Sacroiliac Joint Pain - Evidence-Based Examination and Treatment
What is the sacroiliac joint?
The sacroiliac joint is a diarthrodial synovial joint that joins the sacrum and ilium. "It is surrounded by a fibrous capsule containing a joint space filled with synovial fluid between the articular surfaces. The sacral capsular surface is composed of hyaline cartilage while the iliac capsular surface is composed of fibrocartilage. Hyaline cartilage is made from type II collagen and is the weakest type of cartilage. Fibrocartilage is made from type I collagen and is the strongest type of cartilage." 
Approximately one third of the sacroiliac joint consists of a synovial joint covered with smooth hyaline cartilage on both surfaces – features typical of other joints capable of movement (shoulder, knee, hip, etc). The remaining two thirds of the sacroiliac joint consist of a cartilaginous joint that is composed primarily of the posterior sacroiliac ligament with flexible, yet tough fibrocartilage (think annulus fibrosis of the intervertebral disc, menisci, pubic symphysis) on the bone surfaces.
How big is the sacroiliac joint?
The sacroiliac joint is the largest joint in the axial skeleton of the human body.  While there is considerable variability in the amount of total surface area between individuals (5-20cm2), the average has been observed to be approximately 12cm2 for adult females and 13cm2 for adult males.  By comparison, the average surface area of the acetabulum (hip joint) is 28.8 cm2 .
How stable is the sacroiliac joint?
The sacroiliac joint is one of the most stable joints in the body. The joint surfaces of the sacroiliac joint are ear-shaped and have portions of the same surfaces positioned in different planes appearing to limit motion rather than facilitate it. The sacroiliac joint is then stabilized by a complex cluster of some of the strongest ligaments in the body that limit movement in every plane of motion. These features have led some to conclude that the sacroiliac joint is designed more for stability than mobility: “The SIJ should be classified anatomically as a symphysis [an immovable joint where two bones are closely joined] with some characteristics of a synovial joint.” 
Does the sacroiliac joint move?
Yes, the sacroiliac joint does move - just not in every person. The sacroiliac joint moves a little in healthy young persons. But, in most persons aged 55 and older, the sacroiliac joint is naturally fused and doesn't move at all due to extensive ridging of the joint surfaces as well as ossification of the interosseous sacroiliac ligament.
Sturesson et al  studied 25 patients with suspected SIJ disorders using roentgen stereophotogrammetry [RSA] in physiologic positions as well as in the extreme of physiologic positions. RSA is a highly accurate assessment of three-dimensional migration and micromotion of a joint by placing small markers percutaneously into relevant structures within the body and then taking a stereo image with two synchronized x-ray foci. In this study, markers were implanted into the sacrum and the ilium, and x-rays were taken in end-range positions. Movement was indeed observed in the sacroiliac joints.
However, Rosatelli et al  studied the anatomy of the interosseous region of the sacroiliac joint in cadavers and stumbled across a remarkable finding: “Surface characteristics of the SIJ complex observed in specimens 55 years of age or older included moderate to extensive ridging of the interosseous region of the sacrum and ilium in 100% of specimens and ossification of the central interosseous region of the sacroiliac ligament in 60% of specimens.”
Their conclusion? “Central region ossification of the interosseous SI ligament and the presence of ridges and depressions over the opposing interosseous surfaces of the sacrum and ilium are features common to specimens that are in or beyond their sixth decade. These findings further support the contention that there is little to no movement available at this joint in older individuals.”
How much does the sacroiliac joint move?
The sacroiliac joint does not move at all in most persons aged 55 and older as it is naturally fused by extensive ridging of the joint surfaces as well as ossification of the interosseous sacroiliac ligament. And, even in healthy young persons, there is only minute movement. A study by Sturesson et al found that the degrees of rotation were small with a mean of 2.5 degrees (0.8-3.9) and translation was minute with a mean of 0.7 mm (0.1-1.6 mm). This study was later validated in a systematic review by Goode et al : “Rotation ranged between –1.1 to 2.2 degrees along the X–axis, –0.8 to 4.0 degrees along the Y-axis, and –0.5 to 8.0 degrees along the Z-axis. Translation ranged between –0.3 to 8.0 mm along the X-axis, –0.2 to 7.0 mm along the Y-axis, –0.3 to 6.0 mm along the Z-axis.”
Can the sacroiliac joint hurt?
Yes, it is possible to experience pain in the sacroiliac joints. A study by Sembrano et al observed: "The SI joint is... richly innervated by a combination of unmyelinated free nerve endings and the posterior primary rami of L2-S3." [1-10]
Later, Wong et al wrote: "The sacroiliac joint is well innervated but the pattern of innervation varies among individuals. The sacroiliac joint receives its innervation from the ventral rami of L4 and L5, superior gluteal nerve, and dorsal rami of L5-S2. The nerve supply to the SI joint varies between individuals and innervation may be almost exclusively derived from the sacral dorsal rami." 
Where does the sacroiliac joint refer pain?
The sacroiliac joint may refer pain up to 10 cm below the sacroiliac joint and up to 3 cm laterally to it. A study by Fortin et al  used provocative injections into the right sacroiliac joint of 10 asymptomatic volunteers to determine where they would experience pain. "The injections consisted of contrast material followed by Xylocaine. All 10 individuals experienced discomfort upon initial injection, with the most significant sensation felt directly around the injection site. Subsequent sensory examination revealed an area of hypesthesia [decreased sensation] extending approximately 10 cm caudally and 3 cm laterally from the posterior superior iliac spine. This area of hypesthesia corresponded to the area of maximal pain noted upon injection."
Other studies have proposed that the sacroiliac joint can produce different and unique referral patterns including groin pain, posterolateral thigh pain, and lateral lower leg pain that may mimic a radiculopathy. [11-13, 24] However, these studies had some serious methodological flaws that, I would argue, made their diagnosis of sacroiliac joint pain invalid. More on that to come.
Can the sacroiliac joints dislocate, subluxate, or go out of alignment?
Yes, the sacroiliac joints can dislocate, subluxate, or go out of alignment. However, this is exceedingly rare and has only been documented in cases of severe trauma. A study by Yoon et al included 73 patients with a straddle fracture injury (fracture of both superior and inferior pubic rami). Of the 73 patients, 56 (77%) had a posterior pelvic ring injury and 7 died. In 43 patients, the posterior pelvic ring injuries constituted unstable pelvic injury and were treated surgically. Sacroiliac joint dislocation [occurred] in 18." 
But, the sacroiliac joint doesn't have to be dislocated to cause pain. When comparing the motion of a painful sacroiliac joint with the motion of the pain-free side in 25 subjects, Sturesson et al noted that "there was no difference [in motion] between symptomatic and asymptomatic joints." 
Can the sacroiliac joints be realigned, adjusted, or popped back into place?
No, the sacroiliac joint cannot be realigned, adjusted, or otherwise popped back into place conservatively. In the exceedingly rare event that a sacroiliac joint did get dislocated during severe trauma, surgical fixation is the only plausible treatment option.
After a manual therapy technique - a high-velocity low-amplitude (HVLA) thrust manipulation - targeting the sacroiliac joints was performed on a group of study subjects (not involved in severe trauma), Tullberg et al observed that it was "not accompanied by altered position of the sacroiliac joint".  So, the question is: If a HVLA thrust manipulation did not change the position of the sacroiliac joint, how plausible would it be that other manual techniques or exercises involving less speed and force would be able to do so?
Interestingly, however, the authors remain firm and "are convinced that something happens when manipulating the SIJ" and they've observed "a good clinical outcome after SIJ manipulation." They're onto something there! More on this later.
How common is sacroiliac joint pain?
The prevalence of sacroiliac joint pain is estimated to be between 13-30% in individuals with chronic low back pain [11-13] (and estimated to be as high as 43% in patients after lumbar fusion surgery ). But, I propose the prevalence of sacroiliac joint pain is considerably lower, and my reasons will be presented as we dig into the details of these studies on sacroiliac joint prevalence.
One study by Sembrano et al  comments, “Our finding that the SI joint is a significant pain generator in 14.5% of low back pain patients is very similar to the 18.5% and 13 to 30% findings in the studies of Maigne et al  and Schwarzer et al , respectively. Both studies used diagnostic injections as a reference standard.” So, it does appear that there is a general consensus here, and I've found that most subsequent studies on sacroiliac joint dysfunction have anchored on these figures indiscriminately. But, let's dig deeper.
Regarding the use of diagnostic injections as the reference standard, the injection is best performed using fluoroscopy or CT and contrast. Rosenberg et al  have shown that only 22% of ‘‘blind’’ injections were actually in the joint space. To further confound the issue, there is no guarantee that the injectate is limited exclusively to the sacroiliac joint and does not bleed out - extra-articular spread - and affect other structures such as the lumbar plexus, resulting in false positives.
Sembrano et al then qualifies the estimate of 13-30%:
“Our study has a number of obvious limitations, foremost of which is the lack of a formal diagnostic algorithm implemented during the period of study. Diagnostic workup was performed on the discretion of the treating spine surgeon appropriate to the clinical diagnosis, which, in turn, was based on a synthesis of all available information from the history, physical examination, and imaging studies at the time."
This requires some pause. First of all, no study to date that I'm aware of has concluded that imaging of any kind is helpful in diagnosing sacroiliac joint dysfunction. Second, the subjective interview does not appear to add much value in diagnosing sacroiliac joint pain. Dreyfuss et al concluded: "No historical feature... demonstrated worthwhile diagnostic value."  (More on that in the next section.) And third, the physical examination also falls well short of being incredibly helpful and reliable in diagnosing sacroiliac joint pain as I'll discuss in detail later.
But, the other limitation for diagnosing sacroiliac joint pain is the lack of a gold standard. Returning to the Sembrano et al study: “Ultimately, perhaps the most important limitation of this study pertains to the accuracy of the diagnoses arrived at in each case. Although methods and modalities used were what are presently considered standard armamentarium in the investigation of LBP tempered by physician discretion, none of these could claim 100% accuracy. For example, even as discography has become widely used, its validity to this day remains controversial, in part because postdiscography surgical outcomes have been inconsistent. For epidural injections, sensitivity figures between 65% and 100%, and specificity between 71% and 95% have been quoted. However, obtaining accuracy estimates for spinal injection techniques (e.g.,facet blocks, epidural injections, and selective nerve root blocks) have been problematic primarily because there is no available gold standard that would measure presence or absence of pain to compare them against. Some statements on accuracy may be inferred from reproducibility studies (screening and confirmatory injections) and surgical outcomes. Although the former could measure false positivity and reliability, the limitations of using surgical outcomes as reference standard have already been discussed.”
With the aforementioned limitations, the best we can say at this point is that an estimated 13-30% of patients with chronic low back pain are suspected as having sacroiliac joint dysfunction responsible for their symptoms by these authors. However, it’s not possible to validate that estimate at this time – we simply don’t know how many truly do because there is no gold standard for diagnosis currently available. It is my professional opinion that the actual prevalence of true sacroiliac joint pain is considerably lower than these estimates, and my reasons are provided along with the scientific studies that will be considered a bit later.
What causes sacroiliac joint pain?
There have been many proposed causes of sacroiliac joint pain, but no mechanism of injury has been scientifically correlated with the sacroiliac joint except for cases of severe trauma . Some clinicians specifically inquire about an asymmetrical trauma to the pelvis that could stress the sacroiliac joint – a slip and fall, an unanticipated step down from a curb or into a hole, a motor vehicle accident with one foot on the brake, etc. Others place value on aggravating activities that they suspect would provoke sacroiliac joint pain such as putting on socks, walking up or down stairs, getting into or out of bed, rolling over in bed, bearing weight through the painful side in standing, and the act of standing up from a seated position.
One study set out to determine if any of these potential mechanisms of injury or aggravating activities could be used toward diagnosing sacroiliac joint pain. Dreyfuss et al  gathered a panel of experts from various disciplines including rheumatology, orthopedic surgery, clinical anatomy, orthopedic medicine, chiropractic, manual therapy, physiatry, osteopathy, and radiology to recommend which examination techniques would likely be most helpful in diagnosing sacroiliac joint dysfunction.
Then, historical data was gathered from 85 patients who were then examined and subsequently underwent sacroiliac joint injections with a local anesthetic as the diagnostic reference standard (see the section above for a discussion on the limitations of using intra-articular injections as a diagnostic standard).
Patients were asked if any of the following treatments were used and what effect each treatment had (increased, decreased, or did not affect their pain): anti-inflammatory medications, muscle relaxers, physical therapy, home exercise, application of local heat and cold, and manual manipulations of the sacroiliac joint.
Patients were also asked if a specific, traumatic event caused their pain and if this event was caused by twisting, heavy lifting, a fall on the buttocks, a motor vehicle accident, a fall in a hole, a sports-related injury, a repetitive work injury, or another type of injury.
Patients were then asked if the following activities increased, decreased, or did not affect their pain: walking, sitting, lying down, standing in place, wearing high heels or boots, straining with a bowel movement, coughing or sneezing, and usual job activities. Which of all of these components do you think correlated well with sacroiliac joint dysfunction?
None of them.
The study concluded: “No aggravating or relieving factor was of value for diagnosing the presence of sacroiliac joint pain as established by intra-articular blocks. All of these features in the patients’ medical history had poor sensitivity, poor specificity, or both.”
Unfortunately, it appears that these subjective details are unhelpful in diagnosing sacroiliac joint pain. Additionally, I would argue that none of these aggravating activities would affect only the sacroiliac joint. Wouldn't the lumbar spine or hip joints be involved as well? These aggravating activities are simply not able to differentiate between these neighboring structures.