infections Flashcards
(24 cards)
what is septic arthritis
intra-articular infection that can eventually lead to a destructive arthropathy if left untreated; it is an orthopedic surgical emergency.
Which joints are commonly affected by septic arthritis?
In a descending order, these are: knee, hip, shoulder, elbow, ankle, sternoclavicular and sacroiliac joints (think of IV drug use in the latter two).
Why are the knee, hip and shoulder the most commonly involved joints? in septic
Because they have abundant metaphyseal blood supply.
What would predispose to the development of septic arthritis (risk factors)?
▪ Advanced age.
▪ Comorbidities: diabetes mellitus, rheumatoid arthritis, immuncompromsied (HIV).
▪ Bacteremia.
▪ Crystal-induced arthritis.
▪ Prosthetic joint.
▪ IV drug use.
▪ Intra-articular injections.
What is the most common organisms are involved in the causation of septic arthritis?
Staphylococcus aureus
most common cause in sexually active young adults.
Neisseria
causes septic arthritis in sickle cell disease patients.
Salmonella
mainly affect the extremes of age (neonates and the elderly), IV drug users and diabetics.
Gram-negative bacilli, e.g. E. coli, Klebsiella,
cause arthritis mainly in young infants.
Group B streptococci
causes arthritis mainly in IV drug users.
Pseudomonas aeruginosa
mainly implicated in prosthetic joint infections.
Coagulase-negative staphylococci
arthritis mainly occur in the immunocompromised hosts.
Fungal or candidal
What routes are involved in the pathogenesis of septic arthritis?
▪ Hematogenous spread (most common route), i.e. bacteremia. blood
▪ Direct inoculation, e.g. trauma or surgery.
▪ Contiguous spread, e.g. from adjacent osteomyelitis - due to arteriolar anastomosis
between epiphysis and synovium.
How would a patient with septic arthritis be investigated?
Complete blood count can reveal leukocytosis with a left shift.
▪ Inflammatory markers: ESR and C-RP - help confirm the presence of acute infection
and C-RP is used to monitor response to treatment.
▪ Two sets of blood cultures.
- x-ray of the affected joint (of limited value in diagnosis but to rule out other pathologies as well):
what is gold standard for diagnosis in septic arthritus and to direct antibiotic Rx;
Synovial fluid aspiration and analysis
How is septic arthritis treated?
▪ Aspirate synovial fluid and send it for analysis.
▪ Start IV empiric antibiotic therapy based on patient’s age, risk factors and gram stain
results: if gram+, starts IV vancomycin; if gram-, starts third generation cephalosporins.
so
▪ Once culture and sensitivity results are obtained, switch to organism-specific
antibiotics that should be continued for 6 to 12 weeks.
▪ Operative management should ensue with open or arthroscopic joint arthrotomy forurgent decompression, debridement, irrigation and surgical drainage.
gout
-ve burefringent
urate deposition
needle crystal
pseudogout
+ve bifringent
calcium pyrophosphate
square crytals
what is osteomyelitis
inflammation of bone caused by an infecting organism withprogressive destruction.
What would predispose to the development of osteomyelitis (risk factors)?
▪ Recent trauma or surgery or presence of foreign body.
▪ Comorbidities: diabetes mellitus, sickle cell disease, immuncompromsied (HIV).
▪ Vascular insufficiency.
▪ IV drug use.
How can osteomyelitis be classified?
▶ It can be classified according to timing into:
Acute (within two weeks) hematogenous osteomyelitis; due to bacteremia.
▪ Subacute (from two to six weeks); usually by direct inoculation
▪ Chronic (more than six weeks); due to untreated/inadequately treated disease.
What is the mechanism involved in the pathogenies of osteomyelitis
Biofilm-producing bacteria introduced by blood/trauma to bone—>
Inflammatory reaction and release of lytic enzymes—->
local ischemic necrosis—->
pus collection and abscess formation—->
increased intramedullary pressure—->
cortical ischemia—->
purulent material escapes through thin cortex into subperiosteal space—-> subperiosteal abscess formation
late findi gs in osteomyelitis
♦ Periosteal reaction/thickening/elevation (periostitis) - can manifest as Codman’s triangle.
♦ Lytic lesion (due to presence of intraosseous/Brodie’s abscess) with surrounding sclerosis (wouldn’t show until ~50% of the bone matrix is destroyed) - hence, if x-ray is unrevealing, do not exclude diagnosis in the setting of strong clinical suspicion. ♦ Presence of sequestrum, involucrum and cloaca in chronic OM.
early changes in osteomyelitis include
soft tissue swelling and loss of normal fat planes.
