One of the most common causes of knee pain in young athletes is called patellofemoral pain syndrome. This condition, involving pain in the front of the knee, is related to overuse of the patellofemoral joint the joint between the kneecap (patella) and thighbone. Though this condition is often called runner’s knee, it can also be caused by a direct blow to the kneecap.
Pain in the front of the knee can also be caused by patellar tendinitis (jumper’s knee), which causes pain in the patellar tendon that connects the patella to the tibia (shinbone). The patellar tendon attaches to a bump on the tibia called the tibial tubercle. In growing athletes, pain in this area, called Osgood-Schlatter disease, is due to irritation of the growth plate.
Ligament and Cartilage Injuries
One of the most common ligament knee injuries is a sprain of the medial collateral ligament (MCL). A sprain refers to a ligament injury and a strain refers to a tendon or muscle injury. All sprains are graded on a scale of one to three; grade three sprains are complete tears. An MCL sprain is on the inside (medial) side of the knee, and often occurs when an athlete is hit on the outside (lateral side) of the knee, forcing the knee inward. Most MCL sprains can be treated without surgery.
An injury to the anterior cruciate ligament (ACL) usually occurs as a result of a twisting or pivoting motion. This injury may cause susceptibility to repeat injuries and knee instability, and therefore often requires surgery. Occasionally, a twisting or hyperextension force to the knee may result in a tibial spine fracture. Essentially, this is the same mechanism that causes an ACL injury, but instead of causing injury to the ligament itself, the bone where the ligament attaches is pulled off. This fracture often requires surgery but may be treated in a cast.
Although rare in children, young athletes may injure their meniscus, a type of cartilage that cushions and stabilizes the joint. All knees have two menisci—the medial meniscus on the inside of the knee and the lateral meniscus on the outside of the knee. Meniscal tears usually result from a forceful injury and often accompany ligament tears such as ACL tears. These injuries usually require surgery. In addition, some children are born with an abnormal meniscus, known as a discoid meniscus, which is bigger than a normal meniscus and more prone to tearing.
Growth Plate Injuries, Fractures, and Dislocations
Knee fractures rarely occur in childhood sports, but with any knee injury in a growing child there is a possibility of a fracture related to one of the growth plates. Any of the bones of the knee joint—the bottom of the thighbone, the top of the shinbone, and the kneecap—can be broken. Therefore, a knee injury that impedes a child’s ability to bear weight or does not improve within a few days should be evaluated by a physician. One particularly vulnerable area in a growing child is the tibial tuberosity, which is the bump on the front of the knee where the patellar tendon attaches. Fractures to the growth plate in this area often require surgery.
Dislocations or partial dislocations of the kneecap occasionally occur in children and adolescents. Sometimes there is a visible, obvious deformity of the knee, with the kneecap in a position toward the outside of the knee—or the athlete may simply feel something pop out of the joint and then pop back in. When this occurs, the patella should be placed back in the correct position as soon as possible.