What is anterior cruciate ligament?

The anterior cruciate ligament (ACL) is located in the middle of the knee joint in the bony hollow of the lower part of the femur, extending diagonally to the upper part of the tibia. If we consider the knee as a coordinated system that enables stable and free range of motion, the ACL should be viewed as the most crucial component of that system. The main role of the ACL is to prevent excessive forward movement of the tibia in relation to the femur and ensure good rotational stability of the knee. Most people, after an ACL tear, experience a sense of instability or a feeling of the knee “giving way.” Due to their lifestyle and everyday activities typical for their age, children are often exposed to changes in movement direction, and after an ACL tear, they may feel like their knee is “giving way” or “dancing.” Since children are not small adults, ACL injuries in children and adolescents have specific considerations that need to be taken into consideration.

ACL injuries in children

In the last two decades, the number of ACL injuries in children has increased significantly. The cause is believed to be early specialization in high-intensity sports, meaning that children specialize in one sport early in life, train intensively, and injury prevention programs are not implemented. Another reason for more frequent knee injuries in children is the cessation of playing childhood games around the house, playground, street, or meadow. Girls are more exposed to ACL tears for several reasons: increased ligament flexibility, a thinner ACL, characteristic knee relationships, and hormones. Anterior cruciate ligament tears most commonly occur as non-contact injuries to the knee due to combined lateral and rotational forces in sports with frequent changes of direction, such as soccer, handball, or basketball, Figure 1.

Figure 1.
Figure 2.

How to diagnose ACL tears in children?

Children describe a characteristic event during sports activities when visiting a pediatric orthopedic surgeon after an ACL tear – “my knee popped out and back in.” The injury typically occurs during a sudden change of direction or landing. Children often feel that something has popped in the knee, and some can even hear it. They report experiencing severe pain and an inability to continue sports activities. Typically, children seek emergency care, where the clinical examination and X-ray in two directions are performed. Clinical examination may reveal that the knee is usually swollen – filled with blood, unable to fully extend, and children may limp while walking. X-ray images show bones and cannot show an ACL tear. However, in some cases, the ACL may not tear but “avulse” – break off a piece of the bone to which it attaches, which can be seen on X-ray images, Figure 2. In acute cases, it is challenging to obtain knee instability through clinical examination because the knee is painful, swollen, and the muscles are tense. If there are no bone injuries in X-ray images, the recommendation is to examine such knees a week later. Until the next examination, it is advised to use an elastic bandage, apply cold compresses to the knee, use pain relievers if necessary, and exercise knee range of motion. At the next examination, the knee is usually more relaxed, and specific clinical tests for instability and meniscus injuries can be performed. When conducting clinical tests, it is essential to examine the opposite – healthy knee. Although clinical tests can determine a very high probability of an ACL tear, children are sent for magnetic resonance imaging (MRI) to confirm the diagnosis. An MRI scan of the knee looks for other injuries that may occur along with the ACL tear, most commonly meniscus injuries. Similarly, by analyzing the MRI scan, the location of the ACL is examined because certain types of ACL tears are suitable for acute surgical repair. Other common knee injuries that lead to swelling and bleeding in the joint include meniscus tears and patellar dislocation.

How to treat ACL tears in children?

It is believed that children, after an ACL tear, have knee instability manifested in everyday activities, posing a significant risk of additional cartilage and meniscus injuries over time. Therefore, the prevailing opinion today is that appropriate knee stability should be provided for all children, achieved through surgery. Acutely recognized and proven partial ACL tears in children can be treated conservatively, without surgery, in cases where it is a partial tear. In such cases, the knee is placed in a long knee brace in a 10° flexion position for five weeks. After this treatment, intensive physical therapy and exercises to strengthen the thigh muscles are necessary to achieve better knee stability. Furthermore, acutely recognized and proven complete ACL tears with only the attachment avulsed can be treated arthroscopically by the primary repair technique – suturing the ACL to its anatomical attachment. However, nowadays, arthroscopic ACL reconstruction surgery is most commonly performed. The graft for reconstruction – ACL substitute, is usually taken from the same knee being operated on. Since bones are drilled during ACL reconstruction, it is crucial to correctly assess bone maturity in children and choose the appropriate surgical technique. Leg length growth from growth zones around the knee is approximately 70% of the total leg length. Therefore, it is essential to be as sparing as possible to growth zones during surgery. Simultaneously, during ACL reconstruction surgery, meniscus repair is performed if it is torn. Lately, lateral knee ligament reinforcement is done along with ACL reconstruction surgery to achieve better rotational stability. After surgery, children go through specific physical therapy protocols aiming to achieve full range of motion, followed by strengthening the thigh muscles, especially the posterior muscle group. Subsequently, a return to daily life activities follows, and finally, after a year, a return to full sports activities.

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