Sacroiliac Joint Pain

Dysfunction in the sacroiliac joint, or SI joint, is thought to cause low back and/or leg pain. The leg pain can be particularly difficult, and may feel similar to sciatica or pain caused by a lumbar disc herniation.

Anatomical Source of Sacroiliac Joint Pain

The sacroiliac joint lies next to the bottom of the spine, below the lumbar spine and above the tailbone (coccyx). It connects the sacrum (the triangular bone at the bottom of the spine) with the pelvis (iliac crest).

The joint typically has the following characteristics:

• Small and very strong, reinforced by strong ligaments that surround it
• Does not have much motion
• Transmits all the forces of the upper body to the pelvis (hips) and legs
• Acts as a shock-absorbing structure

While it is not clear how the pain is caused, it is thought that an alteration in the normal joint motion may be the culprit that causes sacroiliac joint pain. This source of pain can be caused by either:

• Too much movement (hypermobility or instability): The pain is typically felt in the lower back and/or hip and may radiate into groin area.
• Too little movement (hypomobility or fixation): The pain is typically felt on one side of the low back or buttocks, and can radiate down the leg. The pain usually remains above the knee, but at times pain can extend to the ankle or foot. The pain is similar to sciatica, or pain that radiates down the sciatic nerve and is caused by a radiculopathy.

This condition is generally more common in young and middle-aged women.

Background on Sacroiliac Joint Dysfunction

For decades, the sacroiliac joint was suspected to be a common cause of low back and/or leg pain, although difficulty in proving it with standard diagnostic tests left many in the medical profession skeptical.

Also, over the last twenty to thirty years, the medical profession has focused more on discogenic pain (herniated disc, degenerative disc disease) as a common cause of low back and/or leg pain. In fact, to this day sacroiliac joint dysfunction remains difficult to diagnose, but anesthetic injection blocks specifically applied to the SI joint are considered the gold standard.

Accurately diagnosing sacroiliac joint pain can be difficult because the symptoms mimic other common conditions, including other mechanical back pain conditions like facet syndrome as well as other lumbar spine conditions including disc herniation and radiculopathy (pain along the sciatic nerve that radiates down the leg).

A diagnosis is usually arrived at through physical examination (eliminating other causes) and/or an injection (utilized to block the pain).

Physical Examination to Determine the Source of Sacroiliac Pain

In physical examination, the doctor may try to determine if the sacroiliac joint is the cause of pain through movement of the joint. If the movement recreates the patient’s pain, and no other cause of pain can explain the patient’s pain and symptoms (such as a disc herniation on an MRI scan), the sacroiliac joint may be the cause of the pain.

There are several orthopedic provocative tests that can be used in an attempt to reproduce the symptoms associated with sacroiliac joint pain. As a rule, several positive tests that reproduce pain specifically located at the sacroiliac joint improves the probability of the diagnosis of sacroiliac joint dysfunction.

For example, a physical exam may consist of the following:

• The patient may lie face up on the edge of an examination table with the leg of the affected side hanging off the side of the table towards the floor or resting on a nearby stool so that the sacroiliac joint lies on the edge of the table.
• The opposite knee can be drawn to the chest to further isolate the SI joint on the side of the hanging leg. In this position, there is no support for the hip joint and pressing down on the iliac crest (pelvis) or upper thigh may reproduce the patient’s pain.
• Care in locating the pain directly over the SI joint is needed as other structures of the lumbar spine and pelvis are also stressed in this position.