Knee arthritis is a condition that causes pain and swelling in the knee. The medial compartment of the knee is most often affected, which refers to one or more of the four bones — tibia, femur, patella (kneecap), fibula—in this area. Knee arthritis is the most common type of arthritis and is often associated with aging, injury, or other conditions like obesity. Knee arthritis can be prevented by avoiding injuries to the knee, maintaining a healthy body weight (especially if overweight), and talking to your doctor about any medications you are taking that could increase your risk of developing this condition. Symptoms include pain in the affected area that may worsen when walking upstairs or hills; swelling around the joint; stiffness in the knee, especially after sitting for long periods; redness over the skin near the injured area; limited mobility; cracking sound while rotating it back-and-forth. Discover facts about Knees Arthritis: Symptoms and Treatment.