Arm and Elbow
The humerus is the bone in the upper arm, and the radius and ulna are the bones in the forearm. The three bones come together to make the hinge-and-pivot elbow joint. The ends of the bones, where they meet to form the joints, are covered in a layer of articular cartilage that absorbs shock and allows the bones to glide smoothly against one another. Tough bands of connective tissue and ligaments hold the bones of the elbow together and provide stability.
Triceps, biceps, flexors, and extensor muscles make it possible to move the arm, wrist, and fingers. The biceps tendon attaches the biceps on the front of the arm to the radius, enabling the elbow to bend. The triceps tendon attaches the triceps to the ulna, enabling the elbow to straighten.
Arthritis 
