There’s a Disc in My Knee? Understanding Discoid Meniscus

There’s often a pause, followed by confusion and a hint of horror when patients hear me describe that there is a disc-like structure in their knee. So let’s clear this up. If you've ever heard of a "discoid meniscus," you might be wondering what it is and how it affects the knee. While this condition isn’t very common, it can cause discomfort and mobility issues for those who have it. In this article, we'll break down what a discoid meniscus is, why it happens, its symptoms, and how it can be treated.

What Is a Meniscus?

To understand a discoid meniscus, we first need to know what a meniscus is. In my previous article entitled “cushioning the blow”, I talked about the functions of the meniscus and common injuries to it. Let’s recap real quick. The menisci (plural for meniscus), act as shock absorbers between the thigh bone (femur) and shin bone (tibia). These menisci help stabilize the knee and prevent excessive wear on the bones.

Normally, the meniscus has a C-shape and provides cushioning during movements like walking, running, and jumping. However, in some people, the meniscus forms differently - becoming thicker, rounder, and more like a disk rather than the usual crescent shape. This is what we call a discoid meniscus.

What Causes a Discoid Meniscus?

Researchers aren’t entirely sure why it happens, but it develops while a baby is growing in the womb.

This condition most commonly affects the lateral meniscus, which is located on the outer side of the knee, though it can also occur in the inner meniscus (medial meniscus), though that’s less common.

Symptoms of a Discoid Meniscus

Many people with a discoid meniscus never experience any symptoms and may go their whole lives without realizing they have it. However, for others, symptoms can start in childhood or early adulthood, especially if the meniscus becomes damaged or torn.

Common symptoms include:

• Clicking or popping sounds when moving the knee

• Pain or discomfort, especially after activity

• Swelling around the knee

• A feeling of instability or weakness in the knee

• Locking or catching, where the knee temporarily gets stuck when trying to move it

The clicking and popping sounds happen because the thickened meniscus doesn’t fit into the knee joint properly. If the meniscus tears, the symptoms may worsen, leading to more pain and trouble moving the knee.

How Is a Discoid Meniscus Diagnosed?

If someone has symptoms like clicking, pain, or instability in their knee, a doctor will first perform a physical examination. They may bend and move the knee to check for unusual movements or sounds.

To confirm the diagnosis, imaging tests such as an MRI (Magnetic Resonance Imaging) are commonly used. An MRI provides a detailed view of the knee’s cartilage, showing if the meniscus is thicker than normal or if there is a tear.

Treatment Options

The treatment for a discoid meniscus depends on whether it is causing problems.

1. If There Are No Symptoms:

   • If a discoid meniscus is discovered by accident (such as during an MRI for another issue) but isn’t causing pain or instability, no treatment is necessary. Many people live with a discoid meniscus without any problems.

2. Surgery (for Severe Cases):

   • If the discoid meniscus is causing significant pain, locking, or tearing, surgery may be needed. The most common procedure is arthroscopic surgery, which is a minimally invasive technique where small instruments are used to trim or reshape the meniscus.

   • After surgery, physical therapy is often recommended to restore knee strength and mobility.

For those who have a discoid meniscus without symptoms, there’s no need to worry—it may never cause problems. But for those who do experience pain or instability, treatment options can help restore knee function and allow them to return to normal activities.