The clinical entity known as "discoid lateral meniscus" was investigated in order to determine its etiology and to explain the mechanism of the click which is frequently observed during fiexion and extension of the knee joint. Inasmuch as treatment consists in removal of the discoid mersiscus, an attempt was also made to find a more direct method of removal which would be more consistent with the surgical anatomy of this condition.
In a recently reported embryological study of the menisci 8, the author established that in no stage of development, from the earliest phase to birth, does the lateral meniscus appear in the form of a disc.
In a series of comparative-anatomy dissections, the author found that none of the animals available to him, representing mammals, birds, amphibians, and reptiles, had a lateral or medial meniscus resembling a disc.
Observations made at operation showed that in individuals with discoid minisci there is no attachment of the posterior horn to the tibial plateau. Instead of this attachment, there is a continuous Wrisberg's ligament (meniscofemoral ligament) which forms a link between the posterior horn of the meniscus and the medial condyle of the femur. This is similar to the normal arrangement observed in all animals except man.
On the basis of these findings, it was concluded that patients with discoid minisci represent individuals who are born with a normal lateral meniscus, as far as form is concerned, but with an anatomical variation which consists in the posterior horn of the lateral meniscus not being attached to the tibial plateau. In these individuals, as in all animals but man, the meniscofemoral ligament joins the meniscus to the medial condyle of the femur. This anatomical variation does not permit the normal limitation of the
movements of the lateral meniscus which is required by the normal range of motion of the human knee joint.
The discoid form develops gradually after birth and is the result of abnormal motion of the lateral meniscus. The hypertrophied meniscus actually varies in shape but has been fancifully called "discoid".