Understanding the Lachman Test: A Standard for Knee Assessment

What is the Lachman test?

The Lachman test is considered one of the most reliable physical tests for detecting anterior cruciate ligament (ACL) injuries in the knee. The ACL is a cruciate ligament that helps stabilise the knee joint by preventing the tibia (shinbone) from moving too far forward relative to the femur (thighbone). 

This test is particularly useful in diagnosing ACL tears, which commonly occur due to sudden stops, changes in direction, or direct trauma to the knee — especially in sports like football, basketball, and skiing. The test is widely preferred over other knee stability tests, such as the anterior drawer test, due to its superior sensitivity and accuracy. 

Why is the Lachman test performed?

It can be done either as part of an on-field evaluation immediately after an acute injury or in a clinical setting for those with knee pain and instability. However, mostly, the Lachman test is conducted when an ACL injury is suspected. 

An ACL tear can lead to knee instability, difficulty in movement, and an increased risk of further joint damage. Therefore, healthcare professionals usually use this test to determine the extent of ligament laxity and whether further imaging, such as a magnetic resonance imaging (MRI) test, is needed to confirm the tear.

This test is performed to evaluate the integrity of the ACL and is commonly done in cases with the following factors:: 

• Trauma, such as a sudden twisting or pivoting motion during sports.

• Symptoms like knee instability, swelling, or difficulty bearing weight.

• A history of popping sounds or sensations in the knee during injury.

How is the Lachman test performed?

Currently, the Lachman test is a simple yet effective manual test that assesses ACL stability. Here is how it’s done:

• Patient positioning: 

  • The patient lies on their back (supine position) with the affected knee slightly bent at an angle of 20 to30 degrees.

• Hand placement: 

  • The examiner places one hand on the lower thigh to stabilise the femur, while the other hand grasps the upper tibia. It is essential that the examiner's thumb be on the tibial tuberosity.

• Test execution: 

  • The examiner applies a gentle forward force on the tibia while keeping the femur stable. This motion assesses knee movement in relation to the femur.

• Assessment:

  • The tibia’s forward movement and the presence or absence of a firm endpoint are noted.

A normal knee will have some give or movement, but not excessive. If the tibia moves significantly more than the unaffected knee, it suggests an ACL tear or instability.

What to prepare before the Lachman test? 

Actually, you are not required to prepare anything before the Lachman test. However, there are some considerations that may enhance the accuracy of the test:

• You should be relaxed to avoid muscle guarding, which may affect the test results.

• The examiner should ensure proper hand placement and apply consistent pressure.

• If you are suffering from significant knee swelling or pain, the test may be more challenging to perform accurately.

Why is the Lachman test important?

The Lachman test is one of the most significant and important assessments for detecting ACL injuries. It plays a significant role in diagnosing knee instability, guiding treatment decisions, and preventing further joint damage. The importance of the Lachman test can be described as follows:

• High accuracy and reliability: 

  • Compared to other ACL assessment tests, such as the anterior drawer test, the Lachman test is more sensitive and provides more reliable results, even in the early stages of injury.

• Early diagnosis and intervention:

  • Identifying an ACL tear early helps in planning appropriate treatment, which may include physiotherapy or surgical intervention. Delayed diagnosis can lead to prolonged instability, which can further damage the knee and increase the risk of meniscus or cartilage injuries.

• Essential for athletes and active individuals: 

  • ACL injuries are common knee disorders for those taking partin sports and high-impact activities. Therefore, a quick and accurate Lachman test result allows athletes to receive timely medical attention, potentially reducing recovery time and improving rehabilitation outcomes.

• Non-invasive and easy to perform: 

  • This test requires no special equipment and can be performed in a clinical setting within minutes. Its simplicity makes it a practical and widely used tool in orthopaedic and sports medicine.

• Surgical decision-making: 

  • If an ACL tear is confirmed, the test helps orthopaedic surgeons determine the severity of the injury and whether ACL reconstruction surgery is necessary.

By providing a quick and accurate assessment of ACL integrity, the Lachman test is instrumental in knee joint injury management and overall joint health preservation.

How is the Lachman test graded?

The Lachman test grades the tibia's amount of forward movement and how firmly the joint stops moving:

• Grade 0 (Normal stability): 

  • No abnormal movement of the tibia.

• Grade 1 (Mild instability): 

  • The tibia moves slightly more than normal but stops with some resistance.

• Grade 2 (Moderate instability): 

  • The tibia moves about twice as much as normal, indicating a partial ACL tear.

• Grade 3 (Severe instability): 

  • The tibia moves significantly forward with little or no resistance, strongly suggesting a complete ACL tear.

A firm endpoint suggests a stable knee, while a soft or absent endpoint is a strong sign of ACL injury. If the test suggests an ACL injury, further imaging, such as an MRI, is often recommended to confirm the diagnosis and assess the severity of the damage.

Complications affecting the Lachman test

While the Lachman test is a safe and non-invasive procedure, there are some factors that may affect its accuracy and interpretation:

• Acute pain and swelling: 

  • Recent knee injuries with swelling may make the test more difficult to perform.

• Muscle guarding: 

  • If your muscles are tensed, it may reduce the apparent laxity, leading to a false-negative result.

• Examiner experience: 

  • The accuracy of the test depends on the skill and experience of the examiner. Inexperienced clinicians may have difficulty detecting subtle differences in tibial movement.

• Obesity or large thigh musculature: 

  • Patients with a larger leg size may require additional force or modifications to the test technique for accurate assessment.

What happens after a positive Lachman test?

If the tibia moves too much and there isn’t a firm endpoint, the Lachman test is considered positive, which is a sign that further evaluation may be necessary to determine the extent of your ACL injury. The next steps typically include:

• Imaging tests: 

  • An MRI scan is often ordered to confirm the diagnosis and assess the severity of the ligament damage. This test helps differentiate between a partial and a complete ACL tear.

• Non-surgical management: 

  • For partial ACL tears or less active individuals, conservative treatment may include:

    • Physical therapy to strengthen surrounding muscles and improve knee stability.

    • You can use bracing to provide additional support, keeping your knee stable and preventing further injury.

    • Activity modification to reduce stress on the knee.

• Surgical treatment: 

  • If a complete ACL tear is diagnosed, especially in active individuals or athletes, ACL reconstruction surgery may be recommended. This procedure involves replacing the torn ligament with a graft to restore knee function.

• Rehabilitation and recovery: 

  • Whether treated surgically or non-surgically, a rehabilitation programme focused on strength, flexibility, and stability exercises is crucial for recovery. Full recovery can take several months, with a progressive return to physical activities.

If you have received a positive Lachman test result, it is essential to consult an orthopaedic specialist to explore treatment options. Whether you require physiotherapy, bracing, or surgical intervention, a specialist can guide you through the best course of action based on your lifestyle and activity level. Request an appointment with Thomson Medical to receive consultations and treatment options for ACL injuries.

FAQ

When should a Lachman test be performed?

A Lachman test should be conducted when:

• A knee injury causes instability or a popping sensation.

• There is knee pain, swelling, or difficulty bearing weight.

• An ACL tear is suspected, especially in athletes.

• Pre-surgical assessment is needed for ACL damage.

What is the difference between the Lachman test and the anterior drawer test?

Both of them are physical examination tests for ACL injuries, but they are done in different ways:

• Lachman test: 

  • The knee is slightly bent (20 to 30 degrees), and the examiner gently pulls the shinbone forward. This test is considered more accurate, especially for recent injuries.

• Anterior drawer test: 

  • The knee is bent more (90 degrees), and the examiner pulls the shinbone forward. This position can make the test less reliable because muscles may tighten and affect the results.

What are the signs of a positive Lachman test?

A positive Lachman test indicates a possible ACL tear. Some common signs include:

• Increased forward movement of the tibia compared to the uninjured knee.

• A soft or absent endpoint, meaning the examiner does not feel a firm stop when pulling the tibia forward.

• Instability or looseness in the knee, suggesting ACL damage.

If the test is positive, further imaging, such as an MRI, may be needed to confirm the injury.

How accurate is the Lachman test?

The Lachman test is one of the most reliable methods for detecting ACL injuries. It has a sensitivity of 77.7–84.6% and a specificity of over 95%, making it highly effective in identifying ACL tears. However, its diagnostic accuracy may be lower if there are other knee injuries, significant swelling, or severe pain.

Can the Lachman test give incorrect results?

Yes, the Lachman test can sometimes give false results. Factors that may affect its accuracy include:

• Muscle guarding: 

  • Tight muscles around the knee can limit movement and make the test less reliable.

• Swelling or pain: 

  • Severe swelling or pain may restrict proper assessment.

• Other knee injuries: 

  • Damage to other structures, such as the meniscus or PCL, can interfere with the test results.

If there is any doubt, additional tests like an MRI may be needed to confirm the diagnosis. 

Can you do the Lachman test on yourself?

It’s not recommended to perform the Lachman test on yourself. The test requires proper technique, including stabilising the thigh while pulling the shinbone forward, which is difficult to do alone. For accurate and reliable results, it’s best to have a doctor or physical therapist perform the test.

The information provided is intended for general guidance only and should not be considered medical advice. For personalised recommendations and tailored advice, please consult a specialist at Thomson Medical. Request an appointment with Thomson Medical today.