Synarthrosis, amphiarthrosis, and diarthrosis are the three main joints in the human. The synarthrosis are fixed or fibrous joints; they're immovable. The amphiarthrosis are two or more bones held tightly together so only limited movement can take place; they're slightly movable. The diarthrosis are joints that have synovial fluid that enables all parts of the joint to smoothly move against each other; they're freely movable.
Examples of Joints
Examples of joints include ball and socket joints, hinge joints, condyloid joints, pivot joints, gliding joints, and saddle joints. Ball and socket joints permit movements in all directions and feature the rounded head of one bone sitting in the cup of another bone; examples include shoulder and hip joints. Hinge joints open and close in one direction along one plane; examples include elbow and knee joints. Condyloid joints allow movement but no rotation; examples include finger joints and your jaw. Pivot joints are characterized by one bone that can swivel in a ring formed from a second bone; examples include joints between the ulna and radius bones that rotate your forearm and the joint between the first and second vertebrae in your neck. Gliding joints only permit limited movement; examples include the joint in your wrist. Saddle joints don't allow rotation, however, they movement back and forth and side to side; examples include the joint at the base of your thumb.
Threats to Joints
Threats to joints include osteoarthritis and bursitis. Osteoarthritis is when the protective cartilage that cushions the ends of the bones wears down over time. Bursitis the inflammation of a bursa. A bursa is a closed, fluid-filled sac that works as a cushion and gliding surface to reduce friction between tissues of the body.
Fun Facts About Joints
Two interesting facts about joints are not all joints move and the biggest joint is the knee joint.