Sacro Joint

The lowest part of the spine is called the lumbar spine. This area usually has five vertebrae.

The base of your spine, called the Sacrum, is a group of specialized vertebrae that connects the spine to the pelvis. When one of the bones forms as a lumbar vertebra rather than part of the sacrum, it is called a transitional, or sixth, vertebra. This occurrence is not dangerous and does not appear to have any serious side effects.

The lumbar spine's shape has a lordotic curve, shaped like a backward "C." If you think of the spine as having an "S"-like shape, the lumbar region would be the bottom of the "S.

The vertebrae in the lumbar spine area are the largest of the entire spine. So the lumbar spinal canal is larger than in the cervical or thoracic parts of the spine. The size of the lumbar spine allows for more space for nerves to move about.

Low back pain is a very common complaint for a simple reason. Since the lumbar spine is connected to your pelvis, this is where most of your weight bearing and body movement takes place. Typically, this is where people tend to place too much pressure, such as when lifting up a heavy box, twisting to move a heavy load, or carrying a heavy object. These activities can cause repetitive injuries that can lead to damage to the parts of the lumbar spine.

There are two sacroiliac joints in your pelvis that connect the sacrum (tailbone) and the ilium (large pelvic bone). The SI joints connect your spine to the pelvis, and thus, to the entire lower half of the skeleton

Like any other joints, there is articular cartilage on both sides of the SI joint surfaces. But unlike most other joints, the SI joints are covered by two different kinds of cartilage. The articular surfaces have both hyaline (glassy, slick) and fibrocartilage (spongy) surfaces that rub against each other. The joints also have many large ridges (bumps) and depressions (dips in the surface that fit together like a puzzle).

The SI joints are also unique in that they are not designed for much motion. It is common for the SI joint to become stiff and actually "lock" as people age.

Sacro Joint

The SI joint only moves about two to four millimetres during weight bearing and forward flexion. This small amount of motion occurring in the joint is described as a "gliding" type of motion. Due to the small amount of movement and the complexity, finding out about the SI joints' motion is very difficult during a physical exam.

The SI joints are viscoelastic joints, meaning that the major movement comes from giving or stretching. This motion is quite different than the hinge motion of the knee or the ball and socket motion of the hip. The main function of the SI joints is to provide shock absorption for the spine through stretching in various directions. The SI joints may also provide a "self-locking" mechanism that helps you to walk. The joints lock on one side as weight is transferred from one leg to the other.

Causes
Many problems can lead to degenerative arthritis of the SI joints. It is often hard to determine exactly what caused the wear and tear to the joints. One of the most common causes of problems at the SI joint is an injury. The injury can come from a direct fall on the buttocks, a motor vehicle accident, or even a blow to the side of your pelvis. The force from these injuries can strain the ligaments around the joint. Ligaments are the tough bands of connective tissue that hold joints together. Tearing of these ligaments can lead to too much motion in the joint. The excessive motion can eventually lead to wear and tear of the joint and pain from degenerative arthritis. Injuries can also cause direct injury of the articular cartilage lining the joint. This too, over time will lead to degenerative arthritis in the joint.

Sacrum and Coccyx

Pain can also be caused by an abnormality of the sacrum bone. The sacrum bone is actually a very specialized set of vertebrae. When your body is undergoing development in the womb, several vertebrae fuse together to form the sacrum. In some people the bones that make up the sacrum never fuse together. In these cases, two or more of the vertebra that should fuse together remain separated. This creates an odd situation where the SI joint is malformed and a false joint occurs (sometimes called a "transitional syndrome"). This abnormality can be seen on X-rays. People who have this syndrome seem to have more problems with their SI joints, as well as back pain that appears to come from that area.

Women are at risk for developing SI joint problems later in life due to childbirth. Female hormones are released during pregnancy that allow the connective tissues in the body to relax. The relaxation is necessary so that during delivery, the female pelvis can stretch enough to allow birth. This stretching results in changes to the SI joints, making them hypermobile (extra or overly mobile). Over a period of years these changes can eventually lead to wear-and-tear arthritis. During pregnancy, the SI joints can cause discomfort both from the effects of the hormones that loosen them and from the stress of carrying a growing baby in the pelvis. The more pregnancies a woman has, the higher her chances of SI joint problems.

The S1 Joint Injection
A local anaesthetic is injected into the joint. The doctor uses the fluoroscope to make sure the needle is actually in the joint before injecting the medication. The SI joints are located fairly deep in the upper buttocks and are covered by thick muscle. It is difficult to put a needle into the joint without some guidance. A fluoroscope is a special TV camera that uses X-rays to allow the doctor to see on the screen the exact placement of the needle and to make sure it is positioned accurately.

Once the needle is in the right place, anaesthetic is injected to numb the joint. If the pain goes away, your doctor can be relatively sure that the problem is coming from the SI joint and not somewhere else in the spine. The doctor may also add a dose of cortisone to the injection to help ease the pain. Cortisone is a powerful anti-inflammatory medication that calms the arthritis inside the joint and reduces pain. The effect is usually temporary, but may last up to several months.