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