Infections of bones and joints Flashcards
What is the medical term for infection of bone?
Osteomyelitis
Is antibiotic treatment sufficient for treatment of osteomyelitis?
If infections is serious, surgery is often needed too
What is the most common presenting symptom of osteomyelitis?
Pain - resting pain which is progressive, usually quite localised (ie not mechanical pain)
What is the most common causative organism of osteomyelitis?
Staphylococcus Aureus
Staphylococcus aureus, most commonly causes osteomyelitis by what spread?
Haematogenous
What are the 5 other common causative organsism of osteomyelitis?
1) Streptococci - group A and B
2) Enterococci
3) Gram negative bacilli
4) Anaerobes
5) Mycobacterium TB, Brucella Spp
What kind of infection does mycobacterium TB tend to cause?
Indolent osteomyelitis of the spine
What is the gold standard diagnostic tool in osteomyelitis?
Cultures and histology of bone biopsy/needle aspirate
Is blood cultures a reliable diagnostic method in osteomyelitis?
About 50% accuracy but avoids need for biopsy
Could superifical swabs be used in diagnosing osteomyelitis?
Have a limited value in contiguous infections
What is the therapy for osteomyelitis?
Antimicrobials +/- surgery depending on stage/site
What are the 3 pathogenic mechanisms of osteomyelitis?
1) Haematogenous - bacteria in the blood seed bone
2) Contiguous factors - spread from adjacent areas of infection
3) Direct inoculation - trauma or surgery
If a patient had a infected diabetic foot ulcer leading to osteomyelitis of the foot, what would be the pathogenic mechanism?
Contiguous spread
What are the 4 classifications of osteomyelitis?
1) Stage 1 - medullary
2) Stage 2 - superficial
3) Stage 3 - Localised
4) Stage 4 - diffuse
What is meant by stage 1 medullary osteomyelitis?
Necrosis of the medullary contents, trabecula bone, cortical bone and periosteum unaffected
What is meant by stage 2 superficial osteomyelitis?
Periosteum is interrupted, necrosis limited to the exposed surface
Stage 1 osteomyelitis is likely to occur by what spread?
Haematogenous
Stage 2 osteomyelitis is likely to occur by what spread?
Contiguous
What is stage 3 localised osteomyelitis?
Full thickness infection, get cortical sequestration (island of cortical bone, now with no blood supply) so cant deliver Abx to that part via the blood stream
What is stage 4 diffuse osteomyelitis?
Get extensive infection of all parts with unstable bone
Why is surgery needed in addition to IV Abx in stage 3 and 4 osteomyelitis, how does the surgery differ between the 2?
Some parts of bone have lost blood supply, cant deliver Abx via the blood stream
Stage 3 - debridement (removal of damaged tissue)
Stage 4 - full resection
In addition to the symptom of pain, what 3 other sets of symptoms could be present in osteomyelitis?
1) Symptoms of soft tissue inflammation, depending on the position of infected bone (tenderness, warm, erythema)
2) Reduced movement of infected limb
3) Systemic symptoms are uncommon (fever, chills and night sweats)
Give the 3 gram negative bacilli which can cause osteomyelitis?
1) Salmonella
2) Klebsiella
3) Pseudomonas aeruginosa
Pseudomonas aeruginosa is a gram negative bacilli which can cause osteomyelitis more commonly in what 3 groups of people?
1) Sickle cell disease
2) Premature babies
3) IVDUs
What are the 5 diagnostic tests that can be used in osteomyelitis?
1) Cultures and biopsy of bone - gold standard
2) Blood cultures
3) Superficial swabs
4) Leukocytosis - not diagnostic
5) C-reactive protein - usually raised, monitor response to therapy
How are Abx delivered in osteomyelitis and why?
IV - to ensure compliance and optimum bone levels - penetration into bone is low
What is the agent of choice for staphylococcus aureus osteomyelitis?
Flucloxacillin IV
What 5 Abx achieve acceptable levels in bone?
1) Clindamycin
2) Ciprofloxacin
3) Vancomycin
4) Beta lactams
5) Gentamicin
What is septic or infective arthritis?
Inflammatory reaction in the joint space caused by infection, result from direct invasion of the joint
Into what 2 classes can septic arthritis be classified?
1) Native joint infection
2) Prosthetic joint infection (early/late)
What is the pathogenesis of native joint infection?
- Organisms enter the joint via haematogenous spread or trauma
- Cartilage erosion causes joint space narrowing/ impaired function
Are native joint infections associated with mortality?
Low mortality but severe dysfunction in general
Can rarely get sepsis
Give the 4 predisposing factors for a native joint infection?
1) Rheumatoid arthritis
2) Trauma
3) IVDU
4) Immunosuppressive disease
What is the pathogenesis of prosthetic joint infection?
- Organisms can enter by haematogenous spread, but more commonly during surgery or following wound infection
- Joint prosthesis and cement provide a surface for bacterial attachment
- Polymorph infiltration results in tissue instability of the prosthesis
What are the 7 predisposing factors for prosthetic joint infection?
1) Prior surgery at the sight of the prosthesis
2) RA
3) Cortiscosteroid therapy
4) Diabetes mellitus
5) Poor nutritional status
6) Obesity
7) Extremely advanced age
What is the clinical presentation of septic arthritis?
1) Pain swelling and tenderness at the joint
2) Limitation of joint movement
3) Systemic upsets: fever, chills, night sweats
What 3 things affect the duration and severity of symptoms in septic arthritis?
1) Site of infection
2) Type of joint (native v prosthetic)
3) Causative organism
What are the 2 types of causative organism of septic arthritis?
1) Bacteria
2) Fungi eg. Candida spp
Can viruses cause septic arthritis?
Yes - parovirus B19, Rubella virus, Mumps virus although less common and are self limiting as part of systemic illness
Organisms that cause native joint infections are the same as those that cause osteomyelitis, plus what 3 other organisms?
1) Haemophilus influenza
2) Neisseria gonorrhoea
3) Neisseria meningitidis
Organisms that cause prosthetic joint infections are the same as those that cause osteomyelitis, plus what 5 others?
1) Coagulase negative staphylococci
2) Enterococci
3) Corynebacteria
4) Proprionibacteria
5) Bacillus spp
What 6 examinations can be carried out on the joint aspirate in septic arthritis?
1) Total white cell count
2) Differential WCC (>75% polymorphs during infection)
3) Gram stain (35-65% positive)
4) Crystal examination (because gout can mimic infection)
5) Culture
6) PCR - for slow growing organisms like M tuberculosis
What are the 3 steps in therapy for a native joint infection?
1) Removal of purulent material - joint drainage/ washout
2) Empirical IV antimicrobial therapy if required
3) Directed IV antimicrobial therapy depending on causative organism
Unlike in osteomyelitis, empirical therapy is used in septic joint, what should be done before it is started?
Shouldn’t be started until after microbiological samples have been taken
What is the duration of antimicrobial therapy for a septic native joint?
2-4 weeks
What are the 3 steps in therapy for prosthetic joint infection?
1) Removal of implant or replacement of some elements and washout
2) Empirical IV antimicrobial therapy if required
3) Directed IV antimicrobial therapy depending on causative organism and susecptibility
What is the duration of antimicrobial therapy in prosthetic joint infection?
6 weeks - oral switch
What is the antibiotic treatment for a prosthetic joint infection with staph aureus?
Flucoxacillin + rifampicin
What is the antibiotic treatment for a prosthetic joint infection with coagulase negative staphylococcus?
Vancomycin IV plus rifampicin
How does antibiotic therapy in prosthetic and native joint infections differ?
Native - monotherapy is sufficient
Prosthetic - longer course and cocktail of antimicrobials, a more complex infection
