An anterior cruciate ligament (ACL) tear is one of the most common and serious types of knee injuries. This injury is usually caused by a combination of the knee twisting and buckling under great force. A tear in the ACL can lead to instability in the knee and usually requires a long recovery time and possibly surgery to restore the full function of the knee joint.

Overview of the cruciate ligament

The knee joint is stabilised by four main ligaments: the anterior and posterior cruciate ligaments and the medial and lateral collateral ligaments. The anterior and posterior cruciate ligaments run inside the knee joint and cross over each other, which gives them a crucial stabilising function. The anterior cruciate ligament (ACL) prevents the lower leg from sliding forwards, while the posterior cruciate ligament (PCL) stops it from sliding backwards. A torn cruciate ligament, especially a tear in the anterior cruciate ligament, results in severe instability of the knee joint.

Cruciate ligament ruptures can often be accompanied by associated injuries such as meniscus tears, cartilage damage or medial collateral ligament injuries.

Causes and risk factors

High-energy impact to the knee, such as twisting, buckling or overstretching, can lead to a tear in the cruciate ligaments. The posterior cruciate ligament tears much less frequently than the anterior cruciate ligament, as the posterior cruciate ligament is much stronger and most trauma tends to affect the anterior cruciate ligament. A rupture of both the posterior and anterior cruciate ligaments at the same time is rare and only occurs in cases of very severe trauma.

Typically, anterior cruciate ligament tears occur during sporting activities that require rapid changes of direction, abrupt stopping, jumping and landing, and physical contact. These include football, basketball, skiing, handball and American football.

In addition to excessive pressure put on the knee joints during sport, there are other risk factors associated with ACL injuries:


Women have a higher risk of ACL tears than men, a fact that is attributed to anatomical divergences and differences in muscle strength and coordination.

Previous knee injuries

People who have already had a knee injury, especially a previous ACL tear, have a higher risk of tearing the ACL again.


Owing to age-related changes in the body, such as a decrease in muscle strength, flexibility and general stability of the knee joint, older adults have an increased risk of ACL ruptures.

Fitness and muscle strength

Insufficient muscle strength, especially in the thigh muscles, and a lack of general physical fitness can increase the risk of an ACL tear.

Biomechanical factors

Certain movement patterns and postures, such as turning the knee inwards when landing or braking with an outstretched leg, can increase the risk of an ACL rupture.

Disease progression 

There are various degrees of severity of an ACL rupture, so a distinction is made between a partial tear of the ACL, a complete tear of the ACL and a tearing of the ACL from the bone that anchors it.

Partial tear of the anterior cruciate ligament

A partial tear of the anterior cruciate ligament occurs when only part of the fibres of the anterior cruciate ligament are severed.

Complete tear of the anterior cruciate ligament

In the case of a complete tear, the anterior cruciate ligament is completely severed, leading to significant instability of the knee joint.

Tearing of the anterior cruciate ligament from the bone

This injury occurs when the anterior cruciate ligament is not only torn, but also pulled directly off the bone anchoring it.



A typical symptom of an ACL tear is immediate, severe pain in the knee joint. The knee swells quickly and bruising often forms. Those affected usually report feeling a tearing sensation or even hearing a snapping sound when the injury occurs. After the acute pain subsides, the knee remains unstable and mobility is considerably restricted. People with this injury may feel like their knee is buckling or giving way. An ACL tear can also lead to a loss of full extension and flexion of the knee joint.


A specialist in orthopaedicsor accident surgery will carry out a targeted clinical examination of the knee joint based on what happened when the injury occurred and the characteristic symptoms in order to make a diagnosis. If the suspicion of an ACL tear is confirmed, an X-ray examination or magnetic resonance imaging (MRI) is usually ordered. These imaging procedures can provide information about the extent of the ACL tear and any associated injuries.


ACL reconstruction (anterior cruciate ligament surgery)

ACL reconstruction is the most common surgical method for treating a torn anterior cruciate ligament. The torn ACL is replaced with a tendon from elsewhere in the body, a donor tendon or an artificial one to restore stability to the knee joint. This operation is often performed if conservative treatment is not sufficient, if there are additional injuries such as meniscus tears or collateral ligament injuries, or if the patient has certain requirements that demand stability of the knee that cannot be achieved with conservative methods alone.

ACL reconstruction is usually performed via knee arthroscopy, a type of keyhole surgery that allows for faster recovery and less post-operative pain. Surgical treatment of the anterior cruciate ligament, including the post-operative phase and intensive physiotherapy, may require anywhere from 6 to 12 months before the patient can resume their previous level of physical exercise and activity.

Conservative treatment for a torn anterior cruciate ligament

Conservative treatment can be considered for patients who do not subject their knee to any significant sports-related or occupational stress. This usually involves targeted physiotherapy exercises to strengthen the thigh muscles and improve knee stability. Conservative treatment aims to maintain the function of the knee and alleviate discomfort without the need for surgery.


There are various measures that can help prevent ACL injuries:

Strengthening the (thigh) muscles

Targeted strength training, particularly of the thigh muscles, can improve the stability of the knee joint, thus reducing the risk of an ACL tear.

Proper warm-up and stretching


A thorough warm-up before playing sport or exercising and regular stretching of the leg muscles can help to improve the flexibility and mobility of the ligaments and prevent knee injuries.

Proper technique


Learning how to move correctly in sports that require rapid changes of direction and abrupt stops can reduce the risk of an ACL tear.

Avoiding excessive strain

It is important to avoid putting excessive strain on the knee joint, especially if the muscles are tired or you have not warmed up properly. The load on the knee should be increased gradually and sufficient breaks should be taken to prevent injuries.

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