Septic arthritis Flashcards
(20 cards)
Risk factors for septic arthritis
• underlying joint disease eg, RA, OA
○ bacteria tend to seed in already damaged joints
○ having underlying joint disease or prosthetic joint increases risk by 10-fold
• prosthetic joint
• immunosuppression
○ immunosuppressive medications
○ diabetes
○ heavy EtOH use
○ HIV
• age, especially if age >80
• Continguous infection eg, skin break, ulcer, skin infection. Or it can cause bacteremia with subsequent seeding of infection
• recent intra-articular joint injection eg, corticosteroids
• IVDU
recent tick bite (Lyme disease)
Causative organisms for septic arthritis and features of each
• S.aureus
○ Most common pathogen. Staph and strep combined causes 91% of cases
○ Gram +ve cocci in clusters
○ need to consider MRSA if risk factors eg, ATSI, recent hospitalisation, nursing home, previous colonisation
• Streptococci
○ next most common organism
○ gram +ve cocci in chains
• Gonococcal septic arthritis
○ consider in young healthy adults with no other risk factors for septic arthritis, and sexually active
○ usually prodrome of polyarthralgia which then localises onto one joint, pustular skin rash, tenosynovitis
• Gram -ve organisms
○ Most common gram -ve organisms are Pseudomonas aeruginosa and E.coli
○ Consider if recurrent/current UTI, IDC, recent abdominal surgery, elderly/frail patients
• Anaerobic organism
○ penetrating trauma
• Acute rheumatic fever
○ May present as acute monoarthritis. Consider if risk factors (eg, ATSI from remote/rural or urban setting)
• TB
○ depends on patient epidemiology
• Lyme disease (Borrelia burgdorferi)
Look for erythema migrans
What organisms would you consider in:
- Diabetes and PVD
- Post-operative shoulder infections
• Special circumstances
○ Diabetes and PVD
§ Can be broader range of pathogens or polymicrobial. See management of DFU.
○ Post-operative shoulder infections
Cutibacterium acnes, in both native and prosthetic joints.
Hot, red, swollen joint is ____ until proven otherwise?
Why?
What percentage of patients with septic arthritis is fever present?
Hot red, swollen, painful joint - septic arthritis until proven otherwise, even in the absence of fevers or blood markers. Delay in diagnosis/management can result in mortality/morbitidy and permanent joint damage.
Only about 60% of patients with septic arthritis have fevers.
Which joint is most commonly affected?
What about in IVDU?
Can it be polyarticular? In what proportion? Is mortality higher with polyarticular septic arthritis?
What about 1st MTP?
Usually monoarthritis
Most commonly knee joint
Axial joints more common in IVDU (eg, sternoclavicular, sacroiliac)
But can affect more than one joint. Can be a polyarthritis in ~20% of cases and mortality is up to 50% in septic polyarthritis
The most common acute monoarthritis in primary care is the 1st MTP joint of great toe. Almost always due to gout and can be clinically diagnosed without a joint aspirate.
When might septic arthritis have an insidious presentation?
• Usually acute presentation of <2 weeks of symptoms
More insidious presentations if: prosthetic joint, low virulence organism, TB
Examination findings of septic arthritis?
• If weight bearing joint, traditionally patients will not be able to weight bear
• Joints are in position of maximal joint volume:
○ Knee - full extension
○ Hip - flexion, abduction, external rotation
• Pain on both active and passive ROM
○ Patients will generally not let you move the joint
○ If pain only on active ROM, indicates extra-articular pathology eg, bursitis
• Reduced ROM
Joint effusion may be present
Should you aspirate a prosthetic joint?
Should you aspirate a hip joint?
DO NOT ASPIRATE A PROSTHETIC JOINT. Need referral to orthopaedics as management of prosthetic joint infection is different.
If hip joint, need to refer to orthopedics as it is difficult to access.
What are the things you assess on joint aspirate?
- Colour, lucency, viscosity
- White cell count
- Microscopy (including gram stain), culture, sensitivity
- Polarised light microscopy
- Can consider N.gonorrhoea and borrelia burgdorferi PCR
Why is WCC helpful in joint aspirate?
Is it perfect?
White cell count: usually first result to come back. Most helpful investigation to help differentiate septic vs. non-septic cause of inflammation/arthritis. However, not 100% sensitive or specific.
What are the different white cell counts and neutrophil percentage in:
- non-goncoccal septic arthritis
- gonococcal septic arthritis
- others
Non-gonococcal septic arthritis: >50,000 WBC/mL (usually >100,000), >75% neutrophils (however, this may also be seen with acute crystal arthropathy)
Gonococcal septic arthritis: >30,000 WBC/mL, usually neutrophilic
Others: can be variable 2000-50,000 WBC with <50% neutrophils
How sensitive is joint aspirate culture in non-goncoccal septic arthritis, goncoccal arthritis, and TB?
Does a negative culture exclude septic arthritis?
Cultures +ve in ~90% of non-gonococcal arthritis
Cultures +ve in 25-70% with gonococcal arthritis
Cultures +ve in ~80% of TB. Synovial biopsy is up to 95% sensitive for TB.
A negative result does not exclude septic arthritis
Borrelia burgdorferi cannot be cultured on synovial fluid.
Describe the different joint aspirate findings in:
- normal
- non-inflammatory arthritis (eg, OA)
- inflammatory crystal arthritis
- inflammatory non-crystal arthritis
- gonococcal arthritis
- non-gonococcal septic arthritis
Normal: clear, transparent, thick viscosity
Non-inflammatory arthritis (eg, OA): straw coloured, transparent, thick viscosity, very few WBC (up to 2000)
Inflammatory crystal arthritis: yellow, cloudy, thin, variable WBC, crystals +ve
Inflammatory non-crystal arthritis: yellow, cloudy, thin, variable WBC, crystals -ve
Gonococcal: yellow, cloudy/opaque, thin, high WBC >30,000, gram stain either +ve or -ve, PCR usually +ve
Non-gonococcal septic arthritis: yellow, opaque, thin, high WBC >50,000, gram stain usually +ve
Contraindications for joint aspiration
○ Contraindications for joint aspiration are debated. Careful consideration is required in the following circumstances:
§ Overlying skin infection
§ Coagulopathy
On anticoagulation (however, British society of rheumatology states warfarin is not a contraindication).
Role of X-ray in septic arthritis
Non-urgent, non-diagnostic
Baseline image for future joint damage
May detect chondrocalcinosis to support diagnosis of pseudogout
What % of patients have positive blood cultures in septic arthritis
25-50% due to haematogenous spread to joints
Describe the role of:
- Swabs in septic arthritis
- Urine microbiology in septic arthritis
- Serum procalcitonin in septic arthritis
- MRI in septic arthritis
• Swabs
○ Of other potential sources of infection eg, ulcers, skin lesions
○ Of potential N.gonorrhoea (eg, penile, cervix, rectal, throat)
• Urine ○ MCS in recurrent UTIs or IDC if suspicious for gram -ve septic arthritis. May have haematogenous spread. May also be able to do gonococcal urine PCR • Serum procalcitonin ○ Pre-cursor for calcitonin ○ Low in healthy individuals. There is a sharp rise in reaction to bacterial endotoxin, hence can be useful to differentiate bacterial septic vs. non-septic arthritis. Procalcitonin level of >0.5ng/mL may be more specific marker for bacterial infection than CRP, ESR, or WCC
MRI - only if suspicious of osteomyelitis
Antibiotics first or cultures first for septic arthritis?
Aim to take cultures (joint aspirate, blood cultures) before antibiotics if safely able to do so.
Describe initial antibiotic choice on septic arthritis
Duration of antibiotics?
Role of joint aspiration?
How is septic arthritis management in PVD or diabetes different especially if contiguous with skin ulcer?
• Septic or non-septic
○ If septic, start empirical antibiotics straight away for S.aureus as it is most common pathogen: IV flucloxacillin 2g Q6H
○ If non-septic, initial empirical antibiotics should be guided by initial gram stain
§ MSSA (G+ve clusters) -> flucloxacillin
§ MRSA -> vancomycin
§ Streptococcal species (G+ve chains) -> ceftriaxone or cefotaxime
§ Gram -ve organisms -> ceftriaxone or cefotaxime
§ If gram stain not available, start empirical treatment for S.aureus
○ Then tailor antibiotic therapy to organism and sensitivity
• Duration of antibiotics:
○ 4 weeks total minimum
§ At least 2 weeks IV then switch to PO. If rapid response and appropriate PO option (has to be as good as IV eg, ciprofloxacin, clindamycin), then may be able to go shorter than 2 weeks IV.
• Joint aspiration to dryness
○ Repeat as necessary
○ Has 3 benefits:
§ Therapeutic - removes pus and reduces bacterial load
§ Symptomatic relief by relieving pressure
§ Diagnostic - helps with diagnosis and microbiological diagnosis
• May need to consider orthopedic referral for joint washout
If septic arthritis is contiguous with skin ulcer in a patient with diabetes or PVD, consider broader causative organism or polymicrobial infection. See management of diabetic foot infection.
What is the organism to consider in post-operative shoulder infections?
How do you make the microbiological diagnosis?
• Cutibacterium acnes causes post-operative infections of the shoulder in both native and prosthetic shoulder joints.
• Diagnosis:
○ Prolonged incubation and culture
○ 16s ribosomal RNA sequencing
Optimal antibiotic regimen for post-operative shoulder infections not well established - discuss with infectious disease
