Abstract

Background: Various indicators of vertebral instability in patients with lumbar degenerative disease can be identified in myelo-computed tomography (CT) studies.

Methods: Of 120 patients, 45 with lumbar degenerative spondylolisthesis (LDS; 53 lumbar lesions) and 75 with lumbar spinal stenosis alone (LSS; 105 lesions) (2015–2019) myelo-CT studies and surgery confirmed the presence of lumbar instability. Myelo-CT findings indicative of instability included facet joint thickness (FJT), fluid in the facet joint, facet tropism, and air in the facet and/or disc.

Results: For the 120 study patients, FJT was significantly elevated in both the LDS and LSS groups.

Conclusion: FJT on myelo-CT is more specific for lumbar instability than other imaging parameters when evaluating LDS. An increase in FJT suggests vertebral instability likely warranting fusion.

Keywords: Facet, Lumbar degenerative disease, Lumbar degenerative spondylolisthesis, Lumbar spinal stenosis, Spine

INTRODUCTION

Facet joint thickness (FJT),[ 5 , 7 , 8 ] facet fluid signs (FFS),[ 1 , 2 , 3 , 8 ] facet tropism,[ 4 , 6 ] air in the facet joint, and air in the disc seen on lumbar MR or computed tomography (CT)/myelo-CT studies often reflect the presence of significant segmental instability. Here, we analyzed the clinical outcomes and radiological findings for 120 patients whose myelo-CT studies documented significant changes in the facet joints consistent with lumbar instability likely warranting fusion.

MATERIALS AND METHODS

Study population

The study was approved by our Institutional Review Board. It included 120 patients, 45 with lumbar degenerative spondylolisthesis [LDS >25% slip or >3 mm, Figure 1 ] (53 lumbar lesions), and 75 with lumbar spinal stenosis (LSS) (105 lesions) aged 60 or older, who underwent presurgical myelo-CT studies of the lumbar spine (2015–2019) confirming instability warranting fusion [ Table 1 ].

Figure 1:

Measurement of vertebral slip. (A) The distance between the tangents drawn on the posterior surface of the upper vertebral body and the posterior surface of the lower vertebral body was measured. (B) The anterior-posterior diameter of the lower vertebral body was measured. A/B × 100(%) >25(%) or A >3 mm was defined as slippage.

Table 1:

Clinical characteristics of 120 patients.

Myelo-CT documentation of instability

Myelo-CT criteria for lumbar instability included the assessment of FJT, FFS, facet tropism, air in the facet, and air in the disc [ Table 2 ]. FJT was defined as the maximum distance between the inferior and superior articular processes of the level [ Figure 2 ]. FFS was defined as a measurable, curvilinear, and high-intensity signal in the facet joint that matched that of cerebrospinal fluid on axial T2-weighted MRI [ Figure 3 ]. Facet tropism measurements were carried out as previously described by Ko et al.[ Figure 4 ].[ 6 ] Surgery included decompressions alone for the LSS group, while those with LDS underwent additional fusions.

Table 2:

Definition of each radiological indicator.

Figure 2:

Measurement of facet joint thickness. The measurement was performed at the site where the joint fissure was the maximum width. The distance between the superior articular process and the articular process cortical bone was measured.

Figure 3:

Facet fluid sign. Water intensity in facet on T2-weighted magnetic resonance imaging was defined as facet fluid sign (white arrowhead).

Figure 4:

Measurement of facet tropism. A line parallel to the posterior surface of the vertebral body was drawn, and a line perpendicular to this line and passing through the base of the spinous process was drawn. The angle between this line and facet was measured on the left and right, and the difference was taken as facet tropism.

Statistical analysis

Student’s t-test, Pearson’s Chi-square test and multivariate analysis with multiple logistic regression analysis were carried out. The level of significance was set at 5% (P ≤ 0.05), and all analyses were performed using SPSS, version 23.0 (IBM, Armonk, NY).

RESULTS

Neuroradiological indices

FJT was significantly elevated (2.6 ± 1.1 mm) in the LSD group versus the LSS group (1.7 ± 0.8 mm) [ Table 3 ]. FFS was more frequently recognized in the LDS group (40 [75%] patients) versus the LSS group 61 [58%] patients); univariate and multivariate analysis confirmed that FJT was significantly related to LDS [ Tables 3 and 4 ]. The LDS group (12.2 ± 6.6°) also had significantly greater facet joint angles versus the LSS group (9.5 ± 7.1°) [ Table 3 ]. However, air in the facet was found in 21 (39.6%) in the LDS group and 38 (36.2%) in the LSS group, and air in the disc in 35 (66.0%) in the LDS group and 61 (58.0%) in the LSS group, with no significant differences between the two groups.

Table 3:

Comparison of neuroradiological parameters among groups.

Table 4:

Multiple logistic regression analyses of association with LDS.

DISCUSSION

FJT major myelo-CT indicator of lds instability warranting fusion

This study demonstrated that FJT was elevated especially in patients with LDS and was thus a crucial sign of dynamic vertebral instability and the need for fusion. Hasegawa et al. verified that an increased facet joint volume was associated with lumbar segmental instability.[ 5 ] Here, we showed that FJT was significantly elevated in patients with LDS (> 3 mm or >25% olisthy).

FSS additional myelo-CT finding for instability

FFS has become an important indicator of lumbar instability. Yamada et al. defined significant facet joint opening as >2 mm as (FJO); 70% of patients with FJO had FFS.[ 8 ] Chaput et al. reported a combination of normal curvature and FFS on MRI as reliable findings of LDS (i.e., high positive predictive value [93.22%]).[ 2 ]

Facet tropism consistent with instability

Facet tropism is indicative of degeneration within a facet joint and is also predominantly associated with the LSD group.[ 4 , 6 ]

Fusion rates

We performed decompression or fusion largely based on dynamic myelo-CT studies confirming significant instability (i.e., >3 mm or 25% olisthy) in LDS patients, while 97.3% of LSS patients without these findings underwent decompressions alone.

CONCLUSION

In patients with LDS, FJT on myelo-CT studies most specifically confirmed lumbar instability warranting fusion versus any other imaging parameter.

Ethical Approval

The author(s) declare that they have obtained ethical approval from IRB/IEC’ to ‘The authors declare that they have obtained ethical approval from our institution’s IRB’ in the Ethical Approval section.

Declaration of patient consent

Patient’s consent not required as there are no patients in this study.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

Use of artificial intelligence (AI)-assisted technology for manuscript preparation

The author(s) confirms that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.

Disclaimer

The views and opinions expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Journal or its management. The information contained in this article should not be considered to be medical advice; patients should consult their own physicians for advice as to their specific medical needs.

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