LIGAMENTS Cruciate Ligaments Anterior Cruciate Ligament

noninvasive tool that can aid in the evaluation of the entire spectrum of internal derangements of the knee. Although the cost varies considerably across the country, the average cost of knee MRI is on the order of several hundred to more than a thousand dollars. The noninvasiveness of MRI combined with its relatively low cost have led to its acceptance by the orthopaedic community, and MRI of the knee is the most frequently ordered MR examination of the musculoskeletal system. The superb soft tissue contrast and multiplanar capabilities of MRI make it ideal for evaluating suspected injuries of the muscles, ligaments, menisci, tendons, and articular cartilage, as well as in the evaluation of bone contusions, occult fractures, and fluid collections about the knee. Also, MRI is a useful adjunctive tool, which when combined with a good physical examination can provide an accurate assessment of the entire knee and thus guide appropriate therapeutic intervention. Equipment and techniques for MRI vary widely, and although it is generally accepted that high field strength magnets provide the highest quality images, there has been considerable advancement in the technology of low field strength systems over the past few years, greatly improving their image quality. A circumferential surface coil is mandatory to ensure uniform signal-to-noise across the entire image. Complete assessment of the knee requires that images be obtained in the sagittal, coronal, and axial planes. T2-weighted images using either fast spin-echo techniques with fat saturation or short inversion time inversion recovery (STIR) imaging are typically performed in all 3 imaging planes. The T2-weighted pulse sequences have been referred to as the “pathology” sequences and are best suited for detecting injuries of the muscles, tendons, ligaments, and articular cartilage. They also clearly depict marrow abnormalities such as edema or contusion. T1-weighted or proton density images should be performed in the sagittal and coronal planes. These sequences typically produce the highest signal-to-noise and have been referred to as the “anatomy” images. They are the most accurate for detecting meniscal injuries and can be used in conjunction with the T2-weighted images to enhance the evaluation of the osseous structures. This article will describe a systematic approach to the interpretation of MR examination of the knee, and the optimal imaging planes and pulses sequence will be discussed for each anatomical structure.