Sacroiliac Joint Shape Research
Sacroiliac Joint Pain
Sacroiliac joint pain is a common problem that accounts for 10-25% of chronic low back pain. However, in patients who have previously had surgery or trauma to the lumbar spine and/or pelvis, the rate can be much higher. Some studies have documented rates of sacroiliac joint pain as high as 75% in patients that have had previous lumbar fusions.
Sacroiliac Joint Pain Diagnosis
Although this problem is quite common, diagnosing it is somewhat of a challenge. Regular studies such as x-rays, CT scans, and MRI scans do not usually show significant findings in the majority of people with sacroiliac joint pain. Physical exam for sacroiliac joint pain is notoriously inconsistent and unreliable for most of the provocation tests. Using a combination of physical exam tests can give a significantly higher likelihood of accurate diagnosis. Even with this, however, the accuracy of the physical exam is only about 80%. The gold standard for diagnosing sacroiliac joint pain is a diagnostic sacroiliac joint injection with local anesthetic. Usually, two injections with different anesthetics are required to rule out placebo effect. Even this injection protocol, however, is not perfect and some studies have questioned the sensitivity and specificity of the dual block diagnostic technique.
SI Joint Pain Treatment
Various treatment options ranging from watchful waiting to physical therapy, joint injection, radiofrequency ablation, and SI joint fusion have been used to try to help those suffering from SI joint pain.
This study was a case-control study that compared the shapes of the sacroiliac joints and 223 normal controls and 34 patients with sacroiliac joint (SI) pain syndrome.
The researchers used CT scans with 3-D reconstructions of the joints. They then took the scans and use virtual reality to disarticulate and measure the joints.
Using this technique, they were able to classify the shape of human sacroiliac joints into three different classifications. Type 1 was described as “scone-shaped”. Type 2 was described as (auricle-shaped). Type 3 was described as "crescent-shaped”.
SI Joint Shapes
Analysis of the morphologies of sacroiliac joints revealed that the shape of the sacroiliac joint did not correlate with pain in men. In women, however, there was a significant correlation with the likelihood of SI joint pain and the shape of the joint. The authors found that approximately 32% of women with a type 3 (Crescent-shaped) joint at SI pain. Approximately 17.5% of women with type 2 joints at SI pain. Only 5% of women with type I SI joints had SI joint pain.
The authors concluded that:
"SI joint morphologic variability can be classified into 3 types (type 1, type 2, type 3) based on the relative width of the joint at the axis nutation… Type 3 (crescent) morphology was more highly represented in the SI joint pain population."