The sacrospinal muscles are located on both sides of the human spine. When looking at the back of the human spine, you can see two very long, elongated muscles on the left and right sides of the posterior midline, which are the sacrospinal muscles. Sacral spine muscle, also known as the erector spinae muscle, is the most common and largest muscle among the back muscles, longitudinally arranged on the back of the trunk, the spine on both sides of the groove, from the outside to the inside of the iliac ribs, the longest muscle, and spinal muscles composed of three muscles. Starting from the back of the iliac bone and the back of the iliac crest, it divides upward into many muscle bundles, stops at the vertebrae and ribs and reaches the mastoid process of the temporal bone, that is, the back of the head, so this muscle reaches from the lumbar-sacral region all the way to the back of the head of the human body. Its role is primarily to extend the spine back and tilt the head, making it a very powerful muscle for straightening. The erector spinae or sacrospinalis muscle plays an important role in maintaining the body in an upright position, and it is possible for this muscle to go into violent spasm when a patient develops tetanus, followed by the specific sign of coracoid arthritis.