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Introduction
  • Vertebral osteomyelitis, also known as spondylodiskitis
  • Epidemiology
    • demographics
      • usually seen in adults (median age for pyogenic osteomyelitis is 50 to 60 years)
    • location
      • 50-60% of cases occur in lumbar spine
      • 30-40% in thoracic spine
      • ~10% in cervical spine
    • risk factors include
      • IV drug abuse
      • diabetes
      • recent systemic infection (UTI, pneumonia)
      • obesity
      • malignancy
      • immunodeficiency or immunosuppressive medications
      • malnutrition (serum albumin < 3 g/dL indicative of malnutrition)
      • trauma
      • smoking
  • Pathophysiology
    • pathogens
      • staph aureus
        • most common (50-65%)
      • staph epidermidis
        • is second most common cause
      • gram negative infections
        • increasing over last decade and often associated with gram negative infections of the GU and respiratory tract
      • pseudomonas
        • seen in patients with IV drug use
      • salmonella
        • seen in patients with sickle cell disease
    • inoculation
      • hematogenous seeding
        • generally agreed that inoculation likely occurs through hematogenous seeding (arterial or venous) of the endplates and intervertebral discs
          • endplates contain area of low-flow vascular anastomosis that may provide an environment suited for inoculation
          • involvement of one endplate leads to direct extension into intervertebral discs, followed by direct extension into the second endplate
      • direct inoculation
        • can occur after penetrating trauma, open fractures, and following surgical procedure
      • contiguous spread from local infection
        • most commonly associated with retropharyngeal and retroperitoneal abscesses
    • neurologic involvement
      • neurologic deficits present in 10-20%
      • results from
        • direct infectious involvement of neural elements
        • compression from an epidural abscess
        • compression from instability of the spine
  • Associated conditions
    • epidural abscess topic
      • defined as a collection of pus or inflammatory granulation tissue between dura mater and surrounding adipose tissue
      • epidemiology
        • usually associated with vertebral osteomyelitis
        • present in ~18% of patients with spondylodiskitis
        • 50% of patients with an epidural abscess will have neurologic symptoms
Presentation
  • History
    • history of UTI, pneumonia, skin infection, of organ transplant are common
  • Symptoms
    • fever is only present in 1/3 of patients
    • pain
      • pain is often severe and insidious in onset
      • pain is usually worse with activity and unrelenting in nature
      • pain that awakens patients at night should raise concern for malignancy and infection
    • neurologic symptoms present in 10-20%
      • radiculopathy
      • myelopathy
  • Physical exam
    • perform careful neurological exam
Imaging
  • Radiographs
    • findings are usually delayed by weeks
    • findings include
      • paraspinous soft tissue swelling (loss of psoas shadow)
        • seen if first few days
      • disc space narrowing and disc destruction
        • seen at 7-10 days 
        • remember disc destruction is atypical of neoplasm
      • endplate erosion or sclerosis seen at 10-21 days
      • local osteopenia
  • CT
    • useful to show bony abnormalities, abscess formation, and extent of bony involvement
  • MRI
    • MRI with gadolinium contrast 
      • indications
        • gold standard for diagnosis and treatment
      • sensitivity and specificity
        • most sensitive (96%) and specific (93%) imaging modality for diagnosis of spinal osteomyelitis
        • also most specific imaging modality to differentiate from tumor
      • findings include
        • paraspinal and epidural inflammation
        • disc and endplate enhancement with gadolinium
        • T2-weighted hyperintensity of the disk and endplate
          • rim enhancing
  • Bone scan
    • Technetium Tc99m bone scans
      • indications
        • patients who can not obtain an MRI
      • sensitivity and specificity
        •  90% sensitive but lack specificity
        • combined Technetium Tc99m and gallium 67 scan is both more specific and more sensitive than Technetium Tc99m alone
    • indium 111 labeled scan
      • not recommended due to poor sensitivity (17%)
Studies
  • Laboratory
    • WBC
      • elevated only in ~ 50%
      • not a sensitive indicator for early infection
    • ESR
      • elevated in 90% of cases
      • can be monitored serially to track success of treatment, however is considered less reliable than CRP
    • CRP
      • elevated in 90% of cases
      • can be monitored serially to track success of treatment and is considered more reliable than ESR
    • Blood cultures
      • identification of organism is mandatory for treatment
      • least invasive method to determine a diagnosis
      • sensitivity & specificity
        • ~33% (reports show 25%-66%) of patients with spondylodiskitis have positive blood cultures
        • when positive 85% are accurate for isolating the correct organism
        • blood culture yield is improved by withholding antibiotic and obtaining cultures when patient is febrile
  • CT guided biopsy
    • indications
      • in patients who do not have indications for immediate open surgery and blood cultures are negative  
    • sensitivity & specificity
      • can provide diagnosis in 68-86% of patients
    • technique
      • can be guided by fluoroscopy or by CT scan  
      • cultures should be sent for
        • aerobic
        • anaerobic
        • fungal
        • acid-fast cultures
  • Open biopsy
    • indications
      •  when tissue/organism diagnosis can not be made with noninvasive techniques
    • technique
      • anterior, costotransversectomy, or transpedicular approach used
Differential
  • Spinal Tumors
    • MRI is the most specific imaging modality to differentiate from tumor
      • features that weigh towards an infection include
        • disc space involvement
        • end-plate erosion
        • significant inflammation
  • Types of Spinal Osteomyelitis
    • Bacterial
    • Viral
    • Tuberculosis
    • Fungal 
Treatment
  • Nonoperative
    • bracing and long term antibiotic (6-12 weeks)
      • indications
        • most cases
      • bracing
        • helps improve pain and prevent deformity
        • rigid cervicothoracic orthosis or halo required for cervical osteomyelitis
      • antibiotics
        • indications
          • once organism has been identified via blood culture or biopsy 
          • if patient is septic or critically ill then start broad spectrum antibiotics immediately which include
            • vancomycin
              • for pencicillin-resistant and gram-positive bacteria
            • third-generation cephalosporin
              •  for gram-negative coverage
        • technique once organism has been identified
          • usually treated with IV culture directed antibiotics until signs of improvement (~ 4-6 weeks) and then converted to PO antibiotics
        • resistant strains
          • new antibiotic-resistant strains of microorganisms are becoming more common and failure to diagnose can have negative consequences
          • organisms include
            • MRSA (methicillin-resistant Staph aureus)
            • VRSA (vancomycin resistant Staph aureus)
            • VRE (vancomycin resistant enterococcus)
          • treatment
            • newer generation antibiotics for antibiotic resistant organisms include linezolid and daptomycin
      • outcomes
        • successful in 80%
  • Operative
    • neurologic decompression, surgical debridement, and spinal stabilization
      • indications
        • refractory cases
        • neurologic deficits
        • progressive deformity & gross spinal instability
      • technique
        • dictated by characteristics of pathology
          • anterior debridement and strut grafting, +/- posterior instrumentation
            • considered to be gold standard
          • posterior debridement and decompression alone
            • usually ineffective for debridement
            • may be indicated in some cases
Techniques
  • Anterior debridement and strut grafting, +/- posterior instrumentation
    • goals
      • identify organism
      • eliminate infection
      • prevent or improve neurologic deficits
      • maintain spinal stability
    • techniques
      • strut graft selection
        • autogenous tricortical iliac crest, rib, or fibula strut grafts have proven safe and effective in presence of acute infection
        • allograft being used with good results, but autogenous sources theoretically have better incorporation
        • a recent study showed improved deformity correction with titanium mesh cages filled with autograft (followed by posterior instrumentation)
      • instrumentation
        • spinal instrumentation in presence of active infection is controversial
          • some advocate I&D followed by staged instrumentation
          • some advocate a single procedure with bone graft and instrumentation in the presence of an active infection
        • titanium is preferred over stainless steel
      • posterior instrumentation
        • posterior instrumentation indicated when severe kyphotic deformity or a multilevel anterior construct required
        • posterior instrumentation can be performed at same time or as a staged procedure
 

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