Hemophilia causes joint disease primarily through repeated bleeding episodes inside the joints, known as hemarthroses. Because hemophilia is a genetic disorder that impairs the blood’s ability to clot properly, even minor injuries or sometimes spontaneous events can lead to bleeding within the joint spaces. This bleeding is not easily stopped, so blood accumulates inside the joint cavity, causing damage over time.
When blood leaks into a joint, it triggers a cascade of harmful effects. The presence of blood inside the joint is toxic to the joint tissues, especially the cartilage and the cells called chondrocytes that maintain it. The iron from the blood’s hemoglobin deposits in the joint lining and cartilage, leading to inflammation and oxidative stress. This inflammation causes the synovium—the thin membrane lining the joint—to thicken and become more fragile, which makes it prone to further bleeding. The cycle of bleeding, inflammation, and tissue damage repeats with each episode.
Over time, the repeated bleeding causes the cartilage to break down and the joint space to narrow. The chondrocytes, which produce the molecules that keep cartilage healthy, undergo apoptosis (cell death) due to the toxic environment. The synthesis of proteoglycans, essential components of cartilage that provide cushioning and elasticity, is impaired. As cartilage deteriorates, the bones within the joint begin to rub directly against each other, causing pain, stiffness, and loss of mobility.
The joint lining’s chronic inflammation also leads to fibrosis and scarring, further restricting joint movement. The joint may become swollen and deformed, and muscles around the joint weaken due to disuse and pain. This progressive joint damage is called hemophilic arthropathy, a form of degenerative joint disease unique to people with hemophilia.
The most commonly affected joints are the knees, elbows, and ankles, which bear weight or are frequently used. Early in the disease, bleeding episodes may cause acute pain and swelling, but with repeated bleeding, the joint damage becomes permanent and disabling. Without proper treatment to prevent or quickly control bleeding, joint disease can severely impair quality of life.
In summary, hemophilia causes joint disease by allowing blood to repeatedly enter the joint spaces, where it damages cartilage cells, disrupts cartilage maintenance, causes inflammation and scarring, and ultimately leads to chronic joint degeneration and disability. Managing hemophilia with clotting factor replacement or other therapies aims to prevent these bleeding episodes and protect joint health.