The purpose of this study is to find out how differences in age can affect the duration of pain relief from a femoral nerve block. Complete recovery after leg surgery involves healing of tissues at the surgical site, recovery of muscle strength and range-of-motion. Some pain is normally experienced after leg surgery. At the hospital, pain is usually treated with pain medicines, and/or a nerve block procedure. A nerve block involves injecting a local anesthetic beside the nerves to numb the nerves that supply feeling to the knee joint and surrounding tissues. The choice as to whether a participant has a nerve block or not is made by the participant and their surgeon and is not determined by this research study. The study aim is to find out how long a nerve block can relieve postsurgical pain, and whether that duration is affected by the age of the participant.