Magnetic resonance imaging (MRI) and standing lateral and flexion-extension (SLFE) radiographs should be obtained in patients thought to have L4-L5 lumbar degenerative spondylolisthesis (LDS). Benjamin D. Kuhns, MS, The Cleveland Clinic, Cleveland, Ohio, USA, presented the results of a retrospective imaging study [Kuhns BD et al. Spine J. 2014] to determine the sensitivity of MRI in diagnosing LDS and whether L4-L5 facet joint effusions predicted LDS.

Mr Kuhns emphasized that detecting LDS can have an impact on decision-making when preparing patients for lumbar surgery. Although the advantages of MRI include the ability to show canal stenosis and facet effusions that have been linked to LDS, Mr Kuhns emphasized that MRI often underestimates the severity of LDS and sometimes misses it altogether.

Mr Kuhns and colleagues retrospectively reviewed 103 patients with LDS. Patients were included in the study if they had a LDS defined radiographically as a slip > 4.5 mm. Mobile LDS was defined as a slip reduction > 3% between SLFE and MRI.

Two independent examiners reviewed other measurements, including the L4–L5 facet effusion diameter on axial MRIs. The kappa coefficient was used to assess the interobserver agreement with > 75 demonstrating excellent agreement.

The study found MRI-detected radiographic spondylolisthesis in 80 of 103 patients (78% sensitivity) vs 101 of 103 patients (98% sensitivity) with SLFE. The interobserver agreement was ≥ 0.8. MRI was associated with a significantly lower slip percentage than SLFE (19.8% vs 22.7%; P < .0001) and a higher anterior height (9.2 mm vs 8.4 mm; P <.0001).

When dividing the cohort of patients into mobile LDS and nonmobile LDS, the data suggest that 48% of the entire cohort had mobile LDS and that mobile LDS had a significantly greater x-ray slip percentage compared with nonmobile LDS (24.4% vs 21.2%; P =.02) and a smaller MRI slip percentage (17.4% vs 22.1%; P = .0007).

In addition, the patients with mobile LDS also had a larger mean effusion width than patients with nonmobile LDS (2.0 mm vs 1.2 mm; P =.0016) and a greater number of effusions > 2 mm (Table 1).

The study also looked at the positive predictive value (PPV) of effusions for mobile LDS and found that the PPV increased from around 50% for a 1 mm effusion to 86% for a 2.5 mm effusion. For effusions > 3.5 mm, the PPV increased to 100% (Figure 1).

Mr Kuhns also highlighted key findings, including the lower sensitivity of MRI compared with SLFE to detect LDS (78% vs 98%) and the PPV of increasing facet effusion width to predict mobile L4–L5 LDS.