Acute Osteomyelitis

• Age
  • Usually affects children
    • Septic arthritis more common in adults; osteomyelitis in children
• 
  Hallmark characteristics
  • Destruction of bone
  • Periosteal new bone formation
    
• Organisms
  • Newborns
    • S. aureus
    • Group B streptococcus
    • E. coli
  • Children
    • S. aureus
  • Adults
    • S. aureus (most common)
    • Enteric species
    • Streptococcus
  • Drug addicts
    • Pseudomonas (most common)
    • Klebsiella
  • Sickle cell disease
    • Salmonella
      
• Pathogenesis
  • Hematogenous spread
  • Direct implantation from a traumatic / iatrogenic source
  • Extension from adjacent soft-tissue infection
    
• Location
  • Lower extremity (most common)
    • Over pressure points in diabetic foot
  • Vertebrae
    • Lumbar  > thoracic > cervical
  • Radial styloid
  • Sacroiliac joint
    
    

ACUTE NEONATAL OSTEOMYELITIS

• Age
  • Onset <30 days of age
• Little or no systemic disturbance
• Multicentric involvement more common
  • Often joint involvement
• Bone scan falsely negative / equivocal in 70%

ACUTE OSTEOMYELITIS IN INFANCY 

• Age
  • <18 months of age
• Pathomechanism
  • Spread to epiphysis through blood vessels
• Marked soft-tissue component
• Subperiosteal abscess with extensive periosteal new bone formation
• Complications
  • Frequent joint involvement
• Prognosis
  • Rapid healing
     

• Age
  • 2-16 years of age
• Pathomechanism
  • Trans-physeal vessels closed
  • Primary focus of infection is in metaphysis
• Findings
  • Sequestration frequent
  • Periosteal elevation
  • Small single / multiple osteolytic areas in metaphysis
  • Extensive periosteal reaction parallel to shaft (after 3-6 weeks)
  • Shortening of bone with destruction of epiphyseal cartilage
  • Growth stimulation by hyperemia and premature maturation of adjacent epiphysis
    
    

ACUTE OSTEOMYELITIS IN ADULTHOOD

• Delicate periosteal new bone
• Joint involvement common
  • Septic arthritis
    
    
• X-ray findings
  
  
  • Initial radiographs often normal for as long as 7-10 days
  • Localized soft-tissue swelling adjacent to metaphysis with obliteration of usual fat planes (after 3-10 days)
  • Area of bone destruction (lags 7-14 days behind pathologic changes)

• Involucrum = cloak of laminated /spiculated periosteal reaction (develops after 20 days)
• Sequestrum = detached necrotic cortical bone (develops after 30 days)
• Cloaca formation = space in which dead bone resides
  
• MR findings
  • Bone marrow hypointense on T1WI + hyperintense on T2WI (= water-rich inflammatory tissue)
    
    
• DDx
  
  
  • Neuropathic osteoarthropathy
  • Aseptic arthritis
  • Acute fracture
  • Recent surgery
  • Ewing’s sarcoma
    
    
• Findings
  
  
  • Focal / linear cortical involvement hyperintense on T2WI
  • Hyperintense halo surrounding cortex on T2WI = subperiosteal infection
  • Hyperintense line on T2WI extending from bone to skin surface and enhancement of borders (= sinus tract)
• Nuclear Medicine (accuracy approx. 90%):
  • Ga-67 scans
    • 100% sensitivity
    • Increased uptake 1 day earlier than for Tc-99m MDP
  • Gallium helpful for chronic osteomyelitis
• Static Tc-99m diphosphonate
  • 83% sensitivity
  • 5-60% false-negative rate in neonates and children
    
    
• Complications of osteomyelitis
  
  
  • Abscess in soft-tissue
  • Fistula or sinus formation
  • Pathologic fracture
  • Extension into joint producing septic arthritis
  • Growth disturbance due to epiphyseal involvement
  • Severe deformity with delayed treatment

Osteomyeltis. Bone destruction of head of 2^nd metatarsal with periosteal new bone formation characteristic of osteomyelitis