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.
Knee effusion, colloquially known as water on the knee, occurs when excess fluid accumulates in or around the knee joint. There are many common causes for the swelling, including arthritis, injury to the ligaments or meniscus, or when fluid collects in the bursa. This condition is known as prepatellar bursitis.