ACL - Anterior Cruciate Ligament Injury

Article by J.Miller, Z.Russell

What Is An ACL Injury?

ACL or anterior cruciate ligament is one of four knee ligaments that are critical to the stability of your knee joint. Your ACL is made of sturdy fibrous material and functions to control excessive knee motion by limiting joint mobility.

One of the most common knee joint problems is an anterior cruciate ligament injury or ACL tear. Of the four major knee ligaments of the knee, an ACL injury or rupture is the most debilitating knee ligament injury.

What Causes an ACL Injury?

ACL injury

An ACL injury is usually a sports-related knee injury. About 80% of sports-related ACL tears are “non-contact” injuries. Non-contact means that the damage occurs without the contact of another player, such as a tackle in football.

Most often, ACL tears occur when pivoting or landing from a jump. Your knee gives out from under you once you tear your ACL.

Female athletes are known to have a higher risk of an ACL tear while participating in competitive sports. Unfortunately, understanding why women are more prone to ACL injury is unclear. There are some suggestions it is biomechanical, strength and hormonally related. In truth, it is probably a factor of all three.

What Sports Have A High Incidence Of ACL Injuries?

Many sports require a functioning ACL to perform joint manoeuvres such as cutting, pivoting, and sudden turns.

These high demand sports include football, rugby, netball, touch, basketball, tennis, volleyball, hockey, dance, gymnastics and much more. You may be able to function in your normal daily activities without an intact standard ACL, but these high-demand sports may prove difficult.

Therefore, athletes contemplate the decision to undergo surgery to return to their previous level of competition. ACL injuries can curtail many promising sporting careers.

What are the Symptoms of an ACL Injury?

Several methods make the diagnosis of an ACL tear. Patients who have an ACL tear commonly sustain a sports-related knee injury.

They may have felt or heard a “pop” in their knee, and the knee usually gives out from under them. ACL tears cause significant knee swelling and pain.

How is an ACL Injury Diagnosed?

On clinical knee examination, your physiotherapist or sports doctor will look for signs of ACL ligament instability. These special ACL tests place stress on the anterior cruciate ligament and detect an ACL tear or rupture.

An MRI may also be used to determine if you have an ACL tear. It will also look for signs of any knee-associated injuries, such as bone bruising or meniscus damage, that regularly occur in combination with an ACL tear.

X-rays are of little clinical value in diagnosing an ACL tear.

For more information, please ask the advice of your knee surgeon or sports and exercise physiotherapist.

ACL Injury Treatment

Many patients with an ACL tear start to feel better within a few days or weeks of an ACL injury. These individuals may feel as though their knee is healthy again because their swelling has started to settle. However, this is when your problems with knee instability and giving way may start or worsen.

ACL tears do not necessarily require ACL reconstruction surgery. There are several important factors to consider before deciding to undergo ACL reconstruction surgery.

  • Your age?
  • Do you regularly perform sports or activities that generally require a functional ACL?
  • Do you experience knee instability?
  • What are your plans for the future?

If you don’t participate in a multi-directional sport requiring a patent ACL and don’t have an unstable knee, you may not need ACL surgery.

Physiotherapy & ACL Exercises

Your best way to avoid ACL reconstructive surgery is to undertake a comprehensive ACL-Deficient Knee Rehabilitation Program. This comprehensive exercise-based program involves leg strengthening, proprioception and high-level balance retraining, plus sport-specific agility and functional enhancement. Your sports physiotherapist is an expert in the prescription of ACL tear exercises.

PhysioWorks has developed a specific ACL Deficient Knee Rehabilitation Program to address ACL injuries for patients who wish to avoid or delay ACL reconstructive surgery.

Your physiotherapy treatment will aim to:

  • Reduce pain and inflammation.
  • Normalise your joint range of motion.
  • Strengthen your knee: esp Quadriceps (esp VMO) and Hamstrings.
  • Strengthen your lower limb: Calves, Hip and Pelvis muscles.
  • Improve patellofemoral (kneecap) alignment
  • Normalise your muscle lengths
  • Improve your proprioception, agility and balance
  • Improve your technique and function, e.g. walking, running, squatting, hopping and landing.
  • Minimise your chance of re-injury.

We strongly suggest discussing your knee injury after a thorough examination from a knee injury clinician such as a sports physiotherapist, sports physician or knee surgeon.

Non-Operative vs ACL Reconstruction

For more information, please read this article: ACL Reconstruction vs Exercise Management.

How to Prevent an ACL Injury?

Recent research has focused on preventing an ACL tear, especially preventing ACL tears in female athletes. Numerous theories propose to explain why people may tear their ACL and how they can avoid it.

Current investigations have focused on neuromuscular training to prevent ACL tears. We know that ACL reconstruction patients who undertake extensive post-operative physiotherapy rehabilitate exceptionally well. The question remains. If you conduct similar ACL exercises, can they prevent an ACL tear in the first place? For more advice, please consult with your sports physiotherapist.

ACL Surgery

Surgery for an ACL tear is called an ACL reconstruction. A repair of the anterior cruciate ligament is rarely a possibility, and thus the ACL is reconstructed using another tendon or ligament to substitute for the torn ligament. There are several options for how to perform ACL surgery.

The most important choice is the type of graft used to reconstruct the torn ACL. There are also variations in the procedure, such as the new ‘double-bundle ACL reconstruction.

Risks of ACL surgery include:

  • infection,
  • persistent instability and pain
  • knee stiffness, and
  • difficulty returning to your previous level of activity.

The good news is that better than 90% of patients have no complications with ACL surgery.

Post-Surgical ACL Rehabilitation

Post-operative ACL rehabilitation is one of the most important, yet too often neglected, aspects of ACL reconstruction surgery. The most successful and quickest outcomes result from the guidance and supervision of an experienced Sports Physiotherapist.

Your rehabilitation following ACL surgery focuses on restoring full knee motion, strength, power and endurance. You’ll also require balance, proprioception and agility retraining individualised towards your specific sporting or functional needs.

Your sports physiotherapist is an expert in this field. We suggest that you contact them for the best advice in your circumstances.

ACL Injuries in Children

ACL reconstruction surgery is the standard treatment for young, active people who sustain an ACL tear. But what happens when you’re young and your bones are still growing?

Should ACL surgery be delayed until the child is older, or should ACL reconstruction occur before skeletal maturity? In this scenario, additional surgery may take place at skeletal maturity.

The concern of performing ACL surgery in children is the risk of causing a growth disturbance in growing children. As a result of ACL surgery, growth plate problems could lead to early growth plate closure or alignment deformities.

However, recent research shows that the risk of growth plate problems and meniscal damage is potentially less than the risk of permanent knee damage if a surgically repaired ACL.

Your knee surgeon is the best person to discuss whether ACL reconstruction is advisable or not.

Return to Sports with an ACL Injury

Athletes often have difficulty returning to their sport once they have sustained an ACL injury, even if they undergo surgical reconstruction.

Researchers have found that your best chance of returning to your sports post-ACL tear is to have undertaken both:

  • ACL reconstruction surgery, and intensive post-operative physiotherapy rehabilitation, or
  • No Surgical ACL Physiotherapy

For more information, please ask the advice of your knee surgeon or knee physiotherapist, who is up to date with the latest in the pros and cons of both ACL treatment approaches.

Common Causes - Knee Pain

Knee pain can have many origins from local injury, referred pain, biomechanical issues and systemic issues. While knee pain can appear simple to the untrained eye, a thorough assessment is often required to ascertain the origin of your symptoms. The good news is that once a definitive diagnosis is determined, most knee pain quickly resolves with the correct treatment and rehabilitation.

Knee Ligament Injuries

Knee Meniscus Injuries

Kneecap Pain

Knee Arthritis

Knee Tendon Injuries

Muscle Injuries

Knee Bursitis

Children’s Knee Conditions

Other Knee-Related Conditions

Knee Surgery

Knee FAQs

For specific information regarding your knee pain, please seek the assistance of a healthcare professional with a particular interest in knee condition, such as your knee physiotherapist.

Acute Injury Signs

Acute Injury Management.

Here are some warning signs that you have an injury. While some injuries are immediately evident, others can creep up slowly and progressively get worse. If you don't pay attention to both types of injuries, chronic problems can develop.

For detailed information on specific injuries, check out the injury by body part section.

Don't Ignore these Injury Warning Signs

Joint Pain

Joint pain, particularly in the knee, ankle, elbow, and wrist joints, should never be ignored. Because these joints are not covered by muscle, pain here is rarely of muscular origin. Joint pain that lasts more than 48 hours requires a professional diagnosis.


If you can elicit pain at a specific point in a bone, muscle, or joint, you may have a significant injury by pressing your finger into it. If the same spot on the other side of the body does not produce the same pain, you should probably see your health professional.  


Nearly all sports or musculoskeletal injuries cause swelling. Swelling is usually quite obvious and can be seen, but occasionally you may feel as though something is swollen or "full" even though it looks normal. Swelling usually goes along with pain, redness and heat.

Reduced Range of Motion

If the swelling isn't obvious, you can usually find it by checking for a reduced range of motion in a joint. If there is significant swelling within a joint, you will lose range of motion. Compare one side of the body with the other to identify major differences. If there are any, you probably have an injury that needs attention.


Compare sides for weakness by performing the same task. One way to tell is to lift the same weight with the right and left sides and look at the result. Or try to place body weight on one leg and then the other. A difference in your ability to support your weight is another suggestion of an injury that requires attention.

Immediate Injury Treatment: Step-by-Step Guidelines

  • Stop the activity immediately.
  • Wrap the injured part in a compression bandage.
  • Apply ice to the injured part (use a bag of crushed ice or a bag of frozen vegetables).
  • Elevate the injured part to reduce swelling.
  • Consult your health practitioner for a proper diagnosis of any serious injury.
  • Rehabilitate your injury under professional guidance.
  • Seek a second opinion if you are not improving.