Synopsis
Recognise native-joint sepsis, aspirate before antibiotics when safe, drain infected synovium urgently and tailor systemic treatment to organism, host and adjacent bone involvement.
- Septic arthritis is infection within a native synovial joint and can destroy cartilage within days; treat the acutely hot restricted joint as infection until adequately assessed.
- First diagnostic priority in a stable patient is urgent synovial aspiration before antibiotics for cell count, Gram stain, culture and crystal analysis.
- Do not delay antibiotics for aspiration in sepsis or haemodynamic instability; take blood cultures and treat immediately.
- Crystals do not exclude infection, and a negative Gram stain or modest synovial white-cell count cannot safely rule it out.
- Use ultrasound to identify and guide aspiration of an effusion; deep joints may require radiology or operative sampling.
- Drainage is definitive source control through serial aspiration or arthroscopic or open washout according to joint, response and surgical assessment.
- Empirical antibiotics follow local native-joint guidance, allergy, renal function, MRSA risk and likely source; narrow promptly to blood and synovial cultures.
- Search for endocarditis, osteomyelitis, skin infection, recent procedure and disseminated gonococcal infection when history or organism suggests them.
Key red flags
Hypotension, confusion, tachypnoea or rising lactate indicates septic shock requiring immediate treatment.
Severe pain on passive movement with an effusion makes an infected joint a priority diagnosis.
Hip, shoulder, sacroiliac or sternoclavicular infection can be deep, clinically subtle and difficult to aspirate.
Immunosuppression, older age or anti-inflammatory therapy can blunt fever and blood inflammatory responses.
Recent surgery, injection, bacteraemia, skin infection or intravenous drug use raises organism and metastatic-focus risk.
A prosthetic joint follows a distinct implant-infection pathway and requires specialist sampling and surgery planning.
Rapid onset of severe pain, swelling, warmth and markedly restricted active and passive movement is the classic native-joint presentation.
Hip infection may present with groin pain and inability to weight bear, while shoulder or sternoclavicular disease can cause chest or proximal limb pain.
Fever, rigors, delirium, hypotension and malaise support invasive infection but may be absent in older or immunosuppressed patients.
Recent skin infection, intravascular access, injection drug use, endocarditis features or a distant infection suggests haematogenous seeding.
Investigation priorities
Obtain the most direct pre-treatment evidence of joint infection and alternative crystal disease.
Management branches
A new hot, swollen or severely restricted native joint has no better established diagnosis.
- Assess ABCDE and sepsis, document every involved joint, skin source, procedure, immune status, sexual exposure and endocarditis risk.
- Take blood cultures and aspirate the joint before antibiotics when the patient is stable and aspiration can occur immediately.
- Send Gram stain, aerobic and anaerobic culture, cell count and crystals and inoculate appropriate culture bottles according to laboratory protocol.
- In sepsis, do not wait for aspiration: give empirical intravenous therapy after blood cultures and arrange drainage at the earliest safe opportunity.