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

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.

Fig. 1

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.

Fig. 2

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

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).

Fig. 4

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°).