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Background
Radiologists and orthopedic surgeons play complementary roles in diagnosing and treating a variety of musculoskeletal pathologies affecting the knee joint. MRI of the knee is considered the gold standard in noninvasive evaluation of knee pain, and more musculoskeletal MRI examinations are performed on the knee than any other region of the body. Similarly, knee arthroscopy is the single most common orthopedic intervention performed in the United States, with an estimated 750,000 procedures each year. Knee MRI has a very high NPV and may help avoid unnecessary and more invasive interventions, including knee arthroscopy. Therefore, it is important for radiologists to be familiar with the general principles, basic procedural steps, and appearances of arthroscopy. A deeper knowledge of the procedure’s limitations and the challenges the arthroscopist may face will help viewers of this educational exhibit tailor their interpretations of knee MRI examinations and better serve our orthopedic surgery colleagues and patients alike.

Educational Goals / Teaching Points
The educational goals of this exhibit are to improve radiologists’ knowledge and familiarity with the procedure and principles of knee arthroscopy, to demonstrate normal knee MRI anatomy and arthroscopic correlates, to compare MR and arthroscopic images for 10 relevant and commonly encountered knee joint pathologies, and review the strengths and limitations of MRI and arthroscopy in the investigation of the knee.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
We will first explain the basics of knee arthroscopy including setup, equipment, and operative portals. Next, we will briefly review normal knee anatomy on both MR and arthroscopy images. Then, we will utilize a quiz-style format to showcase 10 different knee joint pathologies on MR and arthroscopy images. Each example will include a side-by-side comparison and explanation of the MRI appearance and correlating arthroscopic images, so viewers can develop a deeper understanding of what the orthopedic surgeon sees during arthroscopy, compared to what the radiologist perceives on MR. Viewers can expect to see an anterior cruciate ligament (ACL) tear and ACL graft reconstruction failure; bucket handle, horizontal, and complete radial meniscal tears; discoid meniscus; chondral/osteochondral lesions, injuries, and loose bodies; osteochondral allograft; and intraarticular tenosynovial giant cell tumor. We will conclude by briefly comparing the strengths and weaknesses of MRI and arthroscopy.

Conclusion
Radiologists with a stronger understanding of knee arthroscopy can provide more succinct, relevant, and accurate interpretations of knee MRI examinations and potentially avoid unnecessary knee arthroscopy or other more invasive procedures. To that end, this exhibit has reviewed a variety of knee pathologies and their appearances on both MRI and arthroscopy. We hope this will facilitate more accurate image interpretation and further develop effective working relationships with orthopedic surgeons to provide better care for our mutual patients.