The meniscus from the side
The meniscus is a wedge-shaped cartilagenous shock-absorber, which exists between femur and tibia on either side of the joint. Each knee has two menisci.
In the illustration you can see the two menisci between the femur and the tibia bones. For clarity, the cruciate ligaments and quads muscle are removed. The wedge-shaped meniscus accommodates the incongruity between the rounded end of the femur and the flat surface of the tibia.
Each meniscus is curved like a pair of horns - the front bit is called the anterior horn, and the back bit is the posterior horn. The meniscus on the inner side is called the medial meniscus and the one on the outer side is the lateral meniscus.
This next illustration of the front of the left knee shows how the rounded condyle of the end of the femur snugs into the crescentic meniscus.
The inset on the right is a photo taken close-up during arthroscopy, so that you can really see what a meniscus looks like.
The meniscus from above
The previous section on the meniscus from the side will have given you an overview of meniscus anatomy.
Looking down at this schematic representation of the two menisci from above on this right leg the difference in shape between the medial and lateral meniscus can be more clearly appreciated. The medial meniscus is more C-shaped, while the lateral meniscus is more O-shaped. The lateral meniscus is also more mobile as its outer rim is not tethered to the capsule like the medial one is.
The two chopped-off ligaments in the middle of the flattened top of the tibia are the cruciate ligaments - 'chopped off' because of course the femur bone to which they are normally attached has been removed so that you can see the menisci fully like this.
Although it is a rather low-resolution photo, we have displayed below the illustration a real pair of menisci - taken from a transplant donor and awaiting transplantation. The difference in shape of the two menisci can be appreciated, as well as the wedge-profile of each meniscus. You also get some idea of the relationship of the menisci to the capsule around the joint, but we will go into this in more detail later.
Meniscal horns and roots
The pointed ends of each meniscus are referred to as the 'horns' of the meniscus. The anterior horns are at the front and the posterior horns are at the back. It is at the horns that the menisci are directly tethered to the tibia bone, via structures called the meniscal roots.