An increase in the degree of olisthesis during axial loading reduces the dural sac size and worsens clinical symptoms in patients with degenerative spondylolisthesis

Abstract

Background context: Previous studies have shown that axial loading during magnetic resonance imaging (MRI) significantly reduces the size of the dural sac compared with conventional MRI in patients with degenerative lumbar disease. In our previous study, axial-loaded MRI showed a significantly larger degree of olisthesis than conventional MRI in patients with degenerative spondylolisthesis (DS). Furthermore, the degree of olisthesis on axial-loaded MRI correlated more strongly with that observed on X-ray in the upright position. However, no study has investigated whether or not the increase in the degree of olisthesis during axial loading correlates with the reduction in the dural sac size and affects the severity of clinical symptoms in patients with DS.

Purpose: The objective of this study was to determine whether or not the increase in the degree of olisthesis correlates with the reduction of the dural sac cross-sectional area (DCSA) detected on axial-loaded MRI and worsens the severity of clinical symptoms in patients with DS.

Study design/setting: This is an imaging cohort study.

Patient sample: A total of 41 consecutive patients with DS were prospectively evaluated in this study.

Outcome measures: The outcome measures include the degree of olisthesis, the DCSA, the Pearson correlation coefficient, and the severity of clinical symptoms.

Materials and methods: The differences in the degree of olisthesis and the DCSA between conventional and axial-loaded MRIs were determined. The Pearson correlation coefficient of the increase in the degree of olisthesis with the reduction in the DCSA during axial loading was calculated. The reduction in the DCSA and the severity of clinical symptoms in patients exhibiting a ≥2-mm increase in the degree of olisthesis were compared with those in patients exhibiting a <2-mm increase.

Results: The increase in the degree of olisthesis was significantly correlated with the reduction in the DCSA during axial loading (Pearson correlation coefficient=0.63, p<.001). The reduction in the DCSA during axial loading in patients with a ≥2-mm increase in the degree of olisthesis (26±3 mm²) was significantly greater than in those with a <2-mm increase (13±2 mm²) (p<.01). Clinical symptoms such as walking distance and activity of daily living evaluated using the Japanese Orthopaedic Association score were significantly worse in patients with a ≥2-mm increase in the degree of olisthesis (117±19 m and 6.7±0.5 points, respectively) than in those with a <2-mm increase (236±36 m and 8.4±0.4 points, respectively) (p<.05).

Conclusions: The present study demonstrated that the increase in the degree of olisthesis was significantly correlated with the reduction in the dural sac size detected on axial-loaded MRI and worsened the severity of clinical symptoms in patients with DS. These results suggest that axial-loaded MRI may be a useful imaging study for detecting dynamic changes in the degree of olisthesis during axial loading to the lumbar spine related to the narrowing of the spinal canal and the severity of clinical symptoms in the assessment of patients with DS.

Keywords: Axial loading; Degenerative spondylolisthesis; Dural sac; Lumbar spine; Magnetic resonance imaging; Spinal canal stenosis.