Anterior cruciate ligament rupture: Symptoms and Treatment

The anterior cruciate ligament (ACL) is one of the key ligaments that help stabilize your knee joint. A fresh anterior cruciate ligament rupture is the complete or partial interruption (rupture) of the continuity (tear) of the ligament after the overstretch an external force has exceeded reserve. An old anterior cruciate ligament rupture is a permanent, mostly accident-related ligament injury.


Causes are often so-called “flexion-valgus-outside-rotation injuries.” This means that the knee is involuntarily bent, turned into the knock-knee position, and turned outwards.

Typically when skiing or playing football, such injuries occur with a fixed lower leg. An instability of the knee joint due to the loosening of the capsular ligament apparatus can occur. The result is a derailment of the roll-slide mechanism and increasing degenerative (wear-related) cartilage damage and meniscus.

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Symptoms of anterior cruciate ligament rupture

A vital symptom of any acute ligament injury to the knee joint is a pronounced pain that occurs immediately at the moment of the trauma. Immediately subsides and returns when the ligament is reloaded.

The rupture of the ligament structures also leads to a rupture of vessels. This results in bleeding into the knee joint (haemarthrosis). If blood is punctured during a knee joint puncture, this is always highly suspicious of a ligament injury in the knee joint.

After the acute symptoms have subsided, the knee joint becomes unstable in different individuals. An instability is complained about, especially when the patient is descending from a meeting. In some cases, a torn cruciate ligament is only diagnosed years after the accident.

In some cases, a torn anterior cruciate ligament can be combined with a torn posterior cruciate ligament.

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Diagnosis of anterior cruciate ligament rupture

Patients with a torn cruciate ligament sometimes suffer from severe pain in the knee joint, which usually swells up within the first few hours. The doctor will try to examine the knee with so-called stability tests. This is not too easy to do because of the general painfulness, as the patient tenses his muscles against it.

In most cases, the examination can only be carried out a few days after the rupture of the anterior cruciate ligament, as only then is the pain caused by accident reduced to such an extent that the patient can be examined without defensive tension.

A normal X-ray provides information about any bony injuries that may be present at the same time. A larger joint effusion should be punctured to relieve the cartilage and the remaining soft tissue. If the effusion is bloody, there is a suspicion of a torn cruciate ligament, although this is not evidence.

With the widespread use of magnetic resonance imaging, with which the cruciate ligaments or their remnants are very clearly visible, the diagnosis can be predicted with relative certainty. In the picture above, the red arrows indicate the torn cruciate ligament (rupture of the anterior cruciate ligament).

The damage can be verified using magnetic resonance imaging. The slice images show the course of the cruciate ligaments and their attachment to the thigh and lower leg bones. In case of a rupture, the fiber courses are not continuous, and the localization of the tear is possible.

Only a few years ago, all patients would have to undergo surgery due to a lack of diagnostic possibilities.

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These times are over, since with the magnetic resonance tomography / MRI – examination, the damage that has occurred can be estimated very precisely, and possibly necessary operations can be planned. The X-ray image is normally inconspicuous in isolated cruciate ligament ruptures. However, since similar symptoms can also be caused by a torn meniscus, for example, it is difficult for the layperson to make a diagnosis.

Here again, all examination methods to diagnose an anterior cruciate ligament injury

Clinical diagnostics by the orthopedic surgeon:

  • Assessment of knee swelling, joint effusion, range of motion and motion pain
  • Assessment of gait pattern, leg axes
  • Assessment of the femoropatellar joint (sliding bearing of the patella)
  • Assessment of knee stability and meniscus
  • Muscular atrophy (weakening of the muscle relief)
  • Assessment of adjacent joints
  • Assessment of blood circulation, motor skills and sensitivity (feeling on the skin)
  • Apparative diagnostics (diagnosis by devices)

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Necessary instrumental investigations

X-ray: knee joint in 2 planes, patella (kneecap) tangential

Appliances useful in individual cases:

  • X-ray: Knee joint p.a. in standing position in 45-degree flexion
  • Fricke’s image (tunnel image) to show a bony tear of the anterior cruciate ligament of the thigh bone
  • Recordings held
  • Whole leg recordings under load
  • Functional images and special projections
  • Sonography = ultrasound (e.g., for meniscus, Baker’s cyst)
  • Computer tomography (in case of a tibial head fracture = tibial head fracture)
  • Magnetic resonance imaging (cruciate ligaments, menisci, bone injury). The MRI is the most valuable diagnostic tool in the case of an anterior cruciate ligament rupture since the MRI can assess partial damage in particular. An MRI for a torn cruciate ligament helps to assess the prognosis of the knee joint better.
  • Puncture with synovial analysis (for effusion in the knee (water in the knee) and blood in the knee joint)
  • Mechanical drawer testing (not a standard test)

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Classificationof anterior cruciate ligament rupture

The anterior drawer test is often performed to identify ligament injury (tear of the anterior cruciate ligament). In this test, the knee joint is angled at 90°, and the foot is fixed on the base. Now the examiner pulls the lower leg close to the knee joint and assesses whether the lower leg can be pulled out about the thigh.

Classification of the anterior drawer sign according to Debrunn

  • Grade I (+): slight displacement 1/8 inch
  • Grade II (++): average displacement 1/4 inch
  • Grade III (+++): pronounced displacement 1/2 inch

MRI for a torn cruciate ligament

With an experienced examiner, the diagnosis of a cruciate ligament rupture is usually possible very quickly and reliably, even without imaging. Nevertheless, MRI has established itself as the standard method. In contrast to X-rays or CT, MRI allows all ligaments and soft tissues of the knee to be displayed and thus existing tears to be detected in principle.

However, partial tears can often only be displayed very poorly in an MRI. In this respect, the MRI is less reliable for making a diagnosis than a good examination by an experienced examiner.

Nevertheless, an MRI examination of the knee after an injury, in which the cruciate ligament may also be affected, is often useful.

MRI often enables the doctor to assess what treatment is now necessary and how quickly, if necessary, surgery should be performed. Any injuries to other structures (meniscus, inner and outer ligament) of the knee can also often be identified by MRI.

This information then also has a significant influence on whether and how quickly surgery is required.

If, however, the examination already shows a rupture of the cruciate ligament and the course of the accident does not suggest that other structures are also damaged, an MRI is not necessarily necessary and often does not provide any new information. If an injury cannot be precisely detected and localized by MRI, a knee endoscopy is usually necessary.

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Surgery for cruciate ligament rupture

A minimally invasive way of operating is knee endoscopy, also known as arthroscopy. Surgery is usually the method of choice in the case of a torn cruciate ligament. Only in the case of a rupture of the posterior cruciate ligament, or in the case of very slight tears, surgery may not be necessary under certain circumstances. However, this always involves the risk that the knee is less stable and less resilient in the long term. For this reason, the operation is highly recommended, especially for younger people, especially if they are active in sports.

However, the operation is only performed when the inflammation and swelling of the knee has subsided sufficiently. This is usually the case after about 4-6 weeks. This waiting period is important, as surgery in irritated tissue can lead to much worse results. An operation directly after the injury is only carried out in very severe cases involving bone structures.

In the meantime, the cruciate ligament rupture can be operated on minimally invasively, which reduces the complications and accelerates healing. The whole procedure is, therefore, then performed within the framework of a knee endoscopy (arthroscopy). The operation itself then consists of completely replacing the destroyed cruciate ligament with other ligament structures. Repairing the old ligament only leads to insufficient results. For this reason, parts of the ligament from neighboring ligaments are usually removed.

The ligament of the patella or a thigh muscle, for example, is suitable for this purpose. In these cases, the parts are removed while allowing ligaments to fulfill their function without any problems. The removed piece of ligament is then adjusted as precisely as possible to take over the function of the torn cruciate ligament.

However, this method can sometimes cause quite severe pain at the donor site. This is especially the case when a part of the patella tendon is removed. On the other hand, this type of implant usually grows somewhat faster.

Ligament sections obtained from organ donation can also be used, but these have the disadvantage that they can lead to rejection of the foreign material. In return, the pain at the sites where the autogenous tendons are removed is avoided.

Various systems are used to attach the ligament to the knee: On the one hand, simple metal screws or fixation buttons, but also absorbable materials, can be used.

The result of the operation is then, of course, also determined by good rehabilitation.

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Complications of an operation

In addition to the general complications of an operation, such as

  • Infection
  • Bleeding
  • Deafness / Paralysis

there are special risks associated with cruciate ligament surgery. So-called operation-specific complications include:

  • Arthrofibrosis – a particularly dreaded complication. This is a partial stiffening of the knee joint after cruciate ligament plastic surgery through scarring. The risk of arthrofibrosis is particularly high if surgery is performed shortly after the accident.
  • Cyclops syndrome – due to scarring of the cruciate ligament, resulting in an extension deficit.
  • Cruciate ligament plastic impingement – the cruciate ligament graft gets caught between the femoral rolls during stretching, which prevents complete stretching of the knee joint.


It is scientifically proven that damage to the cruciate ligament can cause irreparable damage to the knee joint. With a very high probability, a knee joint will cause premature wear and tear of the knee joint (arthrosis) after damage to the cruciate ligament has been suffered.

According to scientific studies, this wear and tear can be favorably influenced by implantation of an anterior cruciate ligament plastic, but cannot be stopped completely.

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Duration of healing

Until the complete healing of a torn cruciate ligament, one should plan on about 6-9 months only after this time is the knee usually fully resilient again. Immediately after the injury, the knee must first be treated conservatively for about 4-6 weeks.

Anti-inflammatory and decongestant measures are especially important. 

This is followed by the rehabilitation phase, which takes about 12 weeks. After the operation, measures to reduce swelling and inflammation and to stabilize the knee with a splint must be performed. Crutches must be used for a few weeks.

Then the knee will be partially loaded, and physiotherapy will be adapted to the respective condition. After about six weeks, light training on the bicycle ergometer or light walking is often possible. Less strenuous sports can then be resumed after about 3-4 months. Sports that put a lot of strain on the knee, such as tennis or similar, can usually be resumed after about 6-9 months when full resilience is possible again.

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Application of rails

Splints are used at two points in time for cruciate ligament rupture. Firstly, a splint can be used to stabilize the knee immediately after the injury and to support the decongestant swelling and reduction of the inflammation until the operation.

The second important area of application is the phase immediately after the operation. During this time, it is important to stabilize the knee and only allow movement within a certain range. Finally, the ligament implant fixed in operation must first grow together with the bone to be truly stable in the long term.

For this purpose, splints are used in which the radius of movement can be precisely adjusted and limited so that only a certain degree of flexion or extension is possible in the knee. In this way, the knee can initially be fixed in a certain position.

Under this stabilization and within the scope of the movements, physiotherapy can be started after a few weeks. In the course of healing, the range of movement and thus, the load on the knee can always be adapted to the individual healing process.

This greatly reduces the risk of damaging the new ligament again or delaying healing by careless movements or overloading after the operation.

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