What You Need to Know About Meniscus Injuries
The knee is the largest joint in the body, consisting of three compartments
. The thighbone, or femur, meets the shinbone, or tibia, to form the main knee joint. The patella unites with the femur to form the third compartment, the patellofemoral joint. The knee may be the largest joint in the body; however, it is one of the most frequently injured joints especially in individuals involved with contact sports. Additionally, because it is made up many complex supporting structures, it becomes more vulnerable to injuries. Meniscal tears are considered as the most common knee injuries, with a prevalence rate of 61 cases 100,000 persons.
The menisci are two thickened, wedge-shaped cartilage pads positioned between the shin bone and the thigh bone. Each knee joint consists of two menisci: the medial meniscus, which is positioned on its inner side, and the lateral meniscus, which is located on the knee's outer side. The meniscus is composed of 75% water, mostly type I collagen fiber, noncollagenous proteins and cartilage cells. These components make it possible for the meniscus to resist maximum loads while demonstrating elasticity with deformation.
It was once thought that the menisci were useless remnants of leg muscles; however, continued research and advanced imaging techniques revealed that these structures play an important role during knee movements. Aside from providing stability to the knee joint, menisci are also protective and load-sharing structures. Menisci can transmit 50 to 60% of the load applied across the knee joint, resisting large compressive loads. Load transmission increases to 85 to 90% during flexion. Because of their viscoelastic properties, the meniscus can effectively assist in shock absorption. During walking or running, they can stretch in different directions to spread out the forces transmitted between the femur and the tibia, absorbing energy and reducing the amount of stress these structures would otherwise endure. Menisci increases joint congruity by filling in the gap between the tibia and femur. They also limit extremes in flexion and extension. Additionally, they encourage joint lubrication by assisting the compression synovial fluid into the articular cartilage.
Meniscus injuries commonly occur in contact sports, frequently in combination with ligament injuries. Meniscal injuries usually involve the medial meniscus. Compared to lateral meniscus, it is more securely attached by the ligaments, consequently reducing its maneuverability. Thus, it becomes more vulnerable to being squeezed between the femur and tibia. A pinched meniscus is at greater risk for tearing and arthritis in later life. To add, most tackles are often directed toward the lateral side of the knee, resulting in external rotation of the tibia and injuring the medial side in the process.
The mechanism of injury in younger adults frequently involves forceful, twisting impact or change of position of the weight-bearing knee in different degrees of extension or flexion. The medial side is most vulnerable when the foot and the lower leg are in external rotation in relation to the femur during the twisting motion. When the foot and the lower leg are in internal rotation during the twisting motion, the lateral side becomes easily injured.
Meniscus injuries are also caused by hyperflexion of the knee, most especially during weight bearing. The meniscus can recede backward during flexion only at a certain point. Once it reaches its limit and is further flexed, it becomes susceptible to being compressed between the femoral and tibial joint surfaces. This mechanism of injury frequently occurs in occupations where one must frequently move around in a squatting position.
Another common cause of meniscus injuries is direct, blunt trauma to the knee. Although the menisci are deeply located within the knee, they are connected to many ligaments that surround and support the knee joint; thus, they become vulnerable to contact injuries. The ruptures can run vertically or horizontally through the meniscal tissue. Younger adults are more commonly observed with vertical ruptures, whereas, the elderly frequently demonstrate horizontal ruptures.
What You Need to Know About Meniscus Injuries
By: Rick Kaselj
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