Understanding ACL Tears: Symptoms and Causes

What Is an ACL Tear?

An ACL tear is an injury to the anterior cruciate ligament, which is a vital band of tissue in our knees. The ACL helps keep the knee stable during movement. Whether you’re pivoting on the soccer field, running during exercise or sports, or simply climbing stairs, the ACL works to prevent your shinbone from sliding too far forward and to support rotational movements. When this ligament tears, it can cause pain, swelling, and instability, making everyday activities and sports challenging.

The ACL’s Role in Knee Stability

The knee joint connects your thigh bone (femur) to your shinbone (tibia), and the ACL is one of four major ligaments that hold it together. Located deep within the knee, the ACL crosses in front of the posterior cruciate ligament (PCL), forming an “X” shape that stabilises the joint. It’s especially critical during activities involving:

• Sudden stops or changes in direction (e.g., dodging an opponent in basketball).
• Pivoting or twisting motions (e.g., turning while running).
• Landing from jumps (e.g., in netball or volleyball).

Without a healthy ACL, your knee may feel like it’s “giving way,” leading to discomfort or even further injury. In Singapore, where sports like soccer, running, and badminton are popular, ACL injuries are a common concern for both recreational and competitive athletes.

Prevalence of ACL Tears

ACL tears are among the most frequent knee injuries that make up nearly half of all knee-related issues. They’re particularly common in high-impact sports, with thousands of cases reported annually in Singapore due to the city’s active lifestyle. Women are at higher risk than men due to differences in anatomy, muscle strength, and movement patterns, but anyone engaging in sports or activities with sudden movements can be affected. ACL tears are not just associated with athletes, anyone can experience ACL tears from accidents, such as tripping or twisting the knee during daily tasks.

Impact on Daily Life and Sports

An ACL tear can significantly disrupt your routine, whether you’re an athlete or simply navigating Singapore’s fast-paced urban environment. For sports enthusiasts, a torn ACL often means pausing activities like running, cycling, or team sports, as the knee may buckle or feel unstable during dynamic movements. This can sideline you for weeks or months, affecting fitness goals and team commitments.

In daily life, an ACL tear can make simple tasks, like walking, climbing HDB stairs, or carrying groceries, painful or difficult. You might notice swelling, stiffness, or a sense of instability, which can limit mobility and affect your quality of life. For professionals in desk jobs, prolonged sitting may worsen discomfort, while those in active roles (e.g., delivery or construction) may struggle to perform tasks safely.

Types of ACL Tears

ACL tears can primarily be divided into two main types:

Partial ACL Tears

• Happens when the ACL is only partially torn.
• Partial ACL tear symptoms include mild to moderate knee pain, swelling, and instability.
• Associated with a good prognosis.
• Often rare.

Complete ACL Tears

• The majority of ACL tears are complete tears when the ligament is completely torn.
• Symptoms include severe pain and instability in the knee that can cause it to buckle or give away.
• Recovery from an ACL complete tear without surgery is almost impossible without surgery.

ACL and meniscus tears are often confused with each other. To confirm your diagnosis of a particular grade of sprain and see if you have any other types of knee pain or injury, your doctor might call for an X-ray or MRI of your knee and provide a customised treatment plan for you.

Visit our meniscus tear treatment page for more information on the causes, diagnosis and treatment options at Ray of Health.

Causes of ACL Tear Injuries

Image Credit: Cleveland Clinic

There are several causes of ACL tears including:

• Changing direction suddenly while walking or running
• Abruptly stopping while running, for example, in soccer.
• Slowing down your speed abruptly while running
• Jumping and landing from a jump in the wrong posture
• Collision with another person that puts strain on the legs and knees.

ACL Tear Symptoms

Typical signs and symptoms of an ACL tear include:

• You can hear the popping sound of the ligament rupturing when the injury occurs.
• Pain starts immediately after the injury.
• The knee starts to swell within hours.
• It becomes difficult or almost impossible to walk.
• You feel pain in the knee while standing or putting weight on the leg.
• Your knee may feel unstable or loose at the joint making daily activities difficult
• You may lose your range of motion in the knee.

ACL Tear Diagnosis

To diagnose an ACL tear, the qualified orthopaedic specialist will carry out a physical exam to check the knee for any inflammation and other signs of injury. The doctor may move the leg in certain positions to assess the location and extent of the injury. He may order additional imaging tests to view the internal structure of the knee and confirm the diagnosis. These imaging tests include:

• X-rays: X-rays visualise the bony structures in your body. An x-ray of the knee will not specifically show the tear but it can help the doctor see if the knee pain is associated with a broken bone.
• MRIs: MRIs are a good way to see the soft tissues of the knee and can help the doctor diagnose it effectively.

Once the doctor has correctly diagnose an ACL tear, he would be able to create a tailored treatment plan for your condition. Read more about our ACL Tear Treatment with Dr James Tan.

Suffering from an ACL Tear?

Early intervention is key to preventing long-term complications, such as cartilage damage or osteoarthritis, which are concerns in Singapore’s ageing population. At Ray of Health, Dr. James Tan, an experienced orthopaedic surgeon, specialises in diagnosing and treating ACL tears, helping you regain stability and return to the activities you love.

Frequently-Asked Questions

How do you tear your ACL?

The most common cause of an ACL tear is when the ACL is torn during sports activities such as basketball, football, and rugby. You may also tear your ACL if you are old and your ligaments and tendons have started degeneration.

How do I know if I have an ACL tear?

You might have an ACL tear if you experience:

• A “pop” sound during injury, followed by severe pain.
• Swelling within 6–24 hours.
• Instability or buckling when walking, climbing stairs, or turning.
• Difficulty bearing weight on the affected leg.

When is an ACL tear an emergency?

If you have an ACL tear, you will experience intense pain and swelling in the knee with almost the inability to put weight on the affected knee. Whenever you experience such symptoms, you should consult your doctor and get evaluated. However, if you feel that the foot on the side of the affected knee is turning cold and/or blue, it may indicate that the blood is not reaching the foot because of injured blood vessels. This may point toward a dislocated knee joint. This is a medical emergency which should be evaluated by the doctor as soon as possible.

How is an ACL tear different from a meniscus tear?

When comparing ACL tear vs meniscus tear, both may manifest as similar symptoms at the start such as pain, swelling, instability in the knee, and a popping sound and sensation. However, a meniscus tear injury will cause relatively more severe pain as time passes and that too while doing as much as putting weight on the knee. On the other hand, an ACL tear may not cause any increased pain while walking uphill or on flat terrain. A person with an ACL tear injury will experience more pain while walking downhill and ascending stairs. Nevertheless, if you suspect an ACL tear or a meniscus tear, contact us for a thorough examination and diagnosis.

Who is at risk for an ACL tear?

Although anyone can experience an ACL tear, some people are more prone to it. These include:

• Athletes in high-impact sports (e.g., soccer, basketball, netball).
• Women, due to differences in muscle strength, hip alignment, and hormones.
• Individuals with weak knee-supporting muscles or poor movement techniques.
• Those playing on hard or uneven surfaces, common in Singapore’s urban sports facilities.

What sports or activities commonly cause ACL tears?

High-risk activities for ACL tears include:

• Sports: Soccer, basketball, netball, rugby, and skiing, where pivoting or jumping is frequent.
• Recreational Activities: Running, fitness classes (e.g., HIIT), or dance, especially with improper form.
• Daily Mishaps: Tripping or twisting the knee while rushing for the MRT or navigating uneven pavements in Singapore.

How can I prevent an ACL tear?

You can prevent the chances of getting an ACL tear through some measures, such as:

• Strengthening hamstrings, quadriceps, and core muscles through targeted exercises.

• Practising proper landing and cutting techniques (e.g., bending knees, not locking them).
• Wearing supportive, sport-specific footwear.
• Warming up thoroughly and avoiding playing when fatigued.