In the knee the rounded ends of the femur (thigh bone) sit on the flat top of the tibia (shin bone). The femur is supported by the meniscus, which is composed of two “C” shaped cartilage structures: the medial meniscus, which sits on the inner side of the knee, and the lateral meniscus, which sits on the outer side. These are soft cartilage structures that help provide a stable contoured place for the round ends of the thigh bone to fit on the relatively flat top of the shin bone. The meniscus also acts as the shock absorber of the knee.
As many as three out of every 100 kids have an abnormal shape of the lateral meniscus, with the condition being found more often in boys. Rather than having the typical letter “C” shape, the meniscus forms as a solid piece, similar to a Frisbee or disc. The meniscus tissue is not only shaped differently, but it also does not have its normal elastic properties and therefore is more at risk of tearing. Because of the disc shape, it is referred to as a discoid lateral meniscus.
A discoid lateral meniscus does not always cause symptoms. It may go unnoticed throughout adulthood. Sometimes, it is discovered while another problem is being evaluated in a child, teenager or adult. Therefore, it is difficult to quantify how often it occurs in people.
Here are some common scenarios where a discoid lateral meniscus is diagnosed:
A young child, age 4-7, can make his or her knee “pop” or “clunk” when he or she bends and straightens it. This doesn’t cause pain and in most cases does not need treatment.
A pre-teen or teenage athlete, age 9-17, has a twisting injury to the knee with pain localized to the outside of the knee and difficulty straightening the knee.There are no other injuries identified in the physical exam. An MRI reveals a torn discoid lateral meniscus, which in most cases requires surgical treatment.
In our research, we found that patients who were less than 13 years of age that presented with lateral meniscal symptoms were found to have a discoid lateral meniscus 96% of the time. Of those patients two out of every three had no history of an injury that the family or patient could remember.
When meniscus symptoms of knee locking, catching or painful popping keep a child from doing normal activities or sports, surgical treatment may be recommended. The goal of a surgery is to improve the shape of the meniscus and remove any loose or extra tissue that may cause the joint to become stuck.
The surgery performed for this condition is a type of minimally invasive surgery called knee arthroscopy. To perform this procedure, 2-3 very small incisions are made. A small camera, called an arthroscope, and instruments are used to look and work inside the joint. Typically this allows children to return to play and sports quickly, though the recovery will take a while longer if the reshaped meniscus is torn and requires repair.
In the case of knee injuries in young and growing athletes, seeking help from a pediatric specialist ensures that a discoid meniscus is properly diagnosed and treatment options are based on current evidence on pediatric care.
In addition to changing the shape of the meniscus, a pediatric orthopedic specialist will also observe the whole leg. In some cases the alignment of the hips, knees and ankles may put the discoid meniscus at further risk of damage as the child grows. As with many childhood orthopedic conditions, regular follow-up and monitoring of growth are important steps after a discoid meniscus is identified, even if treatment is not needed in early stages.
For information about injury prevention and pediatric sports medicine, please visit our website at scottishritehospital.org/sports.
Charles “Chuck” Wyatt, R.N., C.P.N.P., R.N.F.A. Texas Scottish Rite Hospital for Children
Chuck Wyatt received his master’s degree from Texas Woman’s University’s Parkland School of Nursing. He completed a fellowship program for Pediatric Orthopaedic Advanced Practice. In addition to his more than 13 years practicing alongside Dr. Philip L. Wilson and Dr. Henry B. Ellis, Chuck has completed training as a Registered Nurse First Assistant, making him an invaluable part of the team at Texas Scottish Rite Hospital for Children. Chuck serves on the board of the Fellowship for Pediatric Orthopedic Advanced Practice. He is a founding board member of the Pediatric Orthopaedic Practitioners Society where he currently serves on the executive board. Chuck is active in research regarding the pediatric athlete. He specializes in caring for skeletally immature athletes and pediatric fracture management.