Acute hemarthrosis of the knee.

Rapid swelling of the knee following a blow or twisting injury is considered a significant injury. The history of trauma coupled with a thorough examination should provide an accurate diagnosis in most patients. Although it should not be performed routinely, aspiration of the fluid can be done to aid in making a diagnosis and to alleviate pain. Splinting and re-evaluation are recommended as the initial treatment of an acute hemarthrosis. Ancillary testing that includes x-ray films and MRIs is beneficial. Although arthroscopic evaluation of the knee is not needed in every patient with an acute hemarthrosis, a high percentage of these patients eventually undergo arthroscopy to complete the diagnosis or as a means of early surgical intervention. The decision to surgically repair an injured structure depends on the patient's age, activity level, amount of instability, and associated lesions. Routine arthroscopy is indicated as a means to determine the correct treatment and not merely for diagnosis. With knowledge of the common causes of hemarthrosis and understanding of the knee examination, a trained examiner can make an accurate diagnosis 80% to 90% of the time and prescribe the appropriate treatment.