Arthritis literally means an inflamed joint. The term derives its meaning from the Greek words ‘arthros’ meaning a joint and ‘itis’ meaning inflammation.
Inflammation is a natural physiological response of the body to any injury or damage. Inflammation is usually accompanied by pain, swelling and redness of the affected part.
In routine clinical practice the term “arthritis” is loosely used to describe any painful and swollen joint.
Anatomy of a Joint
A joint is formed where two or more bone ends meet. The joint is the interface where movement takes place. It is the “mobile unit” of the musculo-skeletal system. The function of the joint is to provide mobility as well as stability to the limb, and the structure of the joint has been very carefully designed to strike a balance between ‘mobility’ and ‘stability’.
The ends of a bone are covered with a tough elastic tissue called cartilage. Cartilage is a smooth glistening white structure which keeps the bone ends from rubbing against each other. The bone ends are enclosed by a fibrous tissue called the capsule. The capsule has a smooth inner lining called the synovial membrane which produces a lubricating fluid called the synovial fluid. The smooth cartilage along with the synovial fluid allows for a frictionless movement at the joint interface. The stability of the joint is maintained by ligaments which are made of tough fibrous tissue. The knee joint has two sets of ligaments – the two cruciate ligaments (anterior and posterior) inside the joint and the two collateral ligaments (medial and lateral) which are outside the joint capsule. Additionally the knee joint also has two menisci (medial and lateral). These are interposed between the bone ends, and function as shock absorbers. The joint is powered by the muscles and tendons which are responsible for moving the joint.
Anatomy of the knee joint