Meniscus Injuries in Children: Information for Families

What is the meniscus?

Each knee has two menisci: one on the inner side and one on the outer side. They are C-shaped pads of tough, rubbery cartilage that sit between the thigh bone and the shin bone.

They:

• absorb shock and spread weight across the joint
• help keep the knee stable
• protect the smooth joint cartilage from wear

Losing part of a meniscus raises the risk of arthritis at a young age. This is why keeping the meniscus matters so much in children.

Why children's menisci are different

A child's meniscus has a much better blood supply than an adult's. At birth, blood reaches the whole meniscus. This slowly reduces with age, and by about age 10 to 12 it reaches only the outer part, as in adults. A good blood supply means a better chance of healing after repair.

How do meniscus injuries happen?

There are two main groups.

What is a discoid meniscus?

A discoid meniscus is thicker and shaped like a disc instead of a crescent. It is something a child is born with, almost always on the outer side of the knee. It is weaker than a normal meniscus and tears more easily.

Many children with a discoid meniscus never have symptoms and never know they have one. It only needs treatment if it causes problems.

Signs to look for

After a twisting injury

• pain on the inner or outer side of the knee
• swelling, often within hours
• catching, clicking or a feeling that the knee gets stuck
• the knee locking, or not straightening fully
• the knee giving way, which may mean an ACL injury too

Some tears in children cause few symptoms, even large ones. A child with a swollen knee after a twisting injury should be checked by a doctor.

With a discoid meniscus

• a loud clunk or snap as the knee bends and straightens, often noticed by parents
• a bulge on the outer side of the knee when it bends
• loss of full straightening or full bending
• pain on the outer side of the knee, mostly in older children

How is it diagnosed?

1. Questions and examination. The doctor asks how the injury happened and checks both knees, including the ligaments. Examination tests for a torn meniscus are less reliable in children than in adults.
2. X-ray. This may be done to check for a broken bone. With a discoid meniscus, it can show a wider gap on the outer side of the knee.
3. MRI scan. This is the main test. It shows the meniscus, the type of tear and any ligament damage. It does not use radiation.

MRI can be misleading in children. The rich blood supply can look like a tear when there is none. Some tears, especially at the back of the inner meniscus, can be missed. MRI scans in children are best read by a radiologist experienced with children.

If your child has an ACL tear, an MRI is important to look for a meniscus tear, even if it causes no symptoms.

Treatment choices

The aim is always to keep as much meniscus as possible.

If there is also an ACL tear

The meniscus is usually repaired at the same time as the ACL is reconstructed. An unstable knee puts repaired stitches at risk, and can cause new meniscus tears over time.

Why surgeons try to repair rather than remove

Removing even part of a meniscus increases the load on the joint cartilage. Over years this can lead to arthritis. This has been seen even after partial removal.

Repair keeps the meniscus working. Children are good candidates because:

• their menisci have a better blood supply, so repairs heal better than in adults
• even tears in areas with poor blood supply often heal in children
• tears repaired soon after injury tend to heal better, though a delay does not rule out repair

A repair can fail, and further surgery is sometimes needed. Surgeons still recommend trying repair, because when a repair fails, often only part of it has failed. Less meniscus then needs removing than if it had been trimmed in the first place.

Recovery and getting back to sport

There is no single agreed plan, and it depends on the type of tear and repair. Your surgeon will give you a plan for your child. A typical plan after repair:

Before each step up, the knee should be pain-free and not swollen. Healing takes about 6 months on average.

If the ACL was also reconstructed, recovery follows the longer ACL plan.

In children under 10, a short period in a splint can help with pain, especially after discoid meniscus surgery.

Outlook and risks

Results of meniscus repair in children are generally very good, and better than in adults. Ten years after surgery, arthritis was uncommon, and less common after repair than after removal.

• Most children return to sport. In one study, 24 of 26 young athletes returned to their previous level.
• About 1 in 6 repairs needed further surgery in a review of 301 repairs in children.
• In a larger study of 907 meniscus operations in children, about 1 in 11 needed another operation, on average 2 years later.
• Repeat tears are more common with complex and bucket-handle tears (a large tear that flips into the middle of the knee).
• The risk of a repair failing is highest in the first year.
• In a large recent study, about 1 in 5 children had a problem in the first months after repair, such as stiffness or the repair not holding. About 1 in 11 repairs failed.

After reshaping and repair of a discoid meniscus, most children do very well, and repeat clunking is rare. Reshaping gives better results than removing the whole meniscus, which used to be common.