## Clinical Examination Findings: ACL vs PCL Tears ### Distinguishing Physical Signs **Key Point:** The anterior drawer test (positive in ACL tears) and posterior drawer test (positive in PCL tears) are the gold-standard clinical discriminators between these two ligament injuries. These tests directly assess the direction of abnormal tibial translation relative to the femur. ### Comparative Clinical Examination Table | Clinical Test | ACL Tear | PCL Tear | Mechanism | | --- | --- | --- | --- | | **Anterior Drawer Test** | Positive (tibia subluxates anteriorly) | Negative | Tests anterior tibial translation | | **Posterior Drawer Test** | Negative | Positive (tibia subluxates posteriorly) | Tests posterior tibial translation | | **Lachman Test** | Positive (most sensitive for ACL) | Negative | Tests anterior translation at 20° flexion | | **Posterior Sag Sign** | Negative | Positive (gravity-induced posterior sag) | Passive test; tibia sags back with gravity | | **Pivot Shift Test** | Positive (ACL-specific) | Negative | Tests rotational instability | | **Dial Test** | Negative | May be positive (external rotation) | Tests posterolateral rotatory instability | ### High-Yield Clinical Pearls **High-Yield:** The **anterior drawer test** is performed with the knee flexed to 90°, and a positive test (anterior tibial subluxation) is pathognomonic for ACL insufficiency. The **posterior drawer test** is the direct counterpart, with a positive finding indicating PCL injury. **Clinical Pearl:** The **Lachman test** (performed at 20° knee flexion) is MORE sensitive than the anterior drawer test for detecting ACL tears because it minimizes hamstring muscle guarding. However, the anterior drawer test remains the classical discriminator when comparing ACL to PCL injuries. **Mnemonic:** **ACL = Anterior drawer positive; PCL = Posterior drawer positive** ### Mechanism of Injury Correlation - **ACL tear:** Sudden deceleration, hyperextension, or pivoting on a planted foot ("giving way" sensation) - **PCL tear:** Direct blow to anterior tibia (dashboard injury) or hyperflexion [cite:Clinically Oriented Anatomy Moore 8e Ch 6; Harrison 21e Ch 330] 
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