The quadriceps or patellar tendon can rupture acutely, especially in an older athlete who jumps or falls a great distance The patient will not be able to actively extend the knee and the area over the ruptured tendon may be tender The patella may be positioned abnormally on examination and on radiographs The three hamstring muscles (semitendinosus, semimembranosus, and biceps femoris) flex the knee and may be strained in young athletes The semitendinosus and semimembranosus run along the medial popliteal space, and the biceps femoris tendon runs laterally The patient may describe an acute pain or even a pop in the back of the thigh or may present subacutely with posterior thigh and popliteal knee pain when the hamstrings are strained by repetitive use Palpation of the injured tendons is painful