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 login to view 1 more bullet pain is hypothesized to be generated from login to view 7 more bullets intra-articular mechanisms arthritis login to view 5 more bullets infection login to view 11 more bullets metabolic login to view 8 more bullets tumors login to view 9 more bullets extra-articular mechanisms enthesopathy login to view 3 more bullets insufficiency fractures login to view 2 more bullets post-traumatic login to view 1 more bullet 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 login to view 1 more bullet loss of SI joint motion hinders the ability to dissipate forces complex motion at the SI joint: gliding rotation tilting nodding (nutation) login to view 3 more bullets 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 login to view 3 more bullets wearing a tight-fitting belt may relieve symptoms Physical exam inspection patients may have an antalgic gait palpation identify focal areas of tenderness login to view 2 more bullets motion evaluate hip and knee for underlying pathologies neurovascular in isolated SI joint dysfunction, patients are neurovascularly intact login to view 1 more bullet provocative tests overview login to view 2 more bullets Patrick's test (FABER) login to view 3 more bullets Fortin's finger test login to view 1 more bullet Gaenslen's test login to view 2 more bullets SI compression test login to view 3 more bullets anterior sacral thrust test login to view 3 more bullets SI distraction test login to view 3 more bullets straight leg raise login to view 4 more bullets Imaging Radiographs recommended views AP, lateral, internal oblique, external oblique, inlet, and outlet views of the pelvis login to view 1 more bullet flamingo views login to view 2 more bullets SI joint views AP, lateral, flexion, and extension views of the lumbar spine login to view 1 more bullet 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 login to view 2 more bullets 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 login to view 1 more bullet modalities login to view 15 more bullets outcomes login to view 3 more bullets SI joint corticosteroid injections indications login to view 1 more bullet outcomes login to view 4 more bullets radiofrequency ablation indications login to view 1 more bullet technique login to view 1 more bullet outcomes login to view 1 more bullet Operative open SI joint arthrodesis indications login to view 4 more bullets outcomes login to view 1 more bullet minimally invasive SI joint arthrodesis indications login to view 3 more bullets outcomes vs. open arthrodesis login to view 6 more bullets Techniques SI joint corticosteroid injections technique performed under fluoroscopy or ultrasound guidance login to view 1 more bullet 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 login to view 1 more bullet Open SI joint arthrodesis approach performed through a posterior approach login to view 1 more bullet 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