ACL Tear: Causes, Symptoms, Diagnosis and Treatment Options

An ACL tear is a common knee injury that can affect athletes and individuals who engage in physical activities. It often occurs during sudden movements, such as changing direction, jumping or landing awkwardly. While some people experience immediate pain and difficulty walking, others may still be able to move around despite having a torn ligament.
 

This raises several questions: Can you still walk with a torn ACL? Will the ligament heal on its own? Is surgery always necessary?
 

Understanding how ACL injuries occur, their symptoms and the available treatment options can help you recognise when medical attention may be needed and what to expect during recovery.

What Is the Anterior Cruciate Ligament (ACL)?

The anterior cruciate ligament (ACL) is one of the major ligaments that help stabilise the knee joint. It connects the thigh bone (femur) to the shin bone (tibia) and helps control forward movement and rotation of the knee.
 

The ACL plays an important role in maintaining knee stability, particularly during activities that involve running, jumping, pivoting or sudden changes in direction.
 

An ACL injury occurs when the ligament is stretched beyond its normal capacity, causing damage to its fibres. Depending on the severity, the injury may involve:

• Grade 1 (Mild Sprain): The ligament is slightly stretched but remains intact, with no significant loss of knee stability.
• Grade 2 (Partial Tear): Some ligament fibres are torn, which may result in varying degrees of knee instability.
• Grade 3 (Complete Tear): The ligament is completely torn, potentially affecting the knee's ability to remain stable during movement.

The severity of an ACL injury can influence the symptoms experienced and the type of treatment required.

What Causes an ACL Tear?

An ACL tear typically occurs when excessive force is placed on the knee, particularly during movements that involve sudden changes in speed or direction.
 

Although these injuries are commonly associated with sports, they may also occur during recreational activities or accidents.
 

Some of the common causes include:

• Sudden changes in direction: Quickly turning or pivoting while the foot remains planted can place excessive stress on the ACL.
• Awkward landings: Landing from a jump with poor knee alignment may increase the strain on the ligament.
• Sudden stopping: Rapidly slowing down while running can place additional force on the knee joint.
• Direct impact: Collisions or blows to the knee during contact sports may damage the ACL.
• Twisting movements: Unexpected rotation of the knee, particularly when the foot is fixed in place, can cause ligament damage.

Sports such as football, basketball, badminton, skiing and rugby involve movements that may increase the likelihood of ACL injuries.
 

However, an ACL tear does not always involve direct contact. Many injuries occur during non-contact movements, such as pivoting or landing.

What Are the Signs and Symptoms of a Torn ACL?

The symptoms of an ACL tear can vary depending on the severity of the injury and whether other knee structures are affected.
 

Some individuals experience immediate discomfort, while others may only notice instability when attempting certain movements.
 

Common signs and symptoms include:

1. Popping Sensation in the Knee

Some people report hearing or feeling a popping sensation at the time of injury. This may occur when the ligament is suddenly stretched or torn.
 

However, not everyone with an ACL injury experiences this sensation.

2. Knee Pain and Swelling

Pain may develop immediately after the injury, followed by swelling within the first few hours. Swelling can occur due to bleeding inside the knee joint following ligament damage.

3. Knee Instability

One of the more noticeable symptoms of an ACL tear is a feeling that the knee may buckle or give way, particularly when turning, changing direction or placing weight on the affected leg.

4. Reduced Range of Motion

Swelling and discomfort may make it difficult to fully bend or straighten the knee. Some individuals may also experience stiffness.

5. Difficulty Continuing Physical Activities

An ACL injury may make it difficult to continue running, jumping or participating in sports. Even when pain improves, the knee may still feel unstable during certain movements.
 

These symptoms are not exclusive to ACL tears and may also occur with other knee injuries, such as meniscus tears or ligament sprains. A medical assessment is therefore important to determine the underlying cause.

How Is an ACL Tear Diagnosed?

Diagnosing an ACL tear generally involves reviewing how the injury occurred, examining the knee and, when necessary, performing imaging tests.
 

A doctor may use the following methods to assess the injury:

Medical History and Physical Examination

The doctor will ask about the circumstances of the injury, including whether there was a sudden twisting movement, popping sensation or immediate swelling.
 

During the physical examination, the doctor may assess knee movement, tenderness, swelling and joint stability.
 

Specific tests, such as the Lachman test or anterior drawer test, may be performed to evaluate the ACL's ability to stabilise the knee.

Magnetic Resonance Imaging (MRI)

An MRI scan provides detailed images of the ligaments and other soft tissues inside the knee.
 

It may be recommended to confirm the extent of ACL damage and identify associated injuries involving the meniscus, cartilage or other ligaments.

X-rays

Although X-rays cannot directly show an ACL tear, they may be used to check for fractures or other bone-related injuries.
 

The findings from these assessments help determine the severity of the injury and guide the appropriate treatment approach.

Can You Still Walk With a Torn ACL?

Yes, it is possible to walk with a torn ACL, particularly once the initial pain and swelling have improved.
 

The ability to walk depends on several factors, including the severity of the injury, the stability of the knee and whether other structures have been damaged.
 

Some individuals with a complete ACL tear may still be able to walk on flat surfaces because the surrounding muscles and other knee structures provide some support.
 

However, activities involving sudden turning, pivoting or changes in direction may cause the knee to feel unstable.
 

Being able to walk does not necessarily mean the ACL is intact or that the injury is minor.
 

Continuing strenuous activities with an unstable knee may increase the risk of further damage to the meniscus or cartilage.
 

If you experience significant knee pain, swelling or instability after an injury, it is advisable to stop the activity and seek medical assessment. Avoid forcing weight onto the affected leg if walking is painful or difficult.

Can a Torn ACL Heal on Its Own?

The ACL has a limited ability to heal naturally, particularly when the ligament is completely torn.
 

Unlike some other tissues in the body, the ACL has a relatively limited blood supply and is surrounded by joint fluid, which can make healing more difficult.
 

However, the likelihood of recovery without surgery depends on the extent of the injury and the stability of the knee.

Partial ACL Tears

Some partial ACL tears may be managed without surgery, particularly when the remaining ligament fibres provide sufficient knee stability.
 

Treatment may involve physiotherapy, strengthening exercises, activity modification and, in selected cases, knee bracing.

Complete ACL Tears

Complete ACL tears are less likely to regain normal ligament structure and function without treatment. Although some individuals may develop sufficient functional stability through rehabilitation, others continue to experience episodes of knee instability.
 

Non-surgical management may still be appropriate for certain individuals, particularly those who do not participate in high-demand sports and whose knees remain stable during daily activities.
 

The decision between surgical and non-surgical treatment depends on factors such as knee stability, activity level, associated injuries and personal recovery goals.

What Is ACL Reconstruction Surgery?

ACL reconstruction is a surgical procedure performed to restore knee stability after an ACL tear.
 

Rather than simply stitching the torn ligament together, the procedure typically involves replacing the damaged ACL with a tendon graft. This graft may be taken from another part of the patient's body or, in selected cases, from donor tissue.
 

ACL reconstruction may be considered for individuals who:

• Experience persistent knee instability despite rehabilitation.
• Wish to return to sports involving running, jumping or pivoting.
• Have associated injuries involving the meniscus or other knee structures.
• Experience difficulty performing daily or work-related activities because of knee instability.

However, not every ACL tear requires surgery.
 

Non-surgical management may be suitable for individuals whose knees remain stable and who can comfortably perform their usual activities.
 

When surgery is recommended, a structured rehabilitation programme is an important part of recovery. Physiotherapy helps restore knee movement, rebuild muscle strength and improve joint stability.
 

Individuals considering surgery can learn more about ACL reconstruction surgery in Singapore, including when the procedure may be recommended and what the treatment process involves.
 

How Can You Reduce the Risk of ACL Injuries

Although not all ACL injuries can be prevented, certain exercises and movement techniques may help reduce the risk, particularly during sports and physical activities.

1. Strengthen the Muscles Supporting the Knee

Strengthening the quadriceps, hamstrings, glutes and core muscles can help support knee stability and improve control during movement.

2. Practise Proper Landing Techniques

Learning to land with controlled knee and hip movement may help reduce excessive stress on the ACL.
 

Exercises that focus on landing mechanics can be particularly useful for individuals who participate in jumping sports.

3. Improve Balance and Coordination

Balance and neuromuscular training can help improve control of the knee during sudden movements or changes in direction.
 

These exercises may involve single-leg balance activities, controlled jumping and movement drills.

4. Follow a Structured Warm-Up Programme

A structured warm-up incorporating strengthening, balance exercises and movement training may help prepare the body for physical activity.
 

Sports-specific injury-prevention programmes may be particularly helpful for athletes who regularly perform jumping and pivoting movements.

5. Avoid Returning to Sports Too Early After an Injury

Returning to demanding activities before regaining sufficient knee strength and stability may increase the risk of further injury.
 

Individuals recovering from a previous knee injury should follow their rehabilitation programme and obtain appropriate medical guidance before resuming high-impact sports.

Can You Walk Without an ACL?

Yes, some individuals can continue walking and performing daily activities without a functioning ACL.
 

This is because the knee also relies on other ligaments, muscles and surrounding structures for support.
 

For people who mainly participate in low-impact activities, rehabilitation may help them maintain sufficient knee stability without ACL reconstruction.
 

However, walking without a functioning ACL does not mean the knee will remain stable during every activity.
 

Movements involving sudden turns, jumping or pivoting may place greater demands on the knee and increase the likelihood of instability.
 

Repeated episodes of the knee giving way can also contribute to additional injuries involving the meniscus or cartilage.
 

Whether an individual can manage without a functioning ACL depends on several factors, including:

• The degree of knee instability.
• Strength and control of the surrounding muscles.
• Presence of other knee injuries.
• Daily activity requirements.
• Participation in sports or physically demanding activities.

An orthopaedic assessment can help determine whether rehabilitation alone is sufficient or whether other treatment options should be considered.

When Should You Seek Medical Attention for an ACL Injury?

An ACL tear does not always prevent a person from walking, but persistent pain, swelling or instability should not be overlooked.
 

Early assessment can help identify the extent of ligament damage, detect other knee injuries and determine an appropriate treatment plan.
 

At International Orthopaedic Clinic (IOC), Dr Alan Cheung, a Senior Consultant Orthopaedic Surgeon in Singapore with a focus on sports injuries and knee conditions, provides assessment and management of ACL injuries.
 

Treatment recommendations are based on the severity of the injury, knee stability and the individual's activity requirements, with both non-surgical management and ACL reconstruction considered where appropriate.
 

If you suspect an ACL injury or experience ongoing knee instability, a medical assessment can help clarify the condition and available treatment options.