What is an anteroir cruciate ligament (ACL) sprain?

A sprain is a joint injury that causes a stretch or a tear in a ligament. Ligaments are strong bands of tissue that connect one bone to another. The anterior cruciate ligament (ACL) is one of the major ligaments in the middle of the knee. It connects the thigh bone (femur) to the shin bone (tibia).
 This ligament, along with the posterior cruciate ligament, helps keep the knee stable and protects the femur from sliding or turning on the tibia. Sprains are graded I, II, or III depending on their severity:

• Grade I sprain: pain with minimal damage to the ligaments

• Grade II sprain: more ligament damage and mild looseness of the joint

• Grade III sprain: the ligament is completely torn and the joint is very loose or unstable

How does it occur?

The anterior cruciate ligament is frequently injured in forced twisting motions of the knee. It may also become injured when the knee is straightened further than it normally can straighten (hyperextended). It sometimes occurs when the thigh bone is forcefully pushed across the shin bone, such as with a sudden stop while you are running or a sudden transfer of weight while you are running.

What are the symptoms?

There is usually a loud, painful pop when the joint is first injured. This is often followed by a lot of swelling of the knee within the first several hours after the injury. This swelling is called effusion and is made up of blood in the knee joint. If you have torn your ACL in an injury that occured months or years ago and you haven't had reconstructive surgery, you may have the feeling that the knee is giving way during twisting or pivoting movements.

How is it diagnosed?

Your doctor will examine your knee and may find that your knee has become loose. If you have swelling in the joint, your doctor may decide to remove the blood in your knee with a needle and syringe. You may need x-rays to see if there is an injury to the bones in your knee. An MRI scan may also be done and should clearly show the condition of your ACL (as well as that of other ligaments and cartilage).

How is it treated?

Treatment includes the following:

• Put an ice pack on your knee for 20 to 30 minutes every 3 to 4 hours for 2 to 3 days or until the pain goes away

• Keep your knee elevated whenever possibile by placing a pillow underneath it until the swelling goes away

• Do the exercises recommended by your doctor or physical therapist. For complete tears, you and your doctor will decide if you should have pre or post rehabilitation for your knee. The torn ACL can be reconstructed by taking ligaments or tendons from another part of your leg and connecting them to the tibia and femur