Physical Exam of the Knee

Knee Anatomy and Ligament Testing

Overview of Knee Structure

• The knee is a vital hinge synovial joint essential for movement, comprising the right femur, tibia, fibula, and patella.

• Important ligaments stabilize the femur, tibia, and fibula to maintain normal joint function. The two collateral ligaments are crucial for stability in the coronal plane.

Collateral Ligaments

• Medial Collateral Ligament (MCL): Connects the medial epicondyle of the femur to the surface of the tibia. It stabilizes against valgus forces.

• Lateral Collateral Ligament (LCL): Connects the lateral epicondyle of the femur to the head of the fibula. It stabilizes against varus forces.

• Both collateral ligaments are taut during full extension and slacken during flexion, playing a key role in knee stability.

Cruciate Ligaments

• Anterior Cruciate Ligament (ACL): Connects from the anterior intercondylar area of the tibia to the posteromedial surface of the lateral condyle of the femur; prevents posterior displacement of femur on tibia and hyperextension.

• Posterior Cruciate Ligament (PCL): Connects from posterior intercondylar area of tibia to anterior lateral surface of medial condyle; prevents anterior displacement of femur on tibia and hyperflexion.

Impairments and Injuries

• Knee function can be impaired by hyperextension or hyperflexion; ligament tears often occur during activities involving pressure combined with twisting or cutting motions.

Diagnostic Tests for Knee Injuries

Anterior Drawer Test

• Used to assess ACL integrity; patient lies supine with hip flexed at 45° and knee at 90°. A positive test indicates greater than 5 mm anterior translation or soft end feel suggesting an ACL rupture.

Posterior Drawer Test

• Assesses PCL integrity under similar positioning as anterior drawer test; a lack of firm end feel or excessive posterior translation indicates potential PCL rupture.

Valgus Stress Test (MCL Assessment)

• Patient lies supine with legs relaxed; valgus force applied through ankle while assessing gapping at medial joint line—pain or excessive gapping suggests MCL injury.

Varus Stress Test (LCL Assessment)

• Similar positioning as valgus stress test but applies varus force towards midline; pain or excessive gapping indicates LCL injury risk.