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.
This is often a surgical problem as the piece needs to be taken out for the symptoms to resolve. More commonly, irritation of the front of the knee joint called the patellofemoral region can cause a sudden relaxation of the quadriceps (thigh) muscle leading to a similar giving way sensation. This is very common!