A discoid meniscus is an atypically shaped cartilage (meniscus) inside the knee. The typical shape is crescent-shaped, but a discoid meniscus is more like a saucer or disc (as the name implies). Around 3% to 5% of the United States population has a discoid lateral meniscus, or DLM. This condition is twice as prevalent in Asian countries, with rates as high as 10.6% in Korea and 13% in Japan. In the U.S., about 1 in 4 people (25%) with DLM have the condition in both knees. In Asian countries, the number who have it in both knees is much higher, ranging up to 97% in some studies.

Because the meniscus is bigger and shaped more like a disc, it covers more of the shin bone. This leaves the meniscus more susceptible to injury. Children and teens with this condition might feel pain or have their knee lock up. They also may hear a popping sound or thud sensation in the knee (sometimes called snapping knee syndrome). Although some people with DLM may never experience symptoms, they are at an increased risk of knee injury. Pediatricians and physical therapists most often diagnose this condition in children and young people. Surgery is required once symptoms appear. Physical therapists treat discoid meniscus before and after surgery to help relieve pain, strengthen muscles, and promote a return to regular activity.

Physical therapists are movement experts. They improve quality of life through hands-on care, patient education, and prescribed movement. You can contact a physical therapist directly for an evaluation. To find a physical therapist in your area, visit Find a PT.

Find a PT Near You

On this page

• What Is a Discoid Meniscus?
• How Does It Feel?
• How Is It Diagnosed?
• How Can a Physical Therapist Help?
• Can This Injury or Condition Be Prevented?
• What Kind of Physical Therapist Do I Need?

What Is a Discoid Meniscus?

Humans have two pieces of cartilage in each knee joint called menisci (plural for meniscus). One is on the inner side of the knee (called the medial meniscus) and the other is on the outer side (called the lateral meniscus). Menisci (plural of meniscus) are strong and flexible and help absorb shock and protect the bones of the knee joint from the stresses of body weight and activity. They sit between the ends of the thigh bone (femur) and the shin bone (tibia) inside the knee joint. Similar to shock absorbers in a car, they help cushion forces in the knee. They also provide joint stability.

The medial meniscus (on the inner side) is shaped like a ‘C,’ and covers about half of the medial tibial plateau (flat inner shelf at the top of the shin bone). It is firmly attached along its outer edge to the soft tissue that lines the knee joint (the joint capsule). This is the meniscus tear often occurring due to sports and falls in people with normal knee anatomy.

The lateral meniscus is shaped more like a circle and covers about 70% of the lateral tibial plateau (outer top of the shin bone). In contrast, the lateral meniscus has fewer attachments so that it can move more freely inside the joint.

A discoid meniscus is atypical. It is thicker and more oval-shaped, with reduced blood supply. Because of this, it is less stable, making it more likely to tear or change shape. A discoid meniscus is a congenital condition (present at birth).

Medical providers often use the Watanabe classification (developed in 1969)1-4 to label types of discoid meniscus. There are three types of discoid lateral meniscus:

• Type I (complete/stable): The meniscus is disc-shaped and completely covers the knee end of the shin bone with normal attachments.
• Type II ( incomplete/stable): The meniscus is semi-lunar (half-moon) shaped, covers 80% of the outer top of the shin bone, and has normal attachments.
• Type III (Wrisberg variant/unstable): The shape is similar to a normal disc, but an important ligament attachment (the coronary ligament) is missing. This leaves only the Wrisberg ligament attached, making the knee unstable.

How Does It Feel?

Most discoid meniscus injuries are diagnosed in teens. However, younger children frequently report symptoms of “snapping” or a “thud” in the knee, especially when fully bending (flexing) it. If the lateral meniscus becomes unstable or tears, symptoms can include:

• Knee pain in the front or outside of the knee
• Swelling
• Clicking or locking
• A feeling like the knee might give out

The child or teen may not be able to straighten or bend the knee fully. Often, the thigh muscle shows atrophy (decreased size compared to the unaffected leg).

How Is It Diagnosed?

Your physical therapist will begin by asking about your medical history, including your or your child’s symptoms, any recent injuries, the sport(s) you play, and your training or competition routine. For younger children, parents can help by sharing when symptoms began, where and when they occur, and how long they last.

Next, your physical therapist will conduct a thorough physical examination, which may include:

• Assessing how you walk and run, squat, and go up and down stairs
• Checking your balance
• Measuring how far your knees can bend and straighten (range of motion)
• Testing the strength of both legs
• Identifying any swelling, tenderness, or looseness in the knee(s)

If your physical therapist suspects a discoid meniscus (or other knee joint injury), they will refer you to an orthopedic doctor (a bone and joint specialist). The physician may order an X-ray or MRI to confirm a diagnosis. Since a discoid meniscus can occur in both knees, an orthopedic surgeon likely will order imaging of the opposite knee, even if there are no symptoms. Your surgeon will review your results and work with you to determine the best course of treatment.

If a discoid meniscus is found but isn’t causing pain or problems, your physician may recommend physical therapy, regular check-ups, and holding off on surgery until symptoms that require surgery occur.

How Can a Physical Therapist Help?

If your child’s knee is painful, swollen, or locking up, they may be treated initially with physical therapy. If surgery is needed, physical therapy is recommended both before surgery and after surgery. Most physical therapy programs for discoid meniscus last 3-4 months. Your physical therapist will work with you and your child to develop a plan tailored to their specific needs, symptoms, and goals. Physical therapy may start by helping to relieve your pain, strengthen your muscles, and prepare your body for surgery. Physical therapy will resume after surgery to help you heal and return to your regular activities. The treatment program may include:

Range-of-motion exercises. For a knee to move correctly, it is essential that it bends and straightens all the way (full range of motion). Loss of joint range of motion is a frequent problem after an injury or surgery. Physical therapists are trained in various techniques to help you regain full range of motion and knee function so you can resume your regular activities and sports.

Strength training. Your physical therapist will teach you exercises to strengthen the muscles around your knee, ankle, and hip. All of these muscles need to be strong and efficient to support your knee and allow you to stand, climb stairs, walk, and run.

Manual therapy.  Your physical therapist will assess how your joints move (joint mechanics) and use a variety of hands-on techniques to improve your movement. Manual therapy improves motion, flexibility, and strength. These techniques target areas that are difficult to treat on your own and can help you regain optimal joint function.

Swelling and pain management.  Physical therapists are skilled at reducing swelling that can cause pain and loss of joint function. They will work with your surgeon to make sure you are healing and progressing. A safe, stepwise plan helps protect your knee while helping you achieve the best possible outcome.

Functional training.  Physical therapists are experts in movement training, balance, and coordination. Your physical therapist will assess your overall movement patterns and guide you through regaining functional skills and returning to the activities you love.

Education.  Your physical therapist will develop a personalized program that addresses your child’s needs and goals, and help them return to their desired activities. They also will provide a specific home exercise program to help you make progress and stay on track between your clinical appointments.

Can This Injury or Condition Be Prevented?

A discoid meniscus is something a person is born with and cannot prevent. No known factors increase the risk of injury. Maintaining lower-body mobility and muscle strength are the best ways to prevent knee injuries of any kind, even without a discoid meniscus.

It is important to pay attention to any knee pain, especially when squatting, running, or turning. Pain during these movements could be a sign of a knee injury. Getting help and seeing a physical therapist early can make treatment easier and improve long-term recovery.

What Kind of Physical Therapist Do I Need?

All physical therapists are prepared through education and clinical experience to prevent, manage, and treat a variety of conditions or injuries. You may want to consider:

• A physical therapist who is experienced in treating people with orthopedic or musculoskeletal (muscle, bone, and joint) conditions.
• A physical therapist who is a board-certified clinical specialist or who completed a residency or fellowship in orthopedic, sports, or pediatric physical therapy. This physical therapist has advanced knowledge, experience, and skills that may apply to this condition.

You can find physical therapists in your area with specific clinical expertise by using Find a PT, provided by the American Physical Therapy Association.

General tips when you're looking for a physical therapist (or any other health care provider):

• Ask family, friends, or other health care providers to recommend a physical therapist.
• Ask about the physical therapists' experience in helping children with developmental disorders when you contact the clinic for an appointment.
• Be prepared to describe your child’s symptoms in as much detail as possible and say what makes your child’s symptoms better or worse.

The Academy of Pediatric Physical Therapy contributed to this consumer resource. It is for informational purposes only and is not intended to represent the position of APTA Pediatrics.