Sacroiliac Joint Injection

The sacroiliac (SI) joint can be a source of low back pain. In assessing the etiology of the low back pain, a complete history, physical examination, psychosocial evaluation, and appropriate imaging may be helpful. Various clinical tests specific to the SI joint during the physical examination have been documented in aiding the diagnosis of SI pain.

By using SI anesthetic blocks for diagnosis, the SI joint has been shown to be a source of pain in 10-27% of suspected cases of chronic low back pain.[1]  Patients with medical conditions such as gout, rheumatoid arthritis, Marie-Strumpell or ankylosing spondylitis, psoriasis, fracture, malignancy, congenital deformity, or infection can also develop pain in the SI joint.

Pregnant women are at risk for SI joint pain because pregnant women produce a hormone called relaxin, which causes excess motion at the SI joint.[2]  Patients with a leg length discrepancy can also develop SI joint pain.[3]  In addition, any condition that limits weightbearing (eg, history of surgery on a limb or pain in the lower extremity) may cause SI joint pain because of the uneven distribution of weightbearing during the gait cycle.[3]  Patients who have undergone prior spinal surgery may also have increased SI joint pain.[4, 1]

 Injection of the SI joint (see Technique) can be either diagnostic or therapeutic.

Indications for SI joint injection are as follows:

• Diagnostic - To investigate the SI joint as the etiology of lower back pain
• Therapeutic - To treat SI joint pain (when combined with steroids)

Absolute contraindications for SI joint injection include the following:

• Patient refusal to proceed with the injection procedure
• History of significant allergic reactions to injected solutions - Note that reported allergy to local anesthetic is typically from the preservative in multiple-use containers; anesthetics in single-use containers can generally be used without allergy
• Local malignancy

Relative contraindications include the following:

• Congestive heart failure
• Uncontrolled diabetes mellitus
• Pregnancy
• Systemic or local infection at the site of a planned injection
• Bleeding disorder or fully anticoagulated blood (eg, patient taking blood thinner, multiple anti-inflammatory medications)

Patients taking anticoagulation medications have an increased bleeding time; therefore, such medications should be held for 7 days prior to the injection and for 24 hours after the injection. Patients taking anticoagulants for reasons such as stroke and heart disease should speak to the prescribing physician before holding the anticoagulation medication for the procedure.

Anatomy

The SI articulation is an amphiarthrodial joint, formed between the auricular surfaces of the sacrum and the ilium. The articular surface of each bone is covered with a thin plate of cartilage. They are separated by a space containing a synoviumlike fluid; hence, the joint presents the characteristics of a diarthrosis. The ligaments surrounding the joint are the interosseous ligament and the anterior and posterior SI ligaments.

Motion at the joint is limited; in one analysis, rotation was a mean of 2.5° (0.8-3.9°), and joint translational movement was a mean of 0.7 mm (0.1-1.6 mm).[5]  No difference was reported in the motion between symptomatic and asymptomatic joints.

The morphologic and physiologic base for pain signals originating from the normal anterior capsular and interosseous ligaments is provided by the calcitonin gene-related peptide (CGRP) and substance P immunoreactive fibers present in these ligaments.[6]  Therefore, both extra-articular and intra-articular approaches should be considered for diagnostic infiltration for SI joint pain.

An anatomic study on adult cadavers demonstrated that the SI joint is predominantly, if not entirely, innervated by sacral dorsal rami.[7]

In 2001, Murata et al performed a study to delineate the sensory innervation in the ventral and dorsal sides of the SI joint.[8]  They reported that the dorsal innervation derives from the dorsal root ganglions of the lower lumbar and sacral levels (from L4 to S2), and the ventral innervation originates from the dorsal root ganglions of the upper lumbar, lower lumbar, and sacral levels (from L1 to S2).

The presence of nerve fibers and mechanoreceptors in the SI ligament has been demonstrated.[9]  Referral patterns based on SI joint provocation and analgesia have been published[10, 11, 12] ; however, the only pain pattern found to be associated with patients who responded to SI joint injections was groin pain.[13]

As many as two thirds of patients may have significant improvement of approximately 9 months' duration with steroid injection. The pain may recur, and the injection can be repeated.[14, 15] However, systematic reviews have found the short- and long-term effectiveness of intra-articular SI injections to be poor.[16]

A double-blind study was done in 10 patients with painful sacroiliitis.[17] A total of 13 joints were injected with either steroid (n = 6) or placebo (n = 7). At 1 month, patients described greater than 70% pain relief in five of the six SI joints injected with corticosteroids. No pain relief was reported in the placebo-injected joints.

In assessing the etiology of low back pain, a complete history, physical examination, psychosocial evaluation, and appropriate imaging may be helpful. Various clinical tests specific to the sacroiliac (SI) joint during the physical examination have been documented in aiding the diagnosis of SI pain.

Physical examination

The Gillette test is done with the patient in the standing position. The patient stands on one leg while flexing the opposite hip and knee into the chest. Motion of the SI joint is assessed by placing one thumb under the posterior superior iliac spine (PSIS) on the side of hip flexion, with the other thumb in the midline at the S2 level. Normally, the thumb under the PSIS drops inferiorly and laterally with hip flexion. Restriction is indicated by decreased motion compared to the normal side.

In the Fortin finger test, the patient points to the area of pain with one finger. The result is positive if the site of pain is within 1 cm of the PSIS, generally inferomedially.

The Patrick test or Faber maneuver involves flexion, abduction, and external rotation of the hip. The patient lies supine, with the heel of the tested side placed on the opposite knee. Pressure is put on the flexed knee and the opposite anterior superior iliac spine (ASIS) area. The  test result is positive for SI dysfunction if pain is elicited in the SI joint area. The sensitivity of this test in predicting response from SI joint injection is reportedly low (57%),[18, 19, 20]  whereas others have reported 77% sensitivity and 100% specificity[21] ; however, the accuracy of these studies has been questioned.[22]

In the Gaenslen test, the patient is supine. The hip and knee are maximally flexed toward the trunk, and the opposite leg is extended. Pressure is applied to the flexed extremity. The finding is positive if pain is felt across the SI joint. This test was found to be 68% sensitive and 35% specific.[23, 24]  However, the validity of this test has also been questioned.[25]

In the compression test, the patient lies on one side. The examiner applies pressure on one pelvic brim in the direction of the other. A positive result is pain across the SI joint.

In the Van Durson standing flexion test, the patient is standing with the examiner behind him. The examiner’s thumbs are placed just below each PSIS. The patient flexes the trunk forward without bending the knees. A positive sign is asymmetric motion.

In the Piedallu seated flexion test, the patient is seated with the examiner behind him. The examiner’s thumbs are placed just below the PSIS. The patient flexes the trunk forward. A positive result is asymmetry of motion.

An individual positive clinical test result may not prove to be indicative of SI joint pain. However, if three clinical tests reveal positive results, the likelihood that the pain originates from the SI joint is greatly increased.[26]

Imaging

If the SI joint is strongly suspected as the origin of the pain, imaging may be indicated. Plain radiography, computed tomography (CT), and magnetic resonance imaging (MRI) of the SI joint can be performed, but results can be misleading. In fact, one study showed that CT findings were negative in 42% of symptomatic SI joints.[27]  MRI has not been proved to be positively correlated with the diagnosis of SI joint pain.

The International Association for the Study of Pain (IASP) proposed the following criteria for making the diagnosis of SI joint pain[28] :

• Pain is present in the region of the SI joint
• Stressing the SI joint by performing clinical tests that are selective for the joint reproduces the patient’s pain
• Selectively infiltrating the putatively symptomatic joint with local anesthetic completely relieves the patient of pain

Equipment used for SI joint injection includes the following:

• Standard C-arm fluoroscopy unit with monitor
• Spinal needle, 22 gauge, 3.5 in. (~8.9 cm)
• Contrast agent (eg, iohexol)
• Steroids - Steroids typically used include betamethasone sodium phosphate or acetate and methylprednisolone; there is no consensus on the type of steroids that should be used in this injection

Anesthesia

Procedural sedation (eg, with midazolam or fentanyl) is seldom (but occasionally) used, because it is important for the patient’s perception of pain to remain intact during the injection. For this reason, anxiolytics are preferred to analgesics in this setting.

Positioning

The patient should be in the modified Sims position, with the pelvis rotated until the joint appears clearly under fluoroscopy.[29]  Placing a pillow under the patient's hip can further enhance visualization of the SI joint. A 30º cephalad tilt view and Ferguson view provide good visualization of the anterior and posterior articular margins of the SI joint.[30]

Initial management of patients with pain originating from the sacroiliac (SI) joint may include oral medications, education, and physical therapy. Physical therapy can help relieve pain by strengthening the muscles surrounding the SI joint. In addition, ultrasound, deep heat, electrical stimulation, traction, and mobilization can help with pain relief.[31]  If conservative management techniques fail to resolve the patient’s pain, a diagnostic or therapeutic injection into the joint can be performed.

Platelet-rich plasma (PRP) injection has been studied as an alternative to steroid injection for the treament of SI joint pain; it has been shown to have efficacy in this setting, but its therapeutic value relative to that of steroid injection remains to be fully defined.[32, 33, 34]

Fluoroscopy-guided injection

Position the patient as described (see Patient Preparation). Clean the skin with povidone-iodine solution; chlorhexidine may be substituted for patients with povidone-iodine allergy. The povidone-iodine solution should dry on the skin to have its full antibacterial effect.

An older technique of injection involves the insertion of three 22-gauge spinal needles into the inferior, middle, and superior aspects of the joint. Currently, however, insertion of a single needle in the inferior aspect of the joint is preferred.[13, 35]  Insert the needle in a medial-to-lateral direction. It is recommended that the needle be inserted 1.75 in. (~4.5 cm) caudal to the posterior superior iliac spine (PSIS).[36]

After skin infiltration, place the spinal needle over the joint coaxial on the skin. Advance the needle through the skin, capsule, and ligaments of the joint until it is introduced into the joint. To limit motion at the needle, attach the syringe filled with contrast to the spinal needle with extension tubing.

Inject approximately 1 mL of contrast. This should outline the joint, which can be easily viewed under fluoroscopy (see the image below). Use of pulsed imaging and culmination reduces radiation exposure. Immediately after injecting contrast, ask the patient whether he or she feels any pain and, if so, whether it feels like the typical pain in that location.

After the needle location has been confirmed with contrast, inject 1 mL of lidocaine or bupivacaine (see the images below). A corticosteroid can be combined with the local anesthetic.[37]

After the anesthetic is injected, ask the patient if his or her pain is relieved. Reevaluate the patient’s pain before discharging. A pain scale, such as the Visual Analogue Scale (VAS), is commonly used to monitor patients’ progress. A greater than 75% reduction of pain over the SI joint is considered a definitive response.[13]

Ultrasonography-guided injection

In the ultrasonography (US)-guided approach, as in the fluoroscopy-guided approach, the patient is positioned prone with a pillow under the pelvis. The skin is prepared to reduce infection risk. The ultrasound machine should be on the opposite side of the patient from the practitioner to allow better visualization with minimal movement. 

In most cases, a curvilinear transducer yields the best visualization. First, identify the posterior superior iliac spine (PSIS). After this landmark is seen, translate the probe medially to locate the S1 foramen. Then, move the probe inderiorly from the PSIS to visualize the inferior portion of the SI joint, which is lateral to the S2 foramen. Insert the needle in plane with the probe from medial to lateral to ensure avoidance of the S2 foramen. Needle placement is confirmed with contrast-enhanced real-time fluoroscopy.[38]

Guidance by fluoroscopy vs CT, US, or MRI

Although SI joint injection can be attempted blind, intra-articular injection without fluoroscopy is successful in only 12-56% of attempts.[39, 40] Procedures guided by computed tomography (CT), US, and magnetic resonance imaging (MRI) were also developed; however, as various authors noted, additional data would be needed for definitive comparison of the efficacy of these procedures with that of fluoroscopy-guided injection.[41, 42]

In a prospective, randomized, single-blind study comparing US-guided with fluoroscopy-guided SI joint intra-articular injections in noninflammatory SI joint dysfunction, Jee et al found that the US-guided approach was as therapeutically effective as the fluoroscopy-guided approach but was less diagnostically effective because of its significantly lower accuracy (87.3%).[43]

A cadaveric study of 17 SI joints injected under US guidance found that intra-articular injection was achieved in 88.2%.[44]  In a study comparing fluoroscopically guided SI joint injection with US-guided injection in 40 patients with chronic low back pain, Soneji et al identified no significant difference in pain scores between the fluoroscopy group and the US group at 1 month or at any other follow-up points, nor were there any significant differences in procedure-related variables, physical function, discomfort, opioid utilization, and patient satisfaction.[45]

In a prospective institutional study of the cost-effectiveness of CT-guided SI injection, Bydon et al determined that this approach yielded improvements in pain and activities of daily living, at a cost per quality-adjusted life year (QALY) falling well below the threshold cost of 1 QALY, and was strongly cost-effective.[46]

A study by Althoff et al found that CT-guided intra-articular steroid instillation was able to achieve adequate pain and symptom control for 6 months in patients suffering from active sacroiliitis.[47]

Intra-articular vs periarticular injection

Extra-articular or periarticular corticosteroid injections have been reported to provide significant benefit for SI joint area pain.[48, 49, 50]

In 2007, Murakami et al studied whether intra-articular or periarticular injections were more effective at relieving SI joint pain.[51] They initially gave patients intra-articular SI joint injections and then performed additional periarticular injections in the patients who experienced no improvement from the intra-articular injection. The improvement from the periarticular injections was significantly higher than that from the intra-articular injections. This result could have various causes, including the following:

• The interosseous membrane and the surrounding ligaments have nociceptive fibers, and this may be part of the reason why the injection is effective even if it is periarticular
• The additional quantity of steroid may also be responsible for the improvement with the second injection
• The patients may have been initially misdiagnosed; if they were, in fact, experiencing pain from soft tissue dysfunction, their symptoms may have been improved by the extra-articular injection

In a 2016 study of 113 fluoroscopically guided SI joint injections in 99 patients, Nacey et al found that after adjustments were made for age, sex, preinjection pain score, time of year, and indication for injection, there was no significant difference between intra-articular injection and periarticular injection in terms of the degree of pain relief achieved.[52]

If there is severe arthritis of the SI joint, then the injection often is not very effective on a long-term basis.[53]

If diagnostic injections are positive for SI joint etiology but relief from injection is only temporary, radiofrequency neurotomy of the SI joint can be performed to potentially provide longer results.[54, 55, 56, 57, 58, 59]

Some studies indicated some effectiveness in injecting onabotulinumtoxinA or hypertonic dextrose for SI joint pain.[60, 61, 62]

Surgery is rarely performed for SI joint pain. Surgery has been considered if other treatments do not work; however, results have been very disappointing.[63]

Adverse effects seen with SI joint injection are minimal. The most commonly reported immediate adverse effect is a vasovagal reaction; the most common delayed adverse effect is a temporary increase in pain.[64]

As with any injection through the skin, bacteria may gain entry at the injection site and cause an infection. Some adverse effects may occur as a result of the corticosteroid administered. Patients who have diabetes may notice that their blood sugar levels are elevated for 2-3 days following the procedure.