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Analogous to a fighter pilot’s airplane checklist before takeoff, the radiologist should have an anatomic checklist of the knee that must be evaluated. If an item on the checklist is missed, it can result in a great risk for everyone on board including the radiologist, the surgeon, and more importantly for the patient. Therefore, it must be stressed that one should evaluate the anatomic components of the knee with an organized checklist that should be routinely applied with every case to avoid a significant discrepancy. Given the complex anatomy of the knee, it is imperative that the radiologist should know what his/her audience want to hear and the report lexicon should use the language that meets the expectations of the orthopedic referral base. If a line of communication is absent between the radiologist and the referring physician, then the report is being generated in a vacuum, similar to the pilot flying without navigation. Hence, we will embark on our journey through the knee with a flight path similar to the surgical approach of the arthroscopist which is compartmentalized to the patellofemoral articulation, the intercondylar notch, the medial knee, and the lateral knee. Then, we shall discuss the pathologic and radiologic concept of “Internal Derangement” used to cover a group of disorders that affect the normal functioning ligaments, tendons, meniscus, and cartilage of the knee articulation. From a technical standpoint, this is ideally performed with a high field strength 1.5 or 3 Tesla MRI scanner. Three conventional MR imaging planes are utilized to evaluate the knee and include sagittal (oblique), coronal, and transaxial planes. While a detailed explanation of MR imaging protocols and MR physics is beyond the scope of this text, fast spin-echo (FSE) MR imaging is most commonly utilized for MRI of the knee. Specifically, in the coronal and sagittal planes, T1, T2, and intermediate-weighted proton density sequences are often utilized. Fat saturation is employed on some of the fluid-weighted sequences to better detect the presence of edema in the soft tissues or marrow edema. A spin echo or gradient sequence is often acquired in the trans-axial plane. In each plane a T1 sequence is complemented with a fluid-weighted T2 or proton-density sequence. MR imaging of the knee is most often performed without contrast. However, an MR arthrogram may be performed and is particularly useful in evaluating the postoperative knee. This may be performed with either a direct or an indirect technique. With the more commonly performed direct MR arthrogram, a 1:200 dilution of gadolinium in approximately 30 mL of sterile saline is percutaneously injected into the knee joint using a 20-gauge needle. Less commonly employed, an indirect MR arthrogram is performed after an intravenous injection of gadolinium contrast followed by exercise allowing leakage of contrast agent from the synovium into the joint space and then subsequent MR image acquisition.1 Fluid distension of the joint space assists in identification of intra-articular bodies (Figure 13-1). Distension of the ...

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