The lumbar spine is composed of five vertebrae, and in a normal state the lumbar spine is not straight, but has a forward protruding bend, which is clinically known as the physiological anterior convexity of the lumbar spine. When disease occurs in the lumbar spine, this physiological pronation disappears and straightens due to pain and spasm in the lumbar muscles. Diseases that commonly cause straightening of the physiological curvature of the lumbar spine include lumbar disc herniation and acute lumbar sprain. Also the anterior and posterior diameters of the lumbar vertebrae are consistent; if the anterior and posterior diameters are inconsistent, such as narrow in the front and wide in the back, it suggests a possible lumbar compression fracture. The width of the gap between the upper and lower vertebrae of the normal lumbar spine is also uniform, and if the gap becomes narrow, it is mostly seen in diseases such as lumbar spine osteophytes. The anterior edge of the normal lumbar vertebrae is in a line, and if there is a misalignment between the vertebrae, it suggests the presence of lumbar vertebral slippage.