What is the first step in the diagnosis of septic arthritis?

The first step in the diagnosis of septic arthritis is joint aspiration, often referred to as arthrocentesis. This procedure is critical because it allows for the collection of synovial fluid from the affected joint, which can then be analyzed for signs of infection, such as the presence of white blood cells, bacteria, or crystals.

By obtaining and analyzing this fluid, healthcare providers can rule out or confirm septic arthritis and differentiate it from other conditions like gout or pseudogout. Joint aspiration also provides an opportunity for simultaneous treatment, as the infected or inflamed fluid can be removed, potentially alleviating symptoms and allowing for better management of the infection.

Additionally, while blood cultures and imaging studies like X-rays are important in the overall evaluation of a patient with suspected septic arthritis, they do not provide direct evidence of infection within the joint itself as joint aspiration does. Blood cultures are helpful for identifying systemic infection, and X-rays might show joint effusion or other changes, but they are not diagnostic tools for septic arthritis in isolation.