Micro/ID: Bone & Joint Infections (BC Flashcards
What causes osteomyelitis?
Often post-trauma or surgery (in ~50% of cases)
Haematogenous (~20% of cases)
Can be contiguous with other infections
What happens to the bone during osteomyelitis?
Invasive bacteria cause inflammatory reaction
Leukocytes release enzymes that lyse the bone
Oedema, vascular congestion, and small vessel thrombosis
Impaired flow of both medullary and periosteal blood supply
Impaired blood flow of both medullary and periosteal blood supply
Produces areas of devitalized infected bone, sequestra
Body forms new bone, involucrum
Leads to bone sclerosis and deformity
How is osteomyelitis treated if its acute and chronic?
Acute: May be curable with antibiotics alone
Chronic: Frequently requires surgical debridement and removal of sequestrum and necrotic tissue
What is an involucrum?
Fleshy new bone formation.
What is a sequestrum?
Dead bone found on the outside of the bone that is infected.
What are the stages of osteomyelitis?
Stage 1: Medullary osteomyelitis (in medullary cavity)
Stage 2: Superficial osteomyelitis (inside cortex of bone)
Stage 3: Localized osteomyelitis (both medullary cavity and cortex)
Stage 4: Diffuse osteomyelitis (all the bone and is most dangerous because it can break)
What are the haematogenous causes of osteomyelitis?
From infection elsewhere or skin break/trauma
The bacteria that causes it in adults are:
Staph aureus
Beta-haemolytic strep
Gram-negatives
What causes haematogenous osteomyelitis in infants and pre-school children?
In infants:
Staph and streps
E.coli
In pre-school children:
Staph and streps
H. influenzae
Kingella kingae
What are some dental causes that can result in osteomyelitis due to bacteria in blood?
Dental extraction
periodontic surgery
Chewing candy
Tooth brushing
What is the source of microbe entry into the bloodstream in adults besides the dental causes?
Haematogenous:
Injecting drug users can get bacteria from skin and environment.
Usual bugs if immunocompromised (eg mycobacteria)
Exotic and zoonotic (Brucella, Q fever, and TB)
Contiguous: Staph and streps, enteric bacteria
Post-surgery: S. aureus, CoNS, and other skin flora, gram negatives.
Post-trauma: Compound fractures and penetrating injuries can result in bacteria infecting bones.
What are the symptoms of osteomyelitis?
Fever
Pain
Erythema
Swelling
Children (non-weight bearing child)
What is a Brodie abscess?
Subacute osteomyelitis causes this. it occurs mainly when host immunity controls infection leading to a growth on the bone. The bacteria that most often causes this is staph aureus but it can also be caused by streptococcus
This can often be misdiagnosed as a tumour.
How is osteomyelitis (including brodie’s abscess) diagnosed?
Raised inflammatory markers (CRP, WBC)
Microbiological (Blood cultures, joint aspiration and culture (if septic arthritis)
Bone biopsy
Imaging (plain x-ray should show soft tissue swelling, periosteal reaction “lifting”, and no bone changes for 2/52, CT, and MRI)
How is osteomyelitis treated conservatively?
High dose antibiotics usually IV initially.
Empiric therapy must cover staph aureus (eg flucloxacillin, or vancomycin if patient is septic or at risk of MRSA, cephalosporin for kids)
At least 4 - 6 weeks therapy in adults.
2 - 3 weeks in children
Targeted therapy is always the best
What is the treatment of osteomyelitis if not responding to conservative therapy?
Acute osteomyelitis may require surgery (drainage of sub-periosteal and intra-osseus collections, abscesses.
Chronic osteomyelitis usually requires surgery including debridement of sequestrum, abscess and dead/devitalised tissue.
Posthetic/foreign material must be removed and beware biofilm.
