ACL Tear: Partial vs. Complete - What’s the Difference?

Reviewed by the Physiotherapy Team at Waterloo Sports Medicine Centre  

An ACL tear can be classified as partial or complete, depending on how much of the ligament has been damaged. 

What Is the ACL? 

The anterior cruciate ligament (ACL) is one of the major ligaments inside the knee. It helps control forward movement and rotation of the shinbone relative to the thighbone and contributes to knee stability during activities such as running, jumping, and changing direction. 

An ACL injury occurs when the ligament is overstretched or torn. ACL injuries are common in sports such as soccer, basketball, volleyball, skiing, and football, but they can also occur during everyday activities or non-contact movements. 

Partial vs. Complete ACL Tear 

A partial ACL tear means that some of the ligament fibers remain intact. The amount of damage can vary considerably, and the knee may retain some stability depending on the extent of the injury.  Some people with partial ACL tears don’t need surgery and can successfully manage with structured physiotherapy and rehabilitation.

A complete ACL tear, sometimes called an ACL rupture, means the ligament has been torn through more extensively. This can result in greater knee instability, particularly during pivoting, cutting, or rapid changes of direction. However, a complete ACL tear does not automatically mean that surgery is required. Research suggests that non-operative rehabilitation can be an option for some people with isolated ACL injuries, depending on factors such as knee stability, activity demands, associated injuries, and individual goal.

What Are the Symptoms of an ACL Tear? 

• A popping sensation or sound at the time of injury 

• Sudden knee pain 

• Rapid swelling 

• Reduced knee range of motion 

• Difficulty putting weight on the leg 

• A feeling that the knee is unstable or “giving way” 

• Difficulty in running, jumping, or pivoting activities 

  
  

How Is an ACL Tear Diagnosed? 

A physiotherapist or physician will typically begin with a detailed history and physical examination. They may assess knee swelling, range of motion, strength, and stability using specific clinical tests.  An MRI may be used when additional information is needed to confirm the extent of the ACL injury or identify associated injuries. Your healthcare team can determine whether imaging or referral to an orthopedic specialist is appropriate. 

How Can Physiotherapy Help an ACL Tear? 

Whether you are managing an ACL tear without surgery or recovering post-surgery, physiotherapy is an important part of rehabilitation. Your physiotherapist may focus on: 

Restoring Knee Motion 

Early rehabilitation often focuses on reducing swelling and restoring the ability to fully straighten and bend the knee. 

Building Strength 

Progressive strengthening helps restore the muscles that support the knee, particularly the quadriceps and hamstrings. Exercises may include: 

• Squats 

• Lunges 

• Step-ups 

• Leg presses 

• Hamstring strengthening 

• Single-leg exercises 

• Progressive resistance training 

  
  

Improving Balance and Proprioception 

ACL injuries can affect your sense of knee position and control. Balance and neuromuscular exercises can help improve coordination and confidence during movement. 

Progressing Toward Sport or Activity 

Clinical guidelines emphasize progressive rehabilitation, strength development, functional progression, and objective criteria when determining readiness for higher-level activities

When Should You See a Physiotherapist? 

• Persistent knee pain or swelling after an injury 

• A feeling that your knee is giving way 

• Difficulty returning to sports or exercise 

• Reduced knee strength or mobility 

• Been diagnosed with a partial or complete ACL tear 

• Had ACL surgery and need rehabilitation 

Looking for Torn ACL Physiotherapy in Kitchener-Waterloo? 

At Waterloo Sports Medicine Centre, our physiotherapists provide evidence-based treatment for sports injuries and knee conditions, with rehabilitation tailored to your injury, activity level, and goals!