There are two cartilage structures, called menisci, in each knee joint. A torn meniscus can be caused by a traumatic injury or aging-related degeneration. Osteoarthritis (OA) is a type of arthritis that is caused by the breakdown and eventual loss of another type of cartilage that covers the end of bones within a joint. In people who have knee OA, a meniscal tear can easily lead to disability. This study will compare the effectiveness of two recommended treatments, surgery and physical therapy, for people with a torn meniscus and knee OA.