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Submit your file in just a few minutes and get an expert opinion in under 7 days.
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What is a medical second opinion?
Following a diagnosis or a proposed treatment plan, a medical specialist can analyze your file and provide an additional perspective.
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Your health insurance may cover your second opinion.
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Are you looking for a second opinion for a loved one?
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How does a second opinion work on Diagdoor?
How does a second opinion work on Diagdoor?
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Not sure if your case is eligible?
Our medical team can guide you before you submit your request. Describe your situation, and we will help you determine if Diagdoor can be of assistance.
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Upload your file to Diagdoor. A
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Symptoms of an ACL tear: from the acute phase to instability
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Medically reviewed by
Prof. Matthieu Ollivier
Updated on
August 6, 2026
A pop in the knee during a match, a skiing fall, or a misstep on the stairs: an anterior cruciate ligament (ACL) tear can happen in many different ways. The symptoms evolve over time and can be misleading in the days following the injury. Understanding this progression helps ensure a serious injury isn't overlooked.
Key points
- Three telltale signs: a popping sound at the time of injury, rapid knee swelling (hemarthrosis), and a feeling of instability or the knee giving way are the most characteristic symptoms of an ACL tear.
- Partial or complete, isolated or associated: the clinical picture varies depending on the type of tear and any potential meniscus or cartilage damage.
- Being able to walk does not rule out a tear: it is possible to move around after a complete ACL tear. This does not indicate the severity of the injury.
- Persistent instability warrants a specialist consultation, even if the pain has subsided in the days following the injury.
From the acute phase to chronic instability: how symptoms evolve
The symptoms of an ACL tear are not static: the clinical picture changes significantly between the moment of injury and the weeks that follow.
In the first few hours :
- A popping sound at the time of the injury, often heard or clearly felt by the patient
- Immediate pain, sometimes intense, which may subside quickly
- Progressive swelling of the knee (hemarthrosis: blood in the joint), usually visible within 2 to 4 hours of the injury
- Immediate instability, sometimes with the sensation that the knee is "giving way"
In the following days :
- Pain often decreases, which can lead one to believe it is just a simple sprain
- Instability persists, even if knee mobility partially improves
Long-term effects of the injury :
- Episodes of the knee giving way during changes of direction, walking down stairs, or pivoting
- Functional discomfort during sports or daily activities
- A progressive risk of secondary meniscus damage if the tear remains untreated
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Mild sprain or ACL tear: the main sources of confusion
Three situations frequently cause doubt for the patient and sometimes during the initial examination.
- Mild ligament sprain vs. ACL tear : a medial collateral ligament (MCL) sprain, located on the inner side of the knee, also causes pain and swelling. The difference: an ACL tear is accompanied by rapid hemarthrosis and, most importantly, rotational instability that a mild sprain does not produce.
- ACL tear vs. PCL tear : the posterior cruciate ligament (PCL), which is injured less frequently, typically tears during direct trauma to the tibia, such as a frontal impact or accident. The instability it causes differs from that of the ACL, and the mechanism of injury helps distinguish it.
- Complete tear vs. partial tear : a partial tear may produce less pronounced symptoms, making clinical diagnosis more difficult. This distinction is important because it directly influences the choice between conservative and surgical treatment.
These similarities in presentation make a clinical assessment and imaging essential to confirm the diagnosis with certainty. A surgeon specializing in knee surgery can analyze the MRI and the full clinical assessment to ensure no associated injuries are missed and to guide the right decision from the start.
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Situations that increase the risk of an ACL tear
ACL tears affect a wide range of people, far beyond just elite athletes:
- Pivot and team sports : soccer, alpine skiing, handball, basketball, rugby, and tennis account for the majority of cases due to sudden rotational movements and jump landings.
- Amateur and experienced athletes alike : skill level offers no protection. A tear can occur during a weekly practice just as easily as during a competition.
- Women participating in pivot sports : at equivalent activity levels, they face a higher risk of ACL tears, partly due to anatomical and biomechanical differences.
- Non-sporting accidents : a fall, a misstep, or trauma outside of a sporting context can also cause a tear, regardless of age.
Frequently Asked Questions
What are the symptoms of an anterior cruciate ligament tear?
The three most indicative signs are a popping sound at the time of injury, rapid knee swelling (hemarthrosis), and a feeling of instability. Associated injuries, particularly to the meniscus, are common and can alter the clinical presentation.
How do I know if I have torn my cruciate ligament?
While suggestive symptoms point toward a diagnosis, only a clinical examination by an orthopedic surgeon, supplemented by an MRI, can confirm it with certainty. The Lachman test, which assesses abnormal displacement of the tibia relative to the femur, is the most reliable clinical sign.
Does an ACL tear always cause severe pain?
Not necessarily: pain can be intense in the first few hours and then subside quickly, even in the event of a complete tear. It is instability, rather than pain, that points toward a serious ACL injury.
Can you walk after an ACL tear?
Yes, walking is possible in most cases, even after a complete tear. This ability does not indicate the severity of the injury or the need for specialized care.
How can you distinguish a severe sprain from an ACL tear?
A mild ligament sprain causes pain and swelling, but without rapid hemarthrosis or marked rotational instability. An ACL tear is distinguished primarily by more significant swelling in the first few hours and instability that persists beyond the painful phase.
Need the opinion of a
Knee surgeon
Upload your file to Diagdoor. A
Knee surgeon
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analyzes it and provides a reasoned opinion in less than 7 days.
Sources
- French National Authority for Health (HAS), Meniscal and anterior cruciate ligament injuries
- Ameli.fr, Knee sprain: returning to your activities
Did you know?
Following an ACL tear, it is possible to walk and even resume light activity within the first few days. This apparent improvement can mask the true severity of the injury: residual instability warrants a specialized assessment, even in the absence of significant pain.
Have you been offered surgery?
Have you been offered surgery?
Surgery is never trivial. A medical specialist will analyze your file to confirm the recommendation or explore other therapeutic options.
Is there an alternative to surgery?
Is there an alternative to surgery?
A surgeon specializing in your condition will re-evaluate your file to confirm if surgery is necessary or to identify less invasive solutions.
Have you been presented with several treatment options?
Have you been presented with several treatment options?
Have you been presented with several treatment options?
An expert physician will analyze your medical records and history to help you choose the most appropriate strategy for your situation, whether it be medical treatment, surgery, or monitoring.
Torn between two treatments?
Torn between two treatments?
A specialist will explain exactly what each option entails, including effectiveness, side effects, and daily impact, so you can make your decision with confidence.
Still unsure about your diagnosis?
Still unsure about your diagnosis?
Still unsure about your diagnosis?
A specialist doctor will analyze your complete file (tests, imaging, medical history) to provide you with a reasoned diagnosis and guide your care.
Have you just received a diagnosis?
Have you just received a diagnosis?
Have you just received a diagnosis?
Have your medical file reviewed by a specialist in your condition. You will receive an additional opinion in less than 7 days, helping you move forward with clarity.
Is your condition rare or complex?
Is your condition rare or complex?
Diagdoor gives you access to a doctor who specializes in your condition to confirm your treatment plan, no matter where you live.
When facing cancer or a serious illness, every decision counts.
When facing cancer or a serious illness, every decision counts.
A doctor at an expert center will review your file to confirm your care plan, clarify the available options, and help you make decisions with confidence.
Have you received a diagnosis or been offered a treatment plan?
Have you received a diagnosis or been offered a treatment plan?
Have you received a diagnosis or been offered a treatment plan?
Submit your file in just a few minutes and get an expert opinion in under 7 days.
Have you received a diagnosis or been offered a treatment plan?
Submit your file in just a few minutes and get an expert opinion in under 7 days.
What is a medical second opinion?
What is a medical second opinion?
Following a diagnosis or a proposed treatment plan, a medical specialist can analyze your file and provide an additional perspective.
Your health insurance may cover your second opinion.
Your health insurance may cover your second opinion.
Many partner health insurance providers cover the Diagdoor service with no upfront costs. Check your eligibility as soon as you create your account.
Are you looking for a second opinion for a loved one?
Are you looking for a second opinion for a loved one?
The process is entirely online. Upload your available medical documents, and our team will take care of the rest.
How does a second opinion work on Diagdoor?
How does a second opinion work on Diagdoor?
Upload your medical documents online; our team will review your file within 48 hours, and an expert will provide their opinion in less than 7 days. Simple, secure, 100% online.
Not sure if your case is eligible?
Not sure if your case is eligible?
Our medical team can guide you before you submit your request. Describe your situation, and we will help you determine if Diagdoor can be of assistance.
Need the opinion of a
Knee surgeon
Need the opinion of a
Knee surgeon
Upload your file to Diagdoor. A
Knee surgeon
specialist
on your condition
analyzes it and provides a reasoned opinion in less than 7 days.