Each structure in the low back has a specific referred pain pattern associated with it. For example, the sacroiliac ligaments generally refer pain straight across the lowest portion of the back. The ilio-lumbar ligament refers pain on one side of the low back across the top of the ilium, the lateral hip, and the groin area. The sacrotuberous ligament has a distinctive pattern. It refers pain down the central portion of the back thigh, and if more severe, down the central portion of the calf into the heel. This injury is frequently confused with a hamstring injury when the pain is felt only in the lower buttock and down the back of the thigh.