Bone and joint infection WIP Flashcards
Describe the typical presentation of septic arthritis
- New onset joint pain in the absence of trauma
- hot, red, swollen joint (effusion)
- Reduced range of motion
- Sepsis
What are the differentials associated with septic arthritis?
- Rheumatoid arthritis
- Psoriatic arthritis
- Crystal induced arthritis
- Trauma
- Haemarthrosis
- extra-articular infection (cellulitis/bursitis)
What are the three types of causes of septic arthritis?
- Haematogenous (arising from a distant site e.g. infective endocarditis)
- Direct inoculation (e.g. following arthroscopy or trauma)
- Contiguous spread e.g. cellulitis
What investigations should be carried out in a suspected septic arthritis?
- Blood cultures (sepsis 6)
- FBC, CRP, ESR, U&Es, LFTs
- Joint aspirate looking at the synovial white cell count, microscopy and gram stain and under polarised light to look for evidence of crystals
Describe blood culture one it gets given to the lab
- Loaded into an automated culture system
- Aggregated and intubated
- Colorimetric sensor in the bottom of each bottle with a pH sensitive dye which changes colour in the presence of CO2 indicating that the bottle is motive
Describe the process of gram staining
- Crystal violet applied, staining all purple
- Iodine acts as a fixative
- Alcohol wash removes the purple stain from gram -ve
- Application of safranin stains the gram negative organisms pink
What is a high white cell count in the synovial fluid suggestive of?
- May indicate septic arthritis
* May also occur with crystal induced arthritis or inflammatory arthritis
What is a low synovial white cell count suggestive of?
- Early infections
- Immunocompromised
- Prior antibiotic use
- Low virulence organisms
What are the caustative micro-organisms of septic arthritis?
- Staphylococcus aureus
- Streptococci
- Enterobacteriaceae (coliforms)
- Mycobaterium tuberculosis
- Neisseria gonorrhoeae
What are the causative microorganisms in septic arthritis in children?
- Streptococcus pneumoniae
- Kingella kingae
- Haemophilius influenza type b
If the blood culture of someone with septic arthritis comes back positive for staphylococcus aureus, what additional tests should be carried out?
- Skin swab for culture
- look for infective endocarditis
- Blood cultures, echocardiogram if positive
If the blood cultures of someone with septic arthritis come back positive for viridian’s streptococci, what additional investigations should be carried out?
- Mouth, infective endocarditis
* Blood culture, trnasthroacic echocardiogram if positive
If the blood cultures of someone with septic arthritis come back positive for enterobacteriaceae/enterococci, what investigations should be carried out?
- Source: abdomen or urogenital tract
* Urine culture, imaging of the abdomen pelvis
What antibiotics should be prescribed for a patient with staphylococcus aureus positive septic arthritis?
- IV flucloxacillin if methicillin susceptible
* IV vancomycin if methicillin resistant or beta lactam allergy
What antibiotics should be prescribe for someone with a streptococcus spp. positive septic arthritis?
- IV benzylpenicillin or ceftriaxone
* IV vancomycin if allergy
What antibiotic should be prescribed in a enterococcus spp. positive septic arthritis?
- IV amoxicillin
* IV vancomycin
What antibiotic should be prescribed in a neisseria gonorrhoea positive septic arthritis?
IV ceftriaxone
What are the impacts of a periprosthetic joint infection?
- Pain
- Reduced mobility
- Draining sinus
- Revision surgery
- Prolonged hospital stay
- Long antibiotic course
- Financial cost
Explain the role of biofilm in prosthetic joint infection
- Microorganisms adhere to surface and secrete extracellular substances to form complex glycocalyx structure
- Microorganisms located within biofilm slowly start diving and evade the host defences (quorum sensing) and become more resistant to antimicrobial therapy
- Eradication of the infection may not be possible without removal of the prosthesis/biofilm
Describe Acute prosthetic joint infection
- Red, hot, painful joint
- Fever/sepsis
- Prolonged leaking gowned post-operatively
Describe chronic prosthetic joint infection
- Pain
- Stiffness
- Loosening of prosthesis on X ray
- May be mildly raised inflammatory markers
- Difficult to distinguish from aseptic loosening
What investigations should be carried out in someone presenting with acute prosthetic joint infection?
- Joint aspirate - WCC, microscopy and culture
* Blood cultures
What investigations should be carried out in someone presenting with chronic prosthetic joint infection?
- Look for sinus tract
* Joint aspirate
Describe the diagnosis of PJI
- Stop antibiotics at least two weeks prior to surgery
- Send multiple (5-6) samples: pus, fluid, synovium, membrane, bone
- Separate sites with separate sterile instruments
- Do not send swabs/sinus samples (poorer sensitivity)
