Spinal Infections

Discitis

Epidemiology

  • All age groups but most common in children (mean age 7 years)

Location

  • Lumbar spine 50%
  • Thoracic 40%
  • Cervical 10%

Pathology

  • Haematogenous usually but may be by direct spread
  • Two theories of spread:
    • Batson’s Plexus – valvueless veins (older theory)
    • End-plate origin (more in vogue)
      • Endplates are highly vascular with low-flow vessels
      • Provide an ideal region for bacteria to proliferate
      • Spread occurs into the avascular disc directly
      • Low blood supply means bacteria are relatively protected

Organism

  • Staph Aureus most common
  • Gram-negative rods
  • Others

Risk Factors

  • Paediatric group
  • Diabetes, renal failure, HIV
  • Immunocompromise (suspect fungal organism)

Diagnosis

History
  • Back pain
  • Pain on weight-bearing
  • Fever – uncommon until later
Radiology
XR
  • Under 10-14 days are usually normal
  • Later changes include:
    • End plate erosion
    • Disc space narrowing
MRI
  • Diagnostic
  • Fluid within the disc in acute infection – bright on T2
  • Disc dark on T1
  • Abscess formation
  • Neural compromise
Blood Cultures
  • Isolate the organism in 60% of cases
  • Better chance before antibiotics and while temperature is raised

Management

  • Some advocate biopsy of the disc in all cases to isolate the correct organism
  • Most can be managed with antibiotics for 6-8 weeks
Indications for Surgery
  • Abscess formation
  • Poor response to antibiotics
  • Doubt over organism – biopsy required

Vertebral Osteomyelitis

Epidemiology

  • More common in older patients with systemic disease (diabetes, HIV, etc.)

Pathology

  • Same mode of spread as in discitis – haematogenous
  • Often associated with pneumonia or UTI
  • Originates in endplates
  • Spreads to vertebral bodies & disc – destroys both

Organism

  • Staph Aureus (75%)
  • Gram-negative bacteria
  • Beware fungal infections in HIV patients

Presentation

  • Unremitting spinal pain
  • Neurologic Symptoms – risk factors:
    • Disease in more cephalic levels
    • Older patients
    • Associated systemic disease

Diagnosis

  • Blood cultures
  • History
XR
  • Disc destruction – key differentiator from tumor
  • End-plate erosion
  • Vertebral collapse – kyphosis
  • Anterior disc & vertebra are affected first
  • Late changes but presentation often delayed so XR features may be seen
MRI
  • Disc & vertebral destruction
  • Abscess formation
  • Neural compression
  • Skip lesions

Management

  • Isolate the organism
  • Antibiotic therapy (6-8 weeks)
Indications for Surgery
  • Abscess
  • Spinal instability
  • Neurologic compromise
  • Failure to respond to antibiotics
Technique
  • Usually anterior approach, decompression, debridement, and fusion
  • Pathology is mainly anterior
  • Difficult to address adequately from the back
  • Use autograft struts
  • Supplementary posterior stabilization if multiple levels affected

Spinal Tuberculosis

  • Spine is the most affected area by TB after the lungs

Risk Factors

  • Immunocompromise
  • SE Asian origin or travel
  • Pulmonary TB

Specific Features

  • Discs tend to be spared
  • Focus starts in the metaphysis of the vertebral body
  • Infection spreads under ALL
  • Contiguous vertebrae affected
  • Skip lesions in 15%
  • Propensity for abscess formation
  • Sinus formation
  • Severe kyphotic collapse
  • Paraplegia (Pott’s disease)

Spinal Cord Injury in TB

  • Occurs due to:
    • Direct pressure from abscess (good prognosis)
    • Bony sequestration (good prognosis)
    • Meningomyelitis (poor prognosis)

Diagnosis

  • Classic XR & MRI features
  • Suspect if infection is not responsive to normal antibiotics
Biopsy
  • Tissue positive to Ziehl-Neelsen staining for Acid-Fast Bacilli
  • 80% of acute TB cases are positive to PPD skin test
    • 20% are negative, and some patients are anergic (don’t develop antigens)
    • Polymerase Chain Reaction (PCR) is best

Management

  • Multimodal drug therapy for up to 18 months
  • Isoniazid, Rifampicin, Pyrazinamide & Ethambutol/Streptomycin
Indications for Surgery
  • Severe kyphosis & spinal instability
  • Neurologic involvement
  • Abscess drainage
  • Biopsy for diagnosis
  • Non-responsive to medical therapy
    • May occur in avascular chronic TB
Surgical Techniques
  • Hong Kong Procedure
    • Anterior debridement & strut grafting (autogenous) without instrumentation
  • Combined anterior & posterior debridement & stabilization
    • For severe deformity & neurologic impairment

Epidural Abscess

Aetiology

  1. Secondary to discitis/vertebral infection
  2. Secondary to surgery – direct inoculation
  • Abscess is within the spinal canal and contained there
  • High risk of neurologic compression

Location

  • Thoracic > Lumbar > Cervical
  • Thoracolumbar abscesses are posterior, cervical abscesses tend to be anterior to the cord
  • Often involves 3 or more levels

Diagnosis

  • Patients tend to be sicker than with discitis
  • Neurologic signs may be present
MRI
  • T2 may show abscess
  • T1 post-contrast shows ring enhancement
  • Differentiates from other lesions within the canal

Management

  • Little place for non-operative treatment
  • Antibiotics alone are unable to penetrate abscess
  • Surgical drainage followed by 6-8 weeks of antibiotics for the underlying cause
Surgical Technique
  • Posterior approach via laminectomy to access the abscess
  • If anterior, use an anterior approach
  • If secondary to osteomyelitis/discitis, debride these areas while there
  • Stabilize spine if wide debridement performed, otherwise not necessary
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