Have you ever experienced a decreased range of motion in the knee, clicking or popping sounds? If so, you may have a discoid meniscus. A discoid meniscus is an abnormally shaped and enlarged meniscus in the knee. Because of its shape, it is more prone to injury. Its thick, abnormal shape makes it more likely to tear or get stuck in the knee. While many people are unaware of this issue and it never bothers them, others will have knee problems which can result in instability of the knee and lasting pain. The condition is rare, so it is important to seek out a highly trained and experienced orthopedic specialist. The place to start is Colorado Center of Orthopaedic Excellence in Colorado Springs, Colorado.
OVERVIEW
A discoid meniscus is a congenital, structural defect and does not grow into the normal shape of a healthy meniscus. The tissue grows thicker and larger and also has an abnormal texture. No sudden change occurs in discoid development after birth. The pathology is usually presented in the young population and during adolescence. Because of the high rate of asymptomatic patients, it’s difficult to estimate the actual incidence of discoid meniscus, but it is thought to be present in 3-5% of the general population. It occurs more in males than females and there is a slightly higher prevalence in Asians. A discoid meniscus is encountered more on the lateral or outer side of the knee and in 25% of cases it is bilateral.
ABOUT THE MENISCUS
The meniscus is a wedge-shaped piece of cartilage that sits between the bones of the knee. Each knee has two menisci; the medial meniscus on the inside of the knee, and the lateral meniscus on the outside. Healthy menisci are shaped like crescent moons (in fact, “meniscus” comes from the Greek word for “crescent”). The meniscus acts as a shock absorber between your femur (thighbone) and tibia (shinbone). It protects the thin articular cartilage that covers the ends of the bones and helps the knee to easily bend and straighten. The menisci are attached to the femur bone by a strong tissue called the meniscofemoral ligament. This ligament also provides a blood supply to a small portion of the meniscus.
WHAT IS DISCOID MENISCUS?
There are three types of discoid menisci:
Incomplete—the meniscus is slightly thicker and wider than normal, usually asymptomatic
Complete—the meniscus completely covers the tibia
Hypermobile Wrisberg—this occurs when the ligaments that attach the meniscus to the femur and tibia are not there. Without these ligaments, even a fairly normally shaped meniscus can move around in the joint and cause pain, as well as locking and popping of the knee. A discoid meniscus is more prone to injury than a normal meniscus. The thick, abnormal shape of a discoid meniscus makes it more likely to get stuck in the knee or to tear. If the meniscofemoral ligament attachment to the femur is also missing, the risk for injury is even greater. Once injured, even a normal meniscus is difficult to heal. This is because the meniscus lacks a strong blood supply and the nutrients that are essential to healing cannot reach the injured tissues.
CAUSES
In all cases, discoid meniscus is the result of a congenital birth defect. Injuries to the discoid meniscus often occur with twisting motions to the knee, such as during sports that require pivoting or fast changes in direction. Genetics or family history may play a part in whether a discoid meniscus develops. There have also been incidences reported of bilateral discoid meniscus in identical female twins or a family of three brothers and sisters. This has yet to be proven.
SYMPTOMS
- Popping sensation
- Knee swelling
- Pain along the outer side of the knee
- Feeling that the knee is “giving way”
- Inability to fully extend the knee
- Pain with squatting/kneeling
- Lateral joint pain
- Sharp or stabbing pain when running or jumping
- Stiffness and loss of range of motion
- Catching or locking—the knee “gets stuck” when fully bending or straightening
NON-SURGICAL TREATMENTS
If patients are found to have a discoid meniscus, but it is not causing symptoms, no treatment should be performed. In patients with a painful discoid meniscus, simple treatments consisting of knee exercises and stretching can be performed. Anti-inflammatory medications (NSAIDS) or a cortisone shot may be considered.
WHEN IS SURGERY INDICATED?
Most people with a symptomatic discoid meniscus will ultimately choose to have arthroscopic surgery. This procedure is performed by inserting a small camera into the joint through one small incision and using instruments that can cut, bite, and shave away the abnormal or torn meniscal tissue. If the discoid meniscus is torn, there are several approaches to managing this arthroscopically. Historically, the entire meniscus was removed at the time of arthroscopic surgery. However, removing the entire meniscus had the consequence of leading to increased chances of the development of arthritis in the knee joint because of the removal of meniscus cartilage. This surgical procedure is called a complete meniscectomy. More commonly, the discoid meniscus can be surgically shaped into a normal-appearing meniscus, a procedure called saucerization of the meniscus.
GETTING THE RIGHT DIAGNOSIS. GETTING THE RIGHT DOCTOR.
Often, people with discoid meniscus live normal, active lives—even high-performance athletes. However, it should still be correctly diagnosed to address problems should they occur. Even before ordering any tests, the professional, conscientious, and caring surgeons at Colorado Center of Orthopaedic Excellence in Colorado Springs, Colorado, take the time to discuss and explain what discoid meniscus is in terms you can understand. Because symptoms at times present in younger children and adolescents, both you and your child need to be put at ease.
At CCOE, they’ll take you through everything step by step. After an initial examination, imaging tests may be ordered. Although X-rays do not show tears of soft tissues like the meniscus, they can show whether there are other problems in the knee. In addition, because the discoid meniscus is so thick, the space between the femur and tibia on the lateral part of the knee may appear widened on an X-ray. An MRI creates detailed images of the soft tissues of the knee joint and is, therefore, the best imaging test for discoid meniscus. The MRI can show the abnormal shape of the discoid meniscus, as well as tears within the meniscus. However, the rare Hypermobile Wrisberg type of discoid meniscus cannot be diagnosed with an MRI scan because the problem only occurs when the patient is moving. Once the proper diagnosis is made, a unique treatment plan will be made that you can trust will eventually get you back to sports, work or just doing everyday activities.
