Discoid Meniscus

A discoid meniscus is a meniscus that has formed as a thick, round disc instead of the usual thin C-shape. It nearly always affects the outer (lateral) meniscus, so you may also see it called a discoid lateral meniscus. This page explains what it is, the symptoms to look out for in children and adults, how it is diagnosed and treated, and when surgery is considered.

What is a discoid meniscus?

Each knee has two menisci. These are rubbery, C-shaped pads of cartilage that sit between your thigh bone (femur) and shin bone (tibia), one on the inner (medial) side and one on the outer (lateral) side. They spread load across the joint and act as shock absorbers.

A discoid meniscus is thicker than normal and covers more of the top of the shin bone, like a disc rather than a crescent. Its tissue is less organised than a normal meniscus, and its attachments to the joint lining can be weak or missing.^[1] You are born with it.

Types of discoid meniscus

Doctors describe three main types:

• Complete. The disc covers the whole outer half of the top of the shin bone.
• Incomplete (partial). The meniscus is wider and thicker than normal but leaves part of the bone uncovered.
• Wrisberg type. The meniscus is missing its normal attachment at the back, so it can move around in the joint. This type is rare.

A discoid meniscus is also described as stable or unstable. An unstable meniscus has a loose edge that lets it shift in and out of place as the knee bends and straightens.^[1]

What causes a discoid meniscus?

A discoid meniscus forms before birth, and why it happens is not known. It is found in about 3 to 5 in 100 people in Western countries and about 10 to 13 in 100 people in East Asian countries.^[2]

Because it is thicker, has a poorer blood supply and is less firmly attached, a discoid meniscus tears more easily than a normal one.^[1][2] A normal-shaped meniscus can tear too; you can read more on the meniscus tear page.

Symptoms often begin in childhood. In one children’s sports clinic, 96 of 99 children under 13 who needed keyhole surgery for a problem with the outer meniscus had a discoid meniscus, and two in three of them could not recall an injury.^[3] In teenagers and adults, a tear often follows a twist during sport.

Both knees can have a discoid meniscus. In two large studies of people treated for symptoms, about 1 in 8 and 1 in 6 had symptoms in both knees.^[4][5]

What are the symptoms of a discoid meniscus?

Many people with a discoid meniscus never have symptoms. When symptoms do occur, they usually come from a tear or from the meniscus shifting in the joint. They include:

• A clunk, click or snap on the outer side of the knee, often as it straightens
• Catching, or the knee locking so that it will not straighten fully
• Pain on the outer side of the knee
• Swelling after activity
• The knee giving way.

Young children often do not complain of pain. As a parent, you may notice instead that your child’s knee clunks when they walk, that they limp, or that the knee does not straighten fully. This is sometimes called a snapping knee.

When should you see a doctor?

See your GP or physiotherapist if you or your child has a knee that clicks with pain, swelling or catching, or knee pain that has not settled after a few weeks. Seek medical advice sooner if:

• The knee is locked and will not straighten
• The knee swells quickly after an injury
• You or your child cannot put weight on the leg
• Your child is limping and you do not know why.

How is a discoid meniscus diagnosed?

Your doctor will ask about the symptoms and examine both knees. They will check for tenderness on the outer side, a clunk as the knee moves, and whether the knee straightens fully. X-rays can look normal, but they help rule out problems with the bone. An MRI scan shows the shape of the meniscus, any tear, and whether it has shifted out of place.

A discoid meniscus is also often found by chance on a scan done for another reason. That finding alone does not mean it is the cause of your pain.

How is a discoid meniscus treated without surgery?

A discoid meniscus that causes no symptoms needs no treatment, even if it was found on a scan. Surgery is not done to prevent problems in a knee that feels normal.^[1][2] If the knee later starts to catch, lock, swell or hurt, have it checked again.

If symptoms are mild, such as pain or clicking without locking, treatment usually starts without surgery.^[2]

Physiotherapy

A physiotherapist can strengthen the thigh and hip muscles that support the knee, and guide a gradual return to sport.

Activity changes

Cutting back for a while on deep squatting, kneeling, twisting and high-impact sport can let a sore knee settle.

Ice and simple pain relief

Ice and simple pain relief from the pharmacy can ease a flare. Ask your GP or pharmacist which medicine suits you or your child, and the right dose.

How often does non-surgical care work?

Some knees settle and others do not. In a series of 470 knees in children and teenagers, 83 were first treated without surgery, and 32 of these (39%) went on to have surgery, at a median of about 8 months.^[5]

When is surgery considered?

Surgery is considered only when a discoid meniscus causes symptoms such as locking, catching or a knee that will not straighten, or when pain continues despite non-surgical care and an MRI shows a tear or an unstable meniscus. The usual operation is keyhole (arthroscopic) saucerisation. This trims the thick centre of the disc and leaves a normal-sized C-shaped rim, a form of partial meniscectomy. If the rim is loose or torn, it is stitched back in place with a meniscal repair. Removing most or all of the meniscus is avoided where possible, because long-term results are worse.^[6]

What is the outlook for a discoid meniscus?

Many people with a discoid meniscus never have symptoms and never need treatment.^[1] When symptoms do start, some settle with physiotherapy and time, and others need surgery.^[5][7]

References