The sacroiliac (SI) joints are the connection between right and left iliac bones and the sacrum. The iliac bones are the large bones within the pelvis and are the bones you feel when you put your hands on your hips. As for the sacrum, it is a bone triangular in shape that is below the lumbar spine. The sacrum is commonly referred to as the tail bone. These joints are held together by several strong ligaments, which provides stability for when the body is erect but does not allow for much movement. Since the SI joint must support all of the upper body weight while standing, this joint can be worn down with time.

Due to wear and tear of this joint, several dysfunctions can occur. Pain is the most common symptoms with SI joint dysfunction. A few causes of dysfunctions include: arthritis, wearing of cartilage, pregnancy, leg length discrepancy, changes in walking or other disorders. Basically anything that can cause extra stress on the joints, instability, or inflammation can create pain in the SI area. Pain can be felt in groin, low back, back of the hips or thighs. In addition, a nerve may be irritated or pinched in these situations which can cause a shooting pain down the leg.

Sources: Medicinenet.com