What do you know about the SI Joint?
I recently met a young lady who had this procedure and heard her story. She was a competitive snowboarder - young, healthy, active. When she was in her mid 20’s she landed on her back on a patch of ice on the slopes. This started several years of severe pain and multiple healthcare providers that couldn’t help her. During that time, she had to walk out of work meetings, crying from the pain, and she spent holidays with the family in the restroom, nauseous from the pain. It took 5 years before a healthcare provider finally had the suspicion that her symptoms were coming from the SI Joint. After correct diagnosis and surgery to fuse it, she is finally starting to return to normal activities without pain. She has even taken up snowboarding again. There is no excuse for her to have been misdiagnosed for so long and lose out on half of her 20’s, plagued by severe pain.
Sure we know what the SI joint is, but being able to get to the point where we are confident in isolating it can be tricky. The special tests that are most commonly known are not very accurate, which leaves most providers without confidence that they are completely correct in their diagnosis. Complete and accurate diagnosis of the SI Joint requires 4 components: a relevant history, specific positive special tests, lumbar and hip examinations that rule out other pathology, and a positive response to an intra-articular injection. Let’s get into specifics.
Is the SI Joint really a pain generator?
There has been and continues to be debate about this in some circles. There are still some who do not believe that the SI Joint is a pain generator. Yet studies show that the prevalence of SI joint being a component of chronic low back pain is between 15% and 30%. The prevalence of the SI Joint being symptomatic after a lumbar fusion is between 32% and 43%. There seems to be 2 reasons for that. One reason is that the SI joint was the problem in the first place and a misdiagnosis led to a lumbar fusion. The other reason is adjacent segment degeneration that occurs after a fusion. Basically, if you take away motion in one joint or several joints, the adjacent joints have to absorb new forces and motion. We all are aware of the the levels above a lumbar fusion breaking down faster over time, but now we’re also finding that the SI joint does the same thing. A study by Ha et al in 2008 took a group of patients 5 years after lumbar fusion and performed a CT scan to view degeneration of the SI Joint. It found that 75% of post-lumbar fusion patients showed SI joint degenerative changes, compared to only 38% in age and gender-matched controls without a lumbar fusion. A study by Ivanov et al. in 2009 showed that angular motion and joint stress at the SI joint increases after lumbar fusion as well.
Anatomy of the SI joint
The SI joint is both a synovial and fibrocartilage joint. It has the largest surface area of any joint in the body at 17.5 cm2. The surface of the joint is shown to progressively roughen and change over each decade of life. The joint has hyaline cartilage on both the sacral and iliac sides of the joint, but that cartilage is thinner on the iliac side, leading to faster degenerative changes on that side of the joint.
The SI joint ligaments are some of the strongest in the human body and they are continuous with the joint capsule and some of the surrounding musculature. The anterior ligaments are thinner and primarily resist upward movement of the sacrum and lateral motion of the ilium. Posterior ligaments resist downward motion of the sacrum and medial motion of the ilium.
Motion of the SI joint occurs in 3 planes simultaneously, but there isn’t a lot of motion that occurs. It’s less than 4 degrees in any plane. The sacral base goes through a motion called nutation/counternutation - 1-2 degrees in males and 3-4 degrees in females, and the ilium translates 1.6 mm in AP motion.
The SI joint transfers forces from the lower extremities to the spine. There are both passive structures and active structures that contribute to the stability and function of the joint.
Is imaging useful for diagnosing the SI joint?
Not really. An MRI can catch large issues, but it can miss a lot due to the shape and structure of the joint. The joint itself is shaped like a plane propeller blade, twisting into different planes of motion, which does not allow for a clean slice through the joint. On a microscopic level, the joint has ridges like a ruffles potato chip, which contributes to stability of the joint but is not helpful for imaging it.
Components of a positive subjective history:
When taking a subjective exam, important items to take note of are prior traumas, history of lumbar fusion, pregnancies, and activities in the person’s past that would cause repetitive trauma to the joint.
There are specific mechanisms of injury that can cause SI joint pathology. Car accidents where a person’s foot was on the brake is one big one. If the person is hit in front or behind and their foot is on the brake, the force of the impact is transmitted from the brake pedal up through the right lower extremity, to the SI joint. Another mechanism of injury is falling backwards on the pelvis. Injuries sustained with combination of lifting and twisting will increase strain on the SI joint. The last mechanism of injury that can directly affect the SI joint is a traction injury. This type of injury would happen if a person falls off of a horse and their foot becomes stuck in a stirrup.
When we look at activities in a person’s life, we are listening for jobs or hobbies that utilize repetitive asymmetrical motions, like bending over to dig a ditch or something like that.
Biomechanical abnormalities have to be taken into consideration. Leg length inequality will cause asymmetric stress on an SI joint. Pelvic obliquity or scoliosis will also place abnormal stresses on the joint.
For women, pregnancies are a risk factor due to ligamentous laxity changes and changes in the structure of the pelvis. More pregnancies produces more likelihood of SI joint dysfunction.
Something that is rare but also could be relevant is a history of infection in the SI joint, which will cause degeneration later on.
Listen for exacerbating factors that can more commonly affect the SI joint. Unilateral weight bearing on affected side is one of them. Putting on a sock, ascending/descending stairs, and prolonged walking with pain during weight-bearing are all common. Transitional motions like standing up from a chair, rolling over in bed, and getting into and out of bed or the car are common. Sitting on affected side will also become painful. When conducting your subjective evaluation, you’ll maybe notice that the patient shifts to one side, away from the painful side. I’ll usually stop at that point and ask if the patient was uncomfortable before the shift and if they had decreased pain after the shift. Sometimes they don’t even recognize that they did it.
There are some specific tests, when done in combination, can result in a very high degree of sensitivity and specificity. Laslett 2005/2008 found that if 3 or more of the following special tests are positive, the sensitivity of presence of an SI pathology is 91% and specificity is 78%.
Pain Presentation and Differential Diagnosis
Pain from the SI joint will usually not be midline, is usually below L5, at or lateral to PSIS, and could occasionally be in the groin. Secondary pain could present in lateral thigh, groin, and/or lateral calf. Does this sound like some other pathologies? Lumbar spine and hip joint pathologies can follow these same patterns. So when screening for SI joint dysfunction, the lumbar spine and hip also needs to be thoroughly evaluated to rule out presence of dysfunction.
The gold standard for definitively diagnosing the SI joint is an intra-articular injection. If symptoms cannot be controlled with physical therapy or are too severe to undergo physical therapy, the patient can either be given a diagnostic injection or therapeutic injection with an anti-inflammatory. If this only decreases pain temporarily, the patient can be treated with an RFA (Radio Frequency Ablation) of the sacral nerves. At this point, if Physical Therapy and interventional pain management cannot control symptoms or return function, it’s time to consider the next option - fusion.
Fusions were traditionally performed with round screws. Over time these have shown the propensity to loosen, allowing pain to return into the joint because joint motion is not completely stopped. Over the last few years there has been a new fusion product called i-Fuse. It’s a triangular device that placed instead of round screws that has been shown to be more effective at stopping motion at the SI Joint and decreasing pain. The newest version is called iFuse-3D (pictured), which is 3D printed with a surface that mimics cancellous bone and has openings to allow for greater bone integration and through-growth.
To put it simply, outcomes have been outstanding. The procedure has 75 published studies, including several level 1 evidence studies. It also has a 92% satisfaction rate with patients who have undergone the procedure. The reason is that SI-Bone, the company that produces it, has high standards for identifying patients that are appropriate for this treatment. They make sure that the patient exhausts all conservative options, including Physical Therapy and injection therapy before the fusion is considered. To learn more about the i-Fuse implant, go here.