Arthritis is the swelling and tenderness of one or more of your joints. The main symptoms of arthritis are joint pain and stiffness, which typically worsen with age. The most common types of arthritis are osteoarthritis and rheumatoid arthritis.
 
Symptoms
  • Pain
  • Stiffness
  • Swelling
  • Redness
  • Decreased range of motion

Causes

 

Osteoarthritis
The most common type of arthritis, osteoarthritis involves wear-and-tear damage to your joint’s cartilage — the hard, slick coating on the ends of bones where they form a joint. Cartilage cushions the ends of the bones and allows nearly frictionless joint motion, but enough damage can result in bone grinding directly on bone, which causes pain and restricted movement. This wear and tear can occur over many years, or it can be hastened by a joint injury or infection.

Osteoarthritis also affects the entire joint. It causes changes in the bones and deterioration of the connective tissues that attach muscle to bone and hold the joint together. It also causes inflammation of the joint lining.

Rheumatoid arthritis
The body’s immune system attacks the lining of the joint capsule, a tough membrane that encloses all the joint parts. This lining (synovial membrane) becomes inflamed and swollen. The disease process can eventually destroy cartilage and bone within the joint.

 
Ref.: MayoClinic