle corrected from 10° to 1° and pelvic incidence‐lumbar lordosis (PI‐LL) corrected from 15° to 1°. Preoperative whole‐spine standing posteroanterior (A) and lateral (B) radiographs; postoperative whole‐spine standing posteroanterior (C), and lateral (D) radiographs.
Figure 2.
A 64‐year‐old female patient received a T10–L5 posterior fusion surgery for adult degenerative scoliosis, with the coronal Cobb angle corrected from 28° to 2° and pelvic incidence‐lumbar lordosis (PI‐LL) corrected from 43° to 19°. Preoperative whole‐spine standing posteroanterior (A) and lateral (B) radiographs; postoperative whole‐spine standing posteroanterior (C), and lateral (D) radiographs.
Figure 3.
A 68‐year‐old female patient received a T10‐ilium posterior fusion surgery for adult degenerative scoliosis, with the coronal Cobb angle corrected from 22° to 2° and pelvic incidence‐lumbar lordosis (PI‐LL) corrected from 37° to 28°. Preoperative whole‐spine standing posteroanterior (A) and lateral (B) radiographs; postoperative whole‐spine standing posteroanterior (C), and lateral (D) radiographs.
Effect of pelvic incidence minus lumbar lordosis on the Clinical Outcomes
Grouping
To investigate whether the restoration of PI‐LL influenced the clinical outcomes, we further divided our patients into three groups according to the SRS‐Schwab PI‐LL sagittal modifier, in which 13 patients (29.5%) presented with 0 grade PI‐LL (0 grade PI‐LL group), 19 patients had + grade PI‐LL (+ grade PI‐LL group), and 12 patients had ++ grade PI‐LL (++ grade PI‐LL group)19.
Radiological Outcomes
No significant differences were observed among the three groups, except in the post‐operative radiological evaluations (Cobb’s angle and PI‐LL) and clinical outcomes (ODI and LSDI) (Table 2). The Cobb’s angle was 1.6 times higher in + grade PI‐LL than that in 0 grade PI‐LL (4.4° ± 1.4° vs 2.8° ± 1.1°, P < 0.05), but it was still less than 10°, demonstrating the effectiveness of surgery in restoration of coronal balance. The PI‐LL was 3.6 times lower in 0 grade PI‐LL than that in + grade PI‐LL (5.1 ± 3.3 vs 18.4 ± 2.9, P < 0.05) and 5 times lower in 0 grade PI‐LL than that in the ++ grade PI‐LL group (5.1 ± 3.3 vs 25.8 ± 2.3, P < 0.05). Similarly, a significant difference was also present in PI‐LL between + grade PI‐LL and ++ grade PI‐LL, and PI‐LL reduced 1.4 times in + grade PI‐LL than that in ++ grade PI‐LL (18.4 ± 2.9 vs 25.8 ± 2.3, P < 0.05). This finding indicated that the sagittal balance was not excellently restored in + grade PI‐LL and ++ grade PI‐LL and, thus, the clinical outcomes may also be poor.
Table 2.
Comparison of clinical and radiographic data in the three groups
| Variables | 0 grade PI‐LL(n = 13) | + grade PI‐LL(n = 19) | ++ grade PI‐LL(n = 12) | F/χ2 | P‐value |
|---|---|---|---|---|---|
| Age (years) | 65.5 ± 3.2 | 65.0 ± 2.8 | 64.8 ± 2.3 | 0.173 | 0.842 |
| Sex (M/F) | 4/9 | 6/13 | 3/9 | 0.170 | 0.919 |
| Number of levels fused (n) | 7.2 ± 1.6 | 7.6 ± 1.6 | 6.4 ± 1.7 | 4.580 | 0.101 |
| Number of decompressions (n) | 1.9 ± 0.8 | 2.4 ± 0.7 | 2.4 ± 0.7 | 2.013 | 0.147 |
| Blood loss (mL) | 1470.0 ± 2218.5 | 846.8 ± 92.4 | 881.7 ± 83.3 | 1.220 | 0.543 |
| Operative time (min) | 280.8 ± 33.1 | 293.1 ± 25.5 | 275.0 ± 32.7 | 1.497 | 0.236 |
| Length of hospital stay (d) | 15.0 ± 1.9 | 14.5 ± 1.8 | 14.1 ± 1.9 | 0.760 | 0.474 |
| Preoperative Cobb angle (°) | 18.8 ± 3.4 | 20.6 ± 3.4 | 21.3 ± 3.4 | 1.868 | 0.67 |
| Cobb angle at follow‐up (°) | 2.8 ± 1.1 | 4.4 ± 1.4* | 3.3 ± 1.4 | 6.256 | 0.004* |
| Preoperative PI‐LL (°) | 35.2 ± 6.8 | 36.6 ± 4.6 | 35.4 ± 4.2 | 0.339 | 0.714 |
| Postoperative PI‐LL (°) | 5.1 ± 3.3 | 18.4 ± 2.9* | 25.8 ± 2.3* , † | 171.409 | <0.001* |
| Preoperative ODI | 63.3 ± 3.0 | 62.7 ± 3.9 | 62.3 ± 3.2 | 0.232 | 0.794 |
| ODI at follow‐up | 26.0 ± 5.4 | 17.3 ± 4.9* | 32.4 ± 7.3* , † | 26.114 | <0.001* |
| Preoperative JOA (LBP) | 5.5 ± 0.9 | 5.5 ± 0.9 | 5.8 ± 1.1 | 1.307 | 0.520 |
| JOA at follow‐up (LBP) | 22.9 ± 1.1 | 23.3 ± 1.1 | 23.3 ± 1.0 | 1.452 | 0.484 |
| Preoperative VAS (LBP) | 7.4 ± 1.0 | 7.2 ± 1.0 | 6.7 ± 1.2 | 1.492 | 0.237 |
| VAS at follow‐up (LBP) | 3.0 ± 1.2 | 3.1 ± 0.8 | 3.2 ± 0.6 | 0.110 | 0.896 |
| LSDI | 3.5 ± 0.5 | 1.6 ± 1.0* | 0.6 ± 0.5* | 47.697 | <0.001* |
Value is expressed as the mean ± standard deviation or number. P, comparison among three groups (*, not significant). JOA, Japanese Orthopaedic Association; LBP, low back pain; LL, lumbar lordosis; LSDI, Lumbar Stiffness Disability Index; ODI, Oswestry Disability Index; PI, pelvic incidence; PI‐LL, PI minus LL; VAS, Visual Analog Scale
P < 0.05, compared with 0 grade PI‐LL
P < 0.05, compared with Group + grade PI‐LL.
Clinical Outcomes
Surprisingly, we found that patients in + grade PI‐LL seemed to have a better surgical outcome than 0 grade PI‐LL and ++ grade PI‐LL. The ODI score reduced 1.2 times in + grade PI‐LL than that in 0 grade PI‐LL (17.3 ± 4.9 vs 26.0 ± 5.4, P < 0.05) and reduced 1.9 times in + grade PI‐LL than that in ++ grade PI‐LL (17.3 ± 4.9 vs 32.4 ± 7.3, P < 0.05); LSDI was 2.2 times lower in + grade PI‐LL than that in 0 grade PI‐LL (1.6 ± 1.0 vs 3.5 ± 0.5, P < 0.05), while no significant difference between + grade PI‐LL and ++ grade PI‐LL (1.6 ± 1.0 vs 0.6 ± 0.5, P > 0.05). Although LSDI in + grade PI‐LL was higher than that in ++ grade PI‐LL, no statistical difference was observed between them. Almost 100% of patients in 0 grade PI‐LL could not put on their shoes and socks by themselves. In addition, they could not perform personal hygiene functions after toileting. However, the patients in + grade PI‐LL were able to perform such personal hygiene functions 6 months after the operation and the patients in ++ grade PI‐LL did not have any of the above problems. This negative association between postoperative PI‐LL and postoperative LSDI was further demonstrated by a Pearson correlation analysis (P < 0.001) (Table 3).
Table 3.
Correlations between postoperative pelvic incidence minus lumbar lordosis and postoperative clinical, radiographic data
| Variables | Regression coefficient | Standardized regression coefficient | t‐value | P‐value |
|---|---|---|---|---|
| Cobb (°) | 1.618 | 0.878 | 1.331 | 0.190 |
| ODI | 0.190 | 0.189 | 1.250 | 0.218 |
| JOA (LBP) | 1.729 | 0.214 | 1.421 | 0.163 |
| VAS (LBP) | 1.522 | 0.158 | 1.036 | 0.306 |
| LSDI | −4.910 | −0.798 | −8.572 | <0.001 |
JOA, Japanese Orthopaedic Association; LBP, low back pain; LSDI, Lumbar Stiffness Disability Index; ODI, Oswestry Disability Index; VAS, Visual Analog Scale.
Postoperative Complication
Surgical complications were also assessed. Loosening of implant fixation occurred in one patient in each group and pseudarthrosis was identified at L5–S1 in two patients in the ++ grade PI‐LL group, both of which were not treated because of the lack of related clinical symptoms. Proximal junction kyphosis (PJK) was found at the thoracolumbar region in one patient in the 0 grade PI‐LL group, which was solved by a revision surgery for extension to the T6 to prevent the progression of thoracic kyphosis.
Discussion
Although previous studies have demonstrated the importance to improve the PI‐LL, the optimal PI‐LL for corrective surgery remains controversial15, 21, 22, 24, 25. This was the first study to exclusively investigate the association between postoperative PI‐LL and postoperative clinical outcomes based on three SRS‐Schwab PI‐LL sagittal modifiers (<10°, “0”; 10°–20°, “+”; >20°, ++) in ADS who underwent long posterior instrumentation and fusion. Surprisingly, we found that the patients with postoperative PI‐LL of 10°–20° seemed to have the best surgical outcome, exhibiting the lowest ODI score, lower LSDI, and no significant JOA and VAS scores compared with other groups. Our finding was not consistent with the classical sagittal reconstruction theory (PI‐LL < 10°) in adult spinal deformity (ASD) patients18, 19. This may be attributed to the following reasons. First, the average age of patients with degenerative scoliosis is commonly greater than that of ASD patients, which was also observed in our study when compared with the study of Schwab et al. (mean, 65.1 vs 51.9 years)14. Lafage et al. demonstrated that the ideal spino‐pelvic value increased with age, ranging from PI‐LL = −10.5° for patients aged <35 years to PI‐LL = 16.7° for patients aged >75 years26. Xu et al. proposed estimating the ideal lumbar lordosis to be restored from spinal fusion surgery using a formula which considered the age factor: LL = 0.508 × PI −0.088 × Age + 28.627. Second, using elderly volunteers as a study population, Banno et al. found that normal PI‐LL was significantly higher in women than in men. In our study, the ratio of women and men was 2.4 : 1, which may be one possible reason to induce a higher PI‐LL threshold for corrective surgery28. Third, there may be a difference in the ideal cut‐off for PI‐LL among populations with different ethnic backgrounds29.
In addition to the routinely‐used clinical outcome parameters (ODI, JOA, and VAS), we used the LSDI questionnaire for assessing the functional limitations of ADS patients. Elderly patients spend a lot of time indoors and do not generally participate in a great deal of outdoor activity like younger patients. Most of the questions in LSDI are about indoor activity and, thus, we believe LSDI may be a valid instrument for daily function assessment in ADS patients after fusion surgery30, 31. In our study, LSDI in + grade PI‐LL and ++ grade PI‐LL was significantly higher than that in 0 grade PI‐LL, but no statistical difference was observed between them. Furthermore, a negative association between PI‐LL and LSDI was further confirmed by a multivariate analysis. These results suggested that a smaller lumbar lordosis might lead to good postoperative function.
In line with the achievement of ideal sagittal realignment (20° > PI‐LL > 10°) in our study, the incidence of postoperative complications was also obviously lower in + grade PI‐LL (1/19, 5.26%) than that in 0 grade PI‐LL (2/13, 15.4%) and ++ grade PI‐LL (3/12, 25%). PJK is an important and not so rare complication in spinal deformity surgery. It is reported that patients with large corrections in their LL and sagittal balance are at high risk of developing PJK32. As expected, PJK was identified in one patient of 0 grade PI‐LL, who needed a revision surgery. Although loosening of implant fixation and pseudarthrosis were also observed after fusion surgery, we believe they are not serious complications because no related clinical symptoms were induced.
There are some limitations of this study. First, this is a retrospective study that may result in unavoidable selection bias. Second, this is a single‐center study and sample size is, thus, limited. Third, the follow up was not long, which may influence the evaluation of the possible relationship between radiographic parameters and clinical outcomes. Therefore, large‐scale, multicenter, and prospective studies should be performed to further confirm the optimal PI‐LL for corrective surgery in Chinese ADS patients.
In conclusion, our present study suggests that the ideal PI‐LL value may be achieved between 10° and 20° in ADS patients after long posterior instrumentation and fusion surgery, which is associated with excellent clinical outcomes and low complication rates.
Acknowledgments
We acknowledge that all authors listed meet the authorship criteria according to the latest guidelines of the International Committee of Medical Journal Editors, and that all authors are in agreement with the manuscript.
Disclosure: There are no conflicts of interest to declare.
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