Meniscus

The peripheral portion of the disc attaches to the fibrous capsule of the joint. Most of the disc is avascular, although the peripheral portion may have blood vessels and afferent nerves. The intra-articular disc may play a role in shock absorption, lubrication of the joint, distribution of weight over a large surface, and facilitation or limitation of motions such as rotation and translation.

The menisci of the knee are located between the articular surfaces of the condyles of the femur and the tibial plateaux. The lateral meniscus appears as a circular structure and covers more of the articular surface of the tibia than the medial meniscus. The medial meniscus is semicircular with the width of its central portion being variable. The meniscofemoral ligaments, which are accessory ligaments of the knee that extend from the posterior horn of the lateral meniscus to the lateral aspect of the medial femoral condyle, include the ligament of Humphry and the ligament of Wrisberg.

Meniscal tears may be either traumatic or degenerative. Traumatic tears are usually vertical tears that may propagate in a longitudinal or transverse direction and commonly involve the thin edge of the meniscus; degenerative tears tend to be horizontal cleavage lesions that typically occupy the posterior half of the menisci. The McMurray test, in which an audible snap or pop occurs as an abnormal meniscus extends over a bone protuberance, is helpful in diagnosis of meniscal tear. Bucket-handle tears of the meniscus are characterized by an inner displaced meniscal fragment resembling a handle and a peripheral nondisplaced portion of the meniscus that has the appearance of a bucket. MR imaging findings include a foreshortened and blunted meniscus with central displacement of its inner fragment. On sagittal MR images, the displaced fragment of the medial meniscus often lies in front of, below and parallel to the posterior cruciate ligament. The two MR imaging criteria for diagnosis of meniscal tear are abnormal meniscal morphology and intrameniscal signal intensity that extends to the meniscal surface. Ultrasonography may also be helpful in the diagnosis of tears and cysts.

Meniscocapsular separation represents disruption of the meniscal attachment to the joint capsule. Meniscal cysts are also a common finding. These are multiloculated collections of mucinous material occurring at the periphery of a torn meniscus and appearing as a focal mass or swelling at the joint line. A discoid meniscus is broad and disclike in appearance rather than semilunar. Arthrography and MR imaging reveal the abnormally large and elongated meniscus, frequently extending to the intercondylar notch. Another abnormality of menisci are ossicles, which represent foci of ossification within the menisci. These differ from meniscal calcifications, which relate to calcium pyrophosphate dihydrate crystal deposition in many cases, and from intra-articular osteochondral fragments. Meniscal ossicles are associated with tears of the medial meniscus.

Partial and total meniscectomy is still employed in the treatment of some meniscal tears. Postoperatively, a spectrum of MR imaging findings consisting of altered intrameniscal signal intensity and contour alterations is seen after partial meniscectomy or surgical repair of a torn meniscus. MR arthrography using gadolinium compounds or saline solution may be superior to standard MR imaging in the diagnosis or exclusion of a retorn meniscus.

In the temporomandibular joint, the major soft tissue structure is a meniscus interposed between the adjacent temporal bone and mandible. The disc, which is thin centrally (the intermediate zone) and ridged or thickened peripherally, attaches to capsular, ligamentous and other soft tissue structures about its entire periphery.

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