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Introduction
  • An systemic chronic autoimmune spondyloarthropathy characterized by
    • HLA-B27 histocompatability complex positive (90%) 
    • RF negative (seronegative)
    • primarily affect axial spine
  • Pathoanatomy
    • exact mechanism is unknown, but most likely due to an autoimmune reaction to an environmental pathogen in a genetically susceptible individual.
    • theories of relation to HLA-B27 include
      • HLA-B27 aggregates with peptides in the joint and leads to a degenerative cascade
      • cytotoxic T-cell autoimmune reaction against HLA-B27
    • enthesitis
      • entheses inflammation leads to bony erosion, surrounding soft-tissue ossification, and eventually joint ankylosis
      • preferentially targets sacroiliac joints, spinal apophyseal joints, symphysis pubis
      • this differentiates from RA, which is a synovial process
    • disc space involvement
      • inflammation of the annulus lead to bridging osteophyte formation (syndesmophytes)
  • Genetics
    • there is a genetic predisposition, but mode of inheritance is unknown
    • HLA-B27 is located on sixth chromosome, B locus
  • Epidemiology
    • 4:1 male:female
    • affects ~0.2% of Caucasian population
    • usually presents in 3rd decade of life
      •  juvenile form <16-years-old includes enthesitis 
      • fewer than 10% of HLA-B27 positive patients have symptoms of AS
  • Diagnostic criteria 
    • bilateral sacroiliitis
    • +/- uveitis
    • HLA-B27 positive 
  • Systemic manifestations
    • acute anterior uveitis & iritis
    • heart disease (cardiac conduction abnormalities)
    • pulmonary fibrosis
    • renal amyloidosis
    • ascending aortic conditions (aortitis, stenosis, regurgitation)
    • Klebsilella pneumoniae synovitis
      • HLA-B27 individuals are more susceptible to Klebsilella pneumoniae synovitis
  • Orthopaedic manifestations
    • bilateral sacroiliitis
    • progressive spinal kyphotic deformity
    • cervical spine fractures
    • large-joint arthritis (hip and shoulder)
Anatomy
  • Enthesis
    • defined as the insertion of tendon, ligaments, or muscle into bone
Presentation
  • Symptoms
    • lumbosacral pain and stiffness
      • present in most patients
      • worse in morning
      • insidious onset in 3rd decade of life
    • neck and upper thoracic pain
      • occurs later in life
      • acute neck pain should raise suspicion for fracture
    • sciatic
      • likely originates from sciatic nerve involvement in the pelvic (piriformis spasm)
    • loss of horizontal gaze
    • shortness of breath
      • caused by costovertebral joint involvement, leading to reduced chest expansion
  • Physical exam
    • limitation of chest wall expansion
      • < 2cm of expansion is more specific than HLA-B27 for making diagnosis
    • decreased spine motion
      • Schober test
        • used to evaluate lumbar stiffness
    • kyphotic spine deformity
      • chin-on-chest (flexion) deformity of the spine 
      • caused by multiple microfractures that occur over time
      • chin-brow-to-vertical angle (CBVA)  
        • measured from standing exam of standing lateral radiograph
        • useful for preoperative planning
        • correction of this angle correlates with improved surgical outcomes
    • hip flexion contracture
      • examining patient in supine and sitting position helps differentiate sagittal plane imbalance due to hip flexion contractures or kyphotic spinal deformity
    • sacroiliac provocative tests
      • Faber test
        • flexion abduction external rotation of the ipsilateral hip causes pain
Imaging
  • Radiographs
    • spine
      • recommended views
        • standing full-length AP and lateral of axial spine
      • findings
        • negative in 50% of cases with spine fractures
        • squaring of vertebrae with vertical or marginal syndesmophytes 
        • late vertebral scalloping (bamboo spine)
      • measurements
        • chin-brow to vertical angle
          • used to measure chin-on-chest deformity
          • useful for preoperative planning for osteotomy
    • pelvis & lower extremity
      • recommended views
        • Ferguson pelvic tilt view
          • allows for improved visualization of anterior SI joint
          • xray beam directed 10 to 15 degrees cephalad
      • findings
        • bilateral symmetric sacroiliac erosion 
          • earliest radiographic sign is erosion of iliac side of sacroiliac joint
        • joint space narrowing
        • ankylosis
  • CT
    • will show bony changes but not active inflammation  
    • CT is most sensitive test to diagnose cervical fractures in patients with AS 
  • MRI
    • will detect inflammation, making it the best modality for early detection of AS in young patients
    • obtain with cervical fractures to look for epidural hemorrhage
  • Bone scan
    • will show inflammation in the sacroiliac joints, but lacks specificity
Studies
  • Labs
    • little diagnostic value
    • often see nonspecific elevations in ESR and CRP
  • Diagnostic Injections
    • SI joint injection
      • local anesthetic injected into SI joint under fluoroscopic guidance
      • often most sensitive diagnostic test
Differentials
   DISH Ankylosing spondylitis
Syndesmophytes Nonmarginal   Marginal
Radiographs "Flowing candle wax" "Bamboo spine", squaring of vertebral bodies, "shiny corners" at attachment of annulus fibrosus (Romanus lesions)  
Disc space Preservation of disc space   AS in cervical spine will show ossification of disc space 
Osteopenia No osteopenia (rather, there may be increased radiodensity)
Osteopenia present
HLA

No evidence of association with HLA-B27
Associated with HLA-B8 (common in patients with DISH and diabetes)

Strong association with HLA-B27
Age group Older patients (middle aged) Younger patients
SI joint involvement No involvement (SI joint abnormality generally excludes diagnosis of DISH) Bilateral sacroiliitis
Diabetes Yes No
 
Treatment General
  • Nonoperative
    • NSAIDS, COX-2 inhibitors, and therapy
      • indications
        • first line of treatment for pain and stiffness
        • oral steroids not recommended
      • techniques
        • physical therapy should focus on maintaining flexibility
    • TNF-alpha-blocking agents  
      • indications
        • second line of medical management
      • techniques
        • includes infliximab, etanercept, adalimumab
      • outcomes
        • clinical studies show significant improvement in severity of symptoms
  • Operative 
    • see below
Spine Fractures
  • Introduction
    • most occur in midcervical and cervicothoracic junction (some occur at thoracolumbar junction)
    • often extension-type fracture that involved all three columns  
    • may be occult so if suspicious consider CT scan (best modality to make diagnosis)
    • high mortality rate secondary to epidural hemorrhage
      • 75% neurologic involvement
      • neurologic symptoms often present late
  • Treatment
    • nonoperative
      • traction, orthotic or halo immobilization
        • indications
          • stable spine fractures with no neurologic deficits
        • technique
          • low-weight traction may facilitate reduction
    • operative
      • spinal decompression with instrumented fusion 
        • indications
          • progressive neurologic deficit
          •  epidural hematoma with neurologic compromise  
          • unstable fracture patterns  
        • technique
          • decompression
            • decision to go anterior or posterior depends on fracture level, presence and location of hematoma, and osteoporosis
          • instrumentation 
            • need to obtain long fusion construct
            • multiple points of fixation above and below the fracture are necessary because of
              • osteoporosis
              • long lever arms of the ankylosed spine
            • do not make an effort to correct deformity
        • outcomes & complications
          • high rate of complications including
            • progressive deformity
            • nonunion
            • hardware failure
            • infection
Spinal Deformity
  • Introduction
    • usually a kyphotic deformity of upper spine
    • be sure to eliminate hip contractures as reason for deformity
  • Treatment
    • lumbar osteotomy 
      • indications
        • thoracolumbar kyphotic deformity
      • goals
        • goal is to restore sagittal balance and horizontal gaze
      • techniques
        • closing wedge (pedicle subtracting) osteotomy  
          • transpedicular decancelization procedure with removal of posterior elements
          • location of osteotomy determined by type of spine flexion deformity
          • hinge located on anterior vertebral body
          • considered procedure of choice due to
            • greater deformity correction (30 t0 40 degrees per level)
            • better fusion and stability due to direct bony apposition
        • vertebral body resection   
          • entire vertebral body is removed and replaced with a cage 
        • single-level opening wedge osteotomy
          • hinges on posterior edge of vertebral body
          • requires rupture of ALL
        • multi-segment opening osteotomy
          • advantage of less bone loss and preservation of ALL by distributing correction over multiple levels
      • outcomes & complications
        • lumbar approach avoids complications of thoracic cage, spinal cord injury, and has potential for greater correction due to long lever arm
    • C7-T1 cervicalthoracic osteotomy  
      • indications
        • cervicothoracic kyphotic (chin-on-chest) deformity
      • goals
        • slight under-correction with final brow-to-chin angle of 10 degrees
      • technique
        • osteotomy
          • advantage of  C7-T1 osteotomy include
            • vertebral artery is external to transverse foremen
            • larger canal diameter
          • requires wide decompression with removal of C7 lateral mass and portions of C7-T1 pedicles to prevent iatrogenic SCI
        • instrumentation
          • usually a combination of lateral mass screws, pedicle screws, and sublaminar hooks
      • postoperative
        • postoperative halo immobilization often required in patients with poor bone quality
      • outcomes & complications
        • increased risk of venous air embolus (VAE) in the sitting operative position 
Large-Joint Arthritis
  • Introduction
    • asymmetric involvement of large joints
    • shoulder and hip most commonly involved
  • Treatment
    • total hip replacement
      • indications
        •  in patients with severe arthritis of this hips secondary to AS
      • technique
        • patients have more vertical and anteverted acetabulum (may lead to anterior dislocations after total hip arthroplasty)
    • bilateral total hip arthroplasty
      • indications
        • kyphotic deformity due to hip flexion contracture deformity
      • outcomes & complications
        • at risk for dislocation
 

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