Osteomyelitis

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  • Definition: Inflammation of the bone & marrow
  • Challenging to treat
    • less choice of effective antibiotics
    • less penetrance of antibiotics into the bone
    • infection will lead to disability/morbidity!
      • viruses
      • bacteria
      • parasites
      • fungi

2 types of osteomyelitis

  • Pyogenic osteomyelitis (Acute)
    • Infection reach bone by
      • Hematogenous spread (most common)
      • Extension from contiguous site
      • Direct implantation
    • Microorganisms
      • Staphylococcus Aureus (most common)
      • UTI & IV drug abusers
        • E. Coli
        • Pseudomonas
        • Klebsiella
      • Haemophilus influenza
        • children
      • Salmonella
        • sickle cell anemia
    • Pathophysiology
      • On Location:
        • infection reaches metaphysis
        • bacteria proliferates
          • causing bone death
            • Sequestrum: piece of dead bone
          • bone necrosis
        • sub-periosteal abscess formation
          • lifts the periosteum
          • further impair the blood supply
        • Rupture of Periosteum
          • abscess in surrounding soft tissue
        • Sinus formation
          • to drain fluid
      • Host response:
        • Release cytokines from leukocytes
          • stimulate osteoclastic bone resorption
        • Fibrous tissue formation
          • Reactive bone deposition in periphery
          • Forms a sleeve of new viable bone
            • Involucrum: new bone
    • Clinical course
      • Acute systemic illness
        • Pain
        • Tenderness
        • Immobility
      • Xray
        • Lytic focus of bone destruction
        • Followed by zone of sclerosis
      • Blood culture
        • can be +ve
      • Biopsy
        • invasive
        • confirms the diagnosis
    • Complications
      • Pathological fracture
      • Secondary amyloidosis
      • Endocarditis
      • Sepsis
      • Sinus tract squamous cell carcinoma (rare)
      • Epiphyseal infection
        • Joint cartilage is rigid
          • last to get infected
        • infection spreads to articular surface
        • spreads to joint capsule
          • suppurative/septic arthritis
        • lead to extensive destruction of articular cartilage
          • permanent disability
  • Mycobacterial/Tuberculous osteomyelitis (Chronic)
    • 1-3% of TB cases
    • Infection sites:
      • Ribs
        • direct involvement
      • Vertebrae
        • from lymphatic drainage
        • common in thoracic & lumbar vertebrae
    • Spine TB: Pott’s spine
      • Infection breaks through intervertebral disc
        • involve vertebrae & soft tissue
        • forming abscesses
    • Complications
      • Psoas abscess formation
      • Compression fracture
        • of the vertebrae
      • Scoliosis or kyphosis
      • Spinal cord compression
        • neurological deficits
      • TB arthritis
      • Abscess
        • Sinus tract formation

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Bone tumours

  • Rare
    • 40% malignant
  • Aetiology
    • No obvious cause (usually)
    • Ionising radiation
    • Predisposing conditions:
      • Paget’s disease
      • Fibrous dysplasia
      • Retinoblastoma
        • genetic
      • Syndromes
        • Gardner’s
        • Ollier’s disease

Category/Classification

  • Primary
    • Bone-producing tumours
      • Osteoid osteoma
      • Osteoblastoma
        • paediatric
      • Osteosarcoma*
    • Cartilage-producing tumours
      • Osteochondroma*
      • Chondroma (enchondroma)
      • Chondrosarcoma*
    • Miscellaneous tumors
      • Ewing’s sarcoma*
      • Giant cell tumor of bone*
  • Secondary
    • Metastases

  • Tumour-like bone tumour (mimicry)
    • Bone cysts
      • Simple bone cyst
      • Aneurysmal bone cyst
    • Fibrous-osseous lesion
      • Fibrous dysplasia
    • Eosinophilic granuloma
      • Langerhans histiocytosis

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Primary (more common in the young)

Osteosarcoma

 


Codman’s triangle & Sunburst appearance in Osteosarcoma

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Osteosarcoma – spread towards cortex

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Osteosarcoma – Lacy osteoid

  • Because bone is a CT
  • most common primary tumour
  • young adults (10-25 yo)
  • rare in later age, due to secondary causes
  • Genetic
    • mutations to RG gene
  • Morphology
    • Location
      • metaphysis of long bone
        • around knee
          • tibia, fibula
      • In old age
        • flat & long bones
      • Anatomical portion of bone
        • Intramedullary
          • most common
          • tumour can break through cortex
        • Intracortical
        • Surface
          • good prognosis
    • Gross
      • Form bulky tumours
        • Gritty, gray white, yellowish mass
      • Invasion to surrounding tissues
      • Infiltrate the medullary canal & spread towards cortex
        • epiphyseal penetration is rare
      • Joint invasion
        • later stages
    • Microscopy
      • Tumour cells are osteoblastic cells
        • histologic variants:
          • osteoblastic
          • chrondroblastic
          • small cell
      • Formation of lacy osteoid by tumour cells
      • Variation in size, shape
        • bizarre features
        • Tumour giant cells
      • Hyperchromatism
      • Mitiosis
      • Binucleation
      • Vascular & blood vessels invasion
    • Xray
      • large destructive mass lesion
      • mixed lytic & sclerotic areas
      • Elevation of periosteum
        • Codman’s triangle
      • Sunburst appearance
        • spread of tumour into surrounding soft tissue

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Osteochondroma

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  • Cartilage covered by bony excrescense (exostosis)
    • formation of new bone on surface of bone
  • Can be solitary or multiple
  • Spontaneous
  • Location
    • metaphysis
    • diaphysis
  • Morphology
    • painless skeletal swelling
    • slowly growing mass
      • palpable bony masses
  • Complications
    • can lead to limb shortening
      • when bone is still actively growing
      • 1st – 2nd decade of life
    • fractures
    • bone deformities
    • neurologic/vascular injuries
    • bursa formation
    • malignant transformation
      • rare
  • Osteochondromatosis
    • autosomal dominant condition
      • short stature
      • multiple osteochondroma
        • located close to metaphysis
        • sessile or pedunculated
        • cortex of lesion continuous with cortex of bone
          • with a homogenous continuation of the medulla
      • asymmetric growth
        • knees
        • ankles
      • may lead to deformities

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Chondrosarcoma

 

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Chondrosarcoma – affects axial skeleton

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Chondrosarcoma – affecting the finger

  • 2nd most common malignant primary bone tumour
  • older adults
    • 30-60 yo
  • can arise from previous enchondroma
    • many are sporadic
  • location
    • axial skeleton
      • pelvis
      • pectoral girdles
      • ribs
      • spine
  • Aggressive
    • erodes & invades soft tissue
  • *Metastasize to: (suspect chondrosarcoma)
    • lungs
    • liver
    • kidney
    • brain
  • Gross
    • large bulky tumours
      • grey white, translucent
  • Microscopy
    • malignant cartilage
      • with anaplastic chondrocytes in spaces
    • focal enchondral ossification & calcification
    • hypercellularity, atypia, mitosis
  • Treatment
    • resistant to chemotherapy
      • therefore must be surgical resection

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Giant cell tumour of bone (Osteoclastoma)

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  • Osteoclastoma
    • potentially malignant
      • mostly benign
    • arise in epiphysis
      • develop after fusion of cartilage
      • after epiphyseal plate thins out
    • lytic lesion at end of bone
      • knee
      • elbow
      • ankle
    • Treatment
      • resection
        • recurrence is common
    • Pathology
      • osteoclastic giant cells
        • 100 or more nuclei
        • nuclei similar to those of stromal cells
        • giant cells are not malignant
      • mesenchymal cells
        • ovoid
        • mononuclear cells
    • Haemorrhage and necrosis present

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Secondary (metastatic)

image Looking at the pattern of bone lesion, you should also screen for these primary cancer sites

  • more common in the old
  • most commmon malignant tumour in skeleton
  • metastasize from:
    • breast tumour
    • kidney tumour
    • thyroid
    • lung
  • Generally occur in
    • vertebrae
    • pelvis
      • if primary tumour from pelvis, can spread to lumbosacral spine
    • proximal parts of the
      • femur
      • humerus
    • ribs
    • skull
    • Rare
      • hands
      • feet
  • Marrow neoplasm (hemopoietic):
    • myeloma
    • leukemia
    • lymphoma

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Mixed lytic and sclerotic lesion

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Sclerotic lesions

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Terri is obsessed with making medical school as painless as possible. She studies and compiles medical school notes in a concise, easy-to-understand format. She also enjoys reading contributions by others. She is an investor in sustainability projects. Her ideal weekend is wine tasting and experimenting on bread-making. She has yet to master the art of Sourdough baking.

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