Bone and joint infections Flashcards
What is osteomyelitis?
Infection of bone
What is the pathogenesis of osteomyelitis?
Haematogenous
- bacteria in the blood seed bone (e.g. endocarditis, infants and children)
Contiguous
- focus - spread from adjacent area of infection
Direct inoculation
- trauma or surgery
What are the stages of osteomyelitis?
Stage I Medullary – necrosis medullary contents/endosteal surface (haematogenous)
Stage II Superficial – necrosis limited to exposed surface (contiguous)
Stage III Localised – full thickness cortical sequestation, stable before and after debridement (trauma, stage I/II evolving)
Stage IV Diffuse – extensive, unstable bone
What is the clinical presentation of osteomylitis?
- pain
- (soft tissue swelling)
- (erythema)
- (warmth)
- (localised tenderness)
- reduced movement of affected limb
- systemic upset uncommon (fever, chills, night sweats)
What is the most common causative organism in osteomyelitis?
S. aureus
What other organisms commonly cause oseomyelitis?
- Streptococci (e.g. group A, group B)
- Enterococci
- Gram negative bacilli e.g Salmonella spp, Klebsiella spp, Pseudomonas aeruginosa – (in premature babies, intravenous drug users, sickle cell disease)
- Anaerobes
- Mycobacterium tuberculosis, Brucella spp.
What is the gold standard diagnostic technique in osteomyelitis?
- cultures and histology of bone biopsy / needle aspirate
- blood cultures positive in 50%
- CRP usually raised, monitor in response to therapy
- Leukocytosis - not diagnostic
What is the treatment for osteomyelitis?
- Antimicrobials +/- surgery depending on stage/site
- Give directed antimicrobial therapy guided by causative organism
- Intravenous antimicrobials initially to ensure compliance and optimal bone levels - penetration into bone is low
- clindamycin, ciprofloxacin, vancomycin, ß-lactams and gentamicin achieve acceptable levels in bone
- Flucloxacillin IV – agent of choice for S.aureus OM
What is septic arthritis?
- Inflammatory reaction in joint space (arthritis) caused by infection
- Result from direct invasion of the joint
What are the two types of septic arthritis?
- Native (natural) joint infection
- Prosthetic (artificial) joint infection (early/late)
What is the pathogenesis of a native joint infection?
- Organisms enter a joint via the blood or trauma.
- Synovial tissue is highly vascular and lacks a basement membrane - facilitating “seeding”
- Cartilage erosion causes joint space narrowing/impaired function
- Predisposing factors: rheumatoid arthritis, trauma, intravenous drug use, immunosuppressive disease
What is the pathogenesis of prosthetic joint infection?
- Organisms enter a joint via the blood, during surgery or following wound infection
- Joint prosthesis and cement provide a surface for bacterial attachment
- Polymorph infiltration results in tissue damage instability of the prosthesis
- Predisposing factors: prior surgery at the site of the prosthesis, rheumatoid arthritis, corticosteroid therapy, diabetes mellitus, poor nutritional status, obesity, and extremely advanced age
What is the clinical presentation of septic arthritis?
- Joint: pain, swelling, tenderness, redness and limitation of movement
- systemic upset: fever, chills, night sweats
- Duration of symptoms is variable and influenced by site of infection, type of joint (native vs prosthetic) and causative organism
Which viruses can cause arthritis?
- Parvovirus B19
- Rubella virus
- Mumps virus
Usually self limiting part of systemic illness.
Which organisms are commonly the cause of native joint infections?
- Staphylococcus aureus
- streptococci (A,B,C,G)
- Haemophilus influenzae
- Gram negative bacilli
- Neisseria gonorrhoeae
- Neisseria meningitidis
- Anaerobes
- mycobacteria
Which organism are commonly the cause of prosthetic joint infections?
- Staphylococcus aureus
- Coagulase negative
- staphylococci (CoNS)
- streptococci (A,B,C,G)
- Anaerobes: peptostreptococci, peptococci
- enterococci
- Gram negative bacilli
- corynebacteria
- propionibacteria
- Bacillus spp.
- mycobacteria
What sort of analysis would be performed on a joint aspirate?
Total white cell count
- (>40 000/mm3 during infection)
Differential WCC
- (>75% polymorphs during infection)
Gram stain
- (35-65% positive)
Crystal examination
- (e.g. gout can mimic infection)
Culture
?PCR
- (for slow growing organisms e.g M. tuberculosis)
What is the treatment for a native joint infection?
- Removal of purulent material - joint drainage/washout
- Empirical iv antimicrobial therapy if required (wait until microbiological samples have been taken before starting)
- Directed iv antimicrobial therapy depending on causative organism and susceptibility (e.g. Flucloxacillin for S.aureus)
- Duration: 2-4 weeks (native joint)
What is the treatment for a prosthetic joint infection?
- Removal of implant or replacement of some elements, washout (early vs late)
- Empirical iv antimicrobial therapy if required
- Directed iv antimicrobial therapy depending on causative organism and susceptibility (e.g.
- Flucloxacillin plus rifampicin for S.aureus PJI or vancomycin IV plus rifampicin for CoNS )
- Duration: 6 weeks NB. oral switch.
