Anterior cruciate ligament injury

What is the anterior cruciate ligament?

The anterior cruciate ligament (ACL) is a strong band of cord-like tissue that runs across and inside your knee to keep it stable. The ligament attaches the thigh bone (femur) to the top of your shin bone (tibia).

Your ACL sits in front of your posterior cruciate ligament. They form a cross inside the knee – hence the term 'cruciate' in their names. The ACL serves three key functions:

• It allows your knee to twist with stability. This is especially useful in sports such as football, rugby and skiing
• It protects other structures in the knee from damage, such as the meniscus
• It acts as a shock absorber to limit damage that can result in arthritis

What is an ACL injury?

ACL injuries happen when the ligament is stretched beyond its normal range of motion and are categorised from Grade 1 to Grade 3. At the point of injury, a torn ACL can often be described as sounding like a 'snap' or 'pop', and the amount of pain experienced can vary depending on the severity of the injury. In some instances, people may only suffer slight discomfort, while a tear of the anterior cruciate ligament can be incredibly painful for others. 

Grade 1: An ACL sprain that occurs when ligament fibres remain mostly unbroken. This injury can generally be treated with rest and pain relief. In most cases, an injury like this can heal in anywhere between two and four weeks

Grade 2: A partial ACL tear where some fibres of the ligament break as a result of a sudden impact or twisting movement to your knee. Partial tears of the ACL are less common than complete tears. Physical therapy can help improve the knee’s stability, with recovery often taking up to three months

Grade 3: A full tear – also known as an ACL rupture – is when the ligament snaps completely or becomes detached from the bone. This is a significant injury that is more common among athletes and often results in damage to other areas of the knee, such as the meniscus or other ligaments, at the same time. The tear is highly unlikely to heal without surgical intervention. A full recovery typically takes up to a year.

Causes of ACL injury

A torn ACL can happen during everyday activity but is also a common sports injury that may happen during an awkward landing, impact or sudden change of direction that results in a twisting motion at the knee. Common causes include:

• Getting your feet stuck while twisting – for example, a football boot getting caught on turf
• Landing awkwardly from jumping, perhaps after a gymnastics manoeuvre or when dancing
• Direct impact to the area, such as a bad tackle in football or rugby

Our specialist knee consultants can assess your injury and advise on the best way to treat it.

How are ACL injuries diagnosed?

Our knee specialist will assess you in detail. This will involve asking you a series of questions, examining your knee and typically undergoing an MRI scan. Your scan will be conducted by a consultant musculoskeletal radiologist that specialises in performing scans and passing on key information to your consultant.

The MRI scan helps to confirm the diagnosis and uncover any damage to other parts of the joint. After assessing the severity of your injury, you and your consultant can start planning your onward care.

Potential treatment options

Resting your knee is a key part of the recovery. Your consultant will discuss any further treatment options with you. These may depend on how stable your knee feels, your day-to-day function and your sporting profile. 

Non-surgical ACL treatment

• RICE: Rest, ice, elevation and compression will help your joint recover. It’ll also likely be recommended after any surgery you undergo
• Pain relief: Medication such as paracetamol and ibuprofen will help manage discomfort and may allow you to get back to everyday activities quicker if your ACL injury is mild
• Knee supports: Braces and similar products provide compression to manage inflammation and also support the joint as you bear weight, easing any feelings of weakness or buckling
• Modifying activity: You’ll likely need to change your activities for a period after suffering an ACL injury. Footballers, rugby players and dancers may need to take it easy for many months while recovering.

You may choose not to have surgery on a torn ACL if your joint feels stable and you’re not aiming to return to activities such as sport. Many people can live comfortably after experiencing low-grade tears without surgical repair.

Opting against surgery after experiencing a grade three tear may leave you more vulnerable to damaging your knee further down the line. Most people who suffer serious ACL tears choose surgery to benefit their quality of life.

ACL injuries are also often associated with other injuries like meniscal tears or damage to other ligaments– if the knee has sustained injury to more than one structure, it can be even harder to recover without surgery.

Surgical ACL treatment

In cases of a torn or ruptured ACL, you may need to consider surgery to restore the ligament (ACL restoration). This involves reforming the ACL with other tissue — usually from your hamstrings or patellar tendon. Your consultant will talk this through with you.

Surgery to repair your ACL may be recommended if conservative treatment does not help your symptoms, you’ve suffered a serious ACL tear, or your job is physically strenuous. An operation might also be required if you’ve also damaged other ligaments, cartilage or bone.

Can I prevent an ACL injury?

It’s difficult to fully prevent ACL injuries as they often occur because of unexpected impacts or movements. You can take measures to reduce the chances of them happening in the first place:

• Protective equipment: Knee braces can add support and protection to your knees, potentially limiting the damage done or preventing an ACL tear in some instances
• Resting: Take time to fully recuperate after exercising or playing sport. Pushing your body to its limits can exacerbate smaller injuries and result in being at increased risk of suffering an ACL injury
• Reduce risks: You could suffer a torn ACL by falling at home or work. Clear away tripping hazards and use proper equipment - for example, use a ladder securely if working at heights.
• ACL prevention programmes: if you undertaking high risk sports or have a history of a partial tear, you might consider an ACL prevention programme: these involve exercises designed to reduce the strain on the ACL and have been proven to reduce rates of injury.