Acute knee effusions: a systematic approach to diagnosis.

Knee effusions may be the result of trauma, overuse or systemic disease. An understanding of knee pathoanatomy is an invaluable part of making the correct diagnosis and formulating a treatment plan. Taking a thorough medical history is the key component of the evaluation. The most common traumatic causes of knee effusion are ligamentous, osseous and meniscal injuries, and overuse syndromes. Atraumatic etiologies include arthritis, infection, crystal deposition and tumor. It is essential to compare the affected knee with the unaffected knee. Systematic physical examination of the knee, using specific maneuvers, and the appropriate use of diagnostic imaging studies and arthrocentesis establish the correct diagnosis and treatment.