A positive Lachman test indicates injury to which structure?

A positive Lachman test indicates injury to which structure?

• A. Posterior cruciate ligament
• B. Medial meniscus
• C. Lateral collateral ligament
• D. Anterior cruciate ligament

Answer: (D)

A positive Lachman test points to injury of the anterior cruciate ligament. The test checks how far the tibia can move forward relative to the femur when the knee is only lightly flexed (about 20–30 degrees). The ACL normally prevents this forward translation, so a noticeably increased anterior movement with a soft or absent end feel indicates ACL disruption. In contrast, a posterior cruciate ligament injury would show increased backward movement on a posterior drawer test, and meniscal or collateral ligament injuries produce different signs and tests. Thus, the structure injured is the anterior cruciate ligament.

A positive Lachman test points to injury of the anterior cruciate ligament. The test checks how far the tibia can move forward relative to the femur when the knee is only lightly flexed (about 20–30 degrees). The ACL normally prevents this forward translation, so a noticeably increased anterior movement with a soft or absent end feel indicates ACL disruption. In contrast, a posterior cruciate ligament injury would show increased backward movement on a posterior drawer test, and meniscal or collateral ligament injuries produce different signs and tests. Thus, the structure injured is the anterior cruciate ligament.