Exams and Tests
anterior cruciate ligament (ACL) injury is diagnosed
through a medical history and a physical exam. 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 if there is pain, swelling, or you cannot put your weight on the leg.
Although an ACL injury cannot be directly diagnosed by an X-ray, an X-ray can
show 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
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.
More imaging tests
Other tests that may
help your doctor see how badly the knee is injured include:
- An MRI. It can identify an ACL tear or other problems, such as meniscus tears or other ligament
- A CT scan. It can be
done to see any small breaks in the bones.
Looking at fluid in the knee
If your knee looks red, feels warm to the touch, or is very swollen, a
knee joint aspiration (arthrocentesis) may be done. This involves removing fluid from the knee joint with a needle. It
is done to:
- Help relieve pain and pressure. This may make
the physical exam easier and make you more comfortable.
- Check joint
fluid for possible infection or inflammation.
- Look for blood, which
may mean there is a tear.
- Look for drops of fat, which may mean there is a
Local anesthetic may be injected to reduce
pain and make the knee easier to examine.
- Arthrometric testing: In this test, your doctor uses a tool to
measure the looseness of your knee. This test is especially useful in people
whose pain or size makes a physical exam difficult. An arthrometer has
two sensor pads and a pressure handle that allows your doctor to put force on
- ArthroscopyArthroscopy: This can be used
to diagnose an ACL injury and as a method of
surgery. It involves inserting tools through one or more small
incisions in the knee, which allows 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.