ACL injury (rupture)

ACL injury (rupture)

Injury to the anterior cruciate ligament (ACL) is a surprisingly common injury caused by a wide variety of activities including sport and trauma. The sports that are most commonly associated with ACL damage are those that involve pivoting and twisting, for example, football and skiing. Certain people are more pre-disposed to damaging their ACL, in this group of patients the force required to completely rupture the ACL can be quite minimal.

A complete rupture of the ACL can be associated with an increasing sense of instability as the knee recovers and the swelling settles. Although, in some patients, particularly those not involved in vigorous sporting activity, instability may never be noticed. However, where symptoms of instability do exist, at Schoen Clinic, we have a whole team of experienced knee experts who specialise in minimally invasive ACL reconstructive surgery to restore stability.

Purpose and function of the anterior cruciate ligament (ACL)

The anterior cruciate ligament (ACL) is one of several important stabilising ligaments that connect the tibia (shin bone) to the femur (thigh bone) across the knee. It is one of the key primary stabilisers of the knee. The ACL is the primary stabiliser against rotational forces. Therefore in the absence of a functioning ACL, the knee can be vulnerable to collapse or give way, when twisting and turning forces occur during certain sporting activities.

It may, therefore, be perfectly possible in the presence of an injured (ruptured) ACL, to continue with "in-line" sporting activities, that do not involve twisting. Even with a complete rupture of the ligament, a degree of healing will often occur, with the damaged end of the ligament reattaching itself to the Posterior Cruciate ligament (PCL). This can produce some increased stability although even with some degree of healing, the knee remains vulnerable to "giving way" if the ACL is not functioning fully.

This is the reason why it is important that any injury to the ACL is fully assessed both clinically and using detailed imaging to establish the exact degree of injury and the potential for healing. Once the injury has been fully assessed, the decisions about operative and non-operative treatments can be more accurately made.

Anterior Cruciate Ligament (ACL) rupture: symptoms

The ACL may be damaged either in isolation or as part of a more severe multi-ligament injury. Patients will often describe having either heard or felt a "popping sensation" at the time of the injury. In the presence of a complete rupture of the ACL, it is extremely unusual for patients to be able to continue with sporting activity, and often the knee swells quite quickly due to the disruption of the blood supply to the ligament, causing bleeding within the knee, known as a haemarthrosis. 

Whilst some patients may report an instant sense of "instability", other patients may not be aware of instability until considerably later. In addition, standing on the knee can be uncomfortable due to bruising of the bones or associated meniscal cartilage damage.

Symptoms of an Anterior Cruciate Ligament (ACL) rupture to watch out for:

  • Popping "sound or sensation" at the time of injury
  • Immediate pain
  • Swelling within 12 hours (feeling of instability and a progressive feeling of instability in the knee)
  • Reduced range of motion
  • Discomfort on weight-bearing
  • Generalised tenderness

As mentioned above, the anterior cruciate ligament may be ruptured, either as part of a more significant injury to the knee or in isolation. The other ligament most commonly injured at the same time as the ACL is the Medial Collateral Ligament (MCL). The MCL is the inner one of a pair of strap ligaments that are responsible for stabilising the knee against side to side movements. As the forces that injure the knee are often complex and multidirectional, the combination of these forces can overload the different structures as a part of the same traumatic injury. Unlike the ACL, the MCL is often just stretched or “sprained” and thus whilst painful will usually not need repair. However, occasionally the MCL is completely pulled away from its bony attachments at the same time as ACL rupture.

In these circumstances, the MCL damage becomes the priority and will require a period of immobilisation with a brace to allow it to heal before the ACL treatment can begin. In addition, the meniscal cartilages can be damaged as part of the twisting mechanism and may also require surgery, to treat the unstable fragments.

It is also quite common for the bone to be 'bruised' as a result of the significant pivoting injury that occurs at the instant of the twisting injury. This bone bruising is often self-limiting but can cause a degree of discomfort on weight-bearing. Every knee injury is obviously different but the various patterns of injury are common and treatment plans are therefore well established.

The eventual decision as to whether you proceed to surgery depends entirely on, not only the observed instability but also, the patients' age and sporting aspirations. It is perhaps important to stress that it is not a patient’s age alone which determines the treatment options, but rather their amount of desired activity levels.

Causes: how does an ACL injury occur?

ACL injuries often occur whilst undertaking sports, typically such as football, netball, skiing, or rugby.  These are all activities where a significant amount of twisting stress is put on the knee. Also landing incorrectly from a jump, suddenly stopping, rapid change of direction and even slowing down whilst running, can all result in ACL injury.  If the stress exceeds the tensile strength of the ligament, this generally leads to either a partial or full tear of the fibres. The vulnerability of the ACL is increased when a rotational force occurs whilst the knee is in a flexed position.

Diagnosis of injury to the ACL

As with all surgical conditions, diagnosis of the precise injury is crucial for providing the most effective and appropriate treatment. As specialists we will firstly take a detailed history, to understand how the injury occurred, followed by a clinical examination. Whilst these tests will give a good indication as to whether a significant injury has occurred, we also commonly rely on the use of more detailed diagnostic imaging.

As ligaments are soft tissues, magnetic resonance imaging (MRI scans) are able to provide a detailed look at the condition of your knee ligaments. The advantage of the MRI scan over X-rays alone is that it will also add useful information as to the state of the other structures in the knee, including all ligaments, meniscal cartilages and of course the articular surface itself.

This will allow us to create a full picture of the 'personality' of this unique injury and guide a very specific treatment plan, according to the exact combination of injuries that exist.

The extent of ligament injuries are often divided into three grades. This applies to both the anterior cruciate ligament, as well as the medial collateral ligament.

  • Grade 1: ACL has sustained only a minor sprain and remains stable.
  • Grade 2: ACL has been slightly torn, known as a partial tear.
  • Grade 3: ACL has been completely ruptured and the knee is potentially unstable.

Grade 3 is by far the most common grade of injury to the ACL, unlike the MCL where grades1 and 2 are much more common. Once a definitive diagnosis has been made, we as specialists can discuss with you the best way to proceed, in the short, medium and long-term.