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The word “arthrosis” is used in two different ways. In the first sense, it is used simply to refer to a joint at which two or more bones articulate for the purpose of allowing movement. For example, the knee is an arthrosis. In the second sense, people may use it to talk about disease in the joints; thus, someone may be said to “have arthrosis,” meaning that the cartilage in one or more joints is breaking down.
While joints are often depicted as the place where bones meet, this is not actually quite accurate. The bones in a joint are covered in tough cartilage and surrounded with connective tissue to create an articulated joint which can move smoothly within a range of motion determined by the type of joint and the limitations of the connective tissue. Bone on bone contact within a joint is actually undesirable, as bones are not designed to withstand the pressure and grinding which joints endure on a regular basis.
Ball and socket joints, such as the hip, consist of a bone which articulates with a socket created by another bone. Other types of joints include pivot joints, gliding joints, saddle joints, condyloid joints, and hinge joints. Pivot joints like those in the neck rotate, gliding joints such as the collarbone are designed to accommodate sliding movements, and saddle joints have a range of movement, but cannot rotate, with the thumb being an excellent example of this kind of arthrosis. Condyloid joints such as the wrist have similar patterns of movement, while hinge joints, as seen in the fingers, are designed to fold.
The diversity of arthroses in the body illustrates the many different ways in which the body moves. Different types of joints allow for stable, precise, and highly controlled movement. This is perhaps most notable in the hands, which have a high degree of dexterity. The coordination of the hands permitted in part by the types of joints present in the hand is often credited for the success of humans in general as a species.
When talking about joint disease, arthrosis is a primary disease process in the joint which causes the cartilage in the joint to break down. Over time, the wearing of the cartilage can lead to inflammation, stiffness, and other problems in the joint because the cartilage loss results in less freedom of movement. This can also be very painful, and may be treated in a variety of ways, including with medications to manage pain and inflammation.