U01.11.007 Knee exam

Written by

in

Learning Objectives

  • Master the LAMP mnemonic for cruciate ligament attachments.
  • Differentiate between Anterior and Posterior Drawer signs and the Lachman test.
  • Apply Valgus and Varus stress to identify collateral ligament injuries.
  • Interpret the McMurray test using the LIME rule for meniscal tears.

1. Cruciate Ligament Anatomy: The LAMP Rule

The ACL and PCL are named based on their attachment to the tibia. Their femoral origins follow a specific pattern:

  • Lateral Femoral Condyle → Anterior Tibia: ACL.
  • Medial Femoral Condyle → Posterior Tibia: PCL.

2. Clinical Tests for Ligamentous Laxity

Test Procedure & Finding Injury Suspected
Anterior Drawer / Lachman Tibia glides anteriorly (Lachman at 30° is more sensitive). ACL Tear
Posterior Drawer Tibia glides posteriorly (knee at 90°). PCL Injury
Valgus Stress Test Lateral force → Medial space widening. MCL Injury
Varus Stress Test Medial force → Lateral space widening. LCL Injury

 

3. Meniscal Assessment: The McMurray Test

This test involves flexion, extension, and rotation. Remember LIME:

  • Lateral meniscus = Internal rotation.
    • Pain or “popping” with internal rotation and varus force → Lateral meniscal tear.
  • Medial meniscus = External rotation.
    • Pain or “popping” with external rotation and valgus force → Medial meniscal tear.
Clinical Notes & Corrections:

  • Unhappy Triad: A severe lateral impact can cause simultaneous injury to the ACL, MCL, and Medial Meniscus (though some studies suggest the lateral meniscus is actually more commonly involved in acute cases).
  • Sensitivity: The Lachman test is considered more sensitive than the Anterior Drawer for ACL tears because it avoids the hamstrings’ “guarding” (tightening), which can occur at 90°.

Activity: Knee Exam Diagnostic Challenge

Memory Hooks:

LAMP: Lateral-ACL, Medial-PCL.

LIME: Lateral Internal, Medial External.

ValGus: Force makes the knees Gape together (knock-knees).

Activity: