Why can hemophilia cause repeated bleeding into joints and muscles?

Hemophilia is a hereditary disorder characterized by a deficiency in specific substances necessary for blood coagulation, such as factor VIII, factor IX, or factor XI. Because the body cannot effectively form the clots required to stop bleeding, individuals with this condition are highly susceptible to hemorrhages.1

Repeated bleeding into joints, known as hemarthrosis, and muscles occurs because even trivial, often unnoticed injuries can trigger significant internal bleeding. In the absence of adequate clotting factors, these minor traumas lead to persistent bleeding within the joint spaces—most commonly the knees, ankles, and elbows—and soft tissues. Over time, these recurrent episodes of hemorrhage can result in swelling, severe residual deformities, and a permanent loss of mobility and function in the affected areas. Management of these episodes typically involves the infusion of the missing clotting factors to restore the body's ability to stop the bleeding.12