ACL Injury

How bad can an ACL injury be?

ACL injuries are graded by how much of the ligament is damaged:

• Grade 1 sprain. The ligament is stretched but still holds the knee steady.
• Grade 2, partial tear. Part of the ligament is torn, and the knee may feel loose.
• Grade 3, complete tear (rupture). The ligament is torn right through. This is the type that most often makes the knee give way.

An ACL tear often comes with other damage, such as a tear of the meniscus (the cartilage cushion between the bones), bruising of the bone, or injury to another ligament.

What causes an ACL injury?

The ACL usually tears when your knee twists while your foot is planted. This can happen when you change direction quickly, stop suddenly, or land from a jump with the knee buckling inwards. It can also tear from a direct blow to the knee, such as a tackle. In a review of 45 studies of team ball sports, more than half of ACL injuries happened without contact from another player.^[1]

You are more likely to injure your ACL if you play sports that involve pivoting and jumping, such as soccer, Australian rules football, netball, basketball and skiing. In the same review, female athletes had close to three times the rate of non-contact ACL injuries of male athletes.^[1] Fatigue, the way you land, a previous ACL injury and the shape of your knee can also add to the risk.

What are the symptoms of an ACL injury?

Many people feel or hear a pop as the ligament tears and cannot keep playing. Other symptoms include:

• Swelling that comes on within a few hours, caused by bleeding inside the knee
• Pain, often felt deep inside the knee
• Difficulty fully straightening or bending the knee
• The knee feeling loose or giving way, especially when you turn or pivot.

Pain and swelling often settle over a few weeks, and you may be able to walk normally again. The knee can still give way when you twist or change direction, because the torn ACL no longer holds it steady.

When should you see a doctor?

See your GP or a physiotherapist soon after any twisting knee injury with a pop or rapid swelling, even if the pain eases. Seek medical advice promptly if:

• Your knee locks and you cannot straighten it, which can mean a torn meniscus is caught in the joint
• You cannot put weight on your leg
• The knee keeps giving way
• Your foot is numb, cold or pale, or the pain is severe after a high-energy injury such as a car accident. Seek urgent care, as this can be a sign of a multiligament injury.

How is an ACL injury diagnosed?

The diagnosis is usually made from how the injury happened and an examination of your knee. Tests such as the Lachman test, where the doctor gently draws your shin bone forward, show how much the knee moves compared with your other knee. Pain and swelling can make the knee hard to examine in the first week or two, so the examination is sometimes repeated.

An MRI scan confirms an ACL tear and shows any damage to the meniscus, cartilage, bone or other ligaments. An X-ray may be taken to check for a small fracture. Your GP can arrange either scan.

How is an ACL injury treated without surgery?

Rehabilitation is part of every ACL treatment plan, whether or not you have surgery. Some people choose rehabilitation alone, usually when they do not play pivoting sport and the knee does not give way in daily life. In trials where people started with rehabilitation, about half went on to have a reconstruction, mostly within the first 2 years.^[2][3]

First steps after the injury

In the first few days, the aim is to settle pain and swelling and keep the knee moving:

• Use crutches if you need them. It is safe to put as much weight on the leg as is comfortable.
• Apply an ice pack wrapped in a cloth for 15 to 20 minutes every two to three hours for the first 48 to 72 hours.
• Wear a compression bandage or sleeve to control swelling.
• Do gentle range of motion exercises, especially straightening the knee, but do not force it.
• Ask your pharmacist or GP which pain relief suits you.

Physiotherapy and rehabilitation

Rehabilitation with a physiotherapist is the core of treatment for every ACL injury, with or without surgery. It starts with getting the knee fully straight and the swelling down. It then builds the strength of your thigh and hip muscles, your balance and, later, your running, jumping and landing. Programs take several months. If you are having a reconstruction, getting the swelling down, the knee fully straight and the thigh muscles working before the operation makes the early recovery easier.

Changing your activities

If you do not have a reconstruction, straight-line activities such as running, cycling and swimming put less strain on the knee. Sports with pivoting and cutting are more likely to make the knee give way, and repeated giving way can damage the meniscus and cartilage. In a study of 2,740 teenagers, waiting more than 12 months for a reconstruction was linked to about four times the rate of inner meniscus tears that needed surgery.^[4]

Braces and taping

A brace or tape may help you feel more secure when you return to activity. Neither replaces the ligament or the strength of the muscles around your knee.

Can a torn ACL heal?

Some torn ACLs show signs of healing on MRI. In the KANON trial, 16 of the 30 people treated with rehabilitation alone had a ligament that looked continuous again at 2 years.^[5] A newer approach, the cross bracing protocol, holds the knee bent in a brace for several weeks to bring the torn ends together. It has to start within a few weeks of the injury. In a study of 80 people, 90% showed signs of healing on MRI at 3 months, and 14% later injured the ACL again.^[6]

A ligament that looks healed on MRI is not the same as a stable knee. A healed ACL is usually not the same as it was before the injury. It is often thinner or longer, and it may not hold the knee steady. In the cross bracing study, only 40% of people whose ligament healed thinner or longer, or did not heal, had a normal test of knee looseness at 3 months.^[6] In a study of 80 people who play pivoting sports, 70% of those who used the protocol had their knee give way again within 2 years, compared with 2.5% of those who had surgery.^[7] The protocol has not been tested in a randomised trial. Even if your scan shows healing, what matters is whether your knee gives way, and this is judged by examining your knee and seeing how it copes with activity.

When is surgery considered?

An ACL reconstruction is often advised if you are active and want to return to sport that involves pivoting, cutting or jumping, if your knee keeps giving way despite rehabilitation, or if you also have a meniscus tear that can be repaired. Rehabilitation alone may be reasonable if you do not play pivoting sport and your knee does not give way. You can read how the operation is done and what recovery involves on the ACL reconstruction page. For a stage-by-stage guide, see ACL reconstruction recovery week by week.

Some recent tears where the ligament has pulled away from the bone may suit an ACL repair instead. In children and teenagers, surgery is planned around the growth plates. You can read more about ACL reconstruction in children and teenagers.

What is the outlook after an ACL injury?

Your outlook depends largely on whether your knee stays stable. A knee that keeps giving way is at risk of further damage to the meniscus and cartilage.^[4] An ACL reconstruction aims to restore that stability. Results and return to sport after surgery are covered on the ACL reconstruction page.

An ACL injury raises the chance of arthritis in the knee later in life. In a review of studies that followed people for at least 10 years, about 4 in 10 had signs of arthritis on X-ray around 15 years after the injury.^[8] For answers to more questions, read the ACL injury guide.

References