The effect of experimental hemarthrosis on joint stiffness and synovial histology in a rabbit model.

The effect of a single injection of unpreserved blood on joint stiffness and on synovial and cartilage histomorphology in the ankle joints of rabbits was determined at ten and 28 days after injection. The same volume of saline was placed in the contralateral ankle for comparison. After ten days, the hemarthrosis ankle was stiffer than the control ankle (p < 0.027), whereas at 28 days there was no statistical difference in stiffness between the hemarthrosis and control ankles, regardless of whether the limbs had been immobilized. Also after ten days, the hemarthrosis ankles had varying amounts of clotted blood, darkened articular cartilage, hypertrophic synovium with reactive blood vessels, and macrophages containing heme. The gross and histologic appearance of the saline ankles was normal. After 28 days, there were no differences in gross or microscopic appearance between the two ankles of the caged or immobilized rabbits. All ankles exhibited retreating inflammatory response in the synovium and mild synovial thickening. Acute hemarthrosis, unassociated with fracture or discernible joint injury, caused only transient changes in joint stiffness and synovial histology. These results indicate that the presence of blood in an otherwise grossly uninjured joint should not lead to ultimate compromise in cartilage integrity or joint function. Therapeutic arthrocentesis for acute posttraumatic hemarthrosis does not appear to be necessary for the prevention of permanent problems.