Meniscal tears are a common cause of knee pain and swelling. The meniscus is c-shaped cartilage that sits between the knee bones and acts as a cushion protecting the joint’s surface. Sometimes, the menisci (especially the lateral meniscus) are abnormally shaped, making them more prone to injury. So, what is a discoid lateral meniscus, and what should you do if you have one?

What is a discoid meniscus? 

knee articular cartilage

Generally, a healthy meniscus is crescent-shaped, like a C. However, in some cases, the meniscus is discoid-shaped, like a disc, rather than a normal C-shape. Ususally, this abnormal shape makes the meniscus much larger and more likely to tear. Also, the blood supply to the periphery of the meniscus is reduced.

Discoid meniscus is relatively common, occurring in up to 15% of the population. Most cases occur in the lateral meniscus, i.e., a lateral discoid meniscus.

Is a discoid meniscus hereditary? 

We think so. One study found a discoid meniscus in a father and siblings. 

Symptoms of discoid meniscus 

Most people with a large meniscus don’t even know about it. The majority of people live their life with a discoid meniscus without problems.

Sometimes, we diagnose an abnormally shaped meniscus with an MRI scan or knee arthroscopy. However, in most cases, we ignore the findings and leave the meniscus alone.

However, in some people, the discoid meniscus can cause problems. Due to the abnormal shape of the meniscus, it is more likely to get stuck or tear. In general, common symptoms of a problematic discoid meniscus include:

  • Pain on the inside or outside of the knee
  • Knee joint swelling
  • A popping sensation with activity
  • Catching or locking of the knee
  • Pain with squatting or kneeling

Diagnosis 

In general, we diagnose an abnormal meniscus based on a history of pain and mechanical symptoms in combination with imaging findings. MRI often confirms a diagnosis and rules out other causes of symptoms.

Discoid meniscus MRI findings 

Ususally, a discoid meniscus loses the normal C-shaped contour. In addition, it is thicker than usual, so more meniscus is usually present on more imaging slices. A meniscal tear or meniscal cyst is also seen on MRI.

Treatment of discoid lateral meniscus 

If the meniscus is not causing problems, we suggest you leave it alone.

In people with a sizeable painful meniscus, we recommend simple treatments such as oral NSAIDs and physiotherapy consisting of quadriceps and general lower limb strengthening exercises.

Sometimes, we use cortisone to reduce swelling around a meniscal tear. Generally, we use ultrasound to guide a needle close to the torn meniscus. Then, we inject a small dose of cortisone around the meniscus to reduce inflammation associated with a tear. Again, we use ultrasound to improve the accuracy of injections and minimise side effects.

We suggest surgery only for people with more severe pain or mechanical symptoms.

Surgery 

keyhole surgery for discoid meniscus

Knee arthroscopy, also known as keyhole surgery, is a standard procedure using a camera to guide mini-surgical instruments. For an abnormal meniscus, the surgery depends on the problem.

If you tear a discoid lateral meniscus, we can perform a repair or partial removal of the meniscus. Frequently, we repair a part and remove a part. Sometimes, surgeons cut and shape the abnormally-shaped meniscus into a C-shape, a procedure often referred to as saucerisation of the meniscus.

Generally, results of partial or complete removal of the meniscus are good. However, we see early arthritic changes more commonly if we remove the entire meniscus.

Overall, studies suggest we should preserve the meniscus and only perform a partial excision +/- repair.

Final word from Sportdoctorlondon about discoid lateral meniscus 

Discoid meniscus is a relatively common cause of pain on the outer part of the knee. Most cases are symptom-free and detected on MRI. However, some cases produce pain and mechanical symptoms. See an experienced sports doctor to find the best treatment option.

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Dr. Masci is a specialist sport doctor in London. 

He specialises in muscle, tendon and joint injuries.