A small bulge at the knee may be caused by synovitis, meniscus injury, chronic inflammation and other reasons. 1. Synovitis: This disease can cause swelling and pain in the knee joint, and from the appearance of a small bulge in the knee, it can also be accompanied by limited joint movement, the affected area of the skin fever and other symptoms. It is mainly caused by trauma, infection and joint degeneration. 2. Meniscus injury: usually caused by strenuous exercise or trauma, due to meniscus injury, can lead to cysts or fluid accumulation in the tissues around the meniscus, which may show a small bulge in the knee, accompanied by knee pain, swelling and other symptoms. 3. Chronic inflammation: common in the elderly osteoarthritis, rheumatoid arthritis and other diseases, due to the stimulation of inflammation, can lead to knee joint swelling, sometimes caused by a small bulge in the knee, but also accompanied by claudication, knee joint activity limitation and other symptoms. There is a small bulge at the knee, may also be caused by other reasons, if accompanied by obvious discomfort symptoms, should be as early as possible to seek medical attention, improve the relevant examination, clear the cause of the disease, by the doctor’s guidance for treatment, so as to avoid delaying the condition.