Learning Objectives: 1) Apply a biomechanical approach to knee trauma. 2) Recognize patterns of knee injury to improve detection of subtle, clinically relevant lesions. 3) Identify occult osseous injury following trauma. 4) Determine mechanisms of osseous injury using MR. 5) Understand indications for MR arthrography. 6) Describe pearls and pitfalls in MR arthrographic diagnosis.