Everything you need to know about menisci

The menisci are two fibrocartilaginous structures: an internal (medial) one that is C-shaped, and an external (lateral) one, whose shape can be compared to an O. Both are present in the knee and can be compared to “squid rings”, almost circular and of very similar consistency, triangular in section, with a concave upper part and a flat lower part.

What is the function of the meniscus?

Its main function is, according to the experts in Traumatology, to reduce the direct contact of the femur with the tibia, in order to facilitate the movements of the joint and to avoid the wear that would suppose a direct friction of the surfaces of both bones, as well as to stabilize the joint and to modify the vectors of force of the load in the knee.

This C-O shape and its triangular section are essential as they act as a kind of cushion, resistant but not rigid, providing better congruence to the bones, so that forces and pressures are distributed.

The meniscus explained “in the kitchen”.

Previously, they have been compared to “squid rings”, and since the femoral condyles of the knee are convex, they are now going to be compared to an egg. Since the tibial plateau is flat, it will be compared to a plate. Thus, we could imagine the menisci as a squid ring, which is placed on a plate on which an egg is placed. In this culinary example, we must also add the fact that the section of the meniscus is triangular, with a concave surface on its upper side, and flat on its lower side, which increases the contact surface with both the tibia (flat) and the femur (convex), increasing the stability of the system and decreasing the contact area of the hyaline cartilage of the femoral condyle on the tibia. Thus, when we apply load on the femoral condyle (when jumping for example), this impact force falls on the meniscus and the force vector is transformed towards the periphery, decreasing the load on the femoral condyle and the tibia.

Returning to “cooking”: the egg maintains better balance on the squid, there is less contact area of the egg directly on the plate, reducing impacts and shelling of the surfaces. When the egg is pressed against the dish, the squid ring would act as a protective cushion, cushioning the impact and preventing the egg or dish surface from breaking.

The vascularization of the meniscus

The fact that they are cartilaginous structures makes that the blood irrigation is very scarce and for that reason the capacity of healing of the menisci when they are injured is very reduced.

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Why menisci tear

Although the menisci are fibrocartilaginous structures, not rigid and with relative elasticity, it is not infrequent that they are injured. A violent forced movement or not of the knee, especially if the joint is semi-flexed, can cause injuries of different types: a disinsertion, a tear or a rupture of the same ones. This occurs particularly frequently in sports practice. For example, when an athlete turns sharply while the foot remains fixed to the ground, it causes a rotational movement of the femur over the tibia with the meniscus interposed between the two.

However, it can also occur in any situation of everyday life, such as while walking down the street and turning around because of something that catches our eye, or simply squatting down to tie our shoes. This is because the menisci are not fixed, but have some ability to move, shifting back and forth to maintain a good congruence of the femur with the tibia.

The importance of meniscus surgery

In addition to being a stabilizing complex, the menisci have a protective mission of the articular surfaces, and with it, a protective function of the cartilage surrounding the bone.

A meniscus tear involves a loss of meniscus function in the area where the tear occurred. Thus, the capacity of protection and stabilization in that area disappears, the articular cartilage is unprotected and evolves towards osteoarthritis.

Meniscal tear surgery

The surgery of the meniscus tear is performed by arthroscopy, with 2 millimetric wounds, anesthetizing only the leg. The patient can be discharged from the clinic 4 or 5 hours after the operation, and can walk without crutches with two possibilities:

– Meniscal suture: the meniscus tear is sewn, and once healed, it returns to achieve its full functionality again. Due to its capricious irrigation, only certain types of meniscal tears can be sewn with sufficient guarantee.

– Partial meniscectomy: only the torn meniscus is removed, leaving the rest of the meniscus healthy.

Why meniscus surgery

There are many influencing factors, including the age of the patient who is injured, the degree of osteoarthritis of the knee, the pain of the tear, the occurrence of episodes of joint locking….

In an older person, the meniscal tear should be operated when the discomfort is not relieved, despite 3 or 4 months of evolution with conservative measures and symptomatic treatment.

In the case that the tear occurs in a young person, it should always be operated, because in the case that it could be suturable, with time it can become non-suturable, in addition the tear could increase in size and if the broken fragment is unstable, it can hit in the flexo-extension and rotation against the cartilage of the femur, increasing the chondropathy and the wear of the hyaline cartilage.