Putting local anesthetic next to a nerve is a common way of decreasing the pain that patients feel after surgery. For knee surgery, the local anesthetic is placed next to the femoral nerve in the middle of the crease where the leg meets the body when bending at the hip joint. However, the local anesthetic takes away not only sensation—and therefore pain—but also motor control, leaving muscles weaker. It would greatly improve patient safety if the investigators could administer a very long-acting local anesthetic that decreased postoperative pain, but affected muscle strength only minimally. Currently, the investigators do not know if this is possible with EXPAREL, and the investigators therefore are conducting this study to help determine the dose of EXPAREL that will result in a minimal (20%) decrease in muscle strength.