Bleeding into a joint is referred to as hemarthrosis and is an important cause of monoarticular joint pain and swelling. Hemarthrosis may be suspected on the basis of a suggestive history, physical examination, or imaging studies, but definitive diagnosis usually requires joint aspiration. (See "Evaluation of the adult with monoarticular pain" and "Joint aspiration or injection in adults: Technique and indications" and "Joint aspiration or injection in children: Indications, technique, and complications".)
Synovial fluid obtained from a patient with a hemarthrosis may appear red, pink, or brown. Other abnormalities of the fluid may be noted that depend upon the cause of the bleeding. As an example, the presence of lipid globules strongly suggests an intraarticular fracture, resulting in leakage of marrow fat into the synovial fluid. A true bloody effusion usually fails to clot due to chronic fibrinolysis, while blood from a traumatic aspiration generally does coagulate .
If the aspiration is not bloody initially, but fresh blood appears after some synovial fluid has been withdrawn, the most likely cause is a traumatic arthrocentesis. In this case, centrifugation of the specimen is useful. A serous appearance of the synovial fluid supernatant suggests that fresh blood has been admixed with previously nonbloody fluid. The aspirate from a patient with hemarthrosis will generally exhibit xanthochromia from lysis of the resident erythrocytes.
Although diagnosis of hemarthrosis usually requires joint aspiration, arthrocentesis is generally not required for diagnosis when the underlying cause is known with confidence (eg, patients with hemophilia and a history of hemarthrosis), and when important alternate diagnoses such as septic arthritis can be excluded clinically.
CAUSES OF HEMARTHROSIS
Broad categories of disorders that may result in hemarthrosis include trauma, bleeding disorders, neurologic deficits, arthritis, neoplasms, vascular damage, and other miscellaneous causes (table 1).