ACL Injuries in Children: Information for Families

What is the ACL?

The ACL (anterior cruciate ligament) is a strong band inside the knee. It joins the thigh bone to the shin bone.

It stops the shin bone sliding forwards and twisting. This matters most when you turn, stop suddenly or land from a jump.

When the ACL is torn, the knee can feel loose or "give way". Each time it gives way, other parts of the knee can be damaged. These include the meniscus (the knee's shock absorber) and the smooth cartilage on the ends of the bones.

How does it happen?

Most ACL injuries happen in sports with sudden turns, stops or jumps. Examples are football, netball, basketball, rugby, gymnastics and skiing. Often nobody else is involved. The knee twists while the foot stays planted, or the child lands awkwardly.

Signs to look for:

• A "pop" felt or heard at the time of injury
• The knee swells within a few hours (this is bleeding inside the joint)
• Pain and difficulty carrying on with the activity
• Later, the knee feels wobbly or gives way when turning

A knee that swells quickly after a twisting injury should always be checked by a doctor. Quick swelling usually means something inside the knee is damaged.

Why children's knees are different

Children are not small adults. Their knees have growth plates, which are areas of soft cartilage near the ends of the bones. The growth plates around the knee make the leg grow longer.

This affects ACL care in three ways:

• Growth plates need protecting. Damage to a growth plate can cause one leg to grow shorter, longer or slightly bent. Treatment is planned to keep this risk as low as possible.
• Some injuries look like ACL tears but are not. In younger children, the ACL can pull off a small piece of bone instead of tearing. This is called a tibial spine fracture and is treated differently.
• Children's knees are naturally looser. Doctors examine both knees to compare them.

How is it diagnosed?

A specialist will usually use three things together. No single test is right every time.

1. Questions and examination. The doctor asks how the injury happened and examines both knees. Younger children may find it hard to describe what happened, so parents' accounts help.
2. X-ray. This checks for broken bone, including a tibial spine fracture. It is usually the first scan after a swollen knee.
3. MRI scan. This shows the ACL, the menisci and the cartilage. It does not use radiation.

If the knee is "locked" and cannot straighten fully, an MRI is usually done quickly. A locked knee can mean a torn meniscus that needs early surgery.

Treatment choices

There are two main options. Both include a long, supervised exercise programme (rehabilitation, or "rehab").

When is surgery usually advised?

International experts agree surgery should be considered when:

• there is other damage in the knee that can be repaired, such as a torn meniscus
• the knee keeps giving way, even after a good rehab programme
• the child cannot do the activities that matter to them without the knee giving way

Does waiting cause harm?

Studies suggest that children whose surgery is delayed, or who have no surgery, are more likely to have further damage to the meniscus and cartilage. The more often the knee gives way, the higher this risk seems to be.

These studies have weaknesses, and doctors in different countries do not always agree on the best timing. If your child has rehab alone, they need regular check-ups and sometimes repeat scans. Tell the team straight away if the knee gives way.

What does surgery involve?

The torn ACL is replaced with a new one, called a graft. It is usually done by keyhole surgery under a general anaesthetic.

Working out how much growing is left

Before surgery, the team estimates how much your child has left to grow. This can include:

• an X-ray of the left hand and wrist ("bone age")
• signs of puberty and recent growth spurts
• parents' heights
• a full-length standing X-ray of both legs, to measure them before surgery

Choosing the method

The method is matched to the amount of growth left:

• Lots of growing left (younger children): methods that go around or stay clear of the growth plates.
• Some growing left: small, carefully placed tunnels that cross only a tiny part of the growth plate.
• Nearly finished growing: methods close to those used in adults.

Where the graft comes from

The graft is taken from your child's own body. Common choices are a hamstring tendon (back of the thigh), the quadriceps tendon (above the kneecap) or a strip of tissue from the outside of the thigh. The tendon below the kneecap is usually avoided while a child is growing. Donor tissue is not usually recommended, as it tears more often in young people.

If the meniscus is torn, the surgeon will try to repair it at the same time. Some surgeons also add a small extra procedure on the outside of the knee to help control twisting.

ACL surgery in growing children should be done in a specialist centre with experience in children's knees and rehab.

What are the risks?

Every option carries some risk. The figures below come from published research and are approximate. Your surgeon can explain how they apply to your child.

Most growth problems are small. When they do happen, they can usually be treated, especially if found early.

Recovery and getting back to sport

Rehab is as important as surgery. Good surgery cannot make up for poor rehab. Your child moves to each stage only when they pass checks, not just because time has passed.

1. Settle the knee. Reduce swelling, get the knee fully straight and bending well. Learn to hold the knee straight while standing on one leg. A brace and crutches may be used for the first few weeks.
2. Build strength and balance. Regain full movement. Start jogging once the knee stays settled after 10 minutes.
3. Train for sport. Running, jumping, hopping and changing direction. Learn safe ways to land and turn.
4. Return to sport. Only after passing hop and strength tests, with no pain or swelling, and feeling confident and ready.

How long does it take?

• After surgery: at least 9 months before full sport.
• Turning and twisting sports (football, netball, rugby): ideally not before 12 months, as the risk of a new tear is highest in the first year.
• Rehab without surgery: at least 3 to 6 months.

Tips for families

• A physiotherapist experienced with children should supervise rehab.
• Parents play a big part, especially for younger children. Exercises for younger children are often games done at home.
• Your child can often still go to team training to stay part of the group, doing exercises that are safe for their stage.
• Feeling nervous about getting injured again is normal. Tell the team, as support can help.
• Keep doing injury prevention exercises after returning to sport.

Check-ups until growing stops

If your child has surgery while still growing, they will need check-ups until their growth plates close. This is usually in the mid to late teens.

• Expect regular clinic visits in the first year, then about once a year.
• Check-ups may include a knee X-ray and a full-length X-ray of both legs.
• Measure your child's height at home. If they grow more than 6 cm in 6 months, contact the team, as the next check-up may need to come sooner.
• Tell the team if you notice one leg looking shorter, a limp, or a knee turning in or out.

Preventing ACL injuries

Warm-up programmes can cut leg injuries in young players by about half. They need little or no equipment and are done as part of normal training, 2 to 3 times a week.

Good programmes include:

• strength and balance exercises
• jumping and landing practice (land softly, with knees bent and over the toes)
• safe ways to turn and change direction
• for younger children, learning how to fall safely

One example designed for children is FIFA 11+ Kids. The key is doing it regularly, all season. Ask your child's coach or school whether they use one.