Knee pain can be nagging or debilitating, and is often caused by injury or disease. It can affect muscle control in the sore leg, decrease the strength and endurance of the muscles that support the knee, and can restrict mobility as well. Injuries can occur from a sudden movement that pushes the knee beyond its normal range of movement, or as the result of a direct blow. This can happen in recreational activities, a fall, a sporting event, or a motor vehicle accident. As for disease, Osteoarthritis, also known as Degenerative Joint Disease, is the most common one affecting the knee. This is caused by the cartilage in the knee gradually wearing away, leading to pain and swelling. If the pain in your knee is a result of an injury, the most likely culprits involve cartilage tears (e.g., meniscus tears) and/or ligament tears (e.g., ACL, or Anterior Cruciate Ligament). Knee pain can also be caused by repetitive stress, as often occurs with the kneecap (known as PFPS, or, patellofemoral pain syndrome). Very rarely do knee injuries involve broken bones, with the exception being extreme trauma.