Bone & Joint Infection Flashcards
Label the following diagram of a normal joint [11]
- muscle
- synovial cavity
- bursa
- joint capsule and synovial lining
- tendon
- enthesis
- enthesis
- ligament
- articular cartilage
- epiphysis of bone
- enthesis
Define septic arthritis [1]
infection in a joint
Why should septic arthritis be treated as a medical emergency? [2]
- Treat as a medical emergency as an untreated joint infection can lead to:
- Loss of cartilage → osteoarthritis in later life
- Severe sepsis → septic shock
What are the typical presenting signs & symptoms of septic arthritis? [5]
- Fever (60-80% of cases)
- Single hot joint
- Knee (50%)
- Hip (20%)
- Polyarticular involvement (10-20%)
- Loss of movement
- Pain
What are the key investigations that should be carried when diagnosing suspected septic arthritis? [5]
- Blood cultures
- Joint aspirate (gram, microscopy for crystals and culture)
- FBC
- CRP
- Imaging
What are the common pathogens that cause septic arthritis? [10]
- Gram +ve
- MSSA
- MRSA
- Streptococci
- S. pyogenes
- Group G strep
- Pneumococcus (commoner in children)
- Gram -ve
- H. influenzae (commoner in children)
- Kingella
- N. meningitidis
- N. gonorrhoeae
- E. coli
- P. aeruginosa
- Salmonella species
How should septic arthritis be treated and monitored? [3]
- Often 3 weeks IV antibiotics followed by 3 weeks oral
- Monitor response by CRP and clinical
Define arthroplasty [1]
putting in an artificial joint
What is resection arthroplasty? [1]
taking the diseased joint out and putting in an artificial one
What is revision arthroplasty? [1]
re-operating on an artificial joint
Define arthrodesis [1]
fusing 2 bones together
Define arthrosis [1]
a joint
Define pseudo-arthrosis [1]
allowing 2 bones to articulate against one another but without a joint, e.g. Girdlestone
What are the risk factors for prosthetic joint infections associated with primary arthroplasty? [7]
- Rheumatoid arthritis
- Diabetes mellitus
- Poor nutritional status
- Obesity
- Concurrent UTI
- Steroids
- Malignancy
What are the risk factors for prosthetic joint infections associated with a revision arthroplasty? [3]
- Prior joint surgery
- Prolonged operating room time
- Pre-op infection (teeth, skin, UTI)
What are the microbial causes of prosthetic joint infections? [8]
- Staphylococcus aureus
- Coagulase-negative staphylococci (CoNS)
- Streptococcus
- Gram-negative bacilli
- Anaerobic organisms
- Enterococcus
- Culture negative
- Polymicrobial (mixed)
Describe the pathogenesis of the development of prosthetic joint infections [3]
- Prosthesis requires fewer bacteria to establish sepsis than soft tissue
- Avascular surface allow survival of bacteria as protects from circulating immunological defences and most antibiotics
- Cement can inhibit phagocytosis and lymphocyte/complement function
How can prosthetic joint infections spread and how long does it take for each type to present? [4]
-
Local Spread
- Usually manifests in immediate post-op period
- Acute <4 weeks
- Delayed/late >4 weeks (up to 50% PJIs present two or more years after surgery)
- Usually manifests in immediate post-op period
-
Haematogenous spread
- Presents later
The virulence (ability to infect) of the organism will dictate its presentation. What do low virulence organsims result in and give examples? [2]
- Low virulence organisms result in low grade indolent infections which are tenacious
- e.g. coagulase negative staphylococci
The virulence (ability to infect) of the organism will dictate its presentation. What do high virulence organsims result in and give examples? [4]
- Highly virulent organisms result in fulminant infection or septic shock
- e.g.
- MSSA
- MRSA
- Group A or G Beta Haemolytic Streptococcus
How does prosthetic joint infections typically present (signs & symptoms)? [7]
- Pain
- Effusion
- Warm joint
- Fever and systemic symptoms
- Loosening on X-ray
- Discharging sinus
- Mechanical dysfunction
Describe the antibiotic prophylaxis used for prosthetic joint infections [2]
- Cephalosporin should be given 30-60mins before skin incision
- Evidence supports the use of cephalosporin (+ vancomycin or teicoplanin if MRSA colonised) in prevention of PJI
State the 2 surgical options for treatment of prosthetic joint infections [2]
- DAIR (Debride, Antibiotics, Implant Retained) to Leave the Infected Joint In
- Take the Infected Joint Out
Describe when DAIR is indicated and how the process works [3]
- If prosthesis infection is acute (<30 days since insertion), then it is still mechanically functional and can be kept in
- but infected tissues should be debrided and the joint washed out to reduce the burden of infection
- then IV antibiotics started for 4-6 weeks
Describe when surgical removal of joint is indicated and how the process works [5]
- If the infection occurs over 30 days since surgery then it may no longer be fully functional and may need removed.
- Removal involves taking out the prosthesis and all cement (can’t heal if foreign body retained)
- Options:
- Girdlestone procedure
- One stage revision (put a new one in during the same operation as removing the infected one)
- Two stage revision (delay putting in a new one until treated the existing infection for 4-6 weeks)
Name the antibiotics that are able to penetrate bone [10]
- Cephalosporins
- Tazocin
- Carbapenems
- Fusidic acid
- Doxycycline
- Rifampicin
- Linezolid
- Trimethoprim
- Ciprofloxacin
- Clindamycin
Define osteomyelitis [1]
progressive infection of bone characterised by death of bone and the formation of sequestra
How can osteomyelitis spread? [2]
- Haematogenous spread
- Contiguous spread
- Overlying infection (e.g. cellulitic ulcer)
- Trauma (compound fracture)
- Surgical inoculation
Who most commonly gets affected by acute osteomyelitis? [1]
children
What kinds of bacteria cause osteomyelitis? [2]
similar to septic arthritis but also include anaerobes
How do you treat osteomyelitis? [3]
- surgery to debulk infection back to healthy bone and manage dead space that remains
- (e.g. with muscle flaps)
- stabilise infected fractures (external fixation often used) and to debride sinuses and close wounds
- Antibiotic choice is determined by what grows from debrided bone
- May require long term antibiotic treatment
- 4- 6 weeks IV
How is diabetic food infection more complex than septic arthritis? [1]
usually involves bone (osteomyelitis) but can also involve joints
Define vertebral discitis [1]
Infection of a disc space and adjacent vertebral end plates
What is a possible cause of vertebral discitis that mustn’t be forgotten? [1]
Tuberculosis (TB)
