A joint is the space between two bones. The ends of the bone are covered by cartilage. This cartilage secretes a fluid that lubricates the joint. Where your fingers, thumbs and wrists bend are joints. There are also joints in the hand that are harder to see moving, but they also have important function. There are many conditions that can affect the joint.
Arthritis: This occurs when the cartilage on the bone starts to wear away. The bone ends start rubbing directly on each other, which can be quite painful. This is also known as osteoarthritis, which is different from rheumatoid arthritis. Arthritis can be treated with medications, splints, therapy, and sometimes surgery. Surgery involves removing the joint or replacing it.
This photo below is of the trapezium, a bone in the hand that is removed in patients with thumb arthritis.
Rheumatoid Arthritis: This is an auto-immune condition, which means that the body mistakenly attacks healthy cells. Here the cells lining the joint are attacked, and they become inflamed and swollen.
Gout: This condition is caused when salt deposits build up in the joints. The joint will be very painful, swollen and red. It may sometimes be confused with an infection.