Lie on right side, feet flexed and stacked on top of each other. Place left hand on ground in front of chest to stabilize the body. Keep the body in a straight line, tailbone tucked. With left foot flexed and leg straight, lift leg toward the ceiling. Lift leg upwards as far as is comfortable, then lower.

If you're an active person (and it sounds like you are) you should ask your doctor to prescribe some physical therapy, if that hasn't been done already. Together, your doctor and physical therapist can help you get the knee back in shape.