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Could You Have Torn Your ACL?

An anterior cruciate ligament (ACL) tear is one of the most common knee ligament injuries, particularly in people who participate in sports involving pivoting, jumping or sudden changes in direction.

While some ACL tears occur during contact sports, many happen without any direct impact. Recognising the symptoms early allows timely assessment and appropriate treatment, reducing the risk of further damage to the knee.

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What Does an ACL Tear Feel Like?

Many patients describe a distinct injury event.

Common symptoms include:

• A sudden “pop” or “snapping” sensation
• Immediate knee pain
• Rapid swelling within several hours
• Difficulty continuing the activity
• Feeling that the knee has “given way”
• Loss of confidence when walking or turning

Some patients are able to walk after the injury, while others find it difficult to bear weight.

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1. A Popping Sound or Sensation

One of the classic symptoms of an ACL tear is hearing or feeling a “pop” at the moment of injury.

Not everyone experiences this, but many patients remember the exact moment it happened.

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2. Rapid Knee Swelling

The ACL has a rich blood supply.

When it tears, bleeding into the knee joint often causes swelling within the first few hours.

This rapid swelling is known as a haemarthrosis (bleeding into the knee joint).

While swelling alone does not confirm an ACL tear, rapid swelling following a twisting injury raises suspicion.

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3. Knee Instability

Many patients describe the knee as:

• Giving way
• Buckling
• Feeling unreliable
• Unable to trust it during turning movements

Instability is often more noticeable after the initial pain and swelling have settled.

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4. Pain

Pain varies considerably.

Some patients experience severe pain immediately after injury.

Others report surprisingly little pain once the initial injury settles.

Pain may occur:

• Around the centre of the knee
• During twisting
• When attempting to pivot
• During sporting activities

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5. Difficulty Continuing Sport

Many athletes are unable to continue playing immediately after the injury.

Others may attempt to continue but find that the knee repeatedly gives way.

Repeated episodes of instability increase the risk of damaging the meniscus and joint cartilage.

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6. Reduced Knee Movement

Following injury, patients may find it difficult to:

• Fully straighten the knee
• Bend the knee comfortably
• Walk normally
• Climb stairs

This may be caused by pain, swelling or associated injuries.

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Can You Walk With a Torn ACL?

Yes.

Many patients are surprised that they can still walk despite having a complete ACL tear.

Walking normally does not rule out a serious ligament injury.

The knee often feels unstable only during activities involving:

• Pivoting
• Twisting
• Sudden stopping
• Cutting movements
• Sport

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What Causes an ACL Tear?

Common injury mechanisms include:

• Sudden change of direction
• Landing awkwardly from a jump
• Pivoting on a planted foot
• Sudden deceleration
• Hyperextension
• Direct collision during contact sports

Sports commonly associated with ACL injuries include:

• Football
• Basketball
• Netball
• Rugby
• Skiing
• Tennis
• Badminton
• Martial arts

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How Is an ACL Tear Diagnosed?

Diagnosis begins with a careful clinical assessment.

Dr Puah Ken Lee will:

• Discuss how the injury occurred
• Examine knee stability
• Assess for swelling and range of motion
• Evaluate for associated ligament injuries

Imaging may include:

• X-rays to exclude fractures
• MRI to confirm the ACL tear and identify associated injuries

MRI is particularly useful for detecting:

• Meniscus tears
• Cartilage damage
• Bone bruising
• Other ligament injuries

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Could It Be Something Else?

Not every twisting knee injury is an ACL tear.

Other conditions with similar symptoms include:

• Meniscus tear
• Medial collateral ligament (MCL) injury
• Posterior cruciate ligament (PCL) injury
• Patellar dislocation
• Cartilage injury
• Bone bruising

An accurate diagnosis is important because treatment differs depending on the underlying injury.

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When Should You See an Orthopaedic Surgeon?

Arrange an assessment if you experience:

• A popping sensation during injury
• Rapid knee swelling
• Recurrent knee instability
• Difficulty returning to sport
• Persistent pain after a twisting injury
• Repeated episodes of the knee giving way

Early assessment helps determine whether surgery, physiotherapy or other treatment is most appropriate.

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Frequently Asked Questions

Can an ACL tear be mistaken for a sprain?

Yes. Some ACL tears are initially thought to be a simple knee sprain, particularly if the pain settles quickly. Persistent instability or recurrent giving way should prompt further assessment.

Does every ACL tear cause swelling?

Most complete ACL tears cause swelling within a few hours, but the degree of swelling varies between individuals.

Can I continue exercising with an ACL tear?

Some people can perform straight-line activities such as cycling or jogging. However, pivoting sports may increase the risk of further injury if the knee remains unstable.

Is an MRI always required?

MRI is commonly used to confirm the diagnosis and identify associated injuries, but the need for imaging depends on the clinical assessment.

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Related Conditions

You may also find these pages helpful:

• ACL Reconstruction Singapore
• ACL vs Meniscus Tear
• ACL Graft Options
• ACL Rehabilitation
• Return to Sport After ACL Reconstruction
• Meniscus Tear
• Sports Knee Injuries

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Arrange a Consultation

If you have injured your knee during sport or experienced symptoms suggestive of an ACL tear, an early assessment can help establish the diagnosis and guide treatment.

Dr Puah Ken Lee provides comprehensive evaluation of sports knee injuries, including ACL tears, with personalised treatment plans tailored to your activity level, sporting goals and long-term knee health.

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Dr Puah is regularly invited to teach knee arthroscopy

Book a consultation or contact the clinic via WhatsApp to get started

Book a consultation at 360 Orthopaedics, Mount Elizabeth Novena

ACL tears are common but treatable. Early diagnosis and appropriate management can improve outcomes and prevent long-term problems.
Dr Puah Ken Lee is an orthopaedic surgeon in Singapore specialising in shoulder, elbow and sports injuries at 360 Orthopaedics, Mount Elizabeth Novena. Patients with instability and pain in the knee after a sports injury are encouraged to seek specialist evaluation.