Mechanisms of retrolisthesis in the lower lumbar spine. A radiographic study.

The study investigates lower lumbar segments with posterior vertebral shifts (retrolisthesis) with respect to the orientation of facet joints, disc height, lordosis of the lumbar spine, and orientation of vertebral endplates. Standing lumbar radiographs as well as CT and/or MRI investigations of 69 patients were analyzed. Data from patients with retrolisthesis (20 cases) were compared to data from patients with degenerative spondylolisthesis (DS, 23 cases), and from patients without signs of vertebral shifts (26 cases). The orientation of facet joints in segments with retrolisthesis was not different from segments without shifts, whereas the facet joints in patients with DS were oriented more sagittally. The overall lordosis of the lumbar spine and the endplate inclination were considerably reduced in patients with retrolisthesis, especially compared to those with DS. Disc height was comparable in retrolisthesis and DS, but was reduced compared to segments without shifts. The results support biomechanical considerations, that a retrolisthesis of a lower lumbar spine segment is correlated with a reduction of lumbar lordosis, endplate inclination, and segmental height.