There are two cruciate ligaments in the knee: the anterior cruciate ligament and the posterior cruciate ligament. The main function of the cruciate ligaments is to stabilize the knee. Most cruciate ligament injuries are to the anterior cruciate ligament (known as an ACL tear or an ACL injury) and between 6000–7000 people per year in Sweden injure their anterior cruciate ligament. It is relevantly rare to suffer an isolated ACL tear. Approximately 80% of all ACL injuries occur simultaneously to ligament, meniscus, or cartilage injuries.

When the ACL ruptures, it may feel as if something snaps or pops in the knee. The pain is often immediate and sharp, but for some, a torn ACL can be relatively painless. A few hours after suffering the injury, the knee tends to swell, and standing on the hurt leg may be difficult due to the pain. An ACL tear is often diagnosed based on a Lachman test, which tests the stability of the knee. However, an X-ray should always be performed to rule out skeletal damage. An MRI scan is often also necessary to examine other potential joint injuries.

Women are more prone to ACL tears than men

Young women are 3 to 5 times more likely to injure their ACL than men. Although it is not yet fully understood why this is the case, it is believed that both hormonal and anatomical factors play a role. For example, women often have less muscle mass around the knee, which affects knee stability. New research has also shown that the genetic contribution to ACL injuries is high.

The link between joint injury and OA

A torn ACL increases the risk of developing knee osteoarthritis (OA) later in life. Within 15–20 years, about half of those who have suffered an ACL injury show symptoms of OA in the knee. Since most people who injure their anterior cruciate ligament are below the age of 30, many develop OA as working-age adults. Living with OA and reduced knee function when you are still active both in the workplace and in everyday life, may severely impact your quality of life.

The exact causal mechanisms between a torn ACL and OA are still somewhat unclear, but likely have to do with biomechanical and biochemical changes that occur in the joint after an injury. Other injuries associated with an ACL tear, such as a meniscus tear, may also play role in the development of OA.

Surgical or non-surgical treatment

An ACL injury can either be treated with surgery (ACL reconstruction) followed by rehabilitation or solely with physical therapy. The choice of treatment depends mostly on how stable the knee is if other knee injuries are present, and what level of physical activity level you wish to achieve after treatment. If you are an elite athlete, surgery is often preferable. However, studies have shown that for the vast majority of patients, both treatment methods achieve similar results in terms of knee function and symptoms. The risk of developing OA is about the same regardless of treatment. Physical therapy without surgery should therefore always be recommended as the initial treatment for an ACL injury. Should physical therapy not prove to give satisfactory results, surgery can be performed at a later stage.

Minimizing the risk of a second injury

Undergoing ACL reconstruction surgery does not necessarily mean that you can return to sport immediately. Rehabilitation to rebuild muscle strength and improve coordination should last for at least 6 months before returning to moderate activity. To reduce the risk of a second injury, you should preferably have received physical therapy for at least 9-12 months before returning to sport. About 25% of all athletes re-tear their ACL after surgery, which is often due to returning to sport too soon. It takes time to regain muscle strength, so it is important to have patience and train cautiously.