Comparative morphology of the lateral meniscus of the knee in primates.

The morphology of the lateral meniscus has been studied in a series of 316 non-human primates, representative of 43 genera. The lateral meniscus has a crescentic shape in Prosimii, in Platyrrhinii (New World monkeys) and in Pongo pygmaeus. The lateral meniscus is disc-shaped, with a central foramen, in Catarrhinii (Old World monkeys), in Hylobates, in Gorilla and in Pan Troglodytes. In man, the lateral meniscus has a crescentic shape. Discoid lateral menisci are reported as anomalies in man; their origin has given rise to much discussion, but the comparative data favour a phylogenetic origin. The posterior fasciculus (Wrisberg's ligament) of the posterior menisco-femoral ligament is always present and large in all non-human primates; in man, it may be absent and seems to be a regressive structure. On the other hand, the anterior fasciculus (Humphry's ligament) exists only in man and seems to be a progressive structure. The posterior menisco-tibial attachments are weak or non-existent in non-human primates, but they are well-developed in man. The evolutionary development of these characters can be related to human bipedal locomotion. The lateral meniscus in some Prosimii contains one or two intramensical ossicles (lunulae). These structures are absent or very rare in all other primate groups. In man, intrameniscal ossicles are extremely unusual; their origin, phylogenetic or post-traumatic is controversial, but comparative data favour, at least in some cases, the persistence of an ancestral character.