18th January 2024

Diagnosis

It is vital that a suspected septic joint is investigated and managed as early as possible, as untreated infection quickly leads to joint destruction and can be fatal.

Signs and symptoms

The typical case is of an acute red, hot, swollen joint in a systemically unwell patient with a fever – however, it is important to note that in many cases, the patient may not appear systemically unwell.

Symptoms include pain and swelling, usually in one joint – most commonly the knee (can be polyarticular in a minority of patients). The patient will typically have an inability to weight bear and limited range of motion in the affected joint. Infections in other joints can lead to a variety of symptoms, e.g. sacroiliac joint infections may present as buttock or hip pain, and sternoclavicular joint infections may present with chest pain.

Investigations

A joint aspiration should be prioritised as it ideally needs to be performed prior to antibiotic administration to obtain the highest yield results. The synovial fluid would typically be cloudy in appearance in the presence of infection and should be examined for:

• Culture & Sensitivity
• Gram stain
• White Cell Count (typically >50,000/mm3)
• Polarising crystal microscopy

Other important investigations include: FBC, CRP and blood cultures. U&E and LFTs should be checked, as this may impact on choice of antibiotics. If Neisseria gonorrhoea is suspected, then cultures of extended sites (i.e. rectal, cervical, urethral or pharyngeal) for gonococcal infection will be required as this organism is poorly cultured in synovial fluid.

Plain radiographs are usually of no diagnostic benefit in septic arthritis but should be obtained if there is suspicion of injury or fracture. They may show chondrocalcinosis in pseudogout or osteomyelitis if the infection has progressed further into the bone, necessitating a longer treatment course.