In the Lachman Test, the knee is flexed to approximately how many degrees before applying anterior force to the tibia?

In the Lachman Test, the knee is flexed to approximately how many degrees before applying anterior force to the tibia?

• A. 15 Degrees
• B. 30 Degrees
• C. 60 Degrees
• D. 90 Degrees

Answer: (A)

The main idea is that the Lachman test assesses ACL integrity by measuring how much the tibia can move forward when the knee is placed in a modest bend. The knee is flexed to about 20–30 degrees before you apply anterior force to the tibia. At this angle, the ACL is the primary restraint to forward tibial translation, while the hamstrings are less likely to mask the movement and other structures don’t dominate the motion. If the ACL is torn, you’ll see increased anterior excursion and a softer end feel compared with the uninjured knee. Choosing a much smaller angle, like 15 degrees, provides less reliable isolation of the ACL and can be harder to interpret. If you bend the knee much more, such as 60 or 90 degrees, other structures and hamstring activity come into play, which reduces the test’s specificity for the ACL. So the commonly accepted approximation is around 20–30 degrees, with 30 degrees often used as a standard.

The main idea is that the Lachman test assesses ACL integrity by measuring how much the tibia can move forward when the knee is placed in a modest bend. The knee is flexed to about 20–30 degrees before you apply anterior force to the tibia. At this angle, the ACL is the primary restraint to forward tibial translation, while the hamstrings are less likely to mask the movement and other structures don’t dominate the motion. If the ACL is torn, you’ll see increased anterior excursion and a softer end feel compared with the uninjured knee.

Choosing a much smaller angle, like 15 degrees, provides less reliable isolation of the ACL and can be harder to interpret. If you bend the knee much more, such as 60 or 90 degrees, other structures and hamstring activity come into play, which reduces the test’s specificity for the ACL. So the commonly accepted approximation is around 20–30 degrees, with 30 degrees often used as a standard.