How to read a knee MRI
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First one should consider overall impression of amount of joint fluid.
Next take look at bone structure and signal on all images and sequences. Depending on age of the patient, bones can be uniform in signal (adults), with some non-hommgenities inside medullar part (adolescents), or with growth plates (younger children). Water and fat saturated images as well as STIR and to some extent T2* give good depiction of bone structure.
Cartilage surfaces should be visible on number of sequences, PD and T2* or other gradient sequences should provide good depiction. Position and size of lesion should be described. Signal of underlying bone should also be noted.
Then consider cruciate ligaments. Posterior ligament is usually black, easily seen od many sag. sections. Analysis of frontal ligament can be cumbersome, as it may present with variable signal, usually higher than posterior ligament, but if so, structure will be easily visible. Lesions are usually presented as inhomogenity of structure or signal.
Menisci should be of low signal on many SE sequences, but several gradient sequences can provide inside structure and contrast. Size of lesion, direction, contact with surface and position inside of meniscus should be analyzed and described.
Ligament of vastus muscule should be dark on T2 based sequences, as increase in signal indicates lesion, but as with other linear ligaments beware of "[magic angle effect]", especially on systems with vertical field (open MR). Colateral ligaments are a bit thinner, but wider, and should be analyzed on several images, preferably with water and fat saturation.
Please bear in mind that other structures can also be involved, such as muscules, and blood vessels.