What characteristic symptom distinguishes knee effusion?

The characteristic symptom that distinguishes knee effusion is fluid accumulation. Knee effusion refers to an excess of synovial fluid in the knee joint, which can lead to the swelling of the knee. This swelling is often visible and palpable, making fluid accumulation a hallmark indicator of knee effusion. When there is an increased amount of fluid in the joint space, it results in a noticeable distension of the knee, leading patients to report a feeling of fullness or swelling.

The other symptoms, while they may occur alongside knee effusion, do not specifically indicate the presence of fluid. Joint stiffness can result from various issues affecting the knee, including osteoarthritis or inflammation, but it does not directly signal the accumulation of fluid. Popping sounds during movement, often referred to as crepitus, can occur for multiple reasons and are not exclusive to fluid accumulation in the joint. Joint warmth may indicate inflammation or infection but also does not specifically signify effusion. Therefore, fluid accumulation is the most definitive characteristic symptom of knee effusion.