InnerBody describes the knee joint as a classic example of a synovial joint. The junction of the femur and tibia bones are enclosed in a joint capsule, lined with synovial tissue, encasing synovial fluid and two shock absorbing cartilage pads. The joint capsule is protected by the patella, or kneecap.
Healthline explains that the complete knee joint is a complex mechanism composed of muscles, ligaments, tendons and bones. The joint capsule allows the knee to bend and is held together by ligaments, which also act to flex the leg. The cartilage pads, or menisci, disperse friction between the meeting ends of the femur and tibia. Synovial fluid inside the joint capsule acts as a lubricant and is secreted by the synovial tissue, according to Johns Hopkins.