summary Sacroiliac Joint Dysfunction is a degenerative condition of the sacroiliac joint resulting in lower back pain. Diagnosis is made clinically with pain just inferior to the posterior superior iliac spine that is made worse 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 is frequently overlooked and can explain up to 15% to 30% of cases of lower back pain in the outpatient setting Risk factors previous lumbar spine fusion especially when there is >3 levels 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 mechanism is the most common believed to be a result of repetitive trauma to the SI joint can begin insidiously or acutely pain is hypothesized to be generated from ligamentous/capsule tension extraneous compression or shear forces hypomobility or hypermobility increased levels of estrogen or relaxin during third trimester of pregnancy leading 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 ankyklosing spondylitis Reiter's syndrome results in subchondral sclerosis, subchondral cyts, osteohytes, joint space narrowing, intra-articular gas and ankylosis infection usually the result of hematogenous spread typically unilateral involvement organisms: Staphylococcus aureus Pseudomonas aeruginosa Cryptococcus organisms Mycobacterium tuberculosis predisposing factors: immunosuppression endocarditis IV drug abuse metabolic leads to early degeneration of the joint diseases: calcium pyrophosphate crystal deposition gout ochronosis hyperparathyroidism renal osteodystrophy acromegaly tumors primary very rare for SI joint most common types: giant cell tumor synovial villoadenomas chondrosarcomas secondary (metastatic) most common pelvis accounts for 40% of all oseous metastasis (2nd to spine) extra-articular mechanisms ethesopathy inflammation of the ligamentous attachements to the SI joint frequently occurs with spondyloarthropathies more frequently the posterior ligaments insufficency 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 anklyosing 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 not synovial joint surface area of 17.5 cm^2 articular surface changes with age flat until puberty by age 30 ridges form on the the iliac articular surface synovial surface begins to erode by age 50 ankylosis is common in men by age 50 Muscles gluteus maximus has fibrous extensions that attach to the anterior and posterior joint capsule has attachments into the sacrotuberous ligament gluteus medius erector spinae latissimus dorsi biceps femoris has attachments to the sacrotuberous ligament oblique and transverse abdominus Ligament anterior joint capsule and ligaments are relatively thin posterior interosseous ligament forms the posterior border of the joint capsule there is usually a rudimentary or absent posterior joint capsule sacrotuberous ligament attaches from the anterior sacrum and SI joint to the ishcial 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 faciliates parturition can withstand a medial directed load six times greater than the lumbar spine fails in 1/20th the axial load of the lumbar spine sacral compression with weightbearing results creates "keystone in arch" effect muscles with fibers perpendicular to SI joint also generate compression loss of SI joint motion hinders 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 rotaton 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 decreased with age age 40-50 for men greater than 50 for women Presentation Symptoms pain patterns pain usually present just inferior to the posterior superior iliac spine frequent pain referral area of other spine pathologies only 4% of patients will complain of pain above L5 can radiate past the knee and into the foot wearing a tight fitting belt may improve 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 test has 100% diagnostic accuracy >3 positive tests is highly suggestive of the diagnosis 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 tendonitis or internal hip pathology Fortin's finger test considered positive if patient localizes pain twice to region inferomedial to PSIS Gaenslen's test performed with the affected side hip extended off examination table and unaffected side hip and knee flexed and held by patient shearing across SI joint causes pain SI compression test performed with patient laying lateral on exam table medial directed force applied over the iliac crest on the affected side reproduction of pain is considered positive anterior sacral thrust test performed with patient positioned prone on the examination table anteriorly directed force is applied to the sacrum test is considered positive if pain is reproduced in the SI joint SI distraction test with the patient supine on the examination table a posteriorly directed force 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 setting of SI joint dysfunction may be positive if leg 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 to rule out other pelvic pathology flamingo views indicatedwhen there is suspicion of pelvic instability alternating single leg standing films 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 abnoraml SI joints in radiographs CT indications has poor diagnostic power compared to SI joint injections deformity correction or surgical intervention is planned views pelvis and sacrum sagittal and coronal views 3D reconstructions MRI indications done to exclude other diagnoses identification of tumors, infectious process, or soft tissue components Bone scan indications studies have reported on the predictive power of SI joint pathology with SI joint injections sensitivity and specificity specificity - 90% sensitivity - 12% positive predictive value - 86% negative predictive valuae - 72% Differential Key differential (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 of treatment modalities oral medications mainly involve NSAIDS to reduce inflammatory process associated with pain opioid medications should be used sparingly minimum of 4 week of non-operative modalities trial before proceeding with SI joint injection physical therapy +/- hot/cold therapy treatment focuses on addressing core muscle strengthening, proprioception, and flexibility to correct lumbopelvic and hip biomechanics pelvic belt belt that applies medial directed force on greater trochanters 4 to 8 inch wide belt that is 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 inflammatory response resulting in fibroblastic migration and resultant scar that stabilizes 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 of treatment outcomes 60% success rate in pain relief at 6 months >75% reduction in SI joint pain following a single injection is 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 of treatment technique targets lateral branches of the sacral nerve roots outcomes efficacy is limited due to the inability to denervate the anterior neural structues of the SI joint Operative open SI joint arthrodesis indications confirmed diagnosis of SI joint dysfunction as 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 new literature with 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 shorter hospital stay smaller incision theoretical decrease in surgical site infections decreased limitation of postoperative weightbearing quicker return to full weightbearing than open arthrodesis decreased blood loss Techniques SI joint corticosteroid injections technique performed under fluoroscopy or ultrasound guidance studies have shown that without imaging the injection is in 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 perior 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 SI joint Open SI joint arthrodesis approach performed through posterior approach (anterior is limited by vital neurovascular structures) technique cartilage is removed and bone graft is packed into the obliterated space stabilized with posterior plate and screws, iliosacral screws, or cage construct made 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 SI joint to achieve stability complications patients with a dysmorphic sacrum 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 with open surgical technique Prognosis Natural history of disease quality of life of patients with SIS is more affected than patients with chronic obstructive pulmonary disease and mild heart failure equivalent to patients with hip and knee arthritis