Differential diagnosis of acute knee pain in the young athlete: Part A

Condition	Mechanism of injury	Clinical Features	Comments
Anterior pain
ACL injury	Twisting or hyperextension	Sudden pain and giving way	Often accompanied by MCL and/or meniscal injury
		Unable to ambulate
		Hemarthrosis
		Abnormal anterior drawer, Lachman, or pivot shift test
		Inability to fully squat or duck waddle
Rupture of patellar or quadriceps tendon	Fall on partially flexed knee	Instability with ambulation	May be associated with patellar fracture
		Significant pain and swelling
		Large effusion
Posterior pain
PCL injury	Direct force to anterior knee with the knee in flexion, fall onto flexed knee with foot in plantar flexion; hyperflexion; hyperextension (after rupture of ACL)	Effusion within 24 hours	Usually combined with other injuries
		Limited range of motion
		Instability
		Tibia in posterior position relative to femur
Medial pain
MCL injury	Valgus force without rotation	Localized pain, ecchymosis, swelling and stiffness	Often accompanied by ACL injuries (in which case knee dislocation must be considered)
		Pain along course of ligament
		Laxity with valgus stress in 30 degrees of knee flexion
		Laxity with valgus stress in 0 degrees of knee flexion indicates concurrent ACL injury
Medial meniscal tear	Twisting injury	Usually able to ambulate, but weight bearing is limited by pain
		Knee swelling and stiffness develop over 2 to 3 days
		Mechanical symptoms
		Medial pain with twisting or squatting
		Medial joint line tenderness
		Positive McMurray test
		Positive bounce home test
		Decreased range of motion

DDx_Acute_knee_pain_athlete.htm

ACL: anterior cruciate ligament; MCL: medical collateral ligament; PCL: Posterior cruciate ligament.

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