The medial collateral ligament is the second most commonly injured ligament alongside an ACL rupture. The medial collateral ligament is a very strong structure on the inside of the knee.  It has two components the superficial and the deep medial collateral ligaments. The superficial MCL is the larger component and plays more of a role in knee stability. The MCL ligament is complex, is active throughout the range of movement and is a very important stabiliser. It can be injured as part of the injury pattern of ACL injury. The MCL injury can be divided into three grades:

Grade 1 – Grade 1 MCL injury is a sprain with no tearing of the actual ligament.  

Grade 1 sprains do not require any surgery.

Grade 2 – This is a partial MCL tear.  

Partial tears are generally treated conservatively in a brace and generally tend to go on to heal well without any surgical input required. If it is a high-grade tear i.e. more than 50% then an acute repair can be considered.

Grade 3 – This is a complete tear of the MCL. The MCL can be completely torn either from its attachment on the femur or mid-substance or at its insertion on the tibia.  

Grade 3 tears can also be treated without surgery but can take a very long time to heal. If it is torn as part of an ACL rupture then the best course of treatment is to repair this acutely to ensure early recovery, early mobilisation and to reduce the risk to the ACL reconstruction operation and potential re-rupture.

The posterior cruciate ligament is one of the cruciates in the middle of the knee along with the anterior cruciate ligament. It is less commonly injured than the ACL. Its main function is to stop posterior translation or backwards movement of the tibia on the femur. It is most commonly injured in dashboard injuries and during road traffic accidents when the flexed knees of the passenger hit the dashboard and cause a forceful backward movement of the tibia resulting in a PCL rupture.  It can however be injured in other mechanisms.

The lateral collateral ligament is a thin band of tissue running along the outside of the knee. It connects the thigh bone (femur) to the fibula, which is the small bone of the lower leg that runs down the side of the knee and connects to the ankle. Like the medial collateral ligament, the lateral collateral ligament's main function is to keep the knee stable. There are 2 main regions of the lateral collateral ligament which can be affected: the posterolateral and the anterolateral regions.

Lateral collateral ligament  - posterolateral corner

The posterolateral corner is perhaps the most complicated anatomical area of knee injury and anatomy. It comprises of a number of structures which help knee stability throughout the range of movement in side-to-side and rotational movements. 

The posterolateral corner is comprised of primary and secondary stabilisers. The three major static stabilisers of the posterolateral corner are the lateral collateral ligament, popliteus tendon and the popliteofibular ligament. 

There are secondary stabilisers such as the iliotibial band, the long head of biceps femoris tendon, the fabellofibular ligament, the joint capsule and the coronary ligaments. All these complex structures work together to provide side-to-side and rotational stability to the posterolateral corner of the knee.

The posterolateral corner is very rarely injured in isolation and usually forms part of a constellation of injuries including ACL and sometimes PCL. Failure to recognise and treat posterolateral corner injuries results in ongoing instability around the knee and can jeopardise anterior cruciate ligament reconstruction which usually results in failure if the posterolateral corner is not treated at the same time. 

Anterolateral ligament

The anterolateral ligament is a newly discovered structure which is closely related to the origin of the lateral collateral ligament. It arises around the lateral femoral condyle and attaches to the tibia in between Gerdy’s tubercle and the fibula head. It is thought to help stabilise the knee especially around anterolateral rotatory instability.  

Anterolateral ligament reconstruction is a new operation which helps to provide extra stability to ACL reconstructions. It is also now routinely carried out as part of revision ACL reconstruction.  The anterolateral ligament can be reconstructed using a gracilis tendon autograft, it can also be reconstructed using synthetic material such as fibre tape.