The ends of healthy bones meet in joints and are covered by cartilage, a spongy material that allows almost frictionless motion between bones. Joints are enclosed in a capsule and lined with a tissue called synovium. The synovium releases a lubricating fluid that helps the joint move smoothly and easily, while muscles, tendons, and ligaments support and connect the joint.
However, because of aging, disease, hereditary, structure, overuse, and unknown factors, joints may deviate from the idealistic conditions described above. For example, osteoarthritis upsets this careful balance and causes pain, stiffness, and swelling.
Arthritis is an inflammation of a joint, but is commonly used to describe a condition in which cartilage is damaged. The three main types of arthritis are traumatic, rheumatoid, and osteoarthritis.
Osteoarthritis (OA), the most common type of arthritis, is a disease of the entire joint, typically involving the cartilage, bone, synovial membrane, and ligaments. Cartilage physiology is typically altered, and cartilage is eroded at the location where two bones meet, or articulate.
Traditionally, osteoarthritis was thought to be due to normal "wear and tear" of aging, a degenerative disorder for which little could be done. Since the 1980s, research evidence has shifted the focus of thinking, and now there are a variety of treatment options to relieve pain such as NSAIDs, corticosteroids, acetaminophen, joint replacement, and more recently, hyaluronic acid viscosupplementation.