If you've been dealing with nagging pain deep in the sit-bone area, or a hamstring that flares up every time you increase your running volume, you've probably already heard the standard advice: rest, stretch gently, strengthen slowly, be patient.

If the back of your thigh, right where it meets the sit bone, has been a source of low-grade pain that flares with sprinting, deep hip flexion, or just sitting too long on a hard chair, you've probably already tried the standard advice.

A biceps femoris avulsion fracture is not just "a pulled hamstring." It means a piece of bone, usually at or near the ischial tuberosity, has been torn away along with the tendon that should be anchoring it.