The lower extremity is the most commonly injured anatomic area in sports. An appropriate history and physical examination is sufficient to diagnose most injuries. By knowing the position where a joint has the greatest and least bony stability, one can predict the likelihood of bony and ligament injury. Such information is helpful in determining which structures are most susceptible to injury as well as identifying when radiographs or other diagnostic studies are indicated. An accurate diagnosis is crucial for planning effective therapy and in determining the need for surgical referral. An understanding of common injury patterns is also helpful in differentiating sources of musculoskeletal pain that are not injury related.