The main cause of chronic low back pain is degenerative changes in the lumbar spine. To understand the mechanism by which degenerative changes in the lumbar spine cause low back pain, it is necessary to understand the anatomical knowledge of the lumbar spine. The lumbar spine consists of five vertebrae, and in order to better understand how the lumbar spine affects each other, we introduce a lumbar spine segment. A lumbar segment consists of two vertebrae, the intervertebral disc between the two vertebrae, and two nerve roots leaving the segment, one on each side. The vertebrae are the bony part of the spine and their function is to provide support and protection of the spinal cord. When the vertebrae are stacked on top of each other, they form a column (at the front) and a bony canal – the spinal canal (at the back) – which consists of individual rings with the spinal cord and nerves traveling between them. The small joints make the vertebrae join together like a chain and they provide a dynamic connection between each vertebral body. As we twist or bend, the small joints move and slide, just like other joints in the body, such as the shoulder joint. Between the small joints of the upper and lower vertebrae is where the nerve roots pass through, called the nerve root canal. The small joints can be affected by degenerative arthritis and become degenerated, which can cause narrowing of the nerve root canal. The intervertebral disc is between each of the two vertebral bodies and it is actually a large, round ligament that connects each vertebral body. In the middle of this round ligament is the elastic jelly-like nucleus pulposus, and what is commonly referred to as a herniated lumbar disc is actually a protrusion of the nucleus pulposus. It is very helpful to understand the lumbar spine segments in cross-section. If we look at the intervertebral disc in cross-section, it is composed of two parts: the outer part is the fibrous ring that connects the vertebrae, and the inner nucleus pulposus has the function of shock absorption with the hardness of crab meat. The nerve roots are responsible for connecting the lower extremities to the brain. The nerve roots sometimes cause low back pain, which occurs when the nerve roots are provoked or squeezed by the intervertebral discs or bone spurs.