The anterior cruciate ligament (ACL) is one of the key ligaments that help stabilise the knee joint. ACL injuries are commonly associated with sports involving sudden stops and changes in direction such as football, basketball, and skiing. This type of injury can range from a mild strain to a complete tear, affecting athletic performance and daily activities.

Understanding the common signs and symptoms of an ACL injury can help in timely diagnosis and treatment, potentially preventing further damage. Here’s a detailed look at what you need to watch out for if you suspect an ACL injury.

A Loud “Pop” Sound at the Time of Injury

An ACL injury often presents with a sudden, sharp pain in the knee, typically felt at the moment of injury. Individuals might also hear or feel a noticeable “pop” sound. The knee can quickly swell due to bleeding within the joint, leading to significant discomfort.

Weight-bearing becomes difficult or impossible because the knee feels unstable or gives way. These immediate symptoms can significantly impair mobility and prompt individuals to seek medical attention.

Acute Pain and Swelling

Following an ACL injury, acute pain is frequently experienced around the knee joint. This pain is often intense and worsens with movement. Swelling typically develops rapidly, sometimes within hours of the injury, due to internal bleeding (haemarthrosis).

This swelling causes stiffness and limits the knee’s range of motion. The combination of acute pain and swelling contributes to difficulty in weight-bearing and walking, necessitating rest and the application of ice or compression to reduce discomfort.

Instability and Reduced Range of Motion

An ACL injury often leads to a sensation of instability or a feeling that the knee is “giving way”. This is due to the ligament’s role in maintaining knee joint stability. As a result, everyday activities such as walking or pivoting can become challenging. Reduced range of motion is another common symptom, as swelling and pain inhibit the knee’s ability to bend or straighten.

Functional Impairment and Difficulties in Daily Activities

People with this injury often find it challenging to perform daily activities such as walking up or down stairs, standing up from a seated position, or getting out of a car. They may avoid activities involving pivoting or twisting movements due to the knee’s instability.


ACL injuries can be debilitating, but understanding the common signs and symptoms can lead to prompt treatment and better outcomes. If you suspect an ACL injury, consult with a doctor to determine the best course of action for your recovery. Early intervention and appropriate treatment are key to getting back to your regular activities and maintaining knee health.