Native-joint septic arthritis

Native-joint septic arthritis means microbial infection of a joint without a prosthesis. Ask exactly when pain and immobility began, whether one or several joints are involved and about fever, rigors, recent skin or urinary infection, wounds, injection, surgery, antibiotics, sexual exposure, injecting drug use and travel. Establish diabetes, renal disease, inflammatory arthritis, immunosuppression and anticoagulation. Older or immunocompromised people may present with delirium or loss of function rather than fever, while gonococcal disease may add tenosynovitis, sparse pustules or migratory symptoms.

First assess physiological stability and obtain a full observation set. Examine the joint for effusion, warmth, held position and restriction of both active and passive movement, comparing the opposite side. Inspect overlying skin before choosing an aspiration route and assess distal neurovascular status. Examine other joints, the spine, skin, nails, injection sites and potential respiratory or urinary sources. Cardiac examination and endocarditis assessment are important with S. aureus bacteraemia, persistent positive cultures or embolic features.

Serum FBC, CRP and renal and liver profiles support severity, baseline monitoring and antimicrobial selection but do not exclude infection. Obtain at least two blood-culture sets when febrile or bacteraemia is suspected. Aspirate the joint urgently using sterile technique before antibiotics when the patient is stable. Send enough fluid for microscopy, cell count with differential, Gram stain, aerobic and anaerobic culture and crystals; prioritise microbiology over less decisive tests when volume is scant. Tell the laboratory about prior antibiotics and unusual exposure.

Interpret synovial findings probabilistically. Purulence and a high neutrophil count increase concern, but a lower count occurs early, after antibiotics or with immune suppression. A negative Gram stain has insufficient sensitivity to clear the joint. Crystals can be present alongside infection. Conversely, inflammatory disease can produce very high counts. Culture remains central, and molecular tests may help specialist teams after antibiotics or with culture-negative high suspicion. Never delay source control while waiting for a final culture when the clinical and aspirate picture is dangerous.

Imaging answers anatomical questions rather than replacing aspiration. Plain films document baseline joint damage, fracture, foreign body, calcification and osteomyelitis clues. Ultrasound confirms an effusion and guides hip, shoulder or small-joint access. MRI maps synovitis, subchondral osteomyelitis, abscess and deep-joint extension when results change surgery. CT may guide axial-joint aspiration. Echocardiography is not routine for every hot joint but becomes relevant through a bacteraemia and endocarditis pathway.

Stable patients receive empirical intravenous treatment immediately after cultures and aspiration. Choice follows the local native-joint protocol, considering Gram stain, age, allergy, renal function, MRSA risk, injecting exposure, sexual history and prior organisms. A septic patient receives antibiotics after immediately obtainable blood cultures even if aspiration is delayed. Narrow when microbiology returns and document dose, route and total duration from joint, organism, drainage completeness and adjacent bone infection rather than importing a single schedule into every presentation.

Drainage removes bacteria, inflammatory enzymes and pressure. For a large peripheral native joint, arthroscopic lavage and synovectomy are usually preferred when expertise is available, while open drainage is appropriate for difficult access, advanced intra-articular disease, adhesions or failed arthroscopy. Aspirate fluid before incision and take synovial tissue samples. Serial needle aspiration may be used in selected accessible joints when operative risk or local practice supports it, but failure of fever, pain, function or CRP to improve prompts repeat aspiration, imaging or washout.

After source control, provide analgesia and initially protect the joint, then begin supervised movement as pain and infection settle to limit stiffness and muscle loss. Review cultures and blood-culture clearance, inspect portals and reassess every other painful site. Persistent bacteraemia requires source investigation rather than simply extending antibiotics. At discharge, state the exact agent, dose, route, monitoring and review date, plus urgent return signs. Later care assesses range, strength, cartilage damage, recurrence and the underlying source, including sexual-health partner management when gonococcal infection is confirmed.