Scant attention has been paid to the role of magnetic resonance (MR) imaging in the assessment of posttraumatic disorders of bone and cartilage at the knee. The authors reviewed 66 cases and identified four types of injuries that were not clearly evident on plain radiographs. A bone bruise was the most common lesion, having a high association with anterior cruciate ligament tears. Osteochondral fractures, stress fractures, and supracondylar femoral and tibial plateau fractures were also identified. MR imaging appears extremely useful in the detection and assessment of bone and cartilage disorders around the knee.