On the joint surface of the tibia are medial and lateral meniscus-shaped bones called menisci, which are thick at the edges and closely connected to the joint capsule, and thin and free at the center. The meniscus moves with the movement of the knee joint, moving forward when the knee is extended and backward when the knee is flexed. The meniscus is fibrous cartilage and has no blood supply of its own. Its nutrition mainly comes from synovial fluid, and only the marginal part connected to the joint capsule receives some blood supply from the synovial membrane. Therefore, the meniscus cannot be repaired by itself after rupture, except for the edge part which can be repaired by itself after injury.
1.Cause of development
The meniscus plays an important role in knee joint movement and is easily damaged. Trauma is an important cause of meniscus injury. Meniscus tear is the most common meniscus sports injury, mostly seen in basketball, soccer, gymnastics, weightlifting and other sports.
2.Pathogenesis
Meniscal injuries are mostly caused by torsional external forces. When a leg is weight-bearing and the lower leg is fixed in semi-flexion and external booth, the body and the femur are violently rotated internally and the medial meniscus is between the femoral condyle and the tibia, which is subjected to rotational pressure and causes meniscal tears. The greater the degree of knee flexion at the time of sprain, the more posterior the tear site is. The mechanism of lateral meniscus injury is the same, but the direction of the force is opposite, and the ruptured meniscus slides partially into the joint, causing mechanical obstruction to joint movement and preventing joint extension and flexion, forming an “interlock”.
Meniscal injury can occur at the anterior, posterior, middle or marginal part of the meniscus. The injury can be transverse, longitudinal, horizontal or irregular in shape, or even broken into intra-articular free bodies. After meniscal injury, there is severe pain in the knee joint, inability to straighten itself, and swelling of the joint. The pressure pain at the knee joint gap is an important basis for meniscal injury.
3.Pathophysiology
The meniscus is a half-moon shaped cartilage plate between the knee joints. It is thick on the outside and thin on the inside, depressed on the top (femoral surface) and flat on the bottom (tibial surface). The medial meniscus is “C” shaped, with the edges closely connected to the joint capsule and the medial collateral ligament; the lateral meniscus is “O” shaped, with the posterior 1/3 of it crossed by the N tendon, separating the meniscus from the joint capsule. It is separated from the joint capsule by the N tendon in the posterior 1/3. The meniscus can be divided into: red zone (blood supply zone), located at the edge of the meniscus 5 mm, and synovial continuous part; red-white zone, located in the medial side, blood supply is poor; white zone, located in the inner part of the red-white zone, no blood supply, rely on joint fluid to provide nutrition.
4.The role of meniscus
To put it simply, the function of the meniscus is to stabilize the knee joint, transmit the knee joint load, and promote intra-articular nutrition. It is the stabilizing effect of the meniscus that ensures that the knee joint is not damaged by years of weight-bearing exercise.
4.1. Weight-bearing
When not bearing weight, the tibia is not in contact with the femur, and the meniscus is lined between the two. During weight bearing, approximately 70% of the weight bearing area is on the meniscus, which greatly reduces the stress on the tibial plateau, thus protecting the cartilage and the joint as a whole. If the meniscus is removed, the peak pressure on the tibial plateau can rise twofold and will cause cartilage degeneration. It can be inferred that in the case of transverse meniscal tears, the weight-bearing function of the meniscus is completely lost. This requires us to cut as little as possible during partial meniscectomy.
4.2. Maintenance of knee joint motion coordination
The meniscus moves together with the tibia, the medial meniscus is less displaced than the lateral meniscus, and the meniscus can be deformed during knee flexion and extension to fit the anatomic shape of the knee joint. The coordination of the knee joint geometry is maintained, thus maintaining the coordination of knee motion.
4.3. Maintenance of stability
Meniscectomy does not cause anterior tibial displacement when the ACL is intact, whereas it causes greater anterior tibial displacement when the ACL is ruptured.
4.4. Absorption of concussion
There are such patients with knee pain whose arthroscopic pathology does not reveal any abnormalities, while their symptoms are obvious, and who are later found to have poor meniscal resorption on examination.
4.5. In addition, the meniscus has the function of lubricating the joint, etc. The meniscus can evenly coat the joint surface with joint fluid, so that the friction coefficient of the joint is greatly reduced.
5. Clinical manifestations and examination
Most of them have obvious history of trauma. In the acute phase, the knee joint has obvious pain, swelling and effusion, and the joint flexion and extension activities are impaired, after the acute phase, the swelling and effusion can subside on their own, but the joint still has pain when moving, especially when going up and down stairs, going up and down slopes, squatting and standing, running, jumping, etc. The pain is more obvious, and in serious cases, the patient can limp or have flexion and extension dysfunction, and some patients have the “interlocking” phenomenon. Some patients have the phenomenon of “interlocking” or a popping sound when flexing and extending the knee joint.
5.1. Site of pressure pain
The site of pressure pain is usually the site of the lesion, which is important for the diagnosis of meniscal injury and for determining the site of injury. During the examination, the knee is placed in a semi-flexed position, and pressure is applied with the thumb along the upper edge of the tibial condyle (i.e., the edge of the meniscus) in the medial and lateral gaps of the knee joint, point by point from front to back. If the knee is passively flexed and extended or the calf is rotated internally and externally while the pressure is applied, the pain is more pronounced, and sometimes the abnormally moving meniscus can be palpated.
5.2. McMurray’s test (gyratory compression test)
The patient lies on his back, the examiner holds the ankle of the calf with one hand, and holds the knee with the other hand to flex the hip and knee as much as possible, then make the calf abduct, externally rotate, or abduct, internally rotate, or adduct, internally rotate, or adduct, externally rotate, and gradually straighten. The presence of pain or ringing is considered positive, and the site of injury is determined according to the site of pain and ringing.
5.3. Powerful hyperextension or hyperflexion test
The knee joint will be forcefully and passively hyperextended or hyperextended. If the anterior part of the meniscus is injured, hyperextension can cause pain; if the posterior part of the meniscus is injured, hyperextension can cause pain.
5.4. Lateral compression test
If there is a meniscal injury, the pain will be caused by compression at the joint space on the affected side.
5.5. Grinding test
If the patient is in prone position with the knee flexed, the examiner holds the ankle with both hands and presses the calf down while doing internal and external rotation activities, the injured meniscus causes pain due to compression and grinding; conversely, if the calf is lifted upward and then does internal and external rotation activities, there is no pain.
5.6. X-ray examination: X-ray frontal and lateral radiographs cannot show the meniscus injury, but other bone and joint disorders can be excluded. Knee arthrography has little diagnostic significance and can increase patient pain and should not be used.
5.7. MRI: Magnetic resonance imaging is currently the best non-invasive test for meniscal injuries.
5.8. Knee arthroscopy: Through arthroscopy, the site and type of meniscal injury and other structures in the joint can be directly observed, which can help in the diagnosis of difficult cases, and the damaged meniscus can be treated at the same time of the examination.
6. Disease treatment
6.1.Conservative treatment
Conservative treatment of meniscal tears is limited to acute marginal vertical longitudinal tears within 5 mm or tears or incomplete tears at the joint capsule junction, and conservative treatment such as joint braking can be performed.
6.2. Surgical treatment
If conservative treatment is ineffective for 6 weeks and symptoms persist, surgery should be considered.
(1) Meniscectomy: Arthroscopic meniscectomy is feasible for the treatment of abrasive tears of the meniscus, extensive separation of the synovial attachment of the meniscus with severe injury and tear of the body of the meniscus, severe injury and tear of the body of the white zone of the meniscus, and abrasive injury of the meniscus in the elderly.
(2) Meniscus suture repair: anatomical repair of meniscus injury of knee joint – arthroscopic meniscus suture repair is the ideal surgical method for meniscus injury treatment.