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Anterior Cruciate Ligament (ACL) injury

ACL sprain or rupture happens to the large thick ligament in the centre of the knee. It commonly happens in contact sports when the foot is planted and the body rotates under force causing a twisting of the knee.


The ACL is a thick ligament inside the knee that joins the thigh bone (femur) to the shin bone (tibia). ACL injuries occur when the knee is twisted suddenly, think of a skier who has an accident which causes one of their skis to turn in one direction and the body turns the opposite way. This twisting puts high levels of stress on the ACL as it tries to keep the knee together.


There are different levels of ligament injuries

  • Grade 1 is an over-stretch of the ligament which will leave small tears to some of the fibres.
  • Grade 2 is a partial tear. Somewhere along the ligament, there will be a significant tear to the ligament but it will still be attached
  • Grade 3 is a complete tear through the centre of the ligament. There is also something called an avulsion where the ligament is intact but has been pulled from the bone.


For grades one and two this is often the most painful. For people who experience a sudden sharp pain in the knee with some swelling that builds up over the next 24hr period.


For a grade 3, referred to as a ruptured ACL or ACL tear, you may hear a “pop” in the knee with a short pain. As the ligament has torn you will experience immediate swelling, the knee feeling unstable and painful when you take weight through it.


Depending on the severity you may require surgery to repair the ligament

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Symptoms of an ACL sprain or rupture

You experience a sharp shooting pain inside the knee when you try to take weight through the leg.

The initial injury will feel sharp and sudden, sometimes accompanied by a “pop” depending on the severity of the injury. you will also experience;

  • Rapid and immediate swelling in the knee
  • Reduced range of movement in the knee
  • Feeling unstable or giving way, especially going up and down stairs.
  • Over time it will change to a constant ache throughout the knee with intermitted sharp pain with certain movements


Causes of an ACL sprain or rupture

  • Suddenly slowing down with a change of direction
  • Twisting your torso and your foot remains planted on the ground
  • Landing awkwardly from a fall or jumping
  • A direct blow to the knee such as a contact sport like rugby or American football.


Management of an ACL sprain or rupture

Grade 1 & 2 sprain. 

This is an injury to the ACL where the ligament is still intact. The management is designed to reduce pain and swelling as well as provide adequate support to enable you to strengthen the surrounding muscles.

  • Ice can help to reduce pain and swelling. Apply ice to the knee for 20-30 minutes every 4 hours for the first two days. After the two days apply ice as often as you require to manage the pain and symptoms
  • Knee supports can provide a level of stability to the knee to prevent further injury. There are a number of braces available so it is important that you choose the right one. ACL supportive braces will have large metal or plastic scaffolding that surrounds the knee, held in place by straps and often with an adjustable hinge to limit movement.
  • A strengthening program is essential for low and medium-grade ligament sprains to help prevent any further injury and to strengthen the surrounding muscles in the knee. There are a series of exercises in the next section that can help you start your rehabilitation but it is important to pace yourself and do this under the guidance of a medical or health professional.


Grade 3 (ACL rupture)

  • Pre-surgical strength program. In the majority of cases, but not all, an ACL rupture will require surgery in order to repair the ligament. Prior to the surgery, it is important to maintain a good level of strength and conditioning as this will improve your rehabilitation post-op. The pre-surgical program should focus on all aspects of lower limb strength, but remember to be careful as there is reduced stability to the injured knee.
  • Surgery. If the decision is made to operate on the ACL this will involve taking a small amount of tendon from a part of the body, often the hamstring, and using that to graft the ACL back into place reattaching it where it has torn.
  • Rehabilitation. Immediately after surgery you will be placed into a brace and use crutches to move around. Once it has been removed you will need to follow a structured rehabilitation strength program with exercises like the ones in the next section. These are designed to improve your range of movement, strength & stability of the joins and your neuromuscular control.




Exercises for the rehabilitation of an ACL sprain or rupture.

These exercises are designed to be used for Grade 1 & 2 ligament sprains where the ligament is still intact or after the brace has been removed for any ACL reconstruction surgery.

Single-Leg Standing

This exercise helps with neuromuscular control by strengthening the small intrinsic muscles that help with balance, joint stability and movement feedback to the brain.

  • Place a folded towel or pillow on the floor.
  • Stand with one foot on the object.
  • Lift one foot off the ground keeping your hands by your side and a slight bend in the knee.

Frequency and duration 

  • Stand for 30 seconds for each leg
  • Complete this frequently throughout the day or for a more structured approach, 3 sets of 30 seconds on each leg 4 times a day.


  • Easier - Do this on a hard floor
  • Harder - close your eyes

Heel Slides

This exercise is designed to work on hamstring strength in a controlled environment as well as working on your knee bend.

  • Lie on your back on the ground.
  • Place a tea towel, plastic bag or sheet of paper under your foot.
  • Slide your heel towards your bum making sure to keep contact with the ground throughout the movement.
  • Slide your foot back out.

Frequency and duration 

  • Slide your foot in for a count of 2 seconds
  • Hold for 1 second.
  • Slide your foot out for a count of 2 seconds.


  • Easier - do this seated on a chair

Quads Contraction

This exercise targets the small quad muscle on the inside of the knee that controls the last 10 degrees of extension and helps stabilise the knee.

  • Lie on the ground with a rolled-up towel or foam roller under your mid-thigh causing a bend in your knee.
  • Contract the quads lifting the foot off the ground.
  • Hold at the top then lower the foot back to the floor.

Frequency and duration

  • Raise for a count of 1 second.
  • hold for a count of 3 seconds.
  • lower for a count of 1 second.
  • 3x sets of 15 each leg.


  • Easier - remove the towel and just press the knee into the ground.
  • Harder - add weight around the ankle

Straight Leg Raise

This exercise strengthens muscles in your quadriceps and your hip flexors as a collective group.

  • Lie on the ground on your back.
  • Pull your foot towards you & engage your quads.
  • Push your lower back into the ground, and engage your core and trunk muscles.
  • Lift your leg off the ground as far as you can without arching your lower back.
  • slowly lower your leg back down.

Frequency and duration 

  • Raise for a count of 3 seconds.
  • Hold for a count of 2 seconds.
  • Lower for a count of 2 seconds.
  • 3x sets of 12 on each leg.


  • Easier - bend the knee on the resting leg planting the foot on the ground.

Hamstring Curl

This exercise is designed to strengthen the hamstring muscles on the back of the thigh.

  • Stand on one leg with one foot behind you.
  • You can lean on a pole or wall for stability.
  • Raise your heel to your bum making sure to keep your knees aligned.
  • Lower your foot back down until your toes are touching the ground.

Frequency and duration

  • Raise for a count of 2 seconds.
  • hold for 1 second.
  • lower your foot for a count of 2 seconds.
  • 3x sets of 12 on each leg.


  • Easier - reduce the height you lift your foot off the ground.
  • Harder - add weight to the ankle.

Half Squat

This exercise works all the muscles of the lower body and trunk together as well as taking weight through the knees.

  • Stand with your feet shoulder-width apart.
  • Bend at the hips and at the knees.
  • Lower yourself down in the sitting position.
  • Stop before your knees reach 90 degrees.
  • Return to the standing position.

Frequency and duration

  • Lower for a count of 3 seconds.
  • Hold for 1 second.
  • Return to standing for a count of 2 seconds.
  • 3 sets of 12 squats.


  • Easier - hold on to the back of a chair
  • Harder - hold a weight

The information on this site is intended for educational purposes.

You must not rely on the information on this website as an alternative to medical advice from your doctor or other professional healthcare provider. If you have any specific questions about any medical matter you should consult your doctor or other professional healthcare provider. If you think you may be suffering from any medical condition you should seek immediate medical attention. You should never delay seeking medical advice, disregard medical advice, or discontinue medical treatment because of information on this website.

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