What is the Lachman Test & How Accurate is It?

The Lachman test, named after Dr. John Lachman, an orthopedic surgeon at Temple University, is a diagnostic test that is done to check whether there is an injury or tear to the anterior cruciate ligament (ACL). The ACL is the ligament that connects two of the three bones that comprise your knee joint. These three bones include:

• The tibia or the shin bone.
• Patella or the kneecap.
• The femur or the thigh bone.

The Lachman test is commonly used to diagnose ACL injuries and tears. ACL injuries happen when there are repetitive or violent motions that cause tears due to the wearing away of the ACL ligament over a period of time. When enough repetitive stress is there or there is a sudden forceful motion, then the ACL ligament can even snap into two pieces, making it almost impossible or very painful to move your knee.⁽¹⁾

When there is a tear or injury to the ACL, you might not be able to use your knee joint properly or even move your knee joint. ACL injuries and tears are fairly common in athletes, especially those who play basketball, soccer, and baseball – basically players who use their legs frequently for running, kicking or for tackling other players.

The Lachman test is considered to be one of the most reliable ways of diagnosing an ACL injury and the test results also help doctors determine, which would be the best treatment for the injury.

Your doctor will perform the Lachman test in the following manner:

• You will lie down flat on your back.
• Your legs have to keep straight and your muscles need to be relaxed, especially your hamstring muscles which are present in your upper leg.
• Your doctor will then bend your knee slowly to a 20-degree angle.
• Your doctor might also rotate your leg in order to allow your knee to point outward.
• Your doctor will place one hand on your lower leg and one hand on your lower thigh, just below the point where your leg bends.
• Your doctor will then gently, but firmly, pull your lower leg forward, while with their other hand keeping your thigh stable.

The Lachman test uses two major benchmarks for assigning a grade to your ACL tear or injury. These include:

Laxity: This is a test of how firm the ACL feels when it is moved within the normal range of motion when the doctor is performing the test. If the ACL ligament does not respond with a firm endpoint after reaching the limit of the normal range of motion, doctors suspect the ligament to be torn or injured.

Endpoint: This is a measure of how much the shin bone and knee move during the whole Lachman test. The ACL ligament responds to knee and shin movement by keeping them within a specific limited range of motion. So, if they move beyond the normal range, you are likely to have an ACL injury. This also helps your doctor determine whether any other tissues are also injured and are not working, as they should for stabilizing the knee joint.

The Lachman test will also be performed on your other leg in order to allow doctors to compare the motion in both the legs and see the difference in the motion of your potentially injured leg.

Once the Lachman test has been performed on both the legs using the criteria of endpoint and laxity, your doctor will then grade your injury on the following scale:

Normal Grade: A normal grade in the Lachman test indicates that there is no notable injury to the leg, especially when compared to your other leg.

Grade 1 (Mild): Grade 1 in Lachman test means that your injured leg is moving by 2 to 5 millimeters (mm) more than what is considered to be normal for the range of motion, especially when compared to the other leg.

Grade 2 (Moderate): Grade 2 in Lachman test means that your injured leg is moving by 5 to 10 mm more than what is considered to be normal for the range of motion, especially when compared to the other leg.

Grade 3 (Severe): Grade 3 of Lachman test indicates that your injured leg is moving by 10 to 15 mm more than what is considered to be normal for the range of motion, especially when compared to the other leg.

Some doctors also prefer to use equipment known as the KT-1000 arthrometer in Lachman for getting a better and more accurate reading of the range of motion of the injured leg. The KT-1000 is preferred if your doctor believes that you have an especially serious ACL injury or if you have had a long-term and prolonged injury that is not noticeable immediately. This does happen when the ACL causes scar tissue to develop, limiting the range of motion of your leg.⁽²⁾

Another diagnostic test known as the anterior drawer test (ADT) is also commonly used by doctors at the same time as the Lachman test to confirm the diagnosis of an ACL injury. The ADT test is done by bending your hip at a 45-degree angle and the knee at a 90-degree angle. The doctors then pull the knee forward in a sudden jerk for testing the leg’s range of motion. If the knee moves by 6 mm beyond what is considered to be the normal range of motion, then chances are high that you have an ACL injury or tear in the ACL ligament.

There have been some studies that indicate that the ADT is a little bit more accurate in diagnosing an ACL tear or injury when compared to the Lachman test. However, in the medical fraternity, the ADT is not believed to be as accurate as of the Lachman test, especially when it is done on its own.⁽³⁾

It is always best if both the tests are done together in order to get the most accurate results.

In recent years, there have been many studies done that have shown that the Lachman test is, in fact, a highly accurate test for diagnosing ACL injuries, especially when used along with any other diagnostic tool such as an ADT.

For example, in 1986 a study was done involving 85 participants. Under anesthesia, the Lachman test was performed on these participants who all had knee injuries. It was found that the Lachman test had a 77.7 percent success rate in diagnosing ACL injuries that were caused less than a week or two weeks before the diagnostic test was performed.⁽⁴⁾

However, while there are some positive tests, there is also some subjectivity. In 2015, a study found that two doctors who were testing the same patient agreed on the results 91 percent of the time, raising the question of there being some margin of error that exists between the doctors on whether or not they are interpreting the results of the Lachman test correctly.⁽⁵⁾

A 2013 study done by the Mashhad University of Medical Sciences in Iran, analyzed 653 participants who had ACL ruptures. The researching team found that the Lachman test had a success rate of 93.5 percent, which was only 1 percent less accurate than the results of the ADT. ⁽⁶⁾ At the same time, a 2015 study by the University of Texas Southwestern Medical Center in the US also found a similar success rate of 93 percent.⁽⁷⁾

Lastly, studies have also found that when a patient is put under general anesthesia before undergoing the Lachman test, it makes it more likely that your doctor will make an accurate diagnosis.⁽⁸⁾

Based on the results of the Lachman test, your doctor is likely to recommend one of the following treatments:

Wearing a Knee Brace: This will keep your knee stable and also relieve the pressure on the ACL.

Using the Tried and Tested RICE Method: The RICE Method comprises of Rest, Ice Compression, and Elevation. This will relieve the swelling immediately after you get injured.

Physical Rehabilitation/Therapy: This is used for a scarred, strained, or recently repaired ACL that has earlier been injured or torn; then this will help you regain the motion and strength back in your knee.

Undergoing Surgery for Ligament Restoration: This will replace or restore the tissue that has been damaged or torn with a graft, usually with tissue taken from another ligament in your body or from a donor.

The Lachman test is an accurate test for determining if you have an ACL injury. Injuries to the ACL ligament can not only be painful, but they can also restrict your ability to use your knees and/or legs properly. If you believe that you have an ACL injury, then doctors are likely to use the Lachman test in combination with other diagnostic tests for confirming the injury and determining the course of treatment in the future. With the right treatment, then you can get back the normal movement and strength back in your ACL ligament.

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