Anterior Cruciate Ligament (ACL) Injuries: Exams And Tests

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Exams and Tests

An anterior cruciate ligament (ACL) injury is diagnosed through a medical history and a physical examination. A doctor who specializes in knee injuries (for example, an orthopedic surgeon or sports medicine specialist) will usually be able to accurately diagnose an ACL injury after:

• Taking your medical history. You will be asked how you injured your knee, about your symptoms at the time of injury, whether you have had any other knee injuries, and general questions about your health.
• Checking your knees for stability, strength, range of movement, swelling, and tenderness. Tests for stability include a Lachman test and a pivot shift test. The Lachman test compares the degree of looseness (laxity) in your knees.
• Looking at an X-ray, which is usually done for any knee injury. Although an ACL injury cannot be directly diagnosed by an X-ray, it can determine whether a bone is broken, any bone fragments are in the knee, the ACL is torn from the bone (avulsion), or blood is present in the knee (effusion).

If you see your doctor soon after your injury, the pain and the degree of swelling and muscle tenseness may make it difficult for your doctor to accurately diagnose the condition.

Other tests that may help determine how badly the knee is injured include:

• Magnetic resonance imaging (MRI), which can identify other problems, such as meniscus tears or other ligament injuries.
• Computed tomography (CT), which can be done to see any small breaks in the bones.

If your knee is red, hot, or very swollen, a knee joint aspiration (arthrocentesis) may be done, which involves removing fluid from the knee joint with a syringe (needle). This is done to:

• Help relieve pain and pressure, which may make the physical exam easier and make you more comfortable.
• Check joint fluid for possible infection or inflammation.
• Identify blood, which may indicate a tear.
• Identify drops of fat, which may indicate a broken bone.

Fluid removed from the knee joint may be tested to identify blood and fatty droplets from a hidden fracture. Local anesthetic may be injected to reduce pain and make the knee easier to examine. If the ACL is torn, fluid drained from the knee may contain a lot of blood.

Arthrometric testing of the knee may also be done. In this test, your doctor uses an instrument to measure the looseness of your knee. This test is especially useful in people whose pain or physical size makes a physical exam difficult. An arthrometer has two sensor pads and a pressure handle that allows your doctor to put force on the knee. The instrument is strapped to your lower leg so that the sensor pads are placed on the knee cap and the small bump just below it (tibial tubercle). Your doctor then measures pressure by pulling or pushing on the pressure handle.

Arthroscopy is another procedure used in the diagnosis of an ACL injury and is also usually used as a method of surgery. Arthroscopy involves inserting instruments through one or more small incisions in the knee, allowing your doctor to examine the structures inside the knee joint, including the ACL.

Before arthroscopy, you and your doctor will decide what will be done if certain conditions are found. For example, you may decide in advance that if a complete tear of the ACL is found, it will be reconstructed during the arthroscopy. Or, if a more severe condition is found, you and your doctor may agree to discuss the condition rather than proceeding with surgery at that time.

Last updated:	May 16, 2008
Author:	Shannon Erstad, MBA/MPH
Reviewed By:	Adam Husney, MD - Family Medicine, Patrick J. McMahon, MD - Orthopedics
Editors:	Kathleen M. Ariss, MS, Pat Truman, MATC