In the lower back, approximately 50% of flexion occurs at the hips, and 50% occurs at the lower spine. Motion is divided between the five motion segments in the lower back, although a disproportionate amount of the motion is at L4-L5 (lumbar segment 4 and 5) and L3-L4 (lumbar segment 3 and 4). Consequently, these two segments of the lower back are the most likely to break down and become unstable from osteoarthritis (degenerative spondylolisthesis), with an excess of motion creating low back pain.