Lachman test is positive in
**Question:** Lachman test is positive in
A. anterior tibialis tendon tear
B. anterior cruciate ligament (ACL) tear
C. patellar dislocation
D. femoral condyle fracture
**Correct Answer:** B. anterior cruciate ligament (ACL) tear
**Core Concept:** The Lachman test is a clinical diagnostic test used in orthopedics to evaluate the integrity of the anterior cruciate ligament (ACL) in the knee joint. The ACL is a key stabilizer of the knee, preventing excessive forward movement of the tibia relative to the femur.
**Why the Correct Answer is Right:**
The Lachman test is positive when there is a significant anterior translation of the tibia relative to the femur, indicating potential injury to the ACL. The ACL prevents excessive anterior instability of the knee joint. When it is torn, the tibia moves anteriorly more than 2-3mm during passive anterior stress on the knee, which is detected during the Lachman test.
**Why Each Wrong Option is Incorrect:**
A. Anterior tibialis tendon tear (Option A) does not cause anterior instability in the knee, making the Lachman test negative.
C. Patellar dislocation (Option C) is a separate clinical sign and test (Pivot-Shift test) to assess patellofemoral instability rather than instability in the tibiofemoral joint.
D. Femoral condyle fracture (Option D) may cause knee instability, but the Lachman test is positive in tears of the ACL, not fractures. Additionally, fractures would typically cause pain, swelling, and limited range of motion, not just positive Lachman test findings.
**Clinical Pearl:**
The Lachman test is a valuable clinical test to assess the integrity of the ACL during a physical examination. It is essential to differentiate between a positive test and positive findings in other clinical tests (e.g., Pivot-Shift test for patellofemoral instability) and appropriate clinical presentations (e.g., pain, swelling, limited range of motion for fractures). It is crucial to have a thorough understanding of knee anatomy, physiology, and clinical examination techniques to accurately diagnose ACL tears.