## **Core Concept**
Lachman's test is a clinical examination used to assess the integrity of the **anterior cruciate ligament (ACL)** in the knee. The test is performed with the knee in a specific degree of flexion to optimally evaluate the ACL's function.

## **Why the Correct Answer is Right**
The Lachman test is specifically done with the knee in **20-30 degrees of flexion**. This position is crucial because it allows for the best assessment of the ACL's integrity. At this angle, the **hamstring muscles are relaxed**, which helps in isolating the ACL's function and making the test more accurate. The test involves gently lifting the tibia (shin bone) to check for excessive forward movement relative to the femur (thigh bone), which would indicate an ACL injury.

## **Why Each Wrong Option is Incorrect**
- **Option A:** 0 degrees - This position does not allow for optimal assessment of the ACL as the hamstring muscles are not fully relaxed, potentially leading to false-negative results.
- **Option B:** 60 degrees - At this angle, the test may not specifically isolate the ACL's function as effectively as at 20-30 degrees, potentially leading to inaccurate assessments.
- **Option D:** 90 degrees - This position is typically used for the **posterior drawer test** rather than the Lachman test and is not ideal for assessing ACL integrity.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the Lachman test is highly sensitive and specific for **ACL injuries** when performed correctly. It's considered one of the most reliable tests for diagnosing ACL tears, especially in the acute setting.

## **Correct Answer:** B. 20-30 degrees.