In order to explain the occurrence of malformed meniscus in man, dissections were carried out in various vertebrates; they revealed that menisci shaped like a plate, disc, or ring are physiological components of the knee joint in several vertebrates. Microscopic examinations of tissue sections through the knee joints of human embryos revealed that the meniscus develops from an intermediate mesodermal blastema, which has the shape of a thick plate in the early embryonic period The occurrence of a malformed meniscus in man may be explained by persistence of a very early embryonic stage and also possibly by reversal to a phylogenetic shape.
The occurrence of congenital malformation of the meniscus in the knee joint has been reported l 3, 4, 5, 10, 14, 15 l under the designation of discoid meniscus, which often causes the symptoms of snapping in the knee joint While some authors l 9 l mention the prevalent involvement of the lateral meniscus over the medial meniscus in a proportion of 6:1, none has proferred an explanation as to the etiology of this malformation Smillie l 16 l postulates that the meniscus is formed during early fetal life as a thick plate which undergoes a progressive central resorption, whereupon it assumes a crescent shape; the occasional cessation or lack of the resorptive process in its central portion accounts for the congenital malformation of the meniscus However, Kaplan l 11 l pointed out, on the basis of his embryological studies, that at no time in the development of the human embryo does the meniscus present a discoid shape Nor did he find a discoid meniscus by comparative anatomical dissections of knee joints in various animals l 11 l.