Intermittent hydrarthrosis, unspecified knee

This code describes a condition characterized by recurrent, temporary swelling of the knee joint due to an accumulation of synovial fluid, without a clear underlying cause identified. The effusion is intermittent, meaning it comes and goes, and affects an unspecified knee.

Use this code when documentation indicates episodic, non-inflammatory joint effusion of the knee where the specific knee (left or right) is not documented. This diagnosis is often made after ruling out other causes of knee swelling, such as trauma, infection, or inflammatory arthropathies.

• Ensure the documentation explicitly states "intermittent hydrarthrosis" and does not specify laterality.
• If laterality is documented (e.g., right or left knee), use the more specific codes M12.461 or M12.462.
• Always look for documentation of an underlying cause; if one is found, code that condition first, as intermittent hydrarthrosis may be a manifestation.