Approach

Although there are clinical features and laboratory results that are highly suggestive of septic arthritis, there is no single factor that is 100% sensitive or 100% specific for the diagnosis. The key to diagnosis is the level of clinical suspicion of a clinician experienced in the management of musculoskeletal disease. If clinical suspicion is high then it is imperative to treat for presumed septic arthritis, regardless of the results of blood tests or microbiology.[12] If a patient with signs or symptoms suggestive of infection is acutely deteriorating, clinicians should consider the possibility of sepsis and urgently undertake a systematic evaluation to identify those at risk of deterioration due to organ dysfunction, referring to local guidance where appropriate.[13][14] See Sepsis in adults and Sepsis in children.

History

Septic arthritis usually presents with a short history of a hot, swollen, painful joint (or joints) with associated restriction of movement.[3][4] Presentation may be more insidious in the context of a low-virulence organism or tuberculosis, or if the joint is prosthetic.[4][5] In the context of underlying joint disease, a septic joint should be suspected if symptoms in the affected joint are out of proportion to the disease activity detected elsewhere. In up to 22% of cases septic arthritis is polyarticular.[2][6]

Risk factors

Risk factors for the development of septic arthritis include rheumatoid arthritis, osteoarthritis, joint prostheses, low socioeconomic status, intravenous drug abuse, alcohol use disorder, diabetes, previous intra-articular corticosteroid injection, and the presence of cutaneous ulcers. In sexually active patients gonococcal arthritis may be suspected.[2][3][4][6][7][8] The incidence of MRSA is increasing in North America.[15] Those patients particularly at risk are recent inpatients, nursing home residents, and those with leg ulceration or indwelling urinary catheters. Tuberculous arthritis is also becoming more frequent and should be suspected in immunocompromised people and in those from regions where tuberculosis is prevalent.

Examination

The characteristic features of an infected joint are swelling, warmth, tenderness, and a significant reduction in the range of movement. The presence or absence of a fever is not a reliable indicator of joint sepsis.[3][4][5][6]

Laboratory investigations

If septic arthritis is suspected, it is mandatory to aspirate the joint to obtain a sample of synovial fluid before antimicrobial therapy is started.[11]

A contraindication to simple aspiration is the presence of a joint prosthesis. Under these circumstances it is recommended that any invasive procedure should be undertaken under sterile conditions in an operating room, and therefore referral to an orthopedic surgeon is recommended. It is also recommended that patients with suspected tuberculous arthritis be referred to an orthopedic surgeon, and synovial biopsy may be indicated to confirm the diagnosis.​​

Aspiration and injection of the knee: animated demonstration
Aspiration and injection of the knee: animated demonstration
​
Aspiration and injection of the knee: animated demonstration
Aspiration and injection of the knee: animated demonstration
​

Neither overlying cellulitis nor anticoagulation is an absolute contraindication to joint aspiration. Specialist help should be sought if the attending physician feels uncomfortable performing arthrocentesis under either of these conditions.

Synovial fluid should be sent for immediate Gram stain, white cell count, and subsequent culture. Blood cultures are also recommended at initial presentation before the start of antibiotic therapy.

The serum white cell count, erythrocyte sedimentation rate, and C-reactive protein may be helpful both in the diagnosis and the monitoring of treatment. It is therefore recommended that these investigations be performed routinely if septic arthritis is suspected.

Electrolytes and liver function tests may be performed to indicate whether there is systemic sepsis.

If the history or examination suggests an alternative, nonarticular source of infection then appropriate samples should be taken and sent for culture.

Procalcitonin (PCT) can help identify bacterial infection, and serial measurements may indicate response to therapy.[18] However, serum PCT is not yet recommended as a routine diagnostic tool.[19]

Radiological imaging

There are no radiological investigations that have been found to be reliable in the diagnosis of septic arthritis.[20][21] However, it is recommended that a baseline plain radiograph be performed to establish any underlying joint disease at presentation.[22]

Magnetic resonance imaging may be helpful if associated osteomyelitis is suspected.[22]

If hip sepsis is suspected, it is suggested that aspiration be performed under ultrasound guidance.

Venepuncture and phlebotomy: animated demonstration
Venepuncture and phlebotomy: animated demonstration

How to take a venous blood sample from the antecubital fossa using a vacuum needle.

Use of this content is subject to our disclaimer