Lateral meniscal variations and treatment strategies

The lateral meniscus is more variable than the medial meniscus morphologically in size, thickness, shape, and mobility. The most common lateral meniscal variant is discoid in shape, which implies greater coverage of the tibia and usually increased thickness. Variants can be normal in shape but hypermobile due to abnormal insertions called unstable menisci, or abnormal in shape, such as ring-shaped meniscus. Other anomalies of the lateral meniscus include hypoplasias, abnormal insertions, and double-layered lateral meniscus. The underlying causes of lateral meniscal abnormalities are multifactorial. Several theories try to explain the etiology of the variant lateral meniscus. Some authors favor a failure of formation due to phylogenetic incompletion; whereas others favor a congenital origin. Furthermore, different theories have been proposed that suggest a wide range of abnormalities leading to unstable meniscus presenting with similar symptoms often resulting in the “snapping knee” syndrome. Since it was first described, several classifications were proposed using clinical, radiologic, and arthroscopic findings. Although most of these classifications are descriptive, newer systems focus on influencing treatment. Discoid menisci are more prone to mechanical trauma because of their thickness, relatively bad vascularization, decreased amount of collagen fibers, and weak attachments to the posterior capsule. Therefore discoid menisci are associated with an increased incidence of tears. The most common tear pattern is degenerative horizontal cleavage tear. Many stable lateral meniscal variants are asymptomatic and are found incidentally. The most common symptoms, which usually occur during childhood and adolescence, are a clunking sound with flexion of the knee, pain, decreased range of motion, joint line tenderness, sensation of a foreign object within the knee, quadriceps atrophy, and effusion. Lateral meniscal variation can be associated with other musculoskeletal anomalies. Osteochondral lesion of the lateral femoral condyle, high fibular head, fibular muscular defects, hypoplasia of the lateral femoral condyle with lateral joint-space widening, hypoplasia of the lateral tibial spine, abnormally shaped lateral malleolus of the ankle, and enlarged inferior lateral geniculate artery are examples of such anomalies. The treatment options for the various lateral meniscal variants include observation, partial meniscectomy with or without reattachment, total meniscectomy, and for a normally shaped unstable lesion reattachment to the adjacent capsule. In order to properly choose the treatment method for the lateral meniscal variant, one must consider the age and activity level of the patient, the anatomy of the lesion, the duration and extent of the symptoms, and the amount of joint destruction. One must realize that the patient with a lateral meniscal variant usually has an abnormal knee at the outset. It must be kept in mind that there may be no good treatment option; rather, the only choice may be the lesser of two evils. It is suggested that there is a need for early diagnosis and greater caution in the treatment of discoid lateral menisci. When evaluating the treatment outcome, Ikeuchi rating system and Lysholm knee scale are frequently used. Heightened awareness of the clinician to the possibility of discoid meniscus, its variable presentations and complications, and management considerations may improve therapeutic outcome.