The joint capsule of the knee is a fibrous, thick sac that has a synovial membrane, which nourishes all of the parts surrounding the capsule. The membrane covers the articular surfaces where the condyles of the femur and patella come together, as well as those where the femur and tibia condyles meet.mycontentbreak Within the capsule, the bursa and infrapatellar fat pad cushion the knee against any force that’s placed on it. The ligaments around the capsule keep it strong.