Acute Swollen Joint

Differentials

Infective

• Septic arthritis: Often caused by Staphylococcus aureus or Group A streptococcus

• Osteomyelitis: Can extend into the joint space, leading to septic arthritis

• Viral arthritis: Parvovirus B19, rubella, mumps

• Reactive arthritis: Follows infections such as gastroenteritis or tonsillitis (commonly Campylobacter, Shigella, Salmonella)

Inflammatory

• Systemic juvenile idiopathic arthritis (JIA): Associated fever, rash, multiple joint involvement

• Acute rheumatic fever: Polyarthritis, carditis, history of sore throat, prevalent in some populations

Other

• Ross River virus infection: Fever, rash, polyarthritis lasting up to 3 months

• Parvovirus-associated arthritis: Can mimic rheumatoid arthritis

• Acute leukaemia: Leukaemic infiltration of joints presenting with arthritis

• Transient synovitis: Post-viral inflammation, can resemble septic arthritis

• Non-accidental injury: Unexplained or repeated trauma leading to joint swelling

Acute Swollen Joint with Fever

• Systemic JIA: Fevers, evanescent rash, marked joint involvement

• Acute leukaemia: Persistent bone pain, bruising, fatigue

• Septic arthritis: Surgical emergency requiring drainage and antibiotics

• Osteomyelitis: Can be more common than septic arthritis, look for local bone tenderness

• Viral or reactive arthritis: Consider parvovirus, rubella, mumps, or Ross River infection

• Acute rheumatic fever: Common in some communities, polyarthritis and possible carditis

Septic Arthritis Management

Emergency actions

• Orthopaedic referral for urgent drainage and washout

• Immobilisation and elevation of the joint to reduce pain and swelling

• IV fluids (0.9% saline) if there are signs of haemodynamic compromise

Investigations

• Joint aspirate for Gram stain, culture, and cell count

• Blood cultures, CRP, ESR, and FBC to assess infection and inflammation

• Imaging such as ultrasound or MRI to confirm effusion or adjacent osteomyelitis

Antibiotics

• IV flucloxacillin 25–50 mg/kg (max 2 g/dose) 6-hourly

• IV cephazolin if mild penicillin allergy

• IV vancomycin if MRSA is suspected

Supportive care

• Maintain oxygen saturation above 94%

• Adequate analgesia with paracetamol or ibuprofen

Key Points

• Red flags include fever above 38°C, severe pain, erythema, unwillingness to bear weight, and markedly elevated inflammatory markers

• Differentiate transient synovitis from septic arthritis by evaluating fever, systemic signs, and response to NSAIDs

• Delaying treatment in suspected septic arthritis can lead to joint destruction or systemic sepsis

Treatment of Septic Joint

• Urgent orthopaedic review and surgical drainage

• Support with oxygen therapy if needed

• Establish IV access for fluid resuscitation and antibiotics

• Blood cultures before antibiotic administration

• Immobility with limb elevation to reduce oedema and pain

• Start IV flucloxacillin or appropriate antibiotic cover based on local resistance patterns

• Administer an IV 0.9% normal saline bolus