ObjectiveTo observe vertebral three-dimensional motion characteristics of adjacent segments in patients with symptomatic L4 isthmic spondylolisthesis (IS). MethodsFourteen symptomatic L4 IS patients who underwent surgery treatment (trial group) and 15 asymptomatic volunteers without back pain and other lesions of spine (control group) were recruited. There was no significant difference in gender, age, body mass index, and bone mineral density between the two groups (P>0.05). The three-dimensional reconstruction model of lumbar spine was acquired from the thin slice CT of the lumbar spine of the subjects by combining dual-X-ray fluoroscopy imaging system with spiral CT examination. The model was matched to the double oblique X-ray fluoroscopy images captured by dual-X-ray fluoroscopy imaging system at different active positions of the lumbar spine to reproduce the three-dimensional instantaneous of lumbar spondylolisthesis at different state of motion. The motion and relative displacement of adjacent segments (L3, 4 and L5, S1) of spondylolisthesis were measured quantitatively by establishing a three-dimensional coordinate system at the geometric center of the vertebral body. The results were compared with those of the control group. ResultsWhen L3, 4 in the control group were flexed flexion-extension, left-right twisting, and left-right bending, and when L5, S1 in the control group were flexed left-right twisting and left-right bending, the activity along the main axis of motion (main axis of motion) tended to increase compared with that along the corresponding coupled axis of motion (secondary axis of motion); however, this trend disappeared in the trial group, and the main and secondary movements were disordered. Because of the coronal orientation of the facet joints of L5, S1, the degree of motion along the main axis of motion decreased during flexion and extension, but this trend disappeared in the trial group. Compared with the control group, L3, 4 in the trial group exhibited displacement instability in flexion-extension, left-right twisting, and left-right bending (P<0.05); there was no significant difference in the relative displacement of L5, S1 intervertebral bodies along x, y, and z axes between the trial group and the control group in flexion-extension, left-right twisting, and left-right bending curvature (P>0.05). ConclusionPatients with symptomatic L4 IS have disorders of primary and secondary movement patterns in adjacent segments, while IS showed significantly displacement instability in L3, 4 and significantly decreased motion in L5, S1.