Everything About The Lachman test – For ACL Tear

What is Lachman Test? 

The Lachman test is used to check for an anterior cruciate ligament (ACL) tear or injury in the knee joint. It is considered the most sensitive and specific test for diagnosing acute ACL injuries.

There are also many other special tests like the knee anterior drawer test and pivot shift test. They are also used to diagnose ACL injury or tear, but they are not as reliable as the Lachman test. Hence, it is considered superior to both the anterior drawer test and pivot shift test.

Some briefing about the Anterior cruciate ligament

The anterior cruciate ligament connects the two bones in the knee joint, the femur and the tibia. The main function of the ACL is to prevent the anterior translation of the tibia.

There are generally two types of injuries common in an ACL tear. One is a contact type injury, and the other is a non-contact type injury.

  • Contact injuries occur by the involvement of another person or thing. For example, when a soccer player is hit at the side of the knee.
  • Non-contact injuries occur from movement like when the knee ROM exceeds its limit. For example, when a sports player changes direction too fast or awkwardly jump on the land.

Non-contact injuries are more common in cases of an ACL tear. Based on an individual evaluation, when an ACL rupture occurs in the patient. Some patients generally feel or hear a pop sound within the knee joint. Swelling will develop within 30 minutes to 1 hour after the injury. Other symptoms include

  • The patient will suffer pain during walking.
  • There will be a loss of ROM in the knee (knee flexion and extension).
  • The patient will feel like his/her knee is giving away. The primary function of the ACL is to stop the further anterior translation (forward movement) of the tibia on the femur. In the absence of ACL, the tibia will move forward and cause the knee to buckle out.

How do you Perform a Lachman Maneuver/Test?

Here is the step by step guide on how the examiner or therapist performs the Lachman maneuver/test

  • The patient should lie down in a supine lying position. Make sure that patient’s all leg muscles should be completely relaxed, especially the hamstrings muscles.
  • The examiner then bends or flex the patient’s tested leg into 20 to 30 degrees of flexion. After that, the examiner slightly externally rotates the tested leg, so the patient’s knee should point outward. This external rotation movement relaxes the iliotibial band.
  • The examiner grasps the patient’s lower thigh (femur) with one hand to stabilize the femur. At the same time, the examiner uses the other hand to grasp the proximal tibia just below where the patient’s knee bends.
  • Next, the examiner then firmly pulls the tibia forward (anteriorly) while keeping the femur stabilized.

Lachman-test

What is a positive Lachman’s test?

An excessive anterior translation (forward movement) of the proximal tibia (more than 2 mm) compared to the uninjured side and the lack of firm or hard endpoint indicates a positive Lachman’s test. A positive Lachman test indicates a torn ACL.

What is a negative Lachman’s test?

When there is no further anterior translation (forward movement) of the proximal tibia, and the examiner feels a hard or firm endpoint, this indicates the negative Lachman test.

What are endpoints?

There are two types of endpoints: the soft or mushy endpoint and the hard or firm endpoint. Now talking about ACL, what ACL does? the ACL keeps a check on the tibia by keeping it within a certain limited range of motion relative to the femur. If the tibia moves more than its normal range of motion, then you may have torn your ACL.

Hard Endpoint – An endpoint is hard when the ACL abruptly (suddenly) stops further forward movement (anterior translation) of the tibia on the femur. The examiner feels a hard or firm endpoint when the ACL is intact.

Soft Endpoint – An endpoint is called soft when the ACL is injured or torn. When the ACL is injured or torn, there will be the further anterior translation of the tibia on the femur (tibia moves more than its normal ROM) with no hard or firm endpoint.

Grading of the ACL tear in Lachman Test

Grading of the ACL tear in the Lachman test is described as follows –

Normal – There we be no noticeable injury in the patient’s leg compared to the other leg.

Mild (Grade 1)  – The injured leg moves 2 to 5 mm more than its normal ROM compared to the other leg.

Moderate (Grade 2)  – The injured leg moves 5 to 10 mm more than its normal ROM compared to the other leg.

Severe (Grade 3) – The injured leg moves 10 to 15 mm more than its normal ROM compared to the other leg.

Lachman Test vs Anterior Drawer Test

The procedure for performing the Lachman test and anterior drawer test is different from each other. But both the Lachman and anterior drawer test are performed one by one, as this will help confirm the diagnosis of an ACL tear.

Let’s talk about the difference between the Lachman and anterior drawer test. As, the performing procedure (starting and ending position) of both the test is different.

                Lachman test

         Anterior Drawer Test

In Lachman test only the knee joint is involved as the knee is bent into 20 to 30 degrees of flexion. In anterior drawer test both the knee and hip joint are involved. As the hip is flexed to 45° and the knee is flexed to 90°.
The examiner grasps the patient’s lower thigh (femur) with one hand to stabilize the femur. At the same time, the examiner uses the other hand to grasp the proximal tibia just below where the patient’s knee bends. The examiner sits on the patient’s involved foot to stabilize it’s position. Examiner grasps the patient’s knee with her thumb in the front of the patient’s knee and her fingers behind the patient’s knee as shown in the diagram below.
The examiner then firmly pulls the tibia anteriorly (forward) while keeping the femur stabilized. The examiner then gently pulls the shin bone (tibia) forward while observing how far the tibia moves.
If there is an excessive anterior translation (forward movement) of the proximal tibia (more than 2 mm) compared to the uninjured side and the lack of firm or hard endpoint, Indicating that the patient has torn his/her ACL (positive Lachman test). If the tibia moves more than 5 mm or more than the uninvolved side. Then this will give the examiner an indication that the patient has either sprained or torn the ACL ligament (positive anterior drawer test).

Let’s talk about the accuracy of the Lachman and anterior drawer test

  • Lachman test is generally considered the best test for diagnosing ACL ruptures as it has a sensitivity of 87% and a specificity of 93%. While on the other hand, the anterior drawer test has a sensitivity of 48% and a specificity of 93%.
  • In Benjamin’s meta-evaluation, the accuracy for the Lachman test revealed a pooled sensitivity of 85 percent.
  • Jain demonstrated the sensitivity of the Lachman test under anaesthesia to be 92.9%.
  • Liu revealed the sensitivity of the Lachman test to be 95% and sensitivity of the anterior drawer test to be 61%. Lachman test sensitivity climbed to 100 percent under anaesthesia.
  • Lee et al. revealed that the sensitivity of MRI imaging was 94% compared with the Lachman test, which has a sensitivity of 89% and the anterior drawer test, which has a sensitivity of 78%.
  • Katz et al. concluded in most ACL injuries, no matter age, the Lachman test was 81.8% sensitive, and the anterior drawer sign was 40.9% sensitive.

Jonsson et al. concluded that in analyzing an acutely injured knee in an individual without anaesthesia, the Lachman test was superior to the anterior drawer test. However, in chronic conditions, both the evaluations had higher diagnostic accuracy.

As you have read above, all the individuals who had revealed the sensitivity of Lachman and anterior drawer test. Lachman test turns out to be a winner compared to the anterior drawer test in acute conditions, while both performed equally in chronic conditions.

 Some Important Points 

  • A correct joint angle of 20 to 30 degrees should be maintained because a position close to full extension (knee straight) has a less anterior translation of the tibia and can give a false endpoint.
  • Between 20 to 30° of flexion, the ACL is maximally stressed and can be analyzed more accurately. At this angle, other knee structures move out of the picture and may not limit the anterior translation of the tibia.
  • Experts recommend first exclude a PCL injury before conducting the test for an ACL tear. As in the case of PCL tear, the tibia sets posteriorly. This could give you the impression that there is a lot of tibia movement while conducting the Lachman test for the ACL tear. This can give you a false positive test in the end.
  • The best time to conduct the test is immediately after the injury before swelling occurs or in the chronic state. If the swelling has occurred, the examiner should wait for the swelling to go down and then conduct the test. As swelling restricts the examiner from getting a true indication of the joint’s mobility.
  • Studies have found that when the test is being conducted under general anaesthesia. It becomes easy for the doctor to make an accurate diagnosis.

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