Key facts:
Author: Adrian Jones
Top Tip: Any acute monoarthritis should be treated as septic arthritis until otherwise proven - ie start IV antibiotics soon - preferably after joint aspiration
Key Differential Diagnoses
- Crystal arthropathy
- Osteoarthritis
- Autoimmune arthritis
Key Investigations
- FBC, ESR, CRP
- U+E, LFT, Bone, Glucose
- BC, CXR
- Joint aspiration
Key Treatment
- IV FLUCLOXACILLIN 2 g qds (± other AB)
- Antibiotic policy should reflect local guidance but needs to cover Staphylococci and Streptococci and take into account patient risk groups
- Give IV antibiotics soon, preferably after joint aspiration
Key Management Decisions
- Joint aspiration
- Arthroscopy
Background
Septic arthritis is one of the most important acute rheumatological emergencies
Introduction
- Septic arthritis is the most dangerous form of acute arthritis
- It classically presents with the abrupt onset of a single hot, swollen, and very painful joint
- The joint cavity is usually a sterile space, with synovial fluid and cellular matter including a few white blood cells. A source of infection, often from the skin, lungs or bladder, will be found in 50% of cases
- 50% of attacks affect the knee joint. After that, shoulder, then hip are the most common joints affected. 10-20% are polyarticular
- Diagnosis can be difficult, and can be missed. This is because inflammation may not be overt in elderly/immunocompromised (especially if on steroids). Also, xrays may be normal, as may WC, ESR and CRP
- It has a surprisingly high mortality: 10-15% (30% if pre-existing RA)
- Refer to orthopaedic surgeon, if not getting better or prosthetic joint
- Don't forget tuberculosis and gonorrhoea
- In an attack, 50% of cartilage proteoglycan is lost within 48h; and there is bone loss in 7 days. 25-50% are left with permanent joint damage
- So. If consider diagnosis, start IV antibiotics immediately
- Time is joint
Definition
- Infection, usually bacterial, in the joint cavity
Diagnostic difficulty
- The classic presentation is a febrile patient with a hot swollen joint, having rigors, increased WC and ESR. However, none of these are highly sensitive or specific for septic arthritis
- But covert presentation is well recognised. In different series, only 40-60% of patients with septic arthritis were febrile, only 25-60% had an elevated WC, and only 60-80% had an ESR greater than 50 mm/hr
- Elderly or immunocompromised patients (eg on steroids), or patients with DM, can have few symptoms or signs, and near normal bloods; leading to missed diagnoses
Causes
- Staphylococcus aureus
- Staphylococcus albus
- Streptococci
- Gram negative rods
- Neisseria gonorhoeae (now rare; many of these 'gonococcal' patients, will be meningococcal)[Ref]
Neisseria gonorhoeae; a rare but important cause of septic arthritis
Neisseria gonorhoeae; a gram-negative diplococcus
Risk factors
- Source of infection: lungs, bladder or skin
- DM
- Age > 80 yrs
- Structural joint disease (especially RA (20-30% mortality); OA and gout)
- Immunosuppression, chemotherapy
- Risk factors for HIV
- Risk factors for tuberculosis
Symptoms
- Hot, swollen joint
- Fever
Note: in elderly/immunocompromised (especially those on steroids), symptoms may be few; eg just fever, or no fever and non-specific malaise, with no obvious single joint involved
Key questions
- "How long has the joint be swollen and tender?"
- "Have you had any joints replaced?"
Signs
- Hot, monoarthritis
- Joint line tenderness
- Restricted ROM
- Fever
Note: in elderly/immunocompromised (especially those on steroids), signs may be few; eg no fever, or significant joint swelling and tenderness
Investigation
If at all possible, aspirate the joint BEFORE antibiotics. BC sometimes positive (may grow organism before synovial fluid)
Blood
- FBC, ESR, CRP, Clotting
- U+E, LFT, Bone, Glucose
- BC (only 25-30% positive,if non-gonococcal)
- Rheumatology screen (urate, RF, ANA, dsDNA, C3/4)
Note: serum urate no value in diagnosis of septic arthritis (or gout)
ABG, if unwell
Other
- CXR
- XR joint
Note: may be normal; chondrocalcinosis suggests pseudogout - ECG
Key investigations
- Joint aspiration
- Arthroscopy
Specialist investigations
- Joint aspiration;for synovial fluid analysis:
- WC, microscopy, Gram stain, and polarised microscopy (crystals)
- leucocyte count of 50—150×109/L, predominantly polymorphonuclear cells
- +ve gram stain 10-80%
- +ve fluid culture 90%, but may take a week or more to grow an organism)
Notes: better done before antibiotics, unless gravely ill; aspirate joint to dryness; warfarin does not contraindicate needle aspiration; in fact, cell counts rarely done (not that helpful)
- Viral screen + urine for chlamydia
- HIV/Hep B/C
- Sepsis screen (throat, rectal and cervical swabs)
- Aspirate any cutaneous pustules for gram stain in patients with suspected gonococcal infection
- US/MRI may be more sensitive picking up joint damage than XR
Differential diagnoses
Traumatic
- Fracture
- Haemarthrosis (haemophilia etc)
Non-traumatic
- OA
- Crystals (gout/pseudogout)
- Autoimmune (RA, SLE, seronegative arthritis (Psoriasis, Reiter's))
Treatment
Neither the absence of an organism on Gram stain or a negative subsequent synovial fluid culture excludes the diagnosis; ie if in doubt, treat
Treatment (first line)
Drugs
- IV FLUCLOXACILLIN 2 g qds (± IV CEFTRIAXONE 2 g od + PO RIFAMPICIN 600 mg bd)
(Penicillin Allergy: IV VANCOMYCIN 1 g bd ± IV MEROPENEM 1 g tds + PO RIFAMPICIN 600 mg bd)
Note: traditionally IV for 2 wks, then oral for 4 wks; erythromycin and gentamicin ineffective - Analgesia
Procedures
- IV (+ fluids, if dry)
Key management decision
- Arthroscopy (orthopaedic referral)?, if inflammatory markers slow to fall, or prosthetic joint
Stop/reduce
- Immunosuppression or chemotherapy, after DW specialist
Treatment (second line)
Procedures
- Arthroscopy
Note: especially if prosthetic joint involved; allows biopsy (TB?) - If unwell, urinary catheter, CVP line, arterial line
Prescribing issues
- Try to aspirate joint before first dose of antibiotic; if you cannot, don't wait .. give antibiotics ASAP
- Give IV AB for long enough (2 weeks)
Admit?
- Yes
Bed plan
- Medical admission ward
- Rheumatology
- ± ITU
Referrals
Medical
- Rheumatology
- ± ITU
Other
- Rheumatoid arthritis nurse
The Rest
Mortality is surprisingly high (10-15%; 30% if pre-existing RA)
Maxim
- "Where there is pus, let it out"
Complications
- Severe sepsis/shock [Ref]
- 50% cartilage proteoglycan lost within 48h
- Bone loss in 7 days; 25-50% are left with permanent joint damage
- Septic arthritis can be the cause or effect of infective endocarditis (ie can spread to or from a heart valve)
Note: listen to the heart for murmurs, look for splinters etc; ?refer to cardiology and consider 6 wks IV antibiotics
Follow-up
- Rheumatology
- ± orthopaedic
- ± specialist, if on immunosuppression or chemotherapy
Prognosis
- 10-15% mortality; if pre-existing RA, 20-30% (often due to missed diagnoses)
Risk stratification
- Signs of severe sepsis/shock warrant ITU
2° Prevention + Health promotion
- In RA, report acutely swollen joint immediately
Don't forget
- Orthopaedic referral, if not getting better (or prosthetic joint)
- Gonorrhoea and tuberculosis
- In elderly/immunocompromised, inflammation may not be overt
- Neither absence of organism on Gram stain nor negative subsequent synovial fluid culture excludes diagnosis
- BC sometimes positive (20-30%), before the synovial fluid (90%, but may take a week)
Red flags
- Severe sepsis/shock
