Abstract: Objective To compare the imaging differences between patients with lumbar spinal stenosis combined with
L3 degenerative spondylolisthesis (DS) and patients without L3 DS, and to explore the possible pathological mechanism of L3 DS. Methods A total of 300 patients with lumbar spinal stenosis treated with lumbar posterior lumbar surgery were
selected in the Third Affiliated Hospital of Suzhou University from May 2012 to June 2017. Thirty-five patients from them
with L3 DS alone were selected as L3 DS group. Forty patients with matched age and gender and DS without lumbar spinal
stenosis were selected as non-DS groups. All patients received a standing lumbar vertebrae, a full length spine and lumbar
MRI, and measured pelvic projection angle (PI), pelvic tilt angle (PT), sacral tilt angle (SS), lumbar lordosis angle (LL) on Xray films. The facet joint angles of L3/4 and L4/5, and disc heights of L3/4, L4/5 and L5/S1 were measured on MRI. Statistical analysis was performed on all results. Results There were no significant differences in spine-pelvis sagittal plane
parameters PI, PT, SS and LL between the two groups (P＞0.05). Among the height parameters of intervertebral disc, the
slopes of L3, L4 and L5 were significantly greater in the L3 DS group than those in the non-DS group (P＜0.01). The sagittal angle of l3/4 facet joints was significantly higher in the L3 DS group than that in the non-DS group (P＜0.01). There were no significant differences in disc heights of L3/4, L4/5 and L5/S1 between the two groups (P＞0.05). The lumbar disc height of L4/5 was more lower in the L3 DS group than that in the non-L3 DS group (45.83% vs. 11.11%, χ2=5.357, P＜0.01). Conclusion The increase of slope of L3 segment, the sagittal angle of l3/4 facet joint and the excessive stress may be the important reasons leading to the occurrence of L3 DS.

Key words: spinal stenosis, spondylolysis, zygapophyseal joint, the third lumbar vertebra, pathological mechanism