The Lachman Test: Understanding ACL Injuries and What They Can Reveal About Meniscal Health

Introduction: Why Knee Stability Matters and the Role of the Lachman Test

Our knees are essential for staying active, supporting our weight, and keeping us moving smoothly through daily life. So when a knee injury happens, finding out exactly what’s wrong is crucial for getting the right treatment and making a full recovery. One of the best tools doctors have for checking the stability of the knee is the Lachman test. Widely trusted for assessing the anterior cruciate ligament (ACL)—a major stabilizing ligament in the knee—it can sometimes also offer clues about other structures, like the meniscus. In this article, we’ll break down how the Lachman test works, what it reveals about ACL injuries, and how it can sometimes hint at meniscal issues as well.

How the Lachman Test Works: A Simple but Effective Check for ACL Damage

The Lachman test is simple but powerful. To perform it, the patient’s knee is bent slightly (about 15 degrees). The examiner holds the thigh steady with one hand and gently pulls the shin bone (tibia) forward with the other. This motion checks how much the tibia moves in relation to the thigh bone (femur), helping doctors gauge the integrity of the ACL.

Why use the Lachman test instead of other methods, like the anterior drawer test? The answer is sensitivity—it’s better at detecting even subtle or partial ACL tears, especially soon after an injury. If the tibia moves forward more than expected and there’s a soft or “mushy” endpoint (rather than a firm stop), it points to a torn or compromised ACL. The Lachman test generally provides clearer results than the anterior drawer test, making it a mainstay in sports medicine and orthopedics.

There are also variations of the Lachman test. Research shows that factors such as the clinician’s technique, knee size, and patient relaxation can affect test accuracy. For instance, the prone Lachman test (performed with the patient lying face down) and the drop leg Lachman’s test are modifications developed to make the exam more sensitive and objective in certain scenarios.

What the Lachman Test Can Tell Us About the Meniscus

Although the Lachman test isn’t designed to diagnose meniscus injuries, it can sometimes provide subtle hints when the meniscus is also damaged. The meniscus is a C-shaped cartilage that cushions and stabilizes the knee joint . During the Lachman test, unusual patterns in how the tibia moves—such as a sudden “catch,” buckling, or resistance—may suggest a meniscal tear. These indirect clues can prompt the clinician to investigate further, especially since meniscus injuries often occur alongside ACL tears.

Interestingly, studies have shown that variations in Lachman test technique (like the drop leg method) can result in greater movement of the tibia when the ACL is injured, highlighting how test style can impact the detection of both ligament and meniscal involvement.

Looking Deeper: Complementary Tests for Meniscal Injuries

Because ACL and meniscal injuries frequently happen together, using a combination of tests is important for an accurate diagnosis. While the Lachman test is highly effective for the ACL, other exams are designed specifically for the meniscus.

The McMurray test involves bending and rotating the knee to check for a click or pain, which can signal a meniscal tear. Meanwhile, the Thessaly test has the patient stand and gently twist on the affected leg, looking for sensations like pain or locking. These tests, when used alongside the Lachman test, allow doctors to distinguish between ligament and cartilage injuries, leading to more precise treatment plans.

Conclusion: Taking a Holistic Approach to Knee Injuries

The Lachman test remains the gold standard for detecting ACL injuries, but it’s also wise to remember that it can sometimes hint at meniscal damage. Recognizing these subtle signs encourages a more thorough and holistic approach. By combining the Lachman test with other, more targeted exams—and by paying close attention to nuanced findings—healthcare providers can make more accurate diagnoses and help patients recover faster and more fully, getting them back to their regular activities confidently and safely.