Osteomyelitis and other bone infections Flashcards
What is the most common organism responsible for Osteomyelitis ?
Stap Aureus
What are the two mechanisms through which S. Aureus attach to bones ?
S. aureus expresses a collagen-binding adhesin to attach to bone cartilage and fibronectin-binding adhesin to attach to bone implants.
What are the modes of microbial spread in osteomyelitis ?
1) Hematogenous route of infection through bacteremic seeding from a distant source of infection.
2) contiguous spread from surrounding tissue and joints.
3) direct inoculation of bone from trauma or surgery.
what is the most common type of osteomyelitis in children ?
Hematogenous osteomyelitis of long bones occurs more frequently in children compared to adults.
What is the most common source of osteomyelitis in adults ?
Hematogenous osteomyelitis of the vertebre.
what are the causes of contagious osteomyelitis in young adults ?
Trauma and surgery
what are the causes of contagious osteomyelitis in Older adults ?
decubitus ulcers and infected joint arthroplasties
What is the histology of long bones affected with hematogenous osteomyelitis ?
A well-perfused metaphyses, which have scarce functioning phagocytes, are the most common site of infection in hematogenous osteomyelitis affecting the long bones.
What is the pathophysiology of osteomyelitis ?
The blood supply to the long bones splits at the mid-shaft into two to both metaphyseal endplates. Slowing of blood flow in vascular loops at the metaphysis encourages the deposition of microbes and cause infection. To contain it, phagocytes release enzymes that lyse bone, creating an inflammatory response. This inflammatory response forms pus and causes increased intramedullary pressure. This exudate can rupture through the cortex to the periosteum and disrupt periostial perfusion, ischaemia and necrosis. Pus containing fragments of necrotic bones are called sequestra which can lead to sinus tract formation through the newborn formation over the periostium called involucrum. The whole process is called Osteomyelitis.
What are the main histopathological findings in acute Osteomyelitis ?
The main histopathological finding in acute osteomyelitis are microorganisms, congested or thrombosed blood vessels, and infiltrates of neutrophils.
What are the main histopathological findings in chronic Osteomyelitis ?
The hallmark histopathological finding in chronic osteomyelitis is necrotic bone. Other features of chronic osteomyelitis include a predominance of mononuclear cells, replacement of osteoclast resorbed bone by granulation, and fibrous tissue leading to bone loss and the formation of sinus tracts, which is pathognomic.
Explain the The Cierny and Mader classification of osteomyelitis ?
In this scheme, the classification of osteomyelitis is by anatomic stage and the host health status.
The categories and corresponding anatomic types are:
Stage 1: Disease confined to the medullary of the bone
Stage 2: Superficial disease
Stage 3: Localized spread
Stage 4: Diffuse disease
The local and systemic factors which define host health status are:
A: Normal host
Bs: Host with systemic compromising factors
Bl: Host with local compromising factors
Bsl: Host with both local and systemic compromising factors
C: Host for whom treatment of the osteomyelitis is worse than the disease itself.
What are the blood works in Osteomyelitis ?
They are usually non-specific for osteomyelitis. There may be elevation of WBC, ESR and CRP. CRP can be used to monitor response to Tx in acute osteomyelitis.
What are the radiological studies in Osteomyelitis
It is an essential component in osteomyelitis and consist of X-ray, MRI, and technetium-99 bone scintigraphy. However, MRI has the highest combined sensitivity and specificity with high negative predictive value.
What is the most important diagnostic study in osteomyelitis?
Open or precutaneious bone biopsy is a must to identify the microbial flora, susceptibility testing, and differentiating acute vs chronic osteomyelitis. However, open biopsy is preferred over precutaeneous one.
