Synopsis
Approach an acutely inflamed native joint as a time-dependent diagnostic and source-control problem, aspirate before antibiotics when physiology permits, interpret synovial findings safely, and coordinate drainage and targeted therapy.
- Any acutely hot, swollen and movement-limited native joint warrants septic-arthritis assessment; absence of fever or normal serum markers cannot safely exclude it.
- Aspirate synovial fluid as quickly as practical for cell count and differential, Gram stain, aerobic and anaerobic culture and crystals; inoculation into blood-culture bottles may improve yield under laboratory protocol.
- Take at least two sets of blood cultures in febrile or bacteraemic presentations and investigate the skin, urine, lungs, heart, injection sites and other joints for source and spread.
- In a stable patient, collect synovial and blood specimens before antibiotics. In sepsis or shock, obtain rapidly available blood cultures and give intravenous antibiotics without waiting for aspiration.
- Synovial white-cell count increases probability but no universal cutoff excludes infection; immunosuppression and early disease can produce lower counts, and crystals do not rule out bacteria.
- Plain radiographs establish baseline and alternatives; ultrasound detects and guides aspiration of effusion, while MRI answers deep-joint, osteomyelitis or abscess questions.
- Prompt surgical debridement is generally recommended for a septic large native joint; serial aspiration is an exception selected by senior teams for specific accessible presentations.
- Narrow treatment to cultures, drain again when clinical or CRP response fails, mobilise after infection control and search for endocarditis or metastatic foci when bacteraemia persists.
Key red flags
Hypotension, confusion, lactate elevation, rigors or rapidly progressive illness requires sepsis treatment and antibiotics after blood cultures without waiting for image-guided aspiration.
A hot painful prosthetic joint follows a separate implant-infection pathway; this route applies to native cartilage and must not be used to justify simple aspiration of a prosthesis.
Hip, shoulder, sternoclavicular, sacroiliac or spinal-region symptoms can hide a deep septic focus and require urgent specialist imaging and drainage planning.
Bacteraemia, a new murmur, embolic lesions, multiple painful joints or S. aureus in blood cultures raises concern for endocarditis and metastatic infection.
Investigation priorities
Obtain direct joint microbiology before antibiotics when safe.
Management branches
Organ dysfunction or high-risk sepsis accompanies a suspected infected native joint.
- Start ABCDE sepsis care and call orthopaedics, anaesthesia, microbiology and the relevant medical team.
- Take rapidly obtainable blood cultures, then give local empirical intravenous therapy without waiting for image-guided aspiration.
- Aspirate and drain the joint at the earliest safe opportunity and collect synovial tissue for culture.
- Track blood-culture clearance and investigate endocarditis, osteomyelitis and other metastatic foci.
A native-joint effusion and movement pain are present without physiological instability.
- Obtain blood tests, blood cultures when indicated and urgent sterile synovial fluid before antimicrobial exposure.
- Send differential count, Gram stain, aerobic and anaerobic culture and crystals, preserving volume for microbiology.
- Start protocol intravenous treatment immediately after sampling and arrange prompt operative drainage for a septic large joint.
- Tailor drugs and the need for repeat washout from cultures, anatomy and clinical and CRP trajectory.