Snapshot A 22-year-old man presents to student health with severe knee pain. He was in soccer practice where an opposing team member struck his right leg laterally. He has developed pain since the event. On physical exam, anterior and posterior drawer test are negative. He has increased laxity with valgus stress and no laxity with varus stress to the knee. Introduction Collateral ligaments of the knee include the lateral collateral ligament (LCL) medial collateral ligament (MCL) Function both the lateral and medial collateral ligament are involved in stabilizing the knee LCL resists varus force on the knee MCL resists valgus force on the knee Epidemiology Incidence MCL is most commonly injured knee ligament ETIOLOGY Pathogenesis LCL excessive varus force tears the LCL MCL excessive valgus force tears the MCL Presentation Symptoms knee pain Physical exam increased laxity with valgus stress suggests an MCL injury increased laxity with varus stress suggests an LCL injury Imaging Radiography indication initial imaging modality used to determine if a fracture is present Studies Making the diagnosis a clinical diagnosis supported by imaging Differential Anterior cruciate ligament tear differentiating factor positive anterior drawer test Posterior cruciate ligament tear differentiating factor positive posterior drawer test Treatment Conservative physical therapy indication initial treatment for collateral ligament tears that are not severe Operative orthopedic surgery indication for severe collateral ligament tears Complications