Determination of dynamic instability in lumbar spondylolisthesis using flexion and extension standing radiographs versus neutral standing radiograph and supine MRI.

Objective: In this study the authors sought to compare the proportion of patients with lumbar spondylolisthesis detected to have dynamic instability based on flexion and extension standing radiographs versus neutral standing radiograph and supine MRI.

Methods: This was a single-center retrospective study of all consecutive adult patients diagnosed with spondylolisthesis from January 1, 2013, to July 31, 2018, for whom the required imaging was available for analysis. Two independent observers measured the amount of translation, in millimeters, on supine MRI and flexion, extension, and neutral standing radiographs using the Meyerding technique. Interobserver and intraobserver correlation coefficients were calculated. The difference in amount of translation was compared between 1) flexion and extension standing radiographs and 2) neutral standing radiograph and supine MRI. The proportion of patients with dynamic instability, defined as a ≥ 3 mm difference in the amount of translation measured on different imaging modalities, was reported. Correlation between amount of dynamic instability and change in back pain and leg pain 1 year after decompression and instrumented fusion was analyzed using multivariate regression analysis.

Results: Fifty-six patients were included in this study. The mean patient age was 57.1 years, and 55.4% of patients were female. The most commonly affected levels were L4-5 (60.7%) and L5-S1 (30.4%). The average translations measured on flexion standing radiograph, extension standing radiograph, neutral standing radiograph, and supine MRI were 12.5 mm, 11.9 mm, 10.1 mm, and 7.2 mm, respectively. The average difference between flexion and extension standing radiographs was 0.58 mm, with dynamic instability detected in 21.4% of patients. The average difference between neutral standing radiograph and supine MRI was 3.77 mm, with dynamic instability detected in 60.7% of patients. The intraobserver correlation coefficient ranged from 0.77 to 0.90 mm. The interobserver correlation coefficient ranged from 0.79 to 0.86 mm. In 44 patients who underwent decompression and instrumented fusion, the amount of dynamic instability between standing and supine imaging was significantly correlated with change in back pain (p < 0.001) and leg pain (p = 0.05) at the 12-month postoperative follow-up. There was no correlation between amount of dynamic instability between flexion and extension standing radiographs and postoperative back pain and leg pain.

Conclusions: More patients were found to have dynamic instability by using neutral standing radiograph and supine MRI. In patients who received decompression and instrumented fusion, there was a significant correlation between dynamic instability on neutral standing radiograph and supine MRI and change in back pain and leg pain at 12 months.