What is a knee cyst? Is it serious?

Knee cyst, also known as meniscus cyst, is a disease that mostly occurs in young people, especially athletes. Exercising too much in daily life can lead to sports injuries, inflammatory reactions, and chronic symptoms, which can easily lead to the formation of knee cysts. If not treated in time, it can cause great harm to health, often leading to decreased motor function and symptoms such as swelling and pain.

Etiology and pathology

Knee meniscus injury is common when the knee flexion and extension is accompanied by internal and external rotation or internal and external rotation of the lower leg, causing contradictory movement of the meniscus. A meniscus cyst can cause the femoral condyle to slide on the meniscus, pushing the meniscus forward during extension and backward during flexion. When the knee joint is rotated, the meniscus moves in unison with the medial and lateral condyles of the femur. The rotation occurs between the meniscus and the tibial plateau, with one side of the meniscus moving forward and the other side of the meniscus moving backward. When the knee joint is in semi-flexion and the calf is inwardly or externally rotated, the meniscus is squeezed and cannot move. If it is suddenly straightened or further rotated at this time, the tension on the fibrous cartilage of the meniscus itself or the fibrous tissue around it will exceed its own endurance, and tearing will occur.

1. If the knee joint is flexed, the tibia is fixed, and the femur is strongly externally rotated, it may cause damage to the anterior horn of the lateral meniscus or the posterior horn of the medial meniscus.

2. Strong internal rotation of the femur (or external rotation of the calf) with the knee flexed can easily cause injury to the posterior horn of the lateral meniscus or the anterior part of the medial meniscus. Long-term extrusion and wear can cause degeneration and easily lead to tearing. Abnormal looseness of the meniscus, instability after joint ligament injury, or obesity and excessive weight are all factors that make the meniscus susceptible to injury.

According to foreign literature, meniscus injuries are mostly on the medial side, while domestic reports show that meniscus injuries are more common on the lateral side. Meniscus injuries include edge tears, longitudinal tears, transverse tears, horizontal tears, and anterior and posterior corner tears. Since the meniscus itself has no blood supply, blood circulation only occurs around the periphery. Therefore, only marginal tears are likely to heal.

Injury Type

1. Edge type: The rupture is located at the front, middle and back positions of the edge of the medial meniscus. Severe edge type rupture is a complete rupture of the perimeter, connected only by the front and back corners, and the ruptured waist slides toward the center of the knee. This can lead to locking of the joint. Symptoms are most pronounced when the knee is extended. It is believed that this type of disease may heal on its own. Some patients were healed by suture.

2. Front angle type: The rupture is located at the front angle, which may be just a crack, or the ruptured part may roll back and thicken, and the front angle connecting part may also be broken. The pain is located in front of the knee, but the patient may not be able to distinguish between the inner and outer sides.

3. Posterior horn type: The rupture is located in the posterior horn and may appear as a crack, with the crack curled up and the connecting fibers of the posterior horn broken. The pain is obvious when the knee is excessively flexed. The pain can usually be located on the posterior medial side, but in some cases the side cannot be determined.

4. Horizontal type: It is a horizontal rupture of the waist of the medial meniscus. The location, number and depth of the rupture vary. Medial knee pain is often pointed, and locking of the joint may occasionally occur.

5. Bucket-handle type: The medial meniscus is ruptured longitudinally. The cracks may vary in size and may also be transverse. The rupture opening is obviously thickened and the synovial membrane of the femoral condyle is extensively damaged. The affected knee often "locks", making walking difficult and time-consuming.

6. Inner edge type: There is one or more injuries on the inner edge of the meniscus, which may appear as comminuted damage, with occasional free fragments entering the joint cavity. This type of disease often affects the extension and flexion of the knee, manifesting as long-term pain, obvious damage to the femoral condyle articular surface, and sometimes joint locking. Plain X-rays are occasionally seen. Free bone fragments.

7. Horizontal split type: It is caused by strong rotation between the tibiofemoral joint, resulting in horizontal separation between the upper and lower layers of the medial meniscus. If diagnosed early and good braking is achieved, it may be possible to repair the disease. The affected knee may experience dull pain, instability, or a feeling of slipping.

8. Longitudinal type: longitudinal rupture of the medial meniscus. It may also break at the anterior or posterior corner, with the free part entering the knee, becoming the main factor of knee pain and flexion and extension obstruction.

9. Relaxation type: The medial meniscus is loose at the attachment point of the joint capsule. Every time the knee is extended, flexed, or rotated, there is an unstable and slipping feeling. When the tibiofemoral joint is squeezed toward the center of the knee, the medial joint capsule (and skin) may sink into the joint space. This type may be caused by trauma or congenital structural defects.