Can magnetic resonance imaging findings effectively diagnose the instability observed on radiographs in patients with degenerative lumbar spinal stenosis?

BACKGROUND: Degenerative lumbar spinal stenosis (LSS) is a common condition that involves the narrowing of the spinal canal. Diagnosing instability traditionally requires standing lateral radiographs to detect dynamic translation, but there is debate about relying solely on radiographs due to challenges like patient discomfort and radiation exposure. This study aimed to evaluate if Magnetic Resonance Imaging (MRI) findings could effectively diagnose instability observed on radiographs. METHODS: We reviewed 478 consecutive patients with degenerative LSS who had surgery at our institution. Instability was defined as a sagittal translation exceeding 3 mm on standing lateral radiographs in both extension and flexion. Patients were divided into stable (those with < 3 mm translation) and unstable groups (those with > 3 mm translation). The study assessed potential variables for instability, including MRI findings like facet joint effusion, facet joint angle, disk height index, intradiscal vacuum presence, endplate sclerosis, ligamentum flavum hypertrophy, and multifidus muscle fatty degeneration, comparing these factors between the two groups. RESULTS: A total of 478 consecutive patients diagnosed with degenerative Lumbar Spinal Stenosis (LSS) were included. The average age of the patients was 66.32 years, with 43.3% being male. Approximately 27.6% of the cases exhibited signs of instability on the standing lateral radiograph during extension and flexion. The multivariate analysis using binary logistic regression revealed that facet joint effusion (odds ratio [OR] 2.73; 95% confidence interval [CI] 1.27-3.94; P = 0.002), disk height index (OR 2.22; 95% CI 1.68-3.35; P = 0.009), and the presence of the Vacuum sign (OR 1.77; 95% CI 1.32-2.84; P = 0.021) were identified as factors associated with instability. CONCLUSIONS: Our findings showed thata higher facet joint effusion, the presence of Vacuum sign, and a greater Disk Height Index were associated with the presence of instability on the standing lateral radiograph in extension and flexion in patients with degenerative LSS.