Lumbar Facet Effusions and Other Degeneration Parameters and Its Association with Instability
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.360912
Source of Support: None, Conflict of Interest: None
Keywords: Facet effusions, facet joint, instability, Modic changes, spondylolisthesis
Facet effusions were described by Chaput et al. as a curvilinear, high-intensity signal within the facet joint on the axial T2-weighted images. Controversy exists in the literature about whether they are associated with instability.,,,,,,,, It is thought that they may represent the laxity of the soft tissue of the facet joint, which might allow an abnormal range of motion in the spinal level, corresponding to the second phase of the degeneration process described by Kirkaldy–Willis et al.,,,,, However, it is not the only image finding that is suspected to be associated with instability, but also Modic changes (MC) type one, facet orientation, and spondylolisthesis, among others.,,,,,,,, Existence of segmental instability is an important concern for spine surgeons during the decision-making process as it may lead to choosing a surgical treatment instead of a conservative approach, and it can change our surgical plan as arthrodesis may need to be performed. Moreover, it must be borne in mind that instability is responsible for several cases of residual or recurrent pain following lumbar spine surgery in which fusion was not performed., Thus, it is meaningful to find different MRI features that could be related to instability in order to use them in clinical practice.
The main objective of this paper is to assess the association between facet effusions and segmental instability. Furthermore, we evaluate the relationship between other lumbar degeneration parameters and instability, as well as the association between these image findings and the presence of facet effusions.
Patients with low back pain were included in this study between 2018 and 2020. They were assessed in the office, and all measurements were recorded using a printed form completed by the authors. Then, the data were transferred to our database on the computer. We conducted this study in compliance with the principles of the Declaration of Helsinki. The study's protocol was reviewed and approved by the institute's review board (IRB No. 002-2018). Participants provided informed consent to carry out these measurements and to publish the harvested data or images. Only L4–L5 and L5–S1 levels were assessed, and all analysis was done per level instead of per patient. Both spinal levels were evaluated in all patients but one in whom L4–L5 data was not available because of a filling form problem. In those classifications in which laterality is present (such as facet effusions or Grogan ones), the highest grade of the level was recorded. Inclusion criteria were as follows: patients with low back pain (alone or with associated radicular pain) and age older than 18 years who had undergone flexion and extension dynamic x-rays of the lumbar spine as well as lumbar spine MRI. We do not use CT scan routinely in our clinical practice in lumbar degenerative disease patients. Exclusion criteria were as follows: previous lumbar surgery; recent lumbar facet joint blockage; L5–S1 spondylolisthesis; L4–L5 spondylolisthesis of other suspected etiology than degenerative one; and the presence of scoliosis, spinal tumor, infection, or fracture in the lumbar region. It must be borne in mind that a recent previous facet joint blockage may generate an image in the MRI that could be confused with facet effusion. All patients with spondylolisthesis included had L4–L5 degenerative spondylolisthesis in order to avoid including the different biomechanical population of patients with isthmic spondylolisthesis. Upper lumbar levels have different facet orientations; this may generate a more heterogeneous sample. Instability in the spinal segment was defined with the presence of one or more of the following findings: translation ≥5 mm or angulation ≥10° in dynamic X-rays or a present spondylolisthesis in standing X-rays that reduces in static MRI. We did not use dynamic MRI in this study.
The main objective of this study was to assess whether the existence of large facet effusions is associated with instability of the spinal segment. Facet effusions were assessed in axial T2-weighted MRI images. Based on Chaput et al. description and Tamai et al. grading (0: no effusion, 1: effusion <1.5 mm, and 2: effusion ≥1.5 mm), we decided to divide the spinal levels into two groups: the small facet effusions (SFE) group in whom facet effusions were <1.5 mm and the large facet effusions (LFE) group in whom they were ≥1.5 mm [Figure 1]. The association of both groups with instability was evaluated as the main outcome of the study. Furthermore, we compared the demographic data and the presence of other lumbar degeneration parameters among both groups.
The relationship between other image findings and segmental instability was also assessed. Regarding the assessment of degenerative disc disease (DDD), we used the Pfirmann classification [Figure 2]. We defined two subgroups based on this classification: low-grade DDD (LGDDD) and high-grade DDD (HGDDD). The former was composed of grades 1, 2, and 3, whereas the latter comprised grades 4 and 5. Facet subchondral sclerosis. Facet cartilage degeneration were measured using the pertinent Grogan classifications [Figure 3] and [Figure 4]., Facet orientation in the right and left sides were measured as is shown in [Figure 5]; the difference of degrees between both sides was also recorded. The presence and type of MC were also assessed in the MRI as described elsewhere.,, MC type 1 is hyperintense in T2-weighted images and hypointense in T1-weighted images, whereas the endplates are hyperintense in T1-weighted images and iso or hyperintense in T2-weighted images in MC type 2 and hypointense in both T1- and T2-weighted images in MC type 3.
Finally, we subdivided the levels into subgroups to evaluate the association of LFE and instability within each subgroup: spondylolisthetic, HGDDD, LGDDD, and MC type 1 subsets. In the spondylolisthesis subgroup (L4–L5 degenerative spondylolisthesis), the relationship between MC Type 1 and instability was also analyzed.
Statistical analysis was performed with Mann–Whitney test for quantitative variables and with Fisher exact test and Chi-square test for categorical ones. Statistical significance was accepted if P was <0.05 (to refuse the null hypothesis).
In total, 207 L4–L5 and L5–S1 levels were assessed. When comparing the features of LFE and SFE groups, only the finding of LGDDD had a significant relationship with LFE [Table 1]. The main analysis comparing the presence of instability in SFE and LFE groups showed a non-statistically significant association between larger facet effusions and instability (P = 0.516). Furthermore, other lumbar degeneration parameters did not reach statistical significance: presence of MC types 2 or 3 (P = 0.459 and P = 1, respectively), absence of MC (P = 0.086), presence of LGDDD (P = 0.837), Grogan subchondral sclerosis or cartilage degeneration grades, facet orientation and difference of facet orientation between both sides. In addition, the fact of being L4–L5 or L5–S1 level and gender were not significantly related with instability (P = 0.154 and P = 0.837, respectively) [Table 2]. There were only three patients with synovial cysts; thus, we could not perform a statistical analysis.
In contrast, the presence of MC type 1 and the existence of L4–L5 spondylolisthesis had a statistically significant association with instability (P = 0.001 in both cases). However, only 39% of MC type 1 levels were unstable, whereas almost 70% of levels with spondylolisthesis were stable.
Both in the subset of levels with LGDDD and HGDDD, LFE was not associated with instability (P = 0.782 and P = 0.704, respectively) [Table 3]. In the subset of 43 levels with L4–L5 degenerative spondylolisthesis, the presence of LFE had a significant association with instability (P = 0.046), but only 47.3% of patients with LFE and spondylolisthesis were unstable. In these listhetic levels, the finding of MC type 1 in the MRI was also associated with instability (P = 0.042), which was found in 62.5% of levels with spondylolisthesis and MC type 1 together [Table 3].
In the subset of 23 levels with MC type 1 in the MRI, the appearance of LFE did not reach statistical significance (P = 0.214); however, the resultant subgroups were too small to perform a proper analysis [Table 3].
LFE was associated with instability only within the subset of levels with spondylolisthesis in our study, although only 47.3% of these levels were unstable. Thus, LFE might reflect the facet capsule laxity in these listhetic levels, which allows hypermobility in the segment. Spondylolisthesis itself was also significantly related with instability, but only 30% of levels with listhesis were unstable., Thus, the presence of spondylolisthesis does not mean that the patient is unstable in daily clinical practice. The same occurs with the existence of MC type 1 in the MRI, which achieved a statistically significant association with instability, but 61% of these levels were stable. However, these results are useful to the spine surgeon in order to suspect instability in these groups of patients as it was more frequent in these subsets. Interestingly, the levels with MC type 1 within the subgroup of spondylolisthesis had a statistically significant association with instability and 62.5% of them were unstable. This is a very useful finding as we can suspect strongly the presence of instability when a spinal level shows both features in the MRI: spondylolisthesis and MC type 1. Thus, probably the most interesting and helpful result of our study for clinical practice is that we should suspect instability in discs with spondylolisthesis and MC type 1 and/or LFE.
The association between facet effusions and instability is controversial in the literature. Chaput et al. concluded that facet effusions >1.5 mm in L4–L5 level were predictive of spondylolisthesis in dynamic X-rays when there was no listhesis seen in the supine MRI, which is one of our diagnostic criteria for instability. Furthermore, the authors added that they did not measure an effusion ≥1.5 mm in the group of patients without anterolisthesis in the dynamic radiographs. Lattig et al. also found in their research that facet joint effusion was correlated with spontaneous reduction of the extent of slippage in the supine position compared to the upright position. Fernandes et al. did not find an association between facet effusion and instability and they explained that the presence of facet effusions should not influence the therapeutic decision between decompression alone and decompression with arthrodesis. Tamai et al. reported that facet joint effusion had no effect on the outcome of decompression alone surgery in the absence of preoperative instability. Other studies found an association between facet fluid and instability.,,,
The lack of association of LFE and instability depends on other factors too, such as the definitions of LFE and instability used in the study. Regarding the facet effusion size threshold, we decided to define LFE when they were ≥1.5 mm because Chaput et al. found that effusions larger than this value were predictive of instability. Instability definition varies in the literature. Nowadays, several authors use translation ≥3 mm in dynamic X-rays as a diagnostic criterion for instability instead of translation ≥5 mm as we used here.,, Probably, if we had used the 3-mm threshold, we would have found more unstable levels in our case series and this fact would have changed our outcomes. Nevertheless, we used a classic threshold of translation, which was also utilized by other authors.,
MC type 1 corresponds to vertebral body edema and hypervascularity, whereas MC types 2 and 3 represent fatty replacements of the red bone marrow and subchondral bone sclerosis, respectively. It is thought that the edema and inflammation present in type 1 may be related to instability and could be a sign of pseudarthrosis after spinal fusion surgery.,,,, MC type 1 was also found to be associated with segmental hypermobility by other authors, although some others did not show this association.,,
LFE was associated with LGDDD in our study, and we believed that this is due to a tendency toward facet joint ankylosis in HGDDD. Thus, LFE might be seen in a more initial phase of degeneration cascade. However, LFE did not reach a significant association with instability both in the LGDDD and HGDDD subgroups. Additionally, LGDDD was not related to instability. Grogan grades of facet degeneration (cartilage degeneration and subchondral sclerosis) were also not significantly related with LFE or instability, making this theory less probable in light of our findings. Cho et al. showed that the mean disc and facet joint degeneration was higher in the stable group than in the unstable one. Lattig et al. reported that the degree of facet joint osteoarthritis was significantly greater in the group without segmental hypermobility.
It is thought that increased sagittal lumbar facet orientation would correlate with increased incidence of degenerative spondylolisthesis as it would allow for a greater range of flexion motion.,, The association between facet orientation and instability did not reach statistical significance in our study, while Lattig et al. found a lower mean facet joint angle in the group of patients with instability.
This article has some limitations. Probably, the main limitation is regarding the laterality as we recorded the highest score of both sides in each classification. For example, a level with a LFE in one side but SFE in the other one was recorded as a LFE spinal level. It may lead to some bias in our results. Some authors advocate the term “micro instability,” which refers to an initial phase of the degenerative cascade in which anatomopathological features and mechanical low back pain would be present, but with the absence of spondylolisthesis in the dynamic x-rays. If this clinical entity was actually real, our study would not be able to diagnose neither its presence nor its association with facet effusions. Another limitation is that the difference of facet orientation between both sides, also known as facet joint tropism, may be related to lumbar disk herniation or rotatory hypermobility instead of flexion-extension one, but it was not assessed in our study.,, The prevalence of lumbar synovial cysts found in our study was similar to that published before by other authors. Finally, as this research was carried out with images of non-operated patients, we could not compare the outcome of a decompression without fusion between patients with LFE or SFE.
LFE was not associated with instability in this study, whereas the existence of MC type 1 reached that association. The presence of LFE and/or MC type 1 may act as red flags in patients with L4–L5 degenerative spondylolisthesis in order to suspect segmental instability as both image findings achieved a statistically significant association with instability within this subset. However, more studies are needed to confirm the findings.
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Conflicts of interest
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
[Table 1], [Table 2], [Table 3]