The sacrum

The sacral vertebrae are located near the very bottom of the spinal column. They are located between the lumbar spine and the tailbone, which is also called the coccyx.

The sacrum is shaped like a triangle. Its sacral vertebrae are fused together into one solid bone.

The first three sacral vertebrae come together and form wide bony wings. These are called alae and they connect to the pelvis. Part of the sacral vertebrae help to form the back section of the pelvic girdle and the sacral vertebrae join to the hips at the sacroiliac joints.

 Blood vessels and nerves travel through four openings on the right and on the left side of the sacral vertebrae.  The vertebral canal ends in the center of the end of the sacral canal.  

A severe traumatic accident or fall can result in a fracture of the sacral vertebrae, but when this area of the spine is healthy, fractures rarely occur. People who have rheumatoid arthritis or a condition that causes loss of bone mass, such as osteoporosis, may develop fatigue fractures or stress fractures to the sacral vertebrae.

Pain in the lower back pain or legs or radiating pain from the back to the leg, known as sciatica, often occurs with injuries to the back where the lower back and sacral vertebra meet (L5 - S1). This is common due to the twisting and stress this area is subjected to during prolonged periods of sitting and during some sports activities.

The sacral vertebrae area in women in shorter and wider in most women than it typically is in men.  Sacroiliac joint dysfunction is a condition that causes low back pain that tends to be worse on one side and travels down the thigh into the knee or even the ankle and foot. It is more common in younger and middle-aged women than in men.  

 The exact cause of sacroiliac joint dysfunction is difficult to determine. The normal movement of the joint between the sacral vertebrae and the ilium may be due to either too little motion in the joint or due to restricted movement of the joint. It is sometimes difficult for physicians to diagnose the problem because the symptoms are sometimes similar to those of a herniated disc. 

Normal spine, sacrococcygeal-2