Stapled ligament. X-ray of the knee of a patient with a staple inserted to treat an injured anterior cruciate ligament. The cruciate ligaments attach the femur (thigh bone, top) to the tibia (shin bone, bottom centre), preventing them from moving too much in relation to one another. A rupture or tear of the ligament, which often results from a sporting injury, causes the knee to become unstable and can lead to arthritis and other problems later in life.