Development of the meniscus of the knee joint in human fetuses.

Discoid meniscus of the knee joint occurs at a higher incidence in the lateral than in the medial menisci. Although its developmental origin has been suggested, it remains unclear. To verify the developmental etiology, we examined the meniscus of the knee joint in 41 human fetuses (from 14 to 30 weeks of gestation) and 14 adults (from 56 to 91 years of age) comparatively. The articular surfaces of the tibia and meniscus of the left knees in 40 fetuses and 14 adults were photographed and each area was measured by Scion Image (Scion; http://www.scioncorp.com). Morphometric analyses revealed that the proportion of the area of meniscus to that of the plateau was continuously higher in the lateral side than in the medial side. The right knee joints of seven fetuses were histologically observed, and the layered structure of fibers developed earlier in the lateral meniscus than in the medial in fetuses. The observed differential development of lateral and medial sides of the meniscus may be involved in the etiology of discoid meniscus.