Introduction: Lumbar degenerative spondylolisthesis (LDS) is often diagnosed by supine magnetic resonance imaging (MRI). Numerous studies have shown, however, that the degree of spondylolisthesis can be reduced or disappear when the patient is supine compared to standing.
Methods: Patients diagnosed with L4-5 LDS with both standing lateral and flexion-extension (SLFE) films and supine MRI were evaluated. LDS was defined radiographically as a slip greater than 4.5 mm. Slip distance and L5 width were used to calculate slip percentage. Mobile LDS was defined as a difference of greater than 3% in slip percentage between lateral radiographs and sagittal MRIs. Additional measurements included sagittal translation and segmental angulation on flexion-extension radiographs, and L4-5 facet effusion diameter on axial MRIs.
Results: Of 103 patients assessed, 68% were female and the average age was 66 years. LDS was seen on 103 (100%) flexion-extension films, 101 (98%) lateral films, and 80 (78%) MRIs. Average slip was 10.0 mm for lateral standing radiographs and 6.6 mm on MRI (p<0.0001), yielding slip percentages of 22.7% for lateral radiographs and 19.8% for MRIs (p<0.0001). 50 (48%) patients were identified with mobile LDS. 34 (68%) patients with mobile LDS had radiographic LDS compared to 46 (87%) with non-mobile LDS (p=0.02). The positive predictive value of facet joint effusion for mobile LDS increased from 52% for effusions greater than 1 mm to 100% for patients with effusions greater than 3.5 mm.
Conclusions: MRI had a sensitivity of 78% for detecting L4-5 LDS compared to 100% for flexion-extension and 98% for lateral standing films. Patients with mobile LDS had larger facet effusions than non-mobile LDS and were more likely to be missed on MRI. These findings suggest that, particularly in the setting of facet effusions, the complete workup of patients in whom LDS is possible should include standing lateral or flexion-extension films.
Patient Care: This study demonstrates that supine MRI is less sensitive than SLFE radiographs when diagnosing L4-5 lumbar degenerative spondylolisthesis. Additionally, we show that facet effusion size can predict for mobile LDS. Based on the prevalence of LDS in the elderly population, accurate diagnosis of this condition is necessary for appropriate surgical decision making. Thus, obtaining SLFE radiographs with MRI will provide the surgeon with a more complete assessment of the spinal pathology involved.
Learning Objectives: By the conclusion of this session participants should be able to: 1) Describe the significance of vertebral slip reduction in MRI when compared to SLFE films. 2) Discuss, in small groups, the association between facet joint effusions and mobile LDS, and 3) Identify patients that require SLFE films in addition to MRI when diagnosing LDS.