banner image

Reading Time: 7 minutes 17s

Anterior cruciate ligament injury Symptoms, Signs, Causes and Treatments

An ACL injury involves a tear or sprain of the anterior cruciate ligament (ACL), the key tissue band connecting the thighbone (femur) to the shinbone (tibia). These injuries often happen during sports that require sudden halts, direction changes, jumping and landing. Examples are football, basketball, and downhill skiing.

When an ACL injury occurs, most individuals heara pop sound or "popping" feeling in the knee. The knee might swell, become unstable, and cause severe pain to bear weight.

The treatment for an ACL injury varies based on its severity. It may include resting and rehabilitation workouts to restore strength and stability or surgical procedures to replace the torn ligament and, afterward rehabilitation. Also, engaging in an appropriate training program can help lower the risk of having an ACL injury.

By Able Health I Medically reviewed by Dr. Alireza Estedlal

Page last reviewed: February 2024 I Next review due: February 2026

Understanding Anterior Cruciate Ligament Injury

The anterior cruciate ligament (ACL) is a significant ligament found in the knee joint. Its main function is to provide stability to the knee and prevent too much movement of the shin bone (tibia) that is attached to the thigh bone (femur). Having an injury on the ACL means that damage has occurred to this specific ligament. The damage usually ranges from mild sprains to total tearing of the ligament based on the seriousness of the damage.

It is important to know about the anatomy of ACL so as to understand ACL injuries well. ACL is found in the deepest part of your knee joint. It is made of strong fibrous tissue that joins the femur and tibia and functions alongside other ligaments and muscles to offer stability to the knee joint.

Most ACL injuries result from a sudden movement of the knee joint that causes twisting or hyperextension. These injuries commonly occur in people who engage in sports such as football, basketball, and skiing, which usually require players to suddenly change their direction or stop. Another common cause of ACL injuries is non-contact injuries that occur naturally without putting any force on the knee.

Types of ACL injuries

Typically, healthcare providers grade ACL injuries to quickly describe the extent of the damage. These rankings range from the least severe (grade 1) to the most severe (grade 3):

  • Grade 1: The ACL is stretched and damaged but remains intact and continues to hold the knee bones in place.
  • Grade 2: The ACL is partially torn and loosened due to significant stretching.
  • Grade 3: The ACL is completely torn, resulting in two separate pieces.


The ACL injury signs and symptoms often include:

  • Swelling and pain in the knee
  • Inability to bear weight in the injured knee
  • A feeling of instability or the knee "giving way."
  • Popping or snapping sound at the time of injury
  • A popping sound at the period of injury
  • Loss of movement range in the knee
  • Tenderness alongside the joint line
  • Difficulty walking or running
  • Reduced muscle strength in the affected leg

If you suspect an ACL injury, several signs can indicate the condition. For example, if you find yourself limping or using one leg more, then it may be a sign of an ACL injury. The injury usually causes pain and instability, hence making it difficult to walk properly. It is also common for ACL-injured people to experience a reduced range of motion in the affected knee joint. This makes it hard for one to completely move or stretch the leg.

Another significant sign of an ACL injury is hearing a pop sound immediately after the injury occurs. Most people often describe the sound as a pop because the ligament snaps out. After that, you will experience pain and swelling. Although not all injuries cause an audible pop sound, it could be a significant sign.


Bones are usually connected to each other by strong bonds called ligaments. The knee has two main ligaments, one of which is the ACL. The ACL passes through the center of the knee and joins the thighbone to the shinbone. This enables the knee joint to remain stable.

Participating in sports is the major cause of ACL injuries because the activities may put stress on the knee when;

  • You suddenly stop or change direction.
  • You rotate around with your foot firmly placed in one position.
  • You land in an awkward position after a jump.
  • You are directly hit on your knee or experience a collision like a football tackle.

Notably, ligament damage can either involve a partial or total tearing of the tissue. Although a mild injury might slightly stretch the ligament, it will remain intact.

How ACL Injuries Occur: A Detailed Explanation

When both biomechanical forces and external forces combine, it results in ACL injuries. The process of ACL injury is usually triggered by suddenly slowing down or changing direction, along with twisting or hyperextension on the knee joint, which leads to a lot of stress on the ACL, hence the damage.

Some common activities that result in ACL injuries are sudden stops, pivotal movements in sports, awkward landing from a jump, and direct kicks on the knee joint. You should also note that ACL injuries can happen without any contact. An example is a case where you awkwardly land from a jump or abruptly change direction.

Risk Factors

Several factors are likely to increase the chance of getting an ACL injury. They include:

  • Being female; probably because of the differences in anatomy, hormonal influences, and muscle strength.
  • Engaging in sports activities like football, soccer, basketball, downhill skiing, and gymnastics.
  • Inadequate conditioning
  • Use of faulty or improper motion patterns, including inward movement of the knees in a squat.
  • Wearing shoes that don’t properly fit.
  • Using sports tools that are not well maintained, like improperly adjusted ski bindings.
  • Playing on artificial surfaces.

Talk to our doctor if you’re concerned about symptoms

You can book an appointment with a private GP today for only £20*.

Book an appointment

Diagnosis of ACL Injury: Tests and Examinations

The diagnosis of an ACL injury involves a combined approach of both physical exams and imaging tests. For physical examination, the doctor checks the range of motion in the knee joint, the instability signs, and if there is pain or soreness. The integrity of an ACL can also be assessed through specific tests like the Lachman test or the pivot shift test.

For imaging tests, healthcare providers utilize magnetic resonance imaging (MRI) and X-rays to ascertain diagnosis and to establish the level of the injury. An MRI enables them to clearly see any tears or ACL damage by providing detailed pictures of the knee joint soft tissues. Likewise, X-rays help rule out the possibility of fractures or abnormal bones that may be triggering the symptoms.


How are ACL tears treated?

The treatment options for ACL injuries are based on the grade of tear and additional damage that occurred in the knee.

You should avoid playing sports or doing any activity that might put excess pressure on the knee. Specialists recommend following the RICE technique immediately you feel pain or notice other symptoms:

  • Rest: Refrain from activities that led to the injury and avoid overusing the knee as it recovers.
  • Ice: Place cold compress or ice packs enfolded in a small towel on the injured knee for at least 15 minutes at a time, several times per day.
  • Compression: Wrap the knee using an elastic bandage to ease the swelling.
  • Elevation: Keep the knee and leg elevated above the heart level as many times as possible.

Healthcare professionals usually recommend the treatment method that helps manage your symptoms. Some of these suggestions may include:

  • Crutches
  • A brace to maintain the knees in position.
  • Over-the-counter (OTC) pain medications including NSAIDs (nonsteroidal anti-inflammatory drugs) and acetaminophen.
  • Physical therapy.


How can I prevent a torn ACL?

Preventing an ACL tear can be difficult, particularly for athletes. This is because sports accidents and injuries are often unpredictable. However, you consider these protective measures during sports and physical activities:

  • Putting on the appropriate protective equipment.
  • Avoiding'playing through the pain,'especially if you hurt your knee during or after a physical activity.
  • Stretching and warming up before you play sports or work out.
  • Cooling down and stretching after engaging in physical activities.
  • Engaging in off-season knee and lower body strengthening programs to prepare the

In addition, consider these safety guidelines to minimize your chances of an ACL injury:

  • Do not plant your foot and pivot over the knee. This is the common cause of ACL and meniscus injuries in athletes.
  • Keep your house and workstation clutter-free to avoid tripping or hurting others.
  • Use the right tools when reaching for items at home. Avoid standing on tables, countertops, or chairs.
  • Use a walker or cane if you are experiencing movement difficulty or are at a high risk of falling.

Rehabilitation after an ACL Injury: Importance and Guidelines

During the healing process, rehabilitation plays a significant role, irrespective of whether or not surgery is involved. The main objective is to restore flexibility, strength, as well as stability of the knee joint, enabling people to safely resume daily activities. Typically, rehabilitation combines exercises, including strengthening exercises, a range of movement exercises, and balance training.

While rehabilitation guidelines exercises tend to differ based on factors like injury severity and surgical involvement, certain general principles apply. Rehabilitation initially focused on easing pain and inflammation through ice therapy and rest. But as recovery progresses, some exercises are introduced progressively to help enhance the motion range and strengthen muscles surrounding the knee joint.

Living With

Can you walk if your ACL is torn?

You can still walk even with a torn ACL. However, you should avoid forcing movement or using your knee if it hurts. Seek medical assistance if you are in pain or experience additional injury symptoms. Too much stress on the damaged ACL could worsen the condition.

Recovery Time for ACL Injury: What to Expect

ACL injury recovery period can differ based on a number of factors, such as age, injury severity, overall health and obedience to rehabilitation rules. Generally, it could take a few months to one year to heal completely from ACL tears.

The usual recovery timeline happens in phases. The first phase involves relieving the symptoms of an ACL injury and restoring range of motion. While the healing advances, one can slowly increase the level of activity and take part in strengthening exercises. Most individuals can resume sports and intense activities in 6 to 9 months after injury, while in others, it might take a year.

Complications of ACL Injury: Long-Term Effects and Management

There are certain long-term impacts associated with poorly managed ACL injuries. One major complication is the formation of osteoarthritis in the knee joint. This happens because of the biomechanics changes that occur, as well as increased pressure on the knee joint after an ACL injury. There are also increased risks of re-injury or injuries in other areas of the knee.

Management approaches for complications are constant rehabilitation exercises to help maintain knee joint stability and strength and changing your lifestyle to lower osteoarthritis risk. You should also follow up with your provider regularly to assess any symptoms changes and overall joint health.

ACL Injury in Athletes: Prevalence and Impact

ACL injuries are quite common in athletes, particularly those engaging in high-impact, rigorous sports. However, the type of sport and gender determines the prevalence of these injuries. For example, sports like basketball and soccer that involve pivoting, cutting, and jumping increase the risk of ACL injuries.

In addition, ACL injuries can have significant effects on athletes. It usually results in extended absence during sports season, which could impact performances and possibly jeopardize one's career. Individuals should thus consider rehabilitation and proper management to restore their knee joint stability, strength and confidence, which allows them to resume sports activities safely.

ACL Injury in Women: Gender-Specific Factors and Prevention

Women are more likely to get ACL injuries than men. This is due to a number of gender-specific factors that increase the risk. Examples of these factors are:

  • Anatomy differences like a narrower intercondylar notch and higher joint laxity.
  • Hormonal aspects like estrogen level fluctuations in the menstrual cycle.
  • Neuromuscular control, including cutting and landing strategies.

The prevention approaches for women can aid in minimizing ACL injuries. They include neuromuscular training programs aiming at enhancing strength, balance and appropriate motion patterns. Also, education on the correct landing method and the use of protective equipment like knee braces could be helpful.


It is important to understand ACL injuries to enable proper management and prevention. ACL injuries often take a toll on one's life by hindering their athletic performance and daily routines. Hence, it is essential to know the signs and symptoms of an ACL injury to ensure early diagnosis and effective treatment.

Both surgical and non-surgical methods can be used to treat ACL injuries. The recovery process involves rehabilitation, which helps in restoring strength and stability in the knee joint. Rehabilitation exercises and lifestyle changes can also help manage complications of ACL injuries.

Athletes and women are at a higher risk of getting ACL injuries but there are targeted prevention techniques to help them. Consulting a healthcare professional is also crucial to ensure early detection and proper treatment of ACL injury. This guarantees optimal results for persons with this kind of knee damage.