A hamstring injury refers to an injury to any muscle at the back of the thigh. There are three hamstring muscles: semitendinosus, semimembranosus and biceps femoris. This group of muscles are responsible for leg extension and knee bending. A hamstring injury can be a partial or complete tear, as well as a pull. If the tendon tears away form the bone completely and pulls a piece of the bone with it, this is an avulsion injury.

MRIs showing a proximal hamstring avulsion


Link to procedure here.