Roentgenographic and computed tomographic findings in symptomatic lumbar foraminal stenosis

Purpose To determine the static and dynamic radiological findings characteristic of symptomatic foraminal stenosis. Methods Between 2006 and 2011, a total of 114 patients with unilateral leg pain due to L5 nerve root compression were screened to investigate the characteristic radiological findings of symptomatic foraminal stenosis. Static findings on sagittal CT images and dynamic findings on X-rays were compared between 39 surgically treated L5–S1 foraminal stenosis patients (FS group) and 75 surgically treated L4–5 intra-spinal canal stenosis patients (CS group). Results There was no significant difference between the FS and CS groups in all demographic data and radiologic findings, except for the segmental range of motion in sagittal plane on functional X-rays and posterior translation on extension. The segmental range of motion in sagittal plane at L5–S1 was significantly larger in the FS group (13.4 ± 3.1 vs. 4.2 ± 2.0; p = 0.03) compared to the CS group. The prevalence of 3 mm or more posterior translation at L5 was significantly higher in the FS group (38 vs. 3 %; p = 0.04) compared to the CS group, and the average posterior translation of L5 was significantly greater in the FS group (3.1 ± 1.6 mm) than that in the CS group (0.3 ± 0.6 mm) ( p = 0.02). Conclusions A large segmental range of motion in sagittal plane of L5–S1 and posterior instability of L5 are risk factors for symptomatic L5–S1 foraminal stenosis. These dynamic radiological findings support the diagnosis of symptomatic foraminal stenosis.