• There are several important ligaments in and around the knee
• The ligaments provide stability to the joint
• Damage to the ligaments on the outside of the knee (the collaterals) often heals up without surgery
• Ligament damage inside the knee – especially the anterior cruciate ligament (ACL) – often requires surgical treatment
• Surgical treatment often involves a knee arthroscopy (keyhole surgery) plus ligament reconstruction
• Ligament reconstructions are performed using a tissue graft (a replacement ligament)

The main ligaments of the knee are:

• The anterior cruciate ligament
• The posterior cruciate ligament
• The medial collateral ligament
• The lateral collateral ligament
• The ‘posterolateral corner’

ACL

The anterior cruciate ligament is a thick strong ligament in the middle of the knee. It originates from the middle of the front of the tibia and passes upwards, backwards, and laterally (outwards), attaching to the femur on the medial (inner) side of the lateral femoral condyle. The ligament stops the tibia from sliding too far forwards on the femur (also stopping the femur from slipping too far backwards on the tibia).

PCL

The posterior cruciate ligament is the largest and strongest ligament in the knee. It originates from the middle of the back of the tibia and passes upwards, forwards and medially, attaching to the femur on the lateral side of the medial femoral condyle. The PCL stops the tibia from sliding too far backwards on the femur (also stopping the femur from slipping too far forwards on the tibia).

MCL

The medial collateral ligament is situated on the inner side of the knee. It is a broad thick ligament with a short deep portion and a longer superficial part. It prevents the lower leg from bending outwards (into valgus).

LCL

The lateral collateral ligament is situation on the outer side of the knee and is a thin cord-like ligament. It passes from the lateral epicondyle of the femur to the fibular head and prevents the lower leg from bending inwards (into varus).

PLC

The structures of the posterolateral corner have only really become the focus of particular interest over the last 5 to 10 years or so. The posterolateral corner is a complex region of the knee and includes the popliteus muscle/tendon, the arcuate ligament, the popliteofibular ligament and the lateral collateral ligament. Things are made more difficult by the fact that so many of the descriptions of the anatomy of the PLC differ significantly in their interpretation of the region. Regardless of the finer points, the PLC functions so as to limit excessive external rotation of the tibia on the femur.

Ligament sprains

Ligament sprains (ie partial tears) are common, especially around the ankle joint. Sprains of the knee joint are frequently quite serious. The most common ligament sprain on the knee probably involves the medial collateral ligament. This is the ligament along the inner side of the knee that prevents the knee from bending out sideways. It is particularly vulnerable to twisting injuries or injuries from football or rugby tackles.

The medial collateral ligament of the knee is a thick, strong and broad ligament. Even quite severe tears normally heal up well, with conservative (non-surgical) treatment. The more severe ligament injuries may require treatment in a knee brace, to protect the ligament as it heals. However, management of medial collateral ligament sprains is normally best supervised by an appropriately trained physiotherapist.

Ligaments ruptures/tears

The most common ligament rupture in the knee is a tear of the ACL. However, ligament tears frequently occur in conjunction with other injuries within the knee, such as meniscal cartilage tears, articular cartilage damage or ruptures of other ligaments in or around the knee.

ACL ruptures

The anterior cruciate ligament is the ligament most frequently torn by sportswomen or men, often in sports such as football, netball or skiing.

Arthroscopic view of a normal ACL

Arthroscopic view of a torn ACL

The typical history and symptoms of an ACL tear are:

• History of a specific significant injury, such as a bad fall skiing or a nasty tackle playing football or rugby.
• The knee gives way with severe pain, and sometimes a specific ‘pop’ or ‘tear’ is felt or heard.
• The knee is then severely painful and tends to swell up rapidly, with difficulty weight-bearing.
• The athlete is normally unable to continue with the game.
• The swelling of the knee may take a few weeks to gradually go down (it is caused by bleeding into the knee from the torn ligament).
• Patients may then complain of ongoing instability in the knee, with a regular giving way and a feeling that the knee is ‘wobbly’, ‘unsteady’ or ‘not right’.

An ACL tear is a very significant injury to the knee. ACL tears frequently occur in association with other intra-articular damage. Early referral to a Consultant Orthopaedic Surgeon with a specialist interest in this field is essential.

Depending on the patient’s history, symptoms and clinical signs, patients are often referred for an MRI scan of the knee. MRI scans do not give a 100% accurate image of the inside of the knee; for example the accuracy of MRI for detecting meniscal tears is only in the region of about 80%. However, MRI may give useful information regarding the various structures in the knee, in particular the articular cartilage.

Treatment of ACL tears

Deciding on the correct treatment strategy for an ACL tear is a complex issue and decisions are tailored to specific individual patients based on their age, medical fitness, activity levels, sporting involvement and aspirations.

Even without an anterior cruciate ligament, some patients are able to regain a functionally stable knee without any reconstructive surgery, simply by strengthening up the muscles of the knee and improving the reflexes (proprioception). This is achieved through an intensive rehabilitation programme under the supervision of an appropriately trained physiotherapist. However, with conservative treatment, although a good proportion of patients are able to cope, many end up unable to return to their same pre-injury exercise and sporting levels.

The most clear indication for surgical ACL reconstruction after an ACL tear is in those patients suffering recurrent giving way of the knee. Each time the knee gives way further damage is potentially being caused inside the knee to the articular cartilage and to the meniscal cartilages, with the risk of worsening long-term outcomes.

PCL and PCL tears

90% of PCL tears and 90% of PLC tears occur in association with other ligament injuries within the knee; mainly rupture of the ACL.

Isolated PCL tears have a very good likelihood of responding well to conservative treatment with physiotherapy, without the need for surgical reconstruction.

Combined tears of the ACL + PCL, the ACL + PLC or the PCL + PLC usually cause quite severe functional instability in the knee joint, and normally do require surgical reconstruction.

Complex multi-ligament reconstructions of the knee are a fairly major undertaking – far more so that a simple isolated ACL reconstruction. Multiple ligament reconstructions can normally be undertaken with just 1 or 2 nights’ stay in hospital post-operatively, but usually require a patient to have a knee brace post-op, with a slower more cautious rehab regime.