The sacroiliac joint (SIJ) is a diarthrodial joint stabilized by bony ridges on the articular surface of the sacrum that articulate with reciprocal surfaces on the ilium. An associated network of supporting ligaments also helps stabilize the joint. The anterior sacroiliac ligaments resist external rotation of the ilium relative to the sacrum; the posterior sacroiliac ligaments, which resist both internal rotation and vertical displacement, are essential for stabilizing the pelvic ring.
Degeneration or injury to any aspect of the joint, including the ligament complex, can lead to pain in the low back and sometimes the buttock or proximal thigh.
The SIJ was first identified as a source of back pain at the beginning of the 20th century but was subsequently ignored for decades. It has recently re-emerged as a known pain generator, although it remains underrecognized and underdiagnosed. The current literature suggests SIJ involvement in 15 to 30 percent of patients presenting with low back pain. Some studies report a much higher prevalence — up to 61 percent — in patients who have undergone lumbar fusion procedures, whether or not the fusion involves the sacrum.
High-energy trauma, such as motor vehicle crashes and falls, is responsible for a significant number of SIJ injuries. Repetitive trauma, inflammatory arthritis, osteoarthritis, joint hypermobility — especially during pregnancy — and degeneration of the joint also can cause SIJ pain.
Patients with SIJ disorders typically present with burning, stabbing pain below the L5 vertebral level that may or may not radiate to the buttocks and thigh. About 28 percent have pain that radiates to the knee. Unlike discogenic pain, which usually worsens with sitting, SIJ symptoms are more likely to be worse in transitional movements, such as rising from a chair. Still, the discomfort can often be confused with radicular or discogenic pain. Diagnosis is further complicated because SIJ problems can co-occur with degenerative disk disease, arthritis or sciatica.
In the absence of acute trauma, diagnosis involves a careful combination of clinical history, physical exam, pain provocation tests and image-guided intra-articular anesthetic injections to confirm the diagnosis. William W. Cross III, M.D., an orthopedic trauma surgeon at Mayo Clinic's campus in Rochester, Minnesota, says a different or an additional pain generator may be involved if patients don't experience significant relief from diagnostic injections.
Early imaging is discouraged; SIJ changes are unlikely to show up on radiographs, and decades of research have shown that early imaging not only fails to improve outcomes in patients with low back pain but also can often lead to unnecessary testing and more-aggressive treatment.
Initial treatment for SIJ pain is conservative. It includes measures such as physical therapy, exercise, weight loss, nonsteroidal anti-inflammatories, intra-articular steroid injections, and sometimes SIJ manipulation, massage, or a belt to compress and support the joint. Carefully selected patients who fail a six- to 12-month trial of these measures may be candidates for radiofrequency denervation procedures, which are associated with relief of SIJ pain. The duration of the relief is unknown, however, and some results have been difficult to reproduce.
SIJ arthrodesis may be considered for recalcitrant SIJ pain that has failed all other treatment options. The indications for performing the surgery are complex and depend on individual patient factors. Dr. Cross says his group is currently collecting data to identify the patients most likely to benefit from surgical intervention.
Fusion of the SIJ is defined as the presence of a continuous segment of solid bridging bone that extends from the sacrum to the ilium. Most fusions are currently performed using minimally invasive techniques that require a small lateral incision in the buttocks near the posterior iliac spine.
In this approach, the fascia is dissected to reach the outer table of the ilium, and a hand drill is used to create a pathway across the ilium and SI joint into the sacrum. Bony surfaces are debrided and decorticated with a deployable curet system, after which the debris is removed with irrigation. An autologous bone graft and bone graft extender are then percutaneously placed into the SIJ. An implant matched to the patient's anatomy is placed across the joint under fluoroscopic guidance to fully compress and stabilize the joint. In some cases, a second implant — an anti-rotation screw — may be used to enhance joint stability.
Many limitations of open surgery — relatively large incisions, significant bone harvesting, postoperative pain, and a lengthy hospital stay and postoperative recovery — may be eliminated with minimally invasive techniques.
"What sets this approach apart is that patients may have significant pain relief on day one," Dr. Cross says. "They walk with crutches or a walker for one to two weeks and are able to advance weight bearing as tolerated, whereas with open surgery, some patients may be kept in the hospital for several days and are non-weight-bearing for one to two months."
According to short-term data, some of which was obtained at Mayo Clinic, pain relief is durable for two years post-surgery; extended data collection is expected to show continued positive outcomes.
"Our goal is 100 percent return of quality of life," Dr. Cross says. "If people want to go back to playing tennis, they can do that. The SI joint only has one to two degrees of motion at most, so loss of motion is minimal. Furthermore, patients benefit greatly from our multimodal program that includes orthopedic surgeons, physiatrists, pain medicine specialists, physical and occupational therapists, and specialists in complementary medicine, such as acupuncture and biofeedback."
Dr. Cross says another unique advantage at Mayo Clinic's Rochester campus is that SIJ surgery is performed by a traumatologist, who has a unique background in iliosacral anatomy and a particular understanding of post-traumatic changes in the joint.
"I am a great proponent of trauma surgeons becoming involved in the management of chronic pathology of the SI joint because we have a unique ability to care for these patients and their complex anatomy. Here at Mayo, this has blossomed into a significant subspecialty practice," he says. "The ability to help these patients with their chronic pain and return a meaningful quality of life to them is the greatest feeling."