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Infection of the synovial joint space causing acute inflammation and joint destruction
Infection of the synovial joint space causing acute inflammation and joint destruction
Risk Factors
Pre-existing joint disease (OA, RA, gout, spondyloarthropathy)
Immunocompromised state (diabetes, HIV, malignancy, immunosuppressants)
IV drug use
Recent joint surgery or intra-articular injection
Prosthetic joints
Bacteraemia/sepsis
Aetiology
Staphylococcus aureus – most common overall, especially in adults and prosthetic joints
Streptococcus species – especially in children and elderly
Neisseria gonorrhoeae – in sexually active young adults
Haemophilus influenzae – in unvaccinated children
Gram-negative bacilli – especially in older adults, IVDU, or immunosuppression
Mycobacterium tuberculosis – chronic monoarthritis, often in spine or hip
Viral – parvovirus B19, hepatitis B/C, HIV (self-limiting, polyarticular)
Pathophysiology
Bacteria reach joint via haematogenous spread (most common), direct inoculation, or contiguous spread
Bacterial proliferation → inflammatory response → neutrophil infiltration, cytokine release
Cartilage destruction can occur rapidly – irreversible damage in <24–48 hours
Diagnosis
Acute monoarthritis with pain, swelling, warmth, reduced ROM
Fever, systemic signs in ~50%
Hip and knee most commonly affected in children
Shoulder and knee in adults
Gonococcal arthritis – migratory polyarthritis or tenosynovitis-dermatitis syndrome
Differential Diagnosis
Gout or pseudogout
Reactive arthritis (post-infectious, sterile)
Rheumatoid arthritis flare
Osteomyelitis (esp. in children)
Haemarthrosis (in trauma or coagulopathy)
Investigations
Urgent joint aspiration – gram stain, culture, WCC (>50,000 cells/mm³, mostly neutrophils), glucose, protein, crystals
Blood cultures ×2
FBC, CRP, ESR – usually elevated
Urate, ANA, RF, anti-CCP as indicated
X-ray – usually normal early, may show effusion
Ultrasound – joint effusion, guides aspiration
MRI/CT – if deep joint involved (e.g., hip)
Management
Empiric IV antibiotics after aspiration – tailored once culture results available
Empiric options:
Flucloxacillin (MSSA) or cefazolin
Ceftriaxone for Gram-negative coverage or suspected gonococcal arthritis
Vancomycin if MRSA risk
Drainage of joint – aspiration, arthroscopy, or open washout
Immobilisation initially, then gentle mobilisation
Complications & Prognosis
Rapid joint destruction and permanent damage
Osteomyelitis or chronic infection
Sepsis or systemic complications
Recurrent episodes in prosthetic joints or immunocompromised patients
Good prognosis with early treatment
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