What is A Meniscus? Understanding Knee Cartilage

What is a Meniscus?

The quick answer is the meniscus is a C-shaped piece of soft and fibrous cartilage, also known as fibrocartilage, that provides shock absorption and cushion to your knee. It is also wedge-shaped which improves joint congruency, further adding to knee stability.

Illustration of a human knee showing meniscus and ligaments of the knee. JOI RehabAnatomy of the Knee
Have you ever wondered what makes up your knee joint? The knee is made up of the femur, tibia, and patella. Many ligamentous structures play a crucial role in providing stability of the knee joint, but there is an important piece of cartilage that sits right in the middle of it all. 

Meniscus Anatomy

There are two menisci in each knee, one on the inside of the knee and one on the outside of the knee. These are known as your medial and lateral menisci, respectively. 

The meniscus can withstand tremendous compressive loads that would otherwise degrade the integrity of the knee joint itself in the absence of this piece of fibrocartilage. Think of two ice cubes rubbing together. A healthy meniscus provides a gliding surface 5 times smoother than that.

 The Menisci also triple the joint contact area which decreases the joint pressure by distributing force over a large area. Without menisci, the tibial and femoral condyles would unite in a very small area, causing increased pressure and compression on surrounding articular cartilage. 

Illustration of a normal meniscus showing lateral and medial. JOI RehabIllustration of Meniscus

Just to put it into perspective, if you were to have a complete lateral meniscectomy, contact pressure would increase upwards of 200%. That is a lot of pressure that your knees aren’t built to handle independently.  To learn more about the knee, please watch this Knee Meniscus Anatomy Video.

What if I Tear my Meniscus?

Meniscus tears are extremely common among athletes and even the general population.  The recovery time for a knee sprain or meniscus tear will depend on the severity of the injury.  Any kind of cutting or twisting motion can tear the meniscus. Common symptoms of a meniscus tear include:

  • Catching
  • Clicking
  • Locking
  • Pain along joint line

Decades ago, surgeons would completely remove the menisci thinking its function was not of significance. We now know just how much of an impact that can have on an individual’s knee in terms of shock absorption and decreasing joint forces, ultimately leading to severe arthritis

Many physicians today will argue against surgery, stating that non-operative therapy can be beneficial to the rehabilitation of the meniscus. But is this the truth for everyone? The answer lies within the meniscus itself. 

Vascularity of the Meniscus

The vascularity of the meniscus is unique in that it only has blood vessels supporting its outermost portion. The inner portion of the meniscus receives its nutrients by diffusion alone. 

Because the blood supply to the meniscus is poor, some tears of the meniscus usually do not heal on their own. Tears are often broken down into three zones based on vascularity:

  1. Red Zone – The outer perimeter of the meniscus with adequate blood supply
  2. Red-White Zone – The transitional mid-zone of the meniscus
  3. White Zone – The innermost portion of the meniscus with no vascularity

When will my Meniscus Tear be Healed?

As mentioned above, the type of tear you have will dictate the path and length of recovery. Meniscal tears are classified and treated based on:

  • Location within the knee
  • Tear pattern
  • Complexity of the tear
  • Quality of the tissue

Illustration of the different tears to the meniscus. JOI RehabTypes of Meniscus Tears

Depending on the type and location of the tear, you may not need surgical intervention. Tears of the meniscus usually occur by two different mechanisms. A traumatic meniscal tear occurs when a patient recalls a specific twisting event during sports or a trauma to the knee.  Some meniscal tears can be complicated by also having an MCL Tear.  If you want to learn more about torn MCL symptoms, go to: https://www.joionline.net/trending/content/have-torn-mcl

A degenerative meniscus tear is subtler in onset with a gradual development of symptoms in the inner or outer compartment of the knee. A traumatic tear can occur in a normal meniscus while a degenerative tear usually can occur because the quality of our meniscal tissue decreases with age.

Vascular vs. Avascular Meniscal Tears

To sum it all up in a simple way, if you have a tear in the vascular zone, you’ll probably recover just fine. If you have a tear in the avascular zone, you just might be taking a trip to your nearest surgeon. Now that you’re “in the know” about what a meniscus is, you are more prepared on how to handle the situation if an injury ever occurs!

By: Amelia Son, PTA 

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