1. Infectious bone diseases Flashcards
Types of infectious bone diseases
- Acute pyogenic osteomyelitis
2. Chronic osteomyelitis
Epidemiology & associations with acute pyogenic osteomyelitis
- Occurs in children & young adults
2. May have preceding history of trauma or possible iatrogenic causes (e.g. joint replacement surgery)
Causes of acute pyogenic osteomyelitis
- In most cases (80-90%): Staphylococcus aureus
- UTI patients: Escherichia coli, Pseudomonas, Klebsiella
- Neonates: Hemophilus influenzae, Group B Streptococci
- Sickle cell patients: Salmonella
Route of spread of acute pyogenic osteomyelitis
- Hematogenous (most common)
- Direct extension from contiguous site (chronic sinusitis)
- Direct implantation (trauma)
Pathogenesis of acute pyogenic osteomyelitis
Commonly, bacteria is brought to the bone via hematogenous spread
- Bacteria lodged within metaphyseal (hairpin) blood vessels, setting up an inflammatory reaction in the medullary canal
- Spreads to the cortex & periosteum via the haversian system or medullary cavity
Consequences of acute pyogenic osteomyelitis
- Subperiosteal abscesses form (which can lift the
periosteum, impairing blood supply to the bone, causing necrosis, resulting in the formation of a dead piece of bone known as a sequestrum; reactive bone then forms a shell around the dead bone known as an involucrum) - Septic arthritis results when the infection spreads to the joints
- Septicemia results when the infection spread into the circulatory system
- Sinuses form as a result of pus tracking to the overlying skin
Morphology of acute pyogenic osteomyelitis
Histologically:
- Neutrophils (may persist for weeks), lymphocytes & plasma cells
- Bone necrosis with reactive new bone formation
- Capillary proliferation & fibrosis
Clinical features of acute pyogenic osteomyelitis
- Location: typically in long bones
- Presentation:
- Bone pain, leukocytosis, swelling, malaise, fever
- Note that presentation may be subtle in a young child or an infant - Xray findings:
- Lytic focus of bone destruction surrounded by a zone of sclerosis
Complications of acute pyogenic osteomyelitis
- Septicemia
- Septic arthritis
- Growth retardation & deformities (especially when the epiphyseal plates are affected in growing children)
- Sinuses & abscess in the overlying skin & soft tissue
- Progression to chronic osteomyelitis
Definition of chronic osteomyelitis
Chronic persistent osteomyelitis often with recurrent exacerbation
Forms of chronic osteomyelitis
- Progression from acute osteomyelitis
- Brodie abscess
- Tuberculous osteomyelitis
Progression from acute osteomyelitis resulting in chronic osteomyelitis
- 5-25% of acute osteomyelitis progresses to chronicity
- Due to delay in diagnosis, extensive bone necrosis, inadequate antibiotic treatment, incomplete surgical debridement of necrotic bone or weakened immunity
Brodie abscess in chronic osteomyelitis
- A specific morphological variant of chronic osteomyelitis characterized by localized foci of abscess formation in the metaphysis of long bones
- Small intraosseous abscesses are walled off by reactive bone & granulation tissue
Tuberculous osteomyelitis in chronic osteomyelitis
- Seen in the young, old, immunocompromised, AIDS,
developing nations & lower socioeconomical group - Very difficult to treat as it tends to be more destructive with extensive necrosis
- Sites affected:
- Vertebrae, especially thoracic & lumbar spine (vertebrae TB is known as Pott’s disease)
- Hip, knee, ankle
- Elbow, wrist - Complications
- Pathological fracture (can cause severe scoliotic & kyphotic deformities & neurological deficits due to cord & nerve compression)
Complications of chronic osteomyelitis
- Permanent deformities, fractures & neurological deficits
- Abscesses & discharging sinuses
- Secondary amyloidosis
- Sclerosis of the bones
- Malignant transformations:
- Osteosarcoma in the bone
- Squamous cell carcinoma in the sinuses
