Anatomy
The surfaces of the bones (Humerus, Radius & Ulna) meet to form the elbow joint which are covered with articular cartilage, a smooth substance that protects the bones and acts as a natural cushion to absorb forces across the joint. A thin, smooth tissue called synovial membrane covers all remaining surfaces inside the elbow joint. In a healthy elbow, this membrane makes a small amount of fluid that lubricates the cartilage and eliminates almost any friction as you bend and rotate your arm.