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Discoid Lateral Meniscus
Dong Hoon Lee
Discoid Meniscus: Why Donghoon Advanced Lengthening Reconstruction Institute?
1. Removing a torn or injured meniscus is straightforward, but we carefully consider the long-term effects.
2. We strive to preserve as much of the meniscus as possible, even if it is severely torn.
Let us first discuss the difference between cartilage and meniscus.
In this x-ray, there is space between the bones (red arrow), which is not actually empty space. There is soft tissue.
MRI shows soft tissue that are not visible in x-rays. Below is a patient’s MRI. There is cartilage (yellow arrow) and a discoid meniscus (red arrow).
A meniscus is at the edge of a joint, like a wedge. Since the femur and tibia have different shapes, a wedge shaped meniscus (blue circle) is necessary for congruency. If a meniscus is circular, it is pressed by the femur (red arrow).
All structures of the knee joint have their own role; this is the same for menisci. If they do not function properly, the femur and tibia bump against each other, wearing menisci out (blue circle), eventually leading to degenerative arthritis.
A discoid meniscus is circular in shape. The original shape is crescent form. A complete discoid is a circle and an incomplete discoid is half-moon in shape. The MRI below shows a complete discoid (blue circle).
There are two main problems of a discoid meniscus. First, it can be easily torn. A discoid meniscus is a congenital malformation and it is weaker than a normal meniscus. It receives more pressure from surrounding bone and tears easily. Below is an arthroscopic image of a torn discoid meniscus.
Second, a discoid meniscus is unstable. This is a more significant problem. A discoid meniscus is not in place, moving around in a joint. When it is at the front side of the knee, the knee is not fully extended. It causes pain and the feeling of being stuck. It is important to suture the meniscus in its own place if it is unstable.
Discoid Meniscus in the Front Side of the Knee, Severely Injured. (Left)
Discoid Meniscus in the Back Side of the Knee. (Right)
There are several theories. While some say that it is a defect formed developmentally, most doctors agree that it is a congenital defect.
We cannot know the exact incidence because sometimes it is asymptomatic. Reported incidence is 0.4-17%, being especially high in Asia. While it is reported that if one side of the knee has discoid meniscus, the incidence of the other side is 20%, from actual experience rates are much higher.
In 1910, it was called the ‘snapping knee syndrome’. Its instability causes such symptoms. The shape, level of stability and symptoms of discoid meniscus vary widely. If asymptomatic, there is no need for treatment. The most important factor is ‘instability’. Typical symptoms are inability to extend the knee fully, stiffness and popping, and locking of the knee. Such symptoms appear when the discoid meniscus moves around.
Children’s and adolescent’s discoid meniscus symptoms are also caused by its instability. Discoid menisci are easily torn, causing swelling and pain.
This depends on the condition. If a patient has no symptoms, there is no need for surgery. If there are symptoms, we decide on surgical methods according to symptoms, shape of damage and instability. There are two types of discoid meniscus, complete and incomplete. Complete discoid meniscus accompanies instability and surgery is essential in this case.
In the past, when arthroscopic techniques were not developed, we opened the joint and removed all parts of discoid menisci. However, now we re-shape it into a crescent and suture it in its original place. In particular, Korean surgeons have good skills; many advanced arthroscopic surgical techniques were developed in Korea.
The most important thing is to preserve as much as possible, rather than undergoing total meniscectomy. Donghoon Advanced Limb Lengthening Reconstruction Institute treats discoid meniscus by re-shaping it into a normal shape and suturing its unstable area.
In the case below, we trimmed and sutured (red arrow) the discoid meniscus (yellow arrow). The blue circle shows injured joint cartilage. The unstable discoid meniscus injured surrounding cartilage. In such cases surgery is needed for treatment.
However, if the tear is severe, with no possibility of repair, we perform total meniscectomy. After total meniscectomy, arthritis incidence may occur sooner than others. Therefore, we consider ‘meniscus transplantation’ when growth plates are closed.
MRI of a well treated meniscus, 1 year after surgery.
Most discoid meniscus patients visiting our clinic are children and adolescents. If symptoms appeared at a young age, it proves that there is instability. It needs suture even if the patient is young. It is not an emergency, of course, but it can injure surrounding healthy cartilage in the long term. If we take care of it early, we can preserve some parts of menisci, but in the future all of it might have to be removed.
Normal Joint (Femur Cartilage (yellow arrow) and Normal Meniscus (red arrow)
Meniscus (Femur Cartilage (yellow arrow) and Discoid Meniscus (red arrow)
