Osteoarthritis can be classified as primary or secondary. Primary osteoarthritis has an unknown cause, while secondary osteoarthritis is caused by another disease, infection, injury, or deformity. Osteoarthritis is characterized by the breakdown of cartilage in the joint. As the cartilage wears down, the bone ends may thicken, forming bony growths or spurs that interfere with joint movement. In addition, bits of bone and cartilage may float in the joint space and fluid-filled cysts may form in the bone, limiting joint movement. Several risk factors are associated with osteoarthritis, including the following:
• Heredity - Slight joint defects or double-jointedness (laxity) and genetic defects may contribute to the development of osteoarthritis.
• Obesity - Excessive weight can put undue stress on such joints as the knees over time.
• Injury/overuse - Significant injury to a joint, such as the knee, can later result in osteoarthritis. Injury may also result from repeated overuse or misuse over a period of time.