summary Sacroiliac joint dysfunction is a degenerative condition of the sacroiliac joint resulting in low back pain Diagnosis is made clinically based on pain just inferior to the posterior superior iliac spine that is worsened with hip flexion, abduction, and external rotation Treatment is usually conservative with pain management, physical therapy, and injections. Surgical management is indicated in patients with progressive symptoms who fail nonoperative management Epidemiology Incidence frequently overlooked and can explain up to 15-30% of cases of lower back pain in the outpatient setting Risk factors previous lumbar spine fusion especially when >3 levels are involved considered analogous to adjacent segment disease pregnancy and vaginal delivery previous trauma to the pelvis prior iliac crest bone graft harvesting Etiology Pathophysiology idiopathic causes are most common believed to result from repetitive trauma to the SI joint can present insidiously or acutely pain is hypothesized to be generated from ligamentous/capsule tension extrinsic compression or shear forces hypomobility or hypermobility increased levels of estrogen or relaxin during the third trimester of pregnancy can lead to hypermobility of the SI joint aberrant joint mechanics myofascial or kinetic chain imbalances inflammation intra-articular mechanisms arthritis inflammation and degeneration of the SI joint occurs in nearly 100% of patients with spondyloarthropathies ankylosing spondylitis Reiter's syndrome results in subchondral sclerosis, subchondral cysts, osteophytes, joint space narrowing, intra-articular gas, and ankylosis infection usually the result of hematogenous spread typically unilateral involvement organisms: Staphylococcus aureus Pseudomonas aeruginosa Cryptococcus species Mycobacterium tuberculosis predisposing factors: immunosuppression endocarditis IV drug use metabolic leads to early degeneration of the joint diseases: calcium pyrophosphate crystal deposition gout ochronosis hyperparathyroidism renal osteodystrophy acromegaly tumors primary very rare most common types: giant cell tumor villonodular synovitis chondrosarcomas secondary (metastatic) most common pelvis accounts for 40% of all osseous metastases (secondary to spine) extra-articular mechanisms enthesopathy inflammation of the ligamentous attachments to the SI joint frequently occurs with spondyloarthropathies more frequently involves the posterior ligaments insufficiency fractures osteoporotic fractures in elderly patients repetitive trauma in athletes and military recruits post-traumatic more common after lateral compression pelvic ring injuries Genetics HLA-B27 associated with ankylosing spondylitis Associated conditions orthopaedic conditions lumbar spinal fusion post-traumatic arthritis metastatic tumors medical conditions & comorbidities ankylosing spondylitis gout pseudogout infections Anatomy Osteology articulation of the ilium and the sacrum largest axial joint in the body considered synovial, even though the superior 75% is nonsynovial joint surface area is approximately 17.5 cm² articular surface changes with age flat until puberty by 30 y/o, ridges form on the iliac articular surface synovial surface begins to erode by 50 y/o ankylosis is common in men by 50 y/o Muscles gluteus maximus fibrous extensions that attach to the anterior and posterior joint capsule attachments to the sacrotuberous ligament gluteus medius erector spinae latissimus dorsi biceps femoris attachments to the sacrotuberous ligament oblique and transverse abdominis Ligaments anterior joint capsule and ligaments relatively thin posterior interosseous ligament forms the posterior border of the joint capsule usually a rudimentary or absent posterior joint capsule sacrotuberous ligament attaches from the anterior sacrum and SI joint to the ischial tuberosity sacrospinous ligament attaches from the anterior sacrum and SI joint to the ischial spine Innervation anterior innervation L2-S2 ventral rami and sacral plexus posterior innervation L4-S4 dorsal rami Biomechanics SI joint functions as a triplanar shock absorber dissipates loads of the upper trunk and facilitates parturition can withstand a medially directed load 6x greater than that of the lumbar spine fails at one-twentieth the axial load tolerated by the lumbar spine sacral compression with weight bearing creates "keystone in arch" effect muscles with fibers perpendicular to the SI joint also generate compression loss of SI joint motion hinders the ability to dissipate forces complex motion at the SI joint: gliding rotation tilting nodding (nutation) most common form of motion described as the backward rotation of the ilium on the sacrum counternutation is the forward rotation of the ilium on the sacrum translation joint motion is limited to <4° of rotation and 1.6 mm of translation motion of the joint progressively decreases with age 40-50 y/o for men >50 y/o for women Presentation Symptoms pain patterns pain is usually present just inferior to the posterior superior iliac spine frequently overlaps with referred pain patterns from other spinal pathologies only 4% of patients report pain above L5 can radiate past the knee and into the foot wearing a tight-fitting belt may relieve symptoms Physical exam inspection patients may have an antalgic gait palpation identify focal areas of tenderness sacral sulcus (most tender location) posterior superior iliac spine (second most tender location) motion evaluate hip and knee for underlying pathologies neurovascular in isolated SI joint dysfunction, patients are neurovascularly intact pain-inhibited weakness may be present provocative tests overview based on a battery of tests, no single provocative test has 100% diagnostic accuracy >3 positive tests highly suggestive Patrick's test (FABER) also called flexion, abduction, and external rotation test (FABER) patient will report pain in the SI joint with this maneuver groin pain suggests iliopsoas tendinitis or internal hip pathology Fortin's finger test considered positive if patient localizes pain twice to the region inferomedial to the PSIS Gaenslen's test performed with the affected hip extended off the examination table and the contralateral hip and knee flexed and held by patient shearing across SI joint causes pain SI compression test performed with the patient in the lateral decubitus position medially directed force is applied over the iliac crest on the affected side reproduction of pain is considered positive anterior sacral thrust test performed with patient positioned prone anteriorly directed force is applied to the sacrum test is considered positive if pain is reproduced in the SI joint SI distraction test performed with patient positioned supine posteriorly directed force is applied over the ASIS test is considered positive when pain is reproduced in the SI joint straight leg raise used to detect radiculopathy due to herniated disc usually negative in the setting of SI joint dysfunction may be positive if the leg is brought above 60° of elevation caused by increased SI joint motion at this level of elevation Imaging Radiographs recommended views AP, lateral, internal oblique, external oblique, inlet, and outlet views of the pelvis exclude other pelvic pathology flamingo views indicated when there is suspicion of pelvic instability alternating single-leg standing radiographs of the pelvis SI joint views AP, lateral, flexion, and extension views of the lumbar spine to identify other spinal pain generators findings joint space narrowing subchondral sclerosis subchondral cysts osteophytes ankylosis sensitivity and specificity up to 25% of asymptomatic patients over the age of 50 will have abnormal SI joints on radiographs CT indications deformity correction or surgical intervention is planned views pelvis and sacrum sagittal and coronal views 3D reconstructions poor diagnostic power compared to SI joint injections MRI indications exclude other diagnoses identification of tumors, infectious processes, or soft tissue components Bone scan indications studies have reported on the predictive value of SI joint pathology with SI joint injections sensitivity and specificity specificity 90% sensitivity 12% positive predictive value 86% negative predictive value 72% Differential Key differential diagnoses (top 5) lumbar spinal stenosis degenerative disc disease hip osteoarthritis hip labral tear lumbar disc herniation Treatment Nonoperative oral medication, physical therapy, pelvic belt, and prolotherapy indications first line modalities oral medications NSAIDs to reduce the inflammatory process associated with pain opioid medications should be used sparingly minimum 4-week trial of nonoperative modalities before proceeding with SI joint injection physical therapy +/- hot/cold therapy focuses on core muscle strengthening, proprioception, and flexibility to correct lumbopelvic and hip biomechanics pelvic belt belt applies medially directed force to the greater trochanters 4-8 inch-wide belt applied around the greater trochanters external device that mimics the function of ligaments limits the motion and shear forces across the SI joint by providing compression prolotherapy (controversial) phenol or glucose-based solutions injected at the base of ligamentous complexes to induce scarring generates an inflammatory response resulting in fibroblastic migration and resultant scar tissue that stabilizes the joint outcomes most effective in the acute phase of pain pelvic belt more effective for SI joint pain following pregnancy prolotherapy more effective in the setting of ligamentous laxity SI joint corticosteroid injections indications second line outcomes 60% success rate for pain relief at 6 months >75% reduction in SI joint pain following a single injection is considered confirmatory of the diagnosis >50% reduction in SI joint pain following two injections lower success rate in patients with previous lumbar fusion radiofrequency ablation indications third line technique targets lateral branches of the sacral nerve roots outcomes efficacy is limited due to the inability to denervate the anterior neural structures of the SI joint Operative open SI joint arthrodesis indications confirmed diagnosis of SI joint dysfunction as the primary pain generator poor response to nonoperative treatment options patients with aberrant SI anatomy, sacral dysmorphism, or revision surgery previously infection was the only indication for arthrodesis outcomes recent literature reports favorable outcomes in appropriately selected patients minimally invasive SI joint arthrodesis indications confirmed diagnosis of SI joint dysfunction as primary pain generator poor response to nonoperative treatment normal SI joint anatomy outcomes vs. open arthrodesis shorter hospital stay smaller incision theoretical decrease in surgical site infections decreased limitation of postoperative weight bearing quicker return to full weight bearing than open arthrodesis decreased blood loss Techniques SI joint corticosteroid injections technique performed under fluoroscopy or ultrasound guidance studies have shown that without imaging guidance, the injection reaches the SI joint only 22% of the time can be used as both a diagnostic and therapeutic injection no more than 3 injections in a 6-month period or 4 injections in 1 year Radiofrequency ablation technique targets lateral branches of the sacral nerve roots dorsal nerve ramus ablation L5-S3 dorsal rami innervate the SI joint Open SI joint arthrodesis approach performed through a posterior approach anterior approach is limited by vital neurovascular structures technique cartilage is removed and bone graft is packed into the obliterated space stabilized with a posterior plate and screws, iliosacral screws, or cage construct protected weight bearing for 12 weeks following surgery Minimally invasive SI joint arthrodesis approach percutaneous placement of implants technique newer techniques involve triangular titanium porous coated implants "fusion" occurs by bone growth onto the implant rather than direct fusion of the joint requires multiple implants placed across the SI joint to achieve stability complications patients with sacral dysmorphism have a higher risk of iatrogenic nerve injury Complications Surgical site infections risk factors immunocompromised smoking diabetes Wound complications risk factors open surgical technique (wound is located in the dependent position) Nerve injury risk factors minimally invasive technique sacral dysmorphism injury to the L5, S1, or S2 nerve roots Pseudoarthrosis occurs in up to 5% of cases revision arthrodesis may require open surgical technique Prognosis Natural history of disease quality of life in patients with SI joint dysfunction is more adversely affected than that of patients with chronic obstructive pulmonary disease and mild heart failure impact is equivalent to that experienced by patients with hip and knee arthritis