The knee is a complex joint supported by several ligaments that work together to provide strength and stability. Among them, the anterior cruciate ligament (ACL) plays a vital role in preventing the shinbone from sliding forward and in maintaining balance during sudden movements such as pivots, stops and jumps.

An ACL tear happens when this ligament is stretched beyond its limit or ruptures, often during sports or traumatic accidents. It is one of the most frequent knee injuries seen in active individuals and can greatly compromise stability and mobility if it is not properly treated.

What are the types of ACL Tears?

Not every ACL injury is the same. While some are mild, others completely destabilise the knee. That is why doctors often classify these tears into 3 grades, depending on their severity:

What causes an ACL Tear?

Most ACL tears occur during movements that place sudden stress on the knee joint. The ligament can snap when the knee is forced to twist while the foot is firmly planted on the ground, such as during a quick change in direction, a sharp pivot or a sudden stop in sports. Landing awkwardly from a jump, particularly with the knee slightly bent inward, is another common mechanism.

Similarly, direct impact to the knee, such as a collision during football or a fall while skiing, can also overload the ACL and cause it to rupture. In all these situations, the ligament is stretched beyond its natural capacity, leading to either a partial or complete tear.

What are the symptoms of an ACL Tear?

When the ACL is injured, the effects are usually felt immediately. Many people describe hearing or feeling a distinct ‘pop’ in the knee at the moment of injury. This is often followed by sudden pain that makes it difficult to continue moving.

Some of the other typical symptoms include:

• Difficulty with sports or daily activities, as the knee may feel weak and unreliable
• Instability of the knee, especially during walking or sudden movements
• Persistent discomfort, particularly when putting weight on the affected leg
• Rapid swelling of the knee within the first few hours after injury
• Reduced range of motion, making it hard to fully straighten or bend the knee

Who is at more at risk of an ACL Tear?

Although an ACL tear can happen to anyone, certain factors increase the likelihood of sustaining the injury. This includes, but is not limited to:

• Age – younger individuals, especially those in their teens and twenties, are more prone to tearing their ACL. This is often linked to higher participation in competitive sports and physically demanding activities.
• Gender – women are statistically more susceptible to ACL injuries compared to men. This may be due to differences in anatomy, hormone levels and muscle control. All this together can place more stress on the knee joint during activity.
• High-impact sports – activities that involve sudden stops, pivots and jumps, such as football, basketball, netball and skiing, place significant strain on the ACL. These quick directional changes can overload the ligament and cause it to rupture.
• Poor movement mechanics – weak core or leg muscles, as well as improper landing and pivoting techniques, can increase pressure on the ACL. The risk is especially relevant for athletes who repeat high-intensity movements.
• Previous knee injury – having sustained a prior ACL tear or knee injury increases the risk of reinjury. The ligament and surrounding tissues may be more vulnerable even after recovery.
• Playing surface – hard playing fields or artificial turf can reduce traction or cause the foot to stick. This forces the knee into unnatural movements that strain the ACL.
• Improper footwear – inappropriate footwear heightens the risk of ACL injury due to inadequate balance, stability and grip. These disadvantages subsequently add unnecessary strain on the ACL.

What are the complications of an ACL Tear if left untreated?

Delaying treatment can cause more than persistent pain and instability. Without proper care, an untreated ACL tear may lead to:

• Accelerated wear and tear of the joint
• Increases the risk of early-onset arthritis
• Recurrent knee instability, making it difficult to participate in sports or even daily activities
• Secondary injuries to the meniscus or cartilage

How is an ACL Tear diagnosed in Singapore?

An ACL tear is diagnosed through careful evaluation by an orthopaedic specialist. It involves several steps to determine the extent of the injury accurately and rule out other possible causes of knee pain.

It typically consists of:

• Medical history – the consultation begins with a discussion about how the injury occurred, whether a ‘popping’ sound was heard and what symptoms were experienced immediately after. Additionally, previous knee injuries or ongoing conditions are also reviewed.
• Physical examination – special tests such as the Lachman test and anterior drawer test are performed to check the stability of the knee. These manoeuvres help reveal whether the ligament has been stretched or torn.
• Imaging – X-rays are used to rule out fractures, while magnetic resonance imaging (MRI) scans provide detailed images of the ACL and surrounding structures. MRI is especially valuable in detecting associated injuries, such as meniscus or cartilage damage.

How is an ACL Tear treated in Singapore?

A torn ACL is not just a painful setback but also a destabilising injury that can interfere with walking, sports and even simple daily tasks. Because the ligament plays such a crucial role in stabilising the knee, treatment is carefully designed to restore strength, flexibility and long-term function.

The approach taken depends on the severity of the tear, the patient’s lifestyle and future activity goals. An orthopaedic specialist may recommend a standalone treatment or a combination of the following:

Conservative Management

For partial tears or individuals with lower activity demands, rest and modification of daily routines may be enough to relieve symptoms. This can include avoiding activities that strain the knee, using walking aids if needed and applying the RICE protocol, which stands for Rest, Ice, Compression, Elevation. It is often recommended to control swelling.

Non-Surgical Options

Medications such as non-steroidal anti-inflammatory drugs (NSAIDs) are commonly prescribed to ease pain and reduce inflammation. In certain cases, injections may be offered. Corticosteroid injections help alleviate swelling and discomfort, while biologic injections such as platelet-rich plasma (PRP) injections aim to support tissue healing and reduce inflammation.

Surgical Treatment

When the ligament is completely torn, especially in younger or athletic patients, surgery is often the recommended choice. Arthroscopic ACL reconstruction involves replacing the damaged ligament with a graft, either from the patient’s own tendon or from a donor. This procedure restores stability, enables them to return to sports and helps prevent long-term complications such as further meniscus injuries or early-onset arthritis.

Rehabilitation

Physiotherapy is an essential element of ACL tear treatment, regardless of whether surgery is performed. Early rehabilitation focuses on reducing swelling and regaining motion, while later stages involve strengthening the surrounding muscles and improving coordination. For surgical patients, a structured physiotherapy programme is necessary to safely return to sports and reduce the risk of reinjury.

How long does it take to recover from a Torn ACL?

Recovery from an ACL tear varies depending on the severity of the injury and the treatment chosen. For those managed conservatively, improvement may be seen over a few weeks to months, although complete stability may not always be achieved.

Meanwhile, patients who undergo ACL reconstruction surgery typically require a longer recovery period. Initial healing of the graft takes several weeks, but full rehabilitation can extend to nine months or more. In fact, athletes often need close to a year before safely returning to competitive sport.

Physiotherapy plays a central role throughout this process, guiding patients through each stage to ensure the knee regains strength, flexibility and stability.

Summary

An ACL tear can be life-altering if treatment is delayed, limiting not only athletic performance but also everyday movement and quality of life. The good news is that with timely diagnosis, the right treatment and structured rehabilitation, most people can regain function and return to the activities they enjoy.

If you suspect you may have sustained an ACL injury or continue to struggle with knee instability, we encourage you to seek a consultation with Dr James Tan. It is important to understand that early intervention can make all the difference in achieving a strong and lasting recovery.