The correlation between exaggerated fluid in lumbar facet joints and degenerative spondylolisthesis: prospective study of 52 patients

Several biomechanical studies [5, 10, 18‐20] have demonstrated that facet joint disease and degenerative disc disease in the lumbosacral spine may cause degenerative spondylolisthesis. Standing lateral flexion–extension lumbar radiographs have been used to detect lumbar spine instability. Supine lumbosacral MRI has become routine in the evaluation of many lumbar conditions, but degenerative spondylolisthesis is not always revealed in the supine position. Axial T2-weighted MRI can also detect increased fluid in the lumbar facet joints, but, to the best of our knowledge, few papers have reported a correlation between exaggerated fluid in the lumbar facet joints and radiographic signs of lumbar spine instability [12‐15]. Previously, Mailleux et al. [21] reported 2 cases of degenerative spondylolisthesis which had not been initially detected on the lumbosacral MRI, but in which increased fluid in the lumbar facet joints was observed on the axial T2 MRI at the lumbar segments involved. Rihn et al. [12] reported, in a retrospective study of 51 patients treated surgically for degenerative lumbar disease, that 55% of the cases had exaggerated fluid in the facet joints on MRI. Of those patients whose MRI showed facet fluid, 82% had instability on standing lateral flexion–extension radiographs. The authors concluded that there is a close linear association between the facet fluid index and the amount of radiographic instability at the L4–L5 level. In a retrospective study of 193 patients, Chaput et al. [13] reported 139 patients without degenerative spondylolisthesis and 54 affected by degenerative spondylolisthesis, as shown on standing lateral flexion–extension radiographs. The patients with degenerative spondylolisthesis were more likely to be older, female, to have a greater degree of osteoarthritis, and to have greater facet joint effusion. The authors conclude that extensive (greater than 1.5 mm) facet effusion is highly predictive of degenerative spondylolisthesis at the L4–L5 level in the absence of measurable anterolisthesis on the supine MRI.

Schinnerer et al. [14], in a retrospective review of 118 supine lumbar MRI, reported that 16 had exaggerated fluid in the facets on the axial images (13.6%). Only 2 of these 16 (12.5%) had spondylolisthesis which was appreciable on the supine MRI at that level. In contrast, 8 of the 16 (50%) showed spondylolisthesis at the site of the exaggerated fluid when the corresponding standing radiographs were reviewed. The authors concluded that exaggerated fluid in the facet seen on axial MRI is significantly suggestive that spondylolisthesis will be observed on standing films, even if this is not perceived on the supine sagittal MRI sequences.

In a retrospective study of 54 patients who were diagnosed with degenerative L4–L5 spondylolisthesis and who had both lumbosacral flexion–extension radiographs and MRI, Cho et al. [15] reported that increased facet fluid was noted on MRI in 29 patients (53.7%). The authors concluded that there is a linear correlation between the degree of segmental motion on flexion–extension plain radiography in patients with degenerative spondylolisthesis at L4–L5 and the amount of L4–L5 facet fluid on MRI.

In our series, increased lumbar facet fluid was detected in 15 cases (28.8%); among those with increased fluid, degenerative spondylolisthesis was observed on standing lateral flexion–extension films in 8 cases (53.3%), whereas degenerative spondylolisthesis was absent in 7 patients with increased lumbar facet fluid. However, in agreement with Chaput et al. [13], there was a smaller amount of facet effusion in the cases that were not affected by degenerative spondylolisthesis than in the patients with evident degenerative spondylolisthesis. Moreover, we observed that, in the cases with instability and lumbar facet fluid, the degree of degeneration of the disc disease and facet joint disease was still compatible with the instability stage of the functional spinal unit, as already described by Kirkaldy-Willis and Farfan [22].

The main drawback of our study is that we did not calculate the sample size, but actually this is difficult because the incidence of exaggerated fluid in the lumbar facet joints in the population presenting with lower back pain and/or radicular pain is not properly reported in the literature. The strengths of our study include its prospective design and the strict exclusion criteria, which limited the bias observed in other studies [12‐14]. To the best of our knowledge, this is the first study that has clearly evaluated the incidence of exaggerated fluid in the lumbar facet joints in a population that attended a single institution for lower back pain and/or radicular pain, without confounding spinal pathologies.

In conclusion, in our study, the incidence of exaggerated fluid in the lumbar facet joints seen on the axial T2 MRI was 28.8% in patients who presented with lower back pain and/or radicular leg pain without confounding pathologies. In agreement with the retrospective studies of Schinnerer et al. [14] and Cho et al. [15], in our prospective study we observed a correlation between increased facet fluid detected on MRI and lumbar instability on dynamic X-rays, especially in cases in which the amount of the fluid was greater than 2 mm and when the degenerative disc disease and facet joint degeneration were grade 2 or less. Further studies are necessary to confirm these early data. Until additional data are available, we recommend performing standing lateral flexion–extension radiographs in all patients with increased fluid signal on MRI, particularly when the disc disease and facet degeneration are at an early stage. It would be interesting to compare these data with an MRI study carried out in an asymptomatic group of people; however, it is not easy to do a lumbar MRI in a population without lower back pain. Dynamic MRI could help to discover the missed lumbar instability, but this procedure is currently too expensive and not readily available.