Radiological significance of ligamentum flavum hypertrophy in the occurrence of redundant nerve roots of central lumbar spinal stenosis

Abstract

Objective: There were previous reports of redundant nerve roots (RNRs) focused on their clinical significance and pathogenesis. In this study, we investigated the significant radiologic findings that correlate with RNRs occurrence. These relations would provide an advanced clue for clinical significance and pathogenesis of RNRs.

Methods: Retrospective research was performed with data from 126 patients who underwent surgery for central lumbar spinal stenosis (LSS). Finally, 106 patients with common denominators (inter-observer accuracy : 84%) were included on this study. We divided the patients into two groups by MRI, patients with RNRs and those with no RNRs (NRNRs). Comparative analyses were performed with clinical and radiologic parameters.

Results: RNRs were found in 45 patients (42%) with central LSS. There were no statistically significant differences between the two groups in severity of symptoms. On the other hand, we found statistically significant differences in duration of symptom and number of level included (p<0.05). In the maximal stenotic level, ligamentum flavum (LF) thickness, LF cross-sectional area (CSA), dural sac CSA, and segmental angulation are significantly different in RNRs group compared to NRNRs group (p<0.05).

Conclusion: RNRs patients showed clinically longer duration of symptoms and multiple levels included. We also confirmed that wide segmental angulation and LF hypertrophy play a major role of the development of RNRs in central LSS. Together, our results suggest that wide motion in long period contribute to LF hypertrophy, and it might be the key factor of RNRs formation in central LSS.

Keywords: Central lumbar spinal stenosis; Ligamentum flavum hypertrophy; Redundant nerve roots.

Fig. 1

Demonstration of RNRs (A) and NRNRs (B). Arrow head indicates the maximal stenotic lesion and arrow indicates RNRs.

Fig. 2

Measuring anatomical structures within the maximal stenotic level using T2-weighted axial magnetic resonance (MR) image. We measured bony spinal canal (SC) cross-sectional area (CSA), dural sac CSA, intervertebral disc (IVD) CSA, fat CSA, ligamentum flavum (LF) thickness, and LF CSA within spinal canal, and calculated these parameters using Image J 1.44 NIH software.

Fig. 3

Method of measurement of segmental angulation by dynamic pain lateral radiograph. We measured as the difference of intervertebral angles from flexion (α in A) to extension (β in B) using lower end plate of inferior body and upper endplate of superior body.

Fig. 4

Radiologic differences of anatomical structures within spinal canal (SC) between RNRs group and NRNRs group. At the maximal stenoic level, the CSA of bony SC (A) and fat CSA (D) had no significantly difference between the two groups. However, dural sac CSA (B), LF thickness (E), LF CSA (F) shows statistically significant differences between the two groups. IVD CSA within SC (C) is significantly larger in NRNRs group than RNRs group (significant p-value <0.05). Mean values are presented±standard deviations (SDs).

Fig. 5

Segmental angulation at maximal stenotic level. Segmental angulation shows statistically significant differences between the two groups (p-value=0.004). Mean values are presented±standard deviations (SDs).