Updated: 2/29/2020

Sacroiliac Pain and Dysfunction

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Introduction
  • Overview
    • a degenerative condition of the sacroiliac joint resulting in lower back pain
      • can explain up to 15% to 30% of cases of lower back pain in the outpatient setting
    • quality of life is more affected than patients with chronic obstructive pulmonary disease and mild heart failure
      • equivalent to patients with hip and knee arthritis
    • treatment
      • treatment is generally conservative, with SI joint arthrodesis reserved for patients who fail physical therapy, SI joint injections, radio frequency nerve ablation
  • Epidemiology
    • 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
  • 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 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
  • Prognosis
    • natural history of disease
    • prognostic variable
      • favorable
      • negative
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 
      • based on a battery of tests, no single test has 100% diagnostic accuracy 
        • >3 positive tests is highly suggestive of the diagnosis
      • 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
      • Patrick's test 
        • 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
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 when 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
      • up to 25% of asymptomatic patients over the age of 50 will have abnoraml SI joints in radiographs
    • sensitivity and specificity
  • 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
    • views
      • axial, sagittal, and coronal views
  • 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
    • herniated nucleus pulposus
Treatment
  • Nonoperative
    • Oral medication, physical therapy (+/- hot/cold therapy), pelvic belt, and prolotherapy
      • indications
        • first line of treatment
      • 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 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 of the lateral branches of the sacral nerve roots
      • indications
        • third line of treatment
      • 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
        • no presence of infection
      • outcomes
        • 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
  • Oral medication
    • technique
      • 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)
    • technique
      • treatment focuses on addressing core muscle strengthening, proprioception, and flexibility to correct lumbopelvic and hip biomechanics
  • Pelvic belt 
    • technique
      • 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
    • technique
      • 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
  • SI joint 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 of the lateral branches of the sacral nerve roots
    • technique
      • 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
 

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