The sacrum consists of five fused vertebrae that are in continuity with the lumbar spine proximally and coccyx inferiorly. It articulates with the two ilia laterally, forming the sacroiliac joints. The sacroiliac joint represents the largest axial joint in the body, with an average surface area of 17.5 cm² (Cohen 2005). Although characterized as a diarthrodial synovial joint, only the anterior third of the interface between the sacrum and ilium is a true synovial joint. The posterior two-thirds are comprised of an intricate set of ligamentous connections functioning to reduce movement of the joint (Cohen 2005). Unlike the lumbar facet joints, the sacroiliac joint lacks a well-defined capsule. The anterior joint capsule is thickened and the posterior capsule is either absent or rudimentary. No consensus has been reached with regard to the innervations of the sacroiliac joints. A review by Fortin et al. (1999) concluded that the joint is predominantly innervated by the sacral dorsal rami.

Current indications for sacroiliac joint injections are:

The procedure is usually done as outpatient basis, with no specific pre-procedural preparation or premedication required. It may be performed under fluoroscopic or CT guidance, with the latter being the preferred method in our institution due to the rather complex configuration of the sacroiliac joint. Ultrasound-guided sacroiliac joint injection technique has also been described previously (Pekkafahli et al. 2003; Harmon and O’Sullivan 2008).

The patient is placed in the prone position. The sacral and buttock area is cleaned and draped using an aseptic technique. On fluoroscopy, the frontal projection will show two apparent joint spaces (Fig. 40.3). The more medially located joint space is the lower synovial portion of the true sacroiliac joint, whereas the upper fibrous portion of the joint is projected more laterally (Levin et al. 2009). It is the inferior joint space that is targeted during sacroiliac joint injection. Various techniques of fluoroscopy-guided sacroiliac joint have been described. Levin et al. (2009) used rotation of the fluoroscope away from the site of injection in the transverse plane to visualize the inferior joint space, before advancing the needle towards the joint in a medial to lateral direction. Dussault et al. (2000) suggested tilting the fluoroscope about 20–25° in a cephalic direction to displace the posteroinferior portion of the sacroiliac joint in a caudal direction, separating it from the anterior fibrous portion of the joint, which would then move cephalad on the image. Once the skin entry site is confirmed and marked, local anesthetic is given. A 22-G spinal needle is advanced towards the posteroinferior portion of the joint perpendicular to the fluoroscopic table under fluoroscopic guidance.

Once the needle is correctly placed, its position can be checked by moving the fluoroscopy tube in the right and left oblique positions under continuous fluoroscopy. If the needle tip is within the sacroiliac joint, the needle tip should remain within the joint in all projections and not projected over the bone. Alternatively, a small amount (usually no more than 0.5 ml) of low osmolar nonionic contrast agent can be injected to confirm the intra-articular position. The injected contrast agent should outline the joint space if the needle tip is within the joint. Upon confirmation of position, 3–5 ml of the local anesthetic and steroid mixture (similar to the mixture used for facet joint injection) is injected.

It is more straightforward if the procedure is performed under CT guidance, as the position of the needle tip can be clearly visualized. Another advantage of CT guidance is the ability to identify the sciatic nerve and the adjacent gluteal artery, which should be avoided during needle advancement. Similar to fluoroscopically guided injection, the patient again adopts a prone position, and the poster inferior portion of the sacroiliac joint is targeted (Fig. 40.4).

Standard post-procedure care, as mentioned in the facet joint injection section, is followed. The post-procedure caregiver should ask specifically for lower limb neurological symptoms which can occur after inadvertent sciatic nerve injury. No serious complications after sacroiliac joint injection, related to either needle placement or drug injection, have been reported.

Both observational studies and randomized controlled trials have found imaging-guided sacroiliac joint injection to be effective in providing significant pain relief. Positive response is achieved in 80–90 % of patients, with the pain relief effect lasting up to several months (Bollow et al. 1996; Maugars et al. 1996; Dussault et al. 2000; Slipman et al. 2001; Karabacakoglu et al. 2002). Recurrence of pain is not uncommon and usually occurs after 6–12 months (Hanly et al. 2000). In such cases, repeated injection has been shown to be beneficial (Gunaydin et al. 2006). In difficult cases, periarticular sacroiliac joint injection may be of some value (Luukkainen et al. 1999; Luukkainen et al. 2002).

Unlike the knee joint, the hip joint is more deeply situated and cannot be easily palpated, making accurate intra-articular injection a challenging procedure. The success rate and safety of intra-articular injection without imaging guidance have been reported to be suboptimal in a cadaveric study performed by Leopold et al. (2001). Depending on the experience of the procedurist and availability of imaging facilities, hip injection can be performed under fluoroscopy, ultrasound, or CT guidance. Compared to fluoroscopy, ultrasound and CT enable clear visualization of the important femoral neurovascular bundle. Ultrasound also has the advantages of easy accessibility, compact size, and lack of radiation exposure, but it is also more user dependent.

Fluoroscopy-guided hip injection is performed with the patient placed in the supine position with the foot pointing upwards. An aseptic technique is applied. An anteroposterior approach, under fluoroscopic guidance, is the most commonly used method. The femoral pulse should always be palpated and a marker placed over the pulse to avoid inadvertent femoral vessels and nerve injury. As the hip joint has a large joint capsule that covers up to the mid-femoral neck region, there is a relative large area that could be targeted as needle placement anywhere within the capsule will ensure intra-articular injection. The lateral aspect of the proximal femoral neck at the head-neck junction (Fig. 40.5) is a good needle placement point since it is well within the coverage of the joint capsule and minimizes the risk of femoral vessel and nerve injury.

Once the skin entry site is identified and local anesthetic infiltrated, a 22-G spinal needle is advanced towards the target point on the bone at a cranially oblique angle to the skin. When the needle touches the bone, intra-articular position of the needle tip should then be confirmed with injection of 3–5 ml of contrast agent. The joint capsule should be outlined if the needle tip is within the joint capsule. Corticosteroid injection then can be performed safely.

In our institution, injection of hip joint is performed under CT guidance if a viscosupplement is injected, due to its potential to react with the contrast agent. If CT guidance is used, a preliminary axial scan is performed to determine the skin entry point. The femoral neurovascular bundle is identified, and the skin entry point is lateral to it (Fig. 40.6). Upon confirmation of the entry point, the needle is directly advanced into the inferior part of the hip joint.

Mild pain or discomfort after injection is not uncommon and can be managed with simple oral analgesics. The site of injection should be monitored for any hematoma secondary to inadvertent femoral vessel puncture. If this occurs, sustained firm manual compression is usually effective. Other reported but rare complications include septic arthritis, osteonecrosis, and joint infection after total hip replacement following preoperative intra-articular injection (Chazerain et al. 1999; Nallamshatty et al. 2003; Yamamoto et al. 2006

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