Anterior Cruciate Ligament (ACL) tear signs and symptoms

The dreaded ACL injury is one feared by a lot of active people. Any knee injury can be painful, debilitating and frustrating but ACL injuries are some of the most commonly spoken about injuries in sports like football and rugby, and can lead to months of rehab and quite often surgery. In this blog post I will explain what your anterior cruciate ligament (ACL) is, the role it plays within the knee and what happens when your ACL ruptures.


What is an ACL?

The anterior cruciate ligament (ACL) is one of the four major ligaments that help stabilise the knee joint, inside of the knee. It connects the thighbone (femur) to the shinbone (tibia) and prevents the tibia from sliding out in front of the femur, providing rotational stability to the knee. An ACL injury is a tear or sprain of this ligament, often occurring during sports that involve sudden stops, changes in direction, jumping, or landing, such as basketball, soccer, and football. The injury can be a result of sudden slowing down, changing direction, pivoting with the foot firmly planted, landing awkwardly from a jump, stopping suddenly, or receiving a direct blow to the knee. A torn ligament can be a partial or complete tear, and it is more common in women than in men.


What are the common causes of an ACL injury?

There are a number of risk factors which might mean you could be more susceptible to injuring your anterior cruciate ligament. The risk factors for an ACL injury include:

  1. Gender: Females are at a higher risk of suffering an ACL injury compared to males, especially when participating in the same sports at similar levels of exposure.
  2. Previous ACL Injury: Individuals with a history of a previous ACL tear or reconstruction are at an increased risk of re-injury.
  3. Anatomical and Physiological Factors: Anatomical features such as wider hips and smaller thighbones in females, as well as increased generalised joint laxity, can contribute to a higher risk of ACL injury.
  4. Hormonal and Genetic Factors: Some studies have suggested that hormonal, genetic, and cognitive function factors may influence the risk of suffering an ACL injury.
  5. Sports Participation: Participating in certain sports that involve cutting, pivoting, jumping, and sudden stops, such as soccer, basketball, football, and downhill skiing, can increase the risk of ACL injury.
  6. ACL tears are most common between the ages of 15 and 45, with younger athletes being particularly susceptible.
  7. Neuromuscular Control and Landing Mechanics: Poor proprioception, faulty landing mechanics, and weak core and quadriceps muscles can contribute to an increased risk of ACL injury.

The following infographic from Elsevier shows more clearly what might cause an injury to the ACL:


Risk factors and causes of ACL injuries


It's important to note that these risk factors can act in combination to influence the likelihood of suffering an ACL injury. Understanding these factors can help in identifying individuals at increased risk and in developing targeted prevention strategies.


What are the signs and symptoms of an ACL tear?

The symptoms of an ACL injury typically include:

  • A loud pop or a "popping" sensation in the knee at the time of injury
  • Severe knee pain and inability to continue activity
  • Rapid swelling
  • Loss of range of motion
  • A feeling of instability or "giving way" with weight bearing
  • Pain on the outside and back of the knee
  • Limited knee movement
  • Inability to bear weight on the leg

These symptoms are often the result of sports-related activities involving sudden stops, changes in direction, jumping, or landing, such as basketball, football and netball. If any of these symptoms are present, it is important to seek immediate medical care.


How is an ACL injury diagnosed?

To diagnose an ACL injury, a healthcare provider typically performs a combination of physical examination and imaging tests. During the physical exam, the doctor checks for swelling, tenderness, and range of motion in the knee, and may also perform specific tests to assess the stability of the knee joint. This can often lead to a preliminary diagnosis of an ACL injury.

Imaging tests may be used to confirm the diagnosis and assess the severity of the injury. These tests may include:


X-rays are used to rule out any potential bone fractures in the knee joint.

Magnetic Resonance Imaging (MRI)

An MRI provides detailed images of both hard and soft tissues in the knee, allowing the healthcare provider to assess the extent of the ACL injury and detect any damage to other structures in the knee, such as the cartilage.

These diagnostic methods help healthcare providers determine the most appropriate course of treatment for an ACL injury, whether it involves non-surgical or surgical interventions.


Can you tear your ACL without knowing?

Yes, it is possible to tear your ACL without knowing, especially in the case of a partial tear. Some people may experience minimal pain, swelling, or other symptoms and may feel like they could continue with their activities. However, it's important to be cautious, as walking on a torn ACL can exacerbate the injury and cause additional damage to the knee, such as tears to the cartilage. If there is a suspicion of an ACL tear, it is advisable to seek medical attention for a proper diagnosis and appropriate treatment.

In the majority of cases, ACL tears are extremely painful and can sometimes be followed by a popping sound or feeling in the middle of the knee as the ligament ruptures. A complete ACL tear also tends to bleed quite a lot within the joint which leads to significant swelling and bruising around the knee. As with any instant inflammation, it's indicative of a severe injury so it is important to get some immediate medical attention.

Again, even with a partial ACL tear (ACL sprain), you can experience pain, and swelling due to the number of blood vessels and nerves in the joint. It's important to get it checked out to assess the extent of the damage and rule out any secondary injuries such as a meniscus tear or bone damage.


ACL Injuries in Women's Football

ACL tears in women's football have become a significant concern, with female players being up to six times more likely to suffer an ACL injury compared to their male counterparts.

The 2023 FIFA Women’s World Cup witnessed a notable number of ACL injuries, leading to the absence of several top players from the tournament. Research has highlighted that the majority of these injuries are non-contact, often occurring during abrupt stops, landings, and twisting of the knee.

This trend has raised questions about the factors contributing to the higher incidence of ACL injuries in women's football, leading to calls for greater research, resources, and injury prevention measures to address this issue. The rapid growth of women's football and the increased demands on players have also been cited as potential contributing factors to the rise in ACL injuries. The situation has underscored the need for enhanced support and resources to mitigate the risk of ACL injuries and facilitate the recovery of female footballers.


Why are ACL ruptures becoming more common?

The increasing prevalence of ACL ruptures can be attributed to several factors, including the rise in sports participation and the intensity of athletic activities.

Sports injuries, particularly those involving sudden stops, changes in direction, jumping, or landing, are the most common causes of ACL tears. Additionally, the nature of certain sports, such as football, basketball, and soccer, which involve movements that put significant stress on the knee, can contribute to the higher incidence of anterior cruciate ligament injuries.

Furthermore, the risk of ACL tears is elevated in individuals who have previously torn their ACL, and the age group of 15 to 45 is particularly susceptible to such injuries. The increased awareness and diagnosis of ACL injuries may also contribute to the apparent rise in their occurrence.

Important note: it is important to remember, media attention does sometimes highlight things like this to us and make it appear more common, however this is not always the case. for example it seems like ACL injuries in women's football are sky rocketing however if you think of women's football 10 years ago - you probably wouldn't hear about a female player suffering from an ACL injuries. This is not to say there isn't an increase, but something to bare in mind.


How do you recover from an ACL injury?

Recovering from an ACL injury typically involves a combination of rehabilitative therapy, surgery, and post-operative rehabilitation. The specific approach to recovery depends on the severity of the injury and the individual's activity level and overall health. Here are the general steps involved in recovering from an ACL injury:


Nonsurgical Treatment


For a partial tears of the ACL, the RICE method (rest, ice, compression, and elevation) may be sufficient for recovery along with physical therapy.

Rehabilitative Therapy

A physical therapist will teach exercises to reduce pain and swelling, restore the knee's full range of motion, and strengthen muscles. A structured ACL rehabilitation programme will progress you through each stage of rehabilitation based of progressive criteria and goal setting to ensure optimal recovery.

Bracing and Crutches

In some cases, a brace may be worn to stabilise the knee, and crutches may be used to avoid putting weight on the knee.


Surgical Recovery

ACL Reconstruction Surgery

For a complete tear or in cases where the individual is active and requires knee stability, surgery may be the best treatment as recommended by orthopedic surgeons. This typically involves ACL reconstruction using tissue from another part of the body or a donor.

Post-Operative Rehabilitation

After surgery, formal physical therapy usually begins within a week. The goal is to regain normal knee function, strength, and movement whilst building up proprioception to knee your knee stable in the long term and prevent further damage or reinjury.


ACL surgery, also known as ACL reconstruction, is a common treatment for a torn ACL. During the surgical procedure, the damaged ligament is removed and replaced with a segment of tendon, which is similar to a ligament. This tendon can be harvested from another area of the leg, such as the hamstring or patellar tendon. The surgery is most commonly performed using arthroscopic techniques, which involve making a small incision on the knee. After the surgery, patients are typically in a brace and on crutches for the initial days to allow the body to heal.

Formal physical therapy usually begins within a week of the surgery to restore normal knee function, strength, and movement. The recovery process after ACL surgery is gradual and may vary depending on the individual's activity level and the extent of the injury, with a typical recovery time of six to nine months. The decision to undergo ACL surgery is based on the extent of the damage, the individual's lifestyle, and the presence of other knee injuries.


General Recovery Timeline


Recovery from any ligament injury is dependant on the type of injury, whether that be mild or more severe, like a complete rupture. The average recovery time for an ACL tear is six to nine months, with some individuals taking up to a year or more, especially for a full return to sports activities.

Return to Activity

Athletes should not return to sports or intense athletic activity until their healthcare provider deems it safe to do so, as premature return may increase the risk of re-injury.

Recovery from an ACL injury is a comprehensive process that may involve non-surgical or surgical interventions, followed by rehabilitative therapy to restore knee function and strength. The specific approach should be tailored to the individual's condition and preference of physical activities.


In conclusion, an ACL tear can be a debilitating injury, often characterized by a distinct "pop" at the time of injury, followed by acute pain, swelling, and instability in the knee joint. This injury is particularly common in athletic activities that involve sudden stops, changes in direction, and jumping, such as soccer, basketball, and football. The diagnosis of an ACL tear is typically based on a combination of physical examination and imaging tests, with the Lachman test being a key diagnostic tool. It's important to note that some individuals, especially those with partial tears, may initially experience minimal symptoms, emphasizing the need for caution and proper diagnosis. Understanding the signs and symptoms of an ACL tear is crucial for timely intervention and appropriate treatment, whether through non-surgical or surgical approaches, to facilitate recovery and prevent long-term complications.

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Arun Gray sports therapist strength and conditioning coach skegness

The author

Arun Gray is a sports therapist and strength & conditioning coach with over 15 years experience in the industry. He also has a personal history with chronic shoulder and back pain along with a range of other sporting injuries.

Arun writes about common injuries and aims to help people understand and manage their pain to prevent having to rely on national healthcare.

Read more about Arun