What is the meniscus of the knee?
The menisci are crescent-shaped cartilage structures located between the femur (thigh bone) and the tibia (shin bone) in the knee. There are two menisci in the knee, medial and lateral, both C-shaped, attached to the tibia at their front and back ends. Their shape reduces the mismatch between the joint surfaces of the femur and tibia. In doing so, they increase the contact area between the joint surfaces, help transfer load, reduce pressure on the joint cartilage, and contribute to knee stability and to the distribution of joint fluid within the knee. At birth the entire meniscus has a blood supply; by around age 10, the blood supply to the inner two-thirds of the meniscus is lost, while the outer third continues to be supplied with blood, giving it a better healing potential after a tear. It was previously believed that all meniscus injuries in children were related to a discoid shape. Today, however, an increasing number of young athletes present at the paediatric orthopaedic clinic with tears of a normally shaped meniscus. A meniscus tear is often associated with an ACL tear. In addition, once torn, the meniscus loses its physiological function as the knee's “protector”, setting off unfavourable processes in the knee – predominantly cartilage damage that gradually leads to degenerative changes, i.e. osteoarthritis of the knee.
How is a meniscus tear diagnosed in children?
A meniscus tear is the most common knee injury and accounts for almost 75% of all intra-articular knee pathology. The clinical picture of an acute meniscus injury is characterised by intense pain over the injured meniscus, swelling, and reduced range of motion. Children describe a sudden, sharp pain around the knee when turning or straightening the leg from a partly bent position. A possible clinical sign of an acute meniscus injury is knee locking – the inability to move the knee fully. This occurs when a torn fragment of the meniscus becomes trapped between the bones of the knee. The knee is then held slightly bent, with an inability to achieve full extension. If the meniscus injury occurs together with an ACL tear, the injury event is much more dramatic, and children describe the knee “popping out”.
Clinical suspicion of a meniscus injury is further supported if specific tests for meniscus damage are positive. All meniscus tests involve compression and rotation of the knee in an attempt to provoke pain. Fluid in the knee is not an uncommon finding, nor is limited range of motion. Every injured knee should be X-rayed in at least two views to assess the condition of the bone. Since the menisci are not visible on X-ray, the imaging study used to demonstrate a damaged meniscus is an MRI, on which the site of the tear can be clearly identified after analysis of the images.
There are two characteristic meniscus injuries: the RAMP lesion and the ROOT lesion. A RAMP lesion is a specific type of tear at the back of the medial meniscus, at the junction between the back of the meniscus and the joint capsule. RAMP lesions are, in a large proportion of cases, associated with an ACL tear, and are notable for being very difficult to detect, which is why they are also called a “hidden” meniscus lesion. A ROOT lesion is an injury to the meniscus root and represents a tear of the fibres that anchor the ends of the meniscus to the tibia. Such a meniscus no longer distributes load correctly, functionally or biomechanically, and contact pressure between the tibia and femur increases significantly, ultimately accelerating cartilage wear.
How is a meniscus tear treated in children?
Today's surgical method for a meniscus tear is knee arthroscopy with meniscus repair (suturing). The arthroscopic meniscus repair technique begins with inspection inside the joint and confirmation of the meniscus injury. Once the tear is found, its character is assessed, stability is checked with a probing hook, and the surgeon then decides which meniscus repair technique to use. Before the repair itself, the edges of the meniscus or capsule must always be freshened, especially for older tears, as this triggers the biological processes of tissue healing. This surgical technique should always be used when treating meniscus tears in children and adolescents, and removal of the meniscus – meniscectomy – in this age group is today considered a “vitium artis”, a professional failure. During meniscus repair, small skin incisions on the knee are sometimes made so that the repair sutures can be tied off against the joint capsule.
After meniscus surgery, rehabilitation is essential to allow the meniscus to heal while preserving range of motion and muscle strength, with the goal of returning children to all activities at the same level as before the injury. In the early phase of rehabilitation, a knee brace is worn, and squatting, kneeling and rotation around the knee are forbidden. Gradual physical therapy then leads to readiness for sporting activities around six months after surgery.
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