What is 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 lumbar disc herniation.
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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’s not clear how the pain is caused, it’s thought an alteration in the normal joint motion may be the culprit causing 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.
Sacroiliac joint pain can be caused by too much or too little movement.
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.
Over the last thirty years, the medical profession has focused more on discogenic pain (herniated disc, DDD) as a common cause of lumbar and/or leg pain. To this day sacroiliac joint dysfunction remains difficult to diagnose. Anesthetic injection blocks specifically applied to the SI joint are considered the gold standard for diagnosing this pain.
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).
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 joint movement. If the movement recreates the patient’s pain, and no other cause of pain can explain the patient’s pain and symptoms, the sacroiliac joint may be the cause of pain. Another possible cause for the pain could be a disc herniation, shown on an MRI scan.
There are several orthopedic provocative tests that can be used to attempt reproducing 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 affected side’s leg hanging off of the table. The leg hanging towards the floor so 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 is needed in locating the pain directly over the SI joint. Since other structures of the lumbar spine and pelvis are also stressed in this position.
Injections to Determine the Source of Pain
A sacroiliac joint injection, sometimes called a sacroiliac joint block, can be a useful diagnostic test. It takes a highly skilled and experienced physician to be able to insert a needle into the correct portion of the sacroiliac joint. Because of this, the injection is usually guided by X-ray to make sure the joint is properly injected. Sometimes a dye is injected so that the joint is better visualized, which is called an arthrogram.
In this test, a physician uses fluoroscopic guidance and inserts a needle into the sacroiliac joint to inject lidocaine. If the injection relieves the patient’s pain, it can be inferred the sacroiliac joint is the source of pain. Usually, a steroid solution is injected at the same time to decrease inflammation in the sacroiliac joint and decrease pain.
