Abstract
Study Design.
Retrospective study.
Objective.
To investigate factors associated with cervical sagittal imbalance (CSI) after cervical laminoplasty (LMP).
Summary of Background Data.
Preoperative dynamic cervical sagittal alignment is an important predictor for changes in cervical sagittal alignment and clinical outcomes after LMP. However, the impact of preoperative dynamic cervical sagittal alignment on postoperative changes in the cervical sagittal vertical axis (cSVA) after LMP remains unclear. We hypothesized that preoperative cervical flexion and extension function are associated with the changes in cSVA and clinical outcomes and found potential risk factors for post-LMP CSI.
Patients and Methods.
Patients undergoing LMP at a single institution between January 2019 and December 2021 were retrospectively reviewed. The average follow-up period was 19 months. The parameters were collected before the surgery and at the final follow-up. We defined the changes in cSVA (△cSVA) ≤ −10 mm as the improvement group, −10 mm < △cSVA ≤ 10 mm as the stable group, and △cSVA > 10 mm as the deterioration group. Multivariate logistic regression was used to evaluate factors associated with postoperative CSI. The χ2 test was used to compare categorical data between groups. T tests, analysis of variance, Kruskal-Wallis tests, and Mann-Whitney Wilcoxon tests were used to assess the differences between radiographic and clinical parameters among groups. A receiver operating characteristic curve analysis was used to identify optimal cutoff values.
Results.
The study comprised 102 patients with cervical spondylotic myelopathy. The Japanese Orthopedic Association recovery rate was better in the improvement group and a significant aggravation in neck pain was observed in the deterioration group after surgery. Cervical Flex range of motion (ROM; spine range of flexion) was significantly higher in the deterioration group. The multivariate logistic regression model suggested that greater Flex ROM and starting LMP at C3 were significant risk factors for postoperative deterioration of cervical sagittal balance. Receiver operating characteristic curves showed that the cutoff value for preoperative Flex ROM was 34.10°.
Conclusion.
Preoperative dynamic cervical sagittal alignment influences postoperative cervical sagittal balance after LMP. Cervical LMP should be carefully considered for patients with a preoperative high Flex ROM, as CSI is likely to occur after surgery.
Level of Evidence:
Level 3.
Key words: cervical sagittal balance, cervical spondylotic myelopathy, clinical outcomes, dynamic cervical sagittal alignment, laminoplasty
Cervical spondylotic myelopathy (CSM) is a degenerative spine condition, which is caused by compression of the spinal cord. CSM symptoms include sensory deficits, motor deficits, neck pain, and/or reflex deficits.1,2 Cervical laminoplasty (LMP) has been generally acknowledged as an effective treatment for CSM with long-segment spinal cord compression because of its excellent surgical outcomes.3–5
Although cervical LMP is a mature surgical technique for CSM, the surgical outcome is not always satisfactory. Cervical LMP has potential complications, such as deterioration of cervical sagittal alignment, C5 nerve root palsy, lamina closure, axial neck pain, and decreased cervical range of motion (ROM). Some studies have reported that cervical sagittal balance (CSB) based on the cervical sagittal vertical axis (cSVA) is a significant influencing factor in clinical outcomes after cervical surgery.6–9 Kim et al 10 and Zhang et al 11 reported that preoperative higher cSVA was a risk factor for loss of cervical lordosis (LCL) and poor outcomes after cervical LMP. Pinter et al 9 demonstrated that a significant increase in postoperative cSVA was associated with preoperative paraspinal sarcopenia and less improvement in neck pain and disability after cervical LMP. Recent studies have reported several factors related to the variations in cSVA after LMP.9,12,13 However, the impact of preoperative dynamic cervical sagittal alignment on the postoperative changes in cSVA after LMP remains elusive. Preoperative dynamic cervical sagittal alignment is an important predictor for the changes in cervical sagittal alignment and clinical outcomes after cervical LMP.14–18 Clinicians cannot ignore the influence of dynamic cervical sagittal alignment on post-LMP CSB.
The current retrospective study sought to analyze patients with CSM to explore the influence of preoperative static and dynamic cervical sagittal alignment on postoperative changes in cSVA after LMP. We hypothesized that preoperative cervical flexion and extension function are associated with the changes in cSVA and clinical outcomes and found potential risk factors for post-LMP cervical sagittal imbalance (CSI).
PATIENTS AND METHODS
Patient Enrollment
This study was approved by the Institutional Review Board (IRB) of our affiliated institution (IRB number: 2018-086). From January 2019 to December 2021, consecutive adult patients who underwent cervical LMP for CSM at our hospital were retrospectively evaluated. The inclusion criteria were as follows: (1) aged 18 years or older, (2) at least 3 levels of cervical LMP, (3) symptoms of myelopathy (decreased manual dexterity, sensory impairment, and gait disturbance), (4) complete radiologic imaging data, and (5) last follow-up of ≥12 months. Patients with a history of cervical surgery, tumors, fractures, infections, combinations with cervical fusion surgery, a lesion involving C2 or thoracic spine levels, and unclear T1 superior endplate were excluded. Finally, the study included 102 patients.
Surgical Procedures
Surgeons made an incision in the posterior aspect of the neck and dissected the paravertebral muscles from the spinous process and lamina while preserving the facet capsule. The attachments of semispinalis to C2 and/or C7 were routinely preserved as much as possible. All patients underwent decompression using an open-door LMP technique with a mini titanium plate system. One side of the lamina was opened, whereas the other side acted as the hinge.19 All patients wore collars for 3 to 4 weeks.
Radiologic Parameters
Sagittal alignment parameters of the cervical spine were measured on cervical x-rays (Figure 1). Cervical lordosis (CL) refers to the angle between the lower endplate of C2 and the lower endplate of C7. T1 slope (T1S) is the angle formed by a horizontal plane and a line parallel to the superior endplate of T1. cSVA is defined as the horizontal offset from a plumbline dropped from the C2 vertebral body to the posterosuperior corner of the C7 vertebra. CL in flexion (Flex CL) and CL in extension (Ext CL) represent the measurement of CL in flexion and extension positions, respectively. The ROM of the cervical spine is calculated as Ext CL minus Flex CL. Flex ROM indicates the range of flexion and is calculated as CL minus Flex CL. Ext ROM indicates the range of extension and is calculated as Ext CL minus CL. The changes of cSVA (△cSVA) were defined as postoperative cSVA—preoperative cSVA. Patients were categorized into the following 3 groups based on the changes in cSVA (△cSVA): improvement group (△cSVA ≤ −10 mm); stable group (−10 mm < △cSVA ≤ 10 mm); and deterioration group (△cSVA > 10 mm). The flowchart of the study is depicted in Figure 2.
Figure 1.
A–C, CL (a), T1S (b), and cSVA (c) were measured in the neutral position. Ext CL (d) and Flex CL (e) were measured with the patient in maximal flexion and extension, respectively. CL indicates cervical lordosis; cSVA, cervical sagittal vertical axis; Ext CL, CL in extension; Flex CL, CL in flexion; T1S, T1 slope.
Figure 2.
Flowchart of the study. CSM indicates cervical spondylotic myelopathy; △cSVA, changes of the cervical sagittal vertical axis (postoperation minus preoperation).
Clinical Parameters
The Japanese Orthopedic Association (JOA) score was used to evaluate neurological recovery. The recovery rate was calculated as follows: JOA recovery rate = 100×(postoperative JOA−preoperative JOA)/(17−preoperative JOA). The Visual Analog Scale was used to assess the level of neck pain.
Statistical Analyses
All the data were analyzed using SPSS version 22.0 software (SPSS, Inc., Chicago, IL). Variables were expressed as mean ± SD. Pearson correlation analysis was used to assess for correlations. Multivariate logistic regression was used to evaluate factors associated with postoperative CSI. The χ2 test was used to compare categorical data between groups. T tests, analysis of variance, Kruskal-Wallis tests, and Mann-Whitney Wilcoxon tests were used to assess the differences between radiographic and clinical parameters among groups. A receiver operating characteristic curve analysis was used to identify optimal cutoff values. Statistical significance was defined as a P value <0.05.
RESULTS
A total of 102 patients were enrolled, of which 65 were males and 37 were females, with a mean age of 62.77 years. cSVA showed increasing tendencies after surgery, with no statistical significance (preoperative 28.37 ± 11.86 vs. postoperative 31.38 ± 14.23, P = 0.08). The overall demographic, proximal level, and surgery segments are summarized in Table 1.
TABLE 1.
Summary of the Patient Population (N = 102)
| Demographic | |
|---|---|
| Sex; n (%) | |
| Male | 65 (63.73) |
| Female | 37 (36.27) |
| BMI (kg/m2) | 25.39 ± 3.91 |
| cSVA (mm) | |
| Pre | 28.37 |
| Post | 31.38 |
| P | 0.08 |
| JOA | |
| Pre | 12.83 ± 1.70 |
| Post | 15.28 ± 1.51 |
| Recovery rate (%) | 58.32 ± 29.23 |
| VAS (neck) | |
| Pre | 2.75 ± 1.77 |
| Post | 2.25 ± 1.39 |
| Surgery segment (n) | |
| 3 | 40 |
| 4 | 44 |
| 5 | 18 |
| Proximal level | |
| C3 | 59 |
| C4 | 43 |
BMI indicates Body Mass Index; cSVA, cervical sagittal vertical axis; JOA, Japanese Orthopedic Association; VAS, Visual Analog Scale.
Correlations Between △cSVA and Preoperative Parameters
Correlation analysis revealed that △cSVA was positively correlated with age (r = 0.206, P < 0.05), preoperative CL (r = 0.246, P < 0.05), and cervical spine range of flexion (Flex ROM; r = 0.308, P < 0.01), and negatively correlated with preoperative cSVA (r = −0.251, P < 0.05). No significant correlations were observed among the other assessed parameters (Table 2).
TABLE 2.
△cSVA Correlations (N = 102)
| Parameters | Mean ± SD | Pearson |
|---|---|---|
| Age (yr) | 62.77 ± 9.74 | 0.206 * |
| Follow-up period (mo) | 19.29 ± 8.71 | 0.195 |
| Preoperative CL (°) | 16.52 ± 10.46 | 0.246 * |
| Preoperative T1S (°) | 28.60 ± 7.14 | 0.126 |
| Preoperative cSVA (mm) | 28.37 ± 11.86 | −0.251 * |
| T1S-CL (°) | 12.08 ± 8.68 | −0.194 |
| Flex CL (°) | −16.00 ± 9.86 | −0.066 |
| Ext CL (°) | 26.13 ± 11.68 | 0.137 |
| Total ROM (°) | 42.14 ± 12.20 | 0.185 |
| Flex ROM (°) | 32.52 ± 11.96 | 0.308 † |
| Ext ROM (°) | 9.62 ± 6.58 | −0.154 |
Bold values represent statistical significance.
P < 0.05.
P < 0.01 statistically significant difference.
CL indicates cervical lordosis; cSVA, cervical sagittal vertical axis; △cSVA, changes of cervical sagittal vertical axis (postoperation minus preoperation); Ext CL, CL in extension; Flex CL, CL in flexion; ROM, range of motion; T1S, T1 slope.
Comparison of Clinical Outcomes Based on the Postoperative △cSVA
In terms of clinical outcomes, JOA scores were improved in all groups postoperatively (Table 3). No significant difference was observed in preoperative and postoperative JOA scores among the 3 groups. Compared with the deterioration group, the JOA recovery rate was better in the improvement group (Table 3). As for neck pain, the improvement group showed a significant reduction in neck pain after surgery, whereas the deterioration group showed a significant aggravation in neck pain after surgery. The stable group showed tendencies of reduction in neck pain after surgery, with no statistical significance (Table 3).
TABLE 3.
Comparison of Clinical Outcomes
| Parameters | Improvement group (n = 13) | Stability group (n = 64) | Deterioration group (n = 25) | P |
|---|---|---|---|---|
| Preoperative VAS (neck) | 3.67 ± 2.21* | 2.94 ± 1.72 | 1.80±1.55* | <0.05 |
| Postoperative VAS (neck) | 1.47 ± 1.12 | 2.14 ± 1.43 | 2.97± 1.24 | >0.05 |
| P | <0.05 | >0.05 | <0.05 | — |
| Preoperative JOA | 12.51 ± 2.37 | 12.82 ± 1.49 | 13.03 ± 1.81 | >0.05 |
| Postoperative JOA | 15.61 ± 1.20 | 15.42 ± 1.59 | 14.73 ± 1.44 | >0.05 |
| P | <0.05 | <0.05 | <0.05 | — |
| JOA recovery rate (%) | 69.04 ± 29.84* | 62.20 ± 32.42 | 42.82 ± 28.02* | <0.05 |
Bold values represent statistical significance.
Indicated P value ≤0.05.
JOA indicates Japanese Orthopedic Association; VAS, Visual Analog Scale.
Comparison of Evaluated Parameters Variable According to Postoperative △cSVA
Preoperative CL was significantly higher and preoperative cSVA was significantly lower in the deterioration group compared with the improvement group. Among the 3 groups, postoperative cSVA was the highest in the deterioration group. Compared with the improvement group, Flex ROM was significantly higher in the deterioration group (28.30 ± 11.15 vs. 37.34 ± 13.05, P < 0.05). The cervical Flex ROM of the deteriorated group was also greater than that of the stable group, with no statistical significance (31.49 ± 11.47 vs. 37.34 ± 13.05, P=0.068). Among the 3 groups, cervical spine range of extension (Ext ROM) was the best in the improvement group; however, no significant statistical evidence was found (12.61 ± 8.26 vs. 9.58 ± 6.49 vs. 8.16 ± 5.76, P > 0.05; Table 4).
TABLE 4.
Comparison of Evaluated Parameters Variable According to the Postoperative △cSVA
| Parameters | Improvement group (n = 13) | Stability group (n = 64) | Deterioration group (n = 25) | P |
|---|---|---|---|---|
| Age (yr) | 58.31 ± 9.08 | 63.02 ± 9.45 | 64.48 ± 10.47 | >0.05 |
| Follow-up period (mo) | 17.54 ± 3.36 | 19.20 ±8.75 | 20.44 ± 10.04 | >0.05 |
| Surgery segment | 3.84 ± 0.80 | 3.78 ± 0.72 | 3.76 ± 0.72 | >0.05 |
| Proximal level (C3) | 6/13 | 34/64 | 19/25 | >0.05 |
| Preoperative CL (°) | 13.07 ±7.91* | 16.22 ± 9.99 | 19.08 ± 12.38* | <0.05 |
| Preoperative T1S (°) | 25.36 ± 6.11 | 29.17 ± 7.45 | 28.84 ± 6.60 | >0.05 |
| T1S-CL (°) | 12.28 ±7.86 | 12.96 ± 8.37 | 9.76 ± 9.73 | >0.05 |
| Preoperative cSVA (mm) | 34.27 ± 9.06* | 28.82 ± 11.92 | 24.15 ± 11.85* | <0.05 |
| Postoperative cSVA (mm) | 20.02 ± 9.69@ * | 29.42 ± 11.94*† | 41.82 ± 15.43@† | <0.05 |
| Flex CL (°) | −16.24 ± 11.13 | −15.37 ± 9.43 | −17.48 ± 10.52 | >0.05 |
| Ext CL (°) | 24.70 ± 12.18 | 25.99 ± 11.33 | 27.24 ± 12.65 | >0.05 |
| Total ROM (°) | 40.94 ± 12.25 | 41.37 ± 12.02 | 44.72 ± 12.76 | >0.05 |
| Flex ROM (°) | 28.30 ± 11.15* | 31.49 ± 11.47 | 37.34 ± 13.05* | <0.05 |
| Ext ROM (°) | 12.61 ± 8.26 | 9.58 ± 6.49 | 8.16 ± 5.76 | >0.05 |
Bold values represent statistical significance.
ndicated P < 0.05.
indicated P value ≤ 0.01, between two groups.
CL indicates cervical lordosis; cSVA, cervical sagittal vertical axis; △cSVA, changes of cervical sagittal vertical axis (postoperation minus preoperation); Ext CL, CL in extension; Flex CL, CL in flexion; ROM, range of motion; T1S, T1 slope.
Risk Factors for Postoperative Deterioration of cSVA.
Multivariate logistic regression analysis was performed using variables that exhibited a significant correlation with △cSVA. The results showed that greater Flex ROM and starting LMP at C3 were significant risk factors for postoperative deterioration of CSB (Table 5). The receiver operating characteristic curve in Figure 3 showed a discriminative power of Flex ROM to predict postoperative deterioration of cSVA (area under the curve = 0.613, P < 0.01; cutoff value: 34.10°; sensitivity: 54.3%; specificity: 74.6%).
TABLE 5.
Risk Factors for the Postoperative Deterioration of cSVA (△cSVA >10 mm)
| Variable | P | OR | 95% CI |
|---|---|---|---|
| Proximal level (C3) | 0.020 | 3.669 | 1.224–10.996 |
| Pre cSVA (mm) | 0.063 | 0.953 | 0.906–1.003 |
| Age (yr) | 0.066 | 1.053 | 0.997–1.113 |
| Flex ROM (°) | 0.049 | 1.107 | 0.1003–1.193 |
| Preoperative CL (°) | 0.570 | 0.983 | 0.926–1.043 |
CL indicates cervical lordosis; cSVA, cervical sagittal vertical axis; △cSVA, changes of the cervical sagittal vertical axis (postoperation minus preoperation); Flex ROM, range of motion.
Figure 3.
ROC curve analysis to predict △cSVA >10 mm (AUC = 0.613, P < 0.01). The cutoff value for Flex ROM was 34.10°, with a sensitivity of 54.3% and a specificity of 74.6%. AUC indicates area under the curve; △cSVA, changes of the cervical sagittal vertical axis (postoperation minus preoperation); ROC, receiver operating characteristic; ROM, range of motion.
DISCUSSION
CSB plays an important role in maintaining a neutral head posture and horizontal gaze.20 CSI is a cause of axial pain due to the excessive work of the posterior neck muscles.9,10 CSI is associated with LCL and cervical kyphotic alignment change, which interferes with the dorsal shift of the spinal cord after cervical LMP.8,13 The present study found changes in cSVA and improvement in clinical symptoms at least 12 months after cervical LMP. We showed that the occurrence of postoperative CSI was associated with the aggravation of neck pain and poor recovery of neurological function after cervical LMP. Meanwhile, we discovered that preoperative dynamic cervical sagittal alignment was a useful indicator to predict postoperative CSI.
Several studies have reported the relationship between clinical symptoms and CSB based on cSVA.6–11,21–25 Our study revealed that varying degrees of postoperative △cSVA were associated with different levels of neurological recovery and neck pain. Patients in the deterioration group exhibited a worse JOA recovery rate compared with those in the stable and improvement groups (Table 3). Significant postoperative increase in cSVA was often accompanied by significant LCL and reduced space for the shifting of the spinal cord, which led to poor neurological recovery after surgery.13,26,27 Meanwhile, a larger cSVA might lead to a higher intramedullary cord pressure, which is associated with substantial histologic changes in the spinal cord.28,29 Our study found that more neck pain occurred in patients with larger preoperative and postoperative cSVA (Tables 3 and 4). An improvement in neck pain after surgery was observed in stable and improvement groups. However, significant deterioration in neck pain after surgery was observed in the deterioration group. We believe that this is related to the excessive work of the posterior neck muscles. For example, some researchers noted that patients with larger cSVA had excess suboccipital muscle contraction, which might lead to neck pain.30,31
Previous studies evaluated the relationship between cervical static parameters and postoperative cSVA. They found a significant correlation between cSVA and T1S after surgery and speculated that a larger T1S resulted in a larger postoperative cSVA. However, no significant correlation was observed between T1S and △cSVA in our study (Table 2).32,33 T1S is presented as an index of thoracic inlet alignment, and high T1S compensates with enough CL to maintain a forward gaze. Therefore, T1S has its limitations in accounting for the changes in cSVA after surgery.
Our study found a significant positive correlation between Flex ROM and △cSVA. Postoperative cSVA improvement occurred in patients with a low level of Flex ROM and postoperative cSVA deterioration mainly occurred in patients with a high level of Flex ROM (Table 4, P < 0.05). These data imply that a larger Flex ROM is a risk factor for the increase in postoperative cSVA. Degenerative structures, such as ligaments, muscles, and bones, can restrict cervical flexion mobility15,17,34 It has been speculated that an increase in flexion motion may suggest a weakness in the structural forces that maintain a normal cervical sagittal alignment. LMP—being a posterior procedure—can result in damage and atrophy of posterior structures, such as the nuchal ligament, neck muscles, and bone. As a result, the equilibrium necessary to maintain cervical sagittal alignment is disrupted and the head weight acts as a continuous force for the cervical spine to lean forward, which ultimately leads to CSI. Therefore, postoperative CSI is more likely to occur in patients with preoperatively excessive Flex ROM.
Patients in the cSVA stable group had less Flex ROM compared with those in the cSVA deterioration group and had less Ext ROM than those in the cSVA improvement group, with no statistically significant evidence (Table 4, P > 0.05). From the previously mentioned results, we speculate that preoperative high levels of Ext ROM are beneficial to improving postoperative cSVA, and preoperative high levels of Flex ROM aggravate postoperative cSVA (Figure 4). Compared with the improvement of postoperative cSVA, the deterioration of postoperative cSVA had a greater impact on clinical outcomes. A significant increase in cSVA was associated with poor clinical outcomes after cervical LMP (Table 3). A multivariate logistic regression model showed that greater Flex ROM and starting LMP at C3 were significant risk factors for postoperative deterioration of cSVA (Table 5). The optimal cutoff value of preoperative Flex ROM to discriminate between patients with and without postoperative deterioration of cSVA was 34.1° (Figure 3). Therefore, cervical LMP should be carefully considered for patients with a preoperative low Ext ROM and high Flex ROM, as a significant kyphotic change, and sagittal imbalance is likely to develop after surgery. Early removal of the collars and initiation of systematic rehabilitation exercises are recommended to preserve cervical ROM and enhance the strength of the posterior structure of the neck. In some cases, multilevel posterior cervical fusion or anterior cervical fusion surgery can also be considered, if necessary. Meanwhile, surgeons should avoid performing LMP at the C3 level to reduce the occurrence of postoperative CSI. C3 laminectomy may be considered if the decompression needs to extend proximally to C2-C3 disc levels.35,36
Figure 4.
The description provides preoperative and postoperative sagittal radiograph results for 3 patients who underwent LMP and illustrates the various effects of dynamic cervical sagittal alignment on cervical sagittal alignment after surgery. Patient A, a 53-year-old man who underwent LMP of C3-C7, showed low Ext ROM (6.1°) and Flex ROM (22.8°) in the preoperative radiographs. There was no significant change in cSVA after surgery (preoperative cSVA 16.0 mm vs. postoperative cSVA 18.7 mm). Patient B, a 57-year-old woman who underwent LMP of C3-C7, showed increased Ext ROM (24.9°) but low Flex ROM (12.2°) in the preoperative radiographs. After the surgery, there was a significant decrease in cSVA (preoperative cSVA 23.9 mm vs. postoperative cSVA 5.3 mm). Patient C, a 57-year-old woman who underwent LMP of C4-C7, showed low Ext ROM (9.9°) and increased Flex ROM (32.5°) in the preoperative radiographs. However, there was a significant increase in cSVA after surgery (preoperative cSVA 14.8 mm vs. postoperative cSVA 27.3 mm). cSVA indicates cervical sagittal vertical axis; LMP, laminoplasty; ROM, range of motion.
Nonetheless, the present study has several limitations. First, this is not a randomized and prospective study, and hence a selection bias may exist. Second, paraspinal muscles are not evaluated in this study. Third, the area under the curve is small, which may be related to the relatively small number of patients. Only 25 cases were assigned to the cSVA deterioration group. Finally, the study was designed for 12 months of follow-up, which is relatively short. However, in a study on changes in cervical sagittal alignment after LMP, Choi et al 37 noted that changes generally reach a plateau 6 months after surgery. Thus, the follow-up time is enough for this study.
CONCLUSION
Postoperative CSI is related to poor clinical outcomes. Preoperative dynamic cervical sagittal alignment influences postoperative CSB after LMP. Cervical LMP should be carefully considered for patients with a preoperative high Flex ROM, as CSI is likely to occur after surgery.
Key Points
Preoperative dynamic cervical sagittal alignment influences postoperative cervical sagittal balance after laminoplasty.
High preoperative cervical spine range of flexion and starting the laminoplasty at C3 are significant risk factors for postoperative deterioration of cervical sagittal balance.
Postoperative cervical sagittal imbalance is related to poor clinical outcomes after cervical laminoplasty.
The cut-off value of the preoperative cervical spine range of flexion for pr edicting postoperative deterioration of cervical sagittal balance is 34.10° in patients with cervical laminoplasty.
Footnotes
This work was supported by the National Key Research and Development Program of China (No.2020YFC2004900), the National Natural Youth Cultivation Project of Xuanwu Hospital of Capital Medical University (QNPY2022022), and Beijing Hospitals Authority Ascent Plan (No. DFL20190802).
The authors report no conflicts of interest.
Contributor Information
Chengxin Liu, Email: 15313293840@163.com.
Wei Wang, Email: wangwei37@buaa.edu.cn.
Xiangyu Li, Email: lxyyxl@sina.com.
Bin Shi, Email: shibin16sy@163.com.
Shibao Lu, Email: spinelu@xwhosp.org.
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