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. 2020 Nov 6;479(4):817–825. doi: 10.1097/CORR.0000000000001542

Utility of Natural Sitting Lateral Radiograph in the Diagnosis of Segmental Instability for Patients with Degenerative Lumbar Spondylolisthesis

Qing-shuang Zhou 1,2, Xu Sun 1,2,✉, Xi Chen 1,2, Liang Xu 1,2, Bang-ping Qian 1,2, Zezhang Zhu 1,2, Yong Qiu 1,2
PMCID: PMC8083840  PMID: 33165051

Abstract

Background

Segmental instability in patients with degenerative lumbar spondylolisthesis is an indication for surgical intervention. The most common method to evaluate segmental mobility is lumbar standing flexion-extension radiographs. Meanwhile, other simple radiographs, such as standing upright radiograph, a supine sagittal magnetic resonance imaging (MRI) or supine lateral radiograph, or a slump or natural sitting lateral radiograph, have been reported to diagnose segmental instability. However, those common posture radiographs have not been well characterized in one group of patients. Therefore, we measured slip percentage in a group of patients with degenerative lumbar spondylolisthesis using radiographs of patients in standing upright, natural sitting, standing flexion, and standing extension positions as well as supine MRI.

Questions/purposes

We asked: (1) Does the natural sitting radiograph have a larger slip percentage than the standing upright or standing flexion radiograph? (2) Does the supine sagittal MRI reveal a lower slip percentage than the standing extension radiograph? (3) Does the combination of the natural sitting radiograph and the supine sagittal MRI have a higher translational range of motion (ROM) and positive detection rate of translational instability than traditional flexion-extension mobility using translational instability criteria of greater than or equal to 8%?

Methods

We retrospectively performed a study of 62 patients (18 men and 44 women) with symptomatic degenerative lumbar spondylolisthesis at L4 who planned to undergo a surgical intervention at our institution between September 2018 and June 2019. Each patient underwent radiography in the standing upright, standing flexion, standing extension, and natural sitting positions, as well as MRI in the supine position. The slip percentage was measured three times by single observer on these five radiographs using Meyerding’s technique (intraclass correlation coefficient 0.88 [95% CI 0.86 to 0.90]). Translational ROM was calculated by absolute values of difference between two radiograph positions. Based on the results of comparison of slip percentage and translational ROM, we developed the diagnostic algorithm to evaluate segmental instability. Also, the positive rate of translational instability using our diagnostic algorithms was compared with traditional flexion-extension radiographs.

Results

The natural sitting radiograph revealed a larger mean slip percentage than the standing upright radiograph (21% ± 7.4% versus 17.7% ± 8.2%; p < 0.001) and the standing flexion radiograph (21% ±7.4% versus 18% ± 8.4%; p = 0.002). The supine sagittal MRI revealed a lower slip percentage than the standing extension radiograph (95% CI 0.49% to 2.8%; p = 0.006). The combination of natural sitting radiograph and the supine sagittal MRI had higher translational ROM than the standing flexion and extension radiographs (10% ± 4.8% versus 5.4% ± 3.7%; p < 0.001). More patients were diagnosed with translational instability using the combination of natural sitting radiograph and supine sagittal MRI than the standing flexion and extension radiographs (61% [38 of 62] versus 19% [12 of 62]; odds ratio 3.9; p < 0.001).

Conclusion

Our results indicate that a sitting radiograph reveals high slip percentage, and supine sagittal MRI demonstrated a reduction in anterolisthesis. The combination of natural sitting and supine sagittal MRI was suitable to the traditional flexion-extension modality for assessing translational instability in patients with degenerative lumbar spondylolisthesis.

Level of Evidence

Level III, diagnostic study.

Introduction

Abnormal segmental displacement in patients with degenerative lumbar spondylolisthesis is frequently associated with back pain and nerve root irritation [2, 8, 22, 25]. Segmental instability accompanied by intractable low-back pain is believed to be an indication for surgical intervention, including decompression alone or decompression and fusion with or without instrumentation and interbody fusion [6, 8, 24]. Radiologically, instability in patients with degenerative spondylolisthesis has been interpreted as either excessive mobility or lumbar malalignment at the spondylolisthetic segment [3, 5, 9, 24].

Various imaging techniques have been used to evaluate segmental motion in patients with lumbar spondylolisthesis. Traditionally, standing lateral radiographs taken in flexion-extension have been the most widely used tool to maximize segmental ROM [1, 19, 25]. However, standing flexion-extension radiographs can cause discomfort to the patient. Recently, lumbar segmental instability was evaluated by comparing lateral radiographs taken in the standing upright position with sagittal MRI or computerized tomography (CT) scans taken in the supine position, which was comparable to flexion-extension radiographs for evaluating degenerative spondylolisthesis [1–19]. The supine lateral radiograph was also reported to allow for improved reduction of anterolisthesis compared with the standing extension radiograph [25]. They suggested that the combination of standing flexion and supine radiographs could be more appropriate than standing flexion-extension radiographs for the initial assessment of degenerative spondylolisthesis because the former revealed greater vertebral mobility and reduction. No consensus has been achieved about a single diagnostic modality, therefore, there is a need to standardize the technique for diagnosing segmental instability.

The natural sitting position is a common weightbearing position during activities of daily life [9, 10, 12]. The lumbar spine was kyphotic in the slump sitting lateral radiograph [11, 12]. Compared with standing upright and standing flexion radiographs, the slump sitting radiograph demonstrated decreased ROM in lumbar alignment [10]. The radiograph of the lumbar spine with the patient in the sitting position was superior to the radiograph of the patient in the conventional standing flexion position in terms of assessing angular motion, and the slump sitting radiograph identified greater lumbar sagittal instability than did the standing flexion radiograph [9]. However, in studies of the sitting radiograph, only volunteers with mechanical low back pain were recruited [9, 10]. It is unclear whether the radiograph taken in the sitting position is superior to conventional methods in identifying segmental instability in patients with degenerative spondylolisthesis.

Therefore, we performed this study to compare slip parameters in patients with degenerative lumbar spondylolisthesis measured using radiographs of patients in standing upright, natural sitting, standing flexion, and standing flexion positions as well as supine MRI. We intended to explore: (1) Does the natural sitting radiograph have a larger slip percentage than the standing upright or standing flexion radiograph? (2) Does the supine sagittal MRI reveal a lower slip percentage than the standing extension radiograph? (3) Does the combination of the natural sitting radiograph and the supine sagittal MRI have a higher translational ROM and positive detection rate of translational instability than traditional standing flexion-extension mobility using translational instability criteria of great than or equal to 8%?

Patients and Methods

Study Design and Setting

We performed a retrospective study of patients with symptomatic degenerative lumbar spondylolisthesis who underwent a surgical intervention at our institution between September 2018 and June 2019. All investigations were conducted in conformity with ethical principles of research.

Patients

During the study period, 62 patients with degenerative spondylolisthesis (18 men and 44 women) with an mean age of 59.2 ± 7.1 years were indicated for surgery. The enrolled patients were required to meet the following criteria: adult patients older than 40 years and monosegmental L4 low-grade spondylolisthesis (Meyerding’s Grade I or II). The exclusion criteria were a lumbar scoliosis angle > 10° and a history of spinal surgery, trauma, infection, or fracture of the pelvis or lower limbs. Spondylolisthesis is defined as anterolisthesis of equal to or more than 5% in the standing upright sagittal plane, with an intact isthmic pedicle on a three-dimensional (3-D) CT sagittal radiograph [26]. The patients’ demographic information, including sex, age, and BMI, was recorded.

Radiographic Assessment

Each patient underwent routine the standing flexion and extension radiographs, and supine MRI by a team of experienced technologists. Radiographs of standing upright and sitting naturally were taken by trained radiology technologists using a lower radiation dose of EOS machine (EOS Imaging Inc, Paris, France). The uniformity of these positions was reinforced through standardized verbal instructions (Table 1). Those radiographs for enrolled patients were performed randomly in the order of the patients’ appointments. Patients were required to rest more than 15 minutes to reduce distractions.

Table 1.

Standardized verbal instructions given to the patients

Posture Standardized verbal instructions
Natural sitting radiograph Sit relaxed on a chair without leaning forwards, with hands placed below the thighs and feet on the ground
Standing upright radiograph Stand straight, with fingers touching the collarbones and elbows flexing at 45°
Standing flexion radiograph Stand straight with hands behind the head, and bend forward as far as possible without falling
Standing extension radiograph Stand straight with hands behind the head, and bend backward as far as possible without falling
Supine MRI Lie flat on the couch facing up with hands placed behind the head
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Basic radiographic parameters measured on natural sitting, standing upright, standing flexion, and standing extension lateral radiographs and supine mid-sagittal MRI were adapted for the analysis (Fig. 1) [2, 3, 27]. The slip percentage was calculated as the ratio of the measured slip distance to the measured width of the L5 vertebral upper endplate, according to Meyerding’s technique. The slip angle of the spondylolisthesis level was measured as the angle between the lower endplate of the L4 vertebra and the upper endplate of the L5 vertebra. A positive angle was defined as lordosis and a negative angle was defined as kyphosis.

Fig. 1.

Fig. 1

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This radiograph shows measurement of slip parameters. The slip percentage is calculated as the ratio of the line bc to the line ac × 100%. SA = slip angle.

Segmental Instability Criteria

We calculated ROM, including translational motion and angular motion, using the absolute values of difference between two positions radiograph [1, 5, 9, 19, 25]. Normal spine has a certain ROM during daily activities, which develops into pathology as segmental instability if outside this range [5, 20, 22, 24].

Segmental instability was considered to be present if translational motion between different positions was greater than or equal to 8% [3, 19, 25, 27]. Intervertebral angular rotation between positions that exceeded or was equal to 10° was also regarded as instability [3, 14, 27].

Statistical Analysis

We performed the measurements using SPSS version 20.0 (SPSS, Chicago, IL, USA). All radiographic parameters were measured three times by a single author (QSZ) at different times using Surgimap Spine software (version: 2.2.12.1, New York, NY, USA). We included the average of the three measurements in this study (ICC 0.88 [95% CI 0.86 to 0.90]). Continuous variables were presented as means and SDs. We used a t test for continuous variables, and we used a chi-square test for categorical variables between two groups. Univariate analysis of variance (ANOVA) of random block design was used for continuous variables among multiple groups, and the least significant difference was used for two group comparison if the ANOVA result was significant.

First, measurements of radiographs of patients in the five positions were compared using univariate ANOVA for multiple groups and paired-t test between groups. The aims were to determine the best positions for the larger and lower slip percentage and slip angle. Second, we performed univariate ANOVA to compare the translational ROM and angular ROM among different modalities, which was reported to be crucial for evaluating segmental instability [5, 9, 14, 19, 25]. Finally, a paired chi-square test, also called McNemar test, was used to determine the ability of identifying segmental instability using the algorithms developed in this study versus the traditional standing flexion and extension method. A p value < 0.05 indicated statistical significance.

Results

Segmental Motion Evaluation

After ANOVA revealed that slip percentage had a statistical difference among natural sitting, standing upright, and standing flexion lateral radiographs (p < 0.001; Table 2), we found that the sitting radiograph revealed the greater mean slip percentage compared with the standing upright radiograph (21% ± 7.4% versus 17.7% ± 8.2% [95% CI 2.4% to 4.2%]; p < 0.001; Table 2) or standing flexion radiograph (21% ± 7.4% versus 18% ± 8.4% [95% CI 2.1% to 4.0%]; p = 0.002; Table 2). The mean slip percentage was lower on the supine sagittal MRI than the standing extension radiograph using paired-t test (11% ± 6.9% versus 12.6% ± 6.4% [95% CI 0.49% to 2.8%]; p = 0.006; Table 2). Also, we found that the natural sitting radiograph had a lower slip angle than standing flexion radiograph using paired-t test (-1.4° ± 5.4° versus 1.9° ± 4.3° [95% CI 2.4 to 4.2]; p < 0.001; Table 2). Based on a statistical difference of ANOVA for slip angle among standing upright radiograph, standing extension radiograph, and supine MRI (p < 0.001; Table 2), we found the standing extension radiograph had a larger slip angle than the standing upright radiograph (8.9° ± 4.6° versus 7.1° ± 4.8° [95% CI 0.71 to 2.8]; p = 0.01; Table 2) and the supine MRI (8.9° ± 4.6° versus 6.5° ± 3.9° [95% CI 1.4 to 3.5]; p < 0.001). There was no statistical difference for slip angle between the standing upright radiograph and the supine MRI (7.1° ± 4.8° versus 6.5° ± 3.9° [95% CI -0.38 to 1.73]; p = 0.21; Table 2).

Table 2.

Slip parameters measured in five postures

Examinations Slip percentage (%) Slip angle (°)
Mean ± SD 95% CI Mean ± SD 95% CI
Natural sitting radiograph 21.0 ± 7.4 19.1 to 22.9 -1.4 ± 5.4 -2.7 to -0.05
Standing upright radiograph 17.7 ± 8.2 15.6 to 19.8 7.1 ± 4.8 5.9 to 8.4
Standing flexion radiograph 18.0 ± 8.4 15.8 to 20.1 1.9 ± 4.3 0.75 to 3.0
Standing extension radiograph 12.6 ± 6.4 11.0 to 14.2 8.9 ± 4.6 7.7 to 10.1
Supine MRI 11.0 ± 6.9 9.2 to 12.7 6.5 ± 3.9 5.5 to 7.4
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The mean translational mobility seen on the combination of natural sitting radiograph and the supine sagittal MRI was higher than the combination of standing upright radiograph and the supine sagittal MRI (10% ± 4.8% versus 6.8% ± 6.0% [95% CI 2.0% to 4.5%]; p < 0.001; Fig. 2), or the combination of the standing flexion and extension radiographs (10% ± 4.8% versus 5.4 ± 3.7% [95% CI 3.4% to 5.9%]; p < 0.001; Fig. 2). Meanwhile, the combination of natural sitting and standing extension radiographs had a lager angular motion than the combination of natural sitting and standing upright radiographs (10.3° ± 4.9° versus 8.5° ± 4.9° [95% CI 0.87 to 2.7]; p < 0.001; Fig. 3), and the combination of the standing flexion-extension modality (10.3° ± 4.9° versus 7.0° ± 4.5° [95% CI 2.4 to 4.2]; p < 0.001; Fig. 3). The combination of natural sitting and standing upright radiographs also had a larger angular motion than the combination of the standing flexion-extension modality (8.5° ± 4.9° versus 7.0° ± 4.5° [95% CI 0.62 to 2.4]; p = 0.001; Fig. 3).

Fig. 2.

Fig. 2

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This graph shows the mean segmental translational ROM seen on radiographs in various modalities. Univariate ANOVA shows a statistical difference among the combination of natural sitting radiograph and the supine sagittal MRI (Si-Su), the combination of standing upright radiograph and the supine sagittal MRI (U-Su), and the combination of the standing flexion and extension radiographs (F-E) (10% ± 4.8% versus 6.8% ± 6% versus 5.4% ± 3.7%; p < 0.001).

Fig. 3.

Fig. 3

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This graph shows the mean segmental angular ROM seen on radiographs in various modalities. Univariate ANOVA shows a statistical difference among the combination of natural sitting and standing extension radiographs, the combination of natural sitting and standing upright radiographs, and the combination of the standing flexion-extension radiographs (10.3° ± 4.9° versus 8.5° ± 4.9° versus 7.0° ± 0.5°; p < 0.001).

Comparison Between Our Diagnostic Algorithms and Traditional Method

We found that more patients were diagnosed with translational instability using the combination of the natural sitting radiograph and the supine sagittal MRI than the standing flexion and extension radiographs (61% [38 of 62] versus 19% [12 of 62]; OR 3.9 [95% 0.78 to 19.8]; p < 0.001; Table 3). There were no statistical difference of angular instability between the combination of the natural sitting and standing upright radiographs and the combination of the standing flexion and extension radiographs (34% [21 of 62] versus 18% [11 of 62]; OR 1.8 [95% CI 0.48 to 6.9]; p = 0.05; Table 4).

Table 3.

Comparison of ability to identify translational instability between Si-Su and F-E

Si-Su F-E Total
Translational motion ≥ 8% (translational instability) Translational motion < 8%
Translational motion ≥ 8% (translational instability) 10 28 38
Translational motion < 8% 2 22 24
Total 12 50 62
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Si-Su = the combination of the natural sitting radiograph and the supine MRI; F-E = the combination of the standing flexion radiograph and the standing extension radiograph.

Table 4.

Comparison of ability to identify angular instability between Si-U and F-E

Si-U F-E Total
Angular motion ≥ 10° (angular instability) Angular motion < 10°
Angular motion ≥ 10° (angular instability) 5 16 21
Angular motion < 10° 6 35 41
Total 11 51 62
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Si-U = the combination of the natural sitting radiograph and the standing upright radiograph; F-E = the combination of the standing flexion radiograph and the standing extension radiograph.

Discussion

Lumbar segmental instability of spondylolisthesis is an important factor of back pain, which is vital for treatment options and surgical algorithm [4, 8-12, 14, 19, 20, 24]. The topic of how to reveal physical spinal ROM accurately is a hot-button topic that has sparked numerous conversations [1, 5, 9, 10, 14, 20, 25]. Experts reached a consensus: A simple, convenient and common postural radiography examination without external force or extra supporting facilities is suitable to reveal segmental ROM [1, 9, 10, 19, 25]. Standing flexion-extension modality is the most common method for assessing instability; however, this modality could underestimate physical ROM due to increased paraspinal muscle tension for patients with back/leg pain during examinations [1, 9, 25]. Instability-related clinical symptoms usually stem from increased physiological load and abnormal ROM caused by postural changes during daily life. The topic of physical spinal ROM motivates experts to explore accurate diagnostic algorithms for assessment segmental instability [1, 9, 10, 19]. Meanwhile, other simple examinations, such as standard upright radiographs, supine sagittal MRI or supine lateral radiographs, slump or natural sitting lateral radiographs have been reported to diagnose segmental instability [1, 9, 10, 19, 25]. However, those common posture radiographs have not been well characterized in one group of patients. It remains unclear which posture radiographs reveal maximal physical ROM. This study demonstrates that radiographs taken of patients in daily life positions provide a more meaningful evaluation of lumbar segmental motion in patients with degenerative spondylolisthesis. The combination of natural sitting radiograph and supine sagittal MRI is superior to traditional standing flexion and extension radiographs in evaluating translational ROM, and the combination of natural sitting and standing upright radiographs is comparable to measure angular ROM (Fig. 4A-E).

Fig. 4.

Fig. 4

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A-E A 51-year-old female patient with intractable degenerative spondylolisthesis at L4/L5 received a series of radiographs before surgical intervention, including (A) a lateral radiograph in the natural sitting position with slip percentage of 24% and slip angle of -11.6°. (B) The same patient had a lateral radiograph in the standing upright position, with a slip percentage of 15% and a slip angle of 2.3°. (C) In the lateral radiograph in the standing flexion position, the slip percentage was 16% and the slip angle was -1.9°. (D) In the lateral radiograph in the standing extension position, the slip percentage was 12% and the slip angle was 3.6°. (E) The patient’s mid-sagittal MRI in the supine position had a slip percentage of 11% and a slip angle of 0.9°. The natural sitting lateral radiograph showed the largest with slip percentage and the lowest slip angle. Radiographs of the patient in the combination of natural sitting radiograph and the supine mid-sagittal MRI position were superior to those taken in the combination of the standing flexion and extension position in assessing translational angular motion (13% versus 3%), and radiographs taken with the patient in the combination of natural sitting radiograph and the supine sagittal MRI position were superior to those taken in the combination of the standing flexion and extension position in assessing angular motion (13.9° versus 5.5°).

Limitations

There are several limitations in this study. First, this study enrolled a small sample size of patients with degenerative spondylolisthesis who prepared to undergo surgical intervention at our single center. Also, because it was a retrospective clinical study, the examinations were not performed in a blinded or independent fashion, which resulted in a selection and assessment bias. However, the enrolled patients represented classical spondylolisthesis, and patients were asked to rest for a short time to eliminate assessment bias. Our findings for clinical diagnosis are worth trying to generalize and verify in other patient populations. Second, proper examinations of the positions depended on the different examiners’ instructions and the patient’s adherence to the protocol. To reduce this deviation, standardized verbal instructions (Table 1) were given to the patients. Third, the instability criteria are controversial. It is not clear whether inconsistent criteria are applicable when using radiographs taken with the patient in the sitting position for assessing segmental instability. However, our findings provide a new direction for further studies to investigate the spinal normal ROM and segmental instability.

Segmental Motion Evaluation

Multiple diagnostic modalities have been explored to assess mobility in patients with or without lumbar spondylolisthesis; however, those conclusions were inconsistent due to limitations of their studies [15, 16, 20]. In the past decade, the use of the classic standing flexion and extension lateral method for assessing instability has been challenged because there is an increased physical burden and extra medical cost [18, 19]. The role of the supine lateral radiograph, sagittal CT, and MRI in reducing spondylolisthesis has been studied previously, which is in accordance with our results [1, 19, 25]. Relaxed supine MRI is an excellent tool for reducing spondylolisthesis compared with the standing extension radiograph. The supine MRI is recommended because it is readily available, reduces radiation exposure and medical costs, and the patient tolerates the exam with relaxed muscles [1, 19, 22]. In addition, preoperative, routine MRI can reveal degenerative changes in the spine [16, 17, 24] and symptoms related with instability, such as facet joint effusion and interspinous fluid [5, 16, 17].

This study revealed that the low intervertebral angle was detected using the natural sitting radiograph, which helped us further understand the significance of sitting position radiograph. In reference to the standing upright profile, the natural sitting radiograph was demonstrated with a kyphotic lumbar sagittal profile, and a greater loss of ROM than radiographs carried out in other positions, such as forward bending, half-squatting, supine, and backward bending [10, 12]. A previous study reported that during the performance of various tasks in daily life, load on the lumbar disc was the highest for sitting forward [21]. The ability of the functional spinal unit to withstand shear forces primarily depends on tensile strain on the lumbar vertebral ligaments and anulus fibrosus deriving from swelling pressure on the lumbar disc [13]. The turgor pressure of the disc decreases because of insufficient intervertebral column support, which negatively affects the disc in terms of anterior shear forces [20]. As shown in the current study, the kyphotic alignment of the lumbar spine in the natural sitting position may be associated with reduced tension in the lumbar ligaments and inner anulus, which aggravates the degree of spondylolisthesis. However, the previous study found that the sitting radiograph was noninferior to the standing flexion method in measuring translational motion [9]. This may have occurred because only volunteers with mechanical back pain were enrolled in their study. Furthermore, a biomechanical evaluation demonstrated that the kyphotic configuration of the lumbar spine was the most commonly seen imaging feature in predicting segmental instability [15], which was consistent with our finding that kyphotic lumbar alignment was associated with greater motion.

Based on the above-mentioned radiographic features of lumbar kyphosis, we strive to explain the possible inherent mechanisms for high ROM in natural sitting radiograph. The following reasons support that the natural sitting position is an appropriate position to force the lumbar vertebrae into kyphosis. First, sitting is a natural position [9, 10, 12]. Reduced segmental motion as seen on standing flexion-extension radiographs may be attributable to increased paraspinal muscle tension during radiography [1, 19]. Second, pelvic retroversion and loss of lumbar lordosis in the sitting position may increase the diameter of the spinal canal and neuroforamina [23]. Symptoms of neurogenic claudication in patients who have degenerative spondylolisthesis with stenosis are alleviated temporarily by sitting. Third, this is a relaxed position with physical weightbearing that generates the biomechanics of the lumbar spine under physiologic conditions [10]. Fourth, this natural and relaxed position eliminates confounding factors of the lower limbs that influence standing flexion of the lumbar vertebrae, such as lower-limb deformities or injuries and hamstring tightness [7]. Finally, the bilateral ischial tuberosities are the supporting site during sitting with a fixed pelvis. The natural and relaxed Si position can specifically move the lumbar spine into great kyphosis, causing instability of the lumbar segments [9, 11, 12].

Comparison Between Our Diagnostic Algorithms and Traditional Method

As far as we know, the current study demonstrates the superiority of the combination of the natural sitting radiograph and the supine sagittal MRI over traditional flexion-extension radiographs or the combination of the standing upright radiograph and the supine MRI in detecting translational motion to evaluate lumbar spine stability in patients with degenerative spondylolisthesis. The combination of natural sitting and standing extension radiographs were better than the combination of natural sitting and radiographs or standing flexion-extension radiographs in assessing angular rotation. However, a previous study found that translational motion had greater clinical value than angular rotation in identifying segmental instability, and the presence of two radiographic factors indicated that symptoms could be persistent [14]. In addition, the combination of natural sitting and standing upright radiographs in our study was superior to standing flexion-extension radiographs for evaluation angular ROM. The additional expenditure and radiation with limited clinical relevance make extension radiographs unworthy. Mechanical leg or back pain related to lumbar instability was generated during activities of daily living. Nevertheless, the standing extension position is forced and not usually used in activities of daily living. Diagnosing instability using radiographs taken in positions used during day-to-day living could be more meaningful than diagnosing instability with radiographs taken in uncommon, forced positions or by using extra supporting facilities [20]. Therefore, the traditional standing flexion-extension method or extension-alone method should not be used for evaluating an unstable spine because they have limited clinical value and extra radioactive and physical burdens.

Currently, performing spine fusion according to the spine’s standing shape is the standard practice, but the ideal position in which to fuse the lumbar spine is poorly understood [10]. Given that sitting is an important weightbearing position, it is likely that permanently fixing lumbar lordosis to model the standing profile is an overcorrection in the context of daily living activities [9, 10, 12]. Therefore, common physiologic positions should be considered in attempts to find the best permanent position of compromise that maximizes function and decreases supraphysiologic stress at the adjacent vertebral levels [10]. Those novel but simple and convenient methods should be further explored clinically to evaluate stability and sagittal alignment and create a surgical algorithm [9-12].

Conclusion

We found that the sitting radiograph reveals high slip percentage and kyphotic slip angle, and supine sagittal MRI demonstrates reduction of anterolisthesis. Radiographs carried out in the natural sitting and standing upright positions, along with sagittal MRI in the supine position, can be used instead of the combination of standing flexion and standing extension to diagnose segmental instability in patients with degenerative spondylolisthesis. The combination of natural sitting and supine positions has values for assessment translational motion, and the combination of natural sitting and standing upright positions is comparable for evaluation angular motion. Further studies are required to verify our diagnostic algorithms, and to identify its significance for surgical algorithms.

Footnotes

One of the authors certifies that he (XS), or a member of his immediate family, has received or may receive payments or benefits, during the study period, in an amount of USD 10,000 to USD 100,00 from the Jiangsu Provincial Medical Youth Talent (award #QNRC2016011); and in an amount of USD 10,000 to USD 100,00 from the National Natural Science Foundation of China (award #81772422). Each remaining author certifies, that neither he or she, nor any member of his or her immediate family, has funding or commercial associations (consultancies, stock ownership, equity interest, patent/licensing arrangements, etc.) that might pose a conflict of interest in connection with the submitted article.

All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research® editors and board members are on file with the publication and can be viewed on request.

Each author certifies that his or her institution approved the human protocol of this investigation and that all investigations were conducted in conformity with ethical principles of research.

This work was performed at the Department of Spine Surgery, Drum Tower Hospital, Nanjing, China.

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