Egypt's second faith is Coptic Christianity. Copts are heirs of an ancient Christian rite. Coptic Christianity was the predominant religion in Egypt until the 10th century when a lot of Christians diverted to Islam. Christianity itself was brought in Egypt by St. Mark in the middle of the first century AD.
Other possible causes of swelling behind the knee include abscesses (infections); tumors of the skin, soft tissue, or bones; bleeding; deep venous thrombosis (blood clot in the deep veins of the legs); or deformity of the joint after a fracture of any of the bones of your knee joint.
Your Fit Fix: This same repetitive knee bending and straightening action from excessive overuse leads to accumulation of fluid, which results in a cyst behind the knee. While you can take time off from training, the best way to treat this is to get an injection or have the spot aspirated to draw out the fluid.