What Is Osteoarthritis?
Osteoarthritis (OA) is not a single disease but rather the end result of a variety of disorders leading to the structural or functional failure of one or more of your joints. Osteoarthritis is the most common cause of chronic joint pain, affecting over 25 million Americans. Osteoarthritis involves the entire joint, including the nearby muscles, underlying bone, ligaments, joint lining (synovium), and the joint cover (capsule).
- Osteoarthritis also involves progressive loss of cartilage. The cartilage tries to repair itself, the bone remodels, the underlying (subchondral) bone hardens, and bone cysts form. This process has several phases.
- The stationary phase of disease progression in osteoarthritis involves the formation of osteophytes and joint space narrowing.
- Osteoarthritis progresses further with obliteration of the joint space.
- The appearance of subchondral cysts (cysts in the bone underneath the cartilage) indicates the erosive phase of disease progression in osteoarthritis.
- The last phase in the disease progression involves bone repair and remodeling.
- Joint cartilage is a layer of tissue present at the joint surfaces that sustains joint loading and allows motion. It is gel-like, porous, and elastic. Normal cartilage provides a durable, low-friction, load-bearing surface for joints.
- Articular surface is the area of the joint where the ends of the bones meet, or articulate, and function like a ball bearing.
- Bone remodeling is a process in which damaged bone attempts to repair itself. The damage may occur from either an acute injury or as the result of chronic irritation such as that found in osteoarthritis.
- Collagen is the main supportive protein found in bone tendon, cartilage, skin, and connective tissue.
- Osteophytes are bony outgrowths or lumps, especially at the joint margins. They are thought to develop in order to offload the pressure on the joint by increasing the surface area on which your weight is distributed.
- Synovium is a membrane surrounding the joints that secretes a fluid that lubricates and provides nutrition to tissues.
- Subchondral bone is the part of bone under the cartilage.
- Osteoarthritis is also known as degenerative joint disease.
- Related to its effect on joints, osteoarthritis is sometimes referred to as osteoarthrosis.
What Causes Osteoarthritis?
The causes of osteoarthritis include the following:
- Endocrine: People with diabetes may be prone to osteoarthritis. Other endocrine problems also may promote osteoarthritis development, including acromegaly, hypothyroidism, hyperparathyroidism, and obesity.
- Posttraumatic: Traumatic causes can be further divided into macrotrauma or microtrauma. An example of macrotrauma is an injury to the joint such as a bone break, causing the bones to line up improperly (malalignment), lose stability, or damage cartilage. Microtrauma may occur over time (chronically). An example of this would be repetitive movements or the overuse noted in several occupations.
- Inflammatory joint diseases: This category would include infected joints, chronic gout, and rheumatoid disease.
- Metabolic: Diseases causing errors of metabolism may cause osteoarthritis. Examples include Paget's disease and Wilson disease.
- Congenital or developmental: Abnormal anatomy such as unequal leg length may be a cause of osteoarthritis.
- Genetic: A genetic defect may promote breakdown of the protective architecture of cartilage. Examples include collagen disturbances such as Ehlers-Danlos syndrome.
- Neuropathic: Diseases such as diabetes can cause nerve problems. The loss of sensation may affect how the body knows the position and condition of the joints or limbs. In other words, the body can't tell when it is injured.
- Other: Nutritional problems may cause osteoarthritis. Other diseases such as hemophilia and sickle cell are further examples.
Medically Reviewed by a Doctor on 9/8/2017
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