Introduction
Low back pain remains one of the most debilitating and prevalent symptoms in the United States, with a lifetime prevalence of 65% to 70%. The sacroiliac joint (SIJ) is one of the most common causes of chronic low back pain and is found to be the source in 15% to 30% of cases. As the largest synovial joint in the body, the SIJ remains a difficult location, anatomically, to treat back pain given its location in the pelvis. The SIJ connects the sacrum and the ilium and is centrally located adjacent to many motor and sensory nerves of the lower extremities. It has multiple ligaments and stabilizing muscles that keep the joint stable and allow the pelvis to carry the entire weight of the torso. Multiple causes of SIJ pain exist, and there exist several strategies to target this joint. Radiofrequency ablation (RFA) of the SIJ is one such approach that has recently started to gain traction. This chapter briefly reviews the causes of SIJ pain and dives deeper into the therapeutic approaches to SIJ RFA, as well as the relevant anatomy, indications for therapy, contraindications, and complications of the procedure.
Causes of sacroiliac joint pain
Before a discussion regarding RFA of the SIJ, an understanding of the common causes is needed, which has also been presented in detail in prior chapters. Briefly, traumatic causes of SIJ pain are typically due to mechanisms that create strong shearing and rotational forces on the hips. These are typically caused by falls, motor vehicle accidents, or major pelvic trauma. In contrast, multiple atraumatic causes of SIJ pain exist, including osteoarthritis, rheumatoid arthritis, ankylosing spondylitis, inflammatory bowel disease (IBD), and pregnancy. Osteoarthritis typically occurs in adults toward the fifth and sixth decades of life and presents with chronic low back pain with no clear or definite mechanism of injury or traumatic event. Rheumatoid arthritis has a similar picture clinically and symptomology is typically identical to that of osteoarthritis; however, the patient will have more systemic sequalae of their rheumatoid arthritis. Ankylosing spondylitis is a spondylarthritis with axial involvement and is characterized by enthesitis (pain at ligament–tendon insertion points). Other inflammatory states, including IBD, such as Crohn’s disease and ulcerative colitis, can present with bilateral SI pathology, and a portion of these patients carry the HLA-B27 antigen. Pregnancy has multiple effects on the SIJ, including laxity and movement of the joint. This can change the loading and stressing forces on the joint space and the entire pelvis and commonly results in pain.
Anatomic considerations
The SIJ is centrally located joint that connects the sacrum and the ilium bilaterally and has anterior and posterior components. The SIJ is a synovial joint that is stabilized by multiple ligaments and muscles, including the piriformis, gluteus maximus, and biceps femoris ( Fig. 5.1 ). The posterior two-thirds of the joint include multiple complex ligamentous attachments that help limit the amount of mobility and the effects of weight changes and shearing forces. SIJ innervation can vary greatly and is typically debated by multiple experts. The posterior segment is typically innervated by the S1 to S3 dorsal rami, as well as the L5 dorsal ramus. In contrast, the anterior joint is typically thought to be supplied by the L2 to S2 ventral rami; however, some believe that there is no specific innervation for the anterior segment.
Patient selection and indications
The primary indication for RFA therapy is diagnosing SIJ pain that is refractory to conservative therapies. The most specific test for diagnosing intraarticular SIJ pain is the intraarticular diagnostic block, which should be done before any RFA. This is done via image-guided injection of local anesthetic into the synovial SIJ. The two most common types of SIJ steroid injections and diagnostic nerve blocks are at the L4 to L5 dorsal rami or S1 to S3 lateral branches. After two consecutive blocks that provide more than 50% relief of a patient’s pain symptoms, it can be concluded that a patient is a good candidate for RFA.
Contraindications
Contraindications to any intervention apply in these cases as well. These include overlying skin infection; significant coagulopathies, which increase bleeding risk; and allergies, which prevent the procedure from occurring. Also, most procedures rely on the patient to provide feedback regarding stimulation and sensation (i.e., radicular pain and muscle weakness); therefore, any condition that prevents the patient from being fully alert, awake, and engaged puts the success of the procedure at risk.
Step-by-step guide
Sacroiliac joint RFA is a relatively new intervention, with the first occurrence reported in 2001, when 36% of patients had pain reduction by at least 50% as a result of the procedure. Since then, RFA has become increasingly popular, and advancements have been made, resulting in more effective and safer interventions. However, data still remain sparse and is growing. In its entirety, SIJ RFA aims to destroy nerve endings that transmit pain from the SIJ, therefore relieving pain. Although the innervation of the SIJ varies, most practitioners target the L4 medial branch nerve, L5 dorsal ramus, or S4 lateral branch nerve. RFA is achieved by inserting a probe at the location of the nerve ending and applying electrical current, which then produces a thermal effect thereby lesioning the nerve. There are three common techniques that are used for RFA: Simplicity, strip lesioning, and radiofrequency lesioning. These are discussed in the detail next.
Simplicity
The Simplicity needle was created by Abbott specifically for RFA of the SIJ. Traditional techniques require multiple needle placements for either bipolar or cooled RFA; however, Simplicity requires a single insertion point with a specialized probe that creates five separate lesions to ablate the L5 dorsal ramus and the S1 to S4 lateral branches at a single time ( Figs. 5.2 and 5.3 ). Like traditional RFA, the Simplicity is done under fluoroscopy guidance with a team consisting of the physician, radiology technician, and support staff. The room should be fitted with an adjustable surgical table and a mobile C-arm ( Fig. 5.4 ). First, the patient is placed in the prone position on the table with padding or a pillow beneath their abdomen to reduce lordosis of the spine. Next, the grounding pad is placed on a muscular area of the body near the procedure site, with care to avoid any hair, bony prominences, significant scars, and any location where fluids may accumulate. Next, the patient’s lower back and buttocks are sterilely prepped and draped at the treatment site. Using the C-arm, an anteroposterior (AP) image with the ipsilateral sacrum in view is obtained. This view allows one to identify the insertion point, which is typically 1 cm lateral and inferior to the S4 foramen (see Fig. 5.4 ). Next a 25-gauge spinal needle and local anesthetic (with or without corticosteroid) is used to anesthetize the track that the Simplicity probe will take when performing the RFA. The spinal needle is advanced just lateral to S4 foramen in a cephalad fashion to the sacral foramen and then advanced through the ligaments between the sacrum and ileum ( Fig. 5.5 ). After withdrawing the stylet from the spinal needle, local anesthetic is injected while the entire needle is removed to anesthetize the track. Next, the Simplicity probe is inserted at the original spinal needle entry site. Of note, a small scalpel incision may be necessary to facilitate probe insertion. While advancing the Simplicity probe, lateral images may need to be obtained to ensure lack of probe entry into any of the sacral foramen. The Simplicity probe should then be advanced until contact is made with the sacral ala under AP view, and lateral images should be used to confirm that the three active contacts, identified by three radiopaque markers, are parallel to the S1 to S4 lateral branch pathways. Care should be taken to ensure that the probe remains in contact with the sacral periosteum along its entire pathway. After the appropriate location is obtained, the Simplicity probe is connected to the RFA generator, and an appropriate heating sequence is chosen ( Fig. 5.6 ). The RFA generator allows for procedure settings to be changed, including target temperature and lesion time. After this is done, typical RFA postoperative care should be undertaken, and follow-up should be scheduled.
