Participation in sports increases the risk of joint injuries that can lead to posttraumatic osteoarthritis, a clinical syndrome caused by trauma-initiated joint degeneration that results in permanent and often progressive joint pain and dysfunction. Minimizing the risk of joint injuries and helping people with osteoarthritis participate in regular physical activity, including some sports, requires understanding of the relationships between joint use, joint injury, and joint degeneration. Lifelong participation in sports that cause minimal joint impact and torsional loading by individuals with normal joints and neuromuscular function does not increase the risik of posttraumatic osteoarthritis. In contrast, participation in sports that subject joints to high levels of impact and torsional loading increases the risk of joint injury and subsequent joint degeneration. Immediate diagnosis and appropriate treatment and rehabilitation following joint injuries decrease the risk of subsequent injuries and posttraumatic osteoarthritis. Individuals with abnormaljoint anatomy or alignment, previous significant joint injury, osteoarthritis, joint surgery, joint instability, disturbances of joint or muscle innervation or inadequate muscle strength have increased risk of joint damage during participation in athletics. These individuals can benefit from regular exercise, including selected sports, but they should have an evaluation of their joint structure and function, muscle strength, and neuromuscular function before participating in vigorous physical activity.