An Anterior Cruciate Ligament sprain is one of the most common knee injuries. People who participate in high load sporting activities like soccer, rugby, hockey or sprinting are more likely to injure their ACL compared to the general population. The ACL is the strongest and most important ligament in the knee, yet tears of this ligament are quite common, traumatic and needs attention straight away.

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What does the ACL do?

ACL stands for anterior cruciate ligament. “Anterior” means situated at the front, “cruciate” means shaped like a cross and a “ligament” is a band of tissue connecting bones. It is one of the four ligaments in the knee that help stabilise your knee joint.

The ACL has two main functions: is mainly responsible to provide stability to the knee joint by preventing the shin bone (Tibia) to slide forward on the thigh bone (Femur), thus hyperextension, and also to stop excessive twisting. The ACL is approximately 2 cm long and as thick as a pencil which originates from the back of the Femur (inside the knee towards the back) and runs forward & downwards to insert on the front of the Tibia (inside, towards the front and just below the knee cap). Together with the posterior cruciate ligament, it forms an “X” inside the knee joint therefore preventing excessive movement.

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Causes of an ACL tear or sprain

Although Anterior Cruciate Ligament sprains are one of the most popular sports injuries, most ACL tears happen when there is no impact or contact with another player. It occurs mostly when you land from a jump and your knee twists. This pressure from your body weight and the angle of pull on the ligament pushes it beyond its normal limits.

For example, you play a rugby match and your teammate passes you the ball. The defender from the opposing team is approaching you from the front at speed and within milliseconds you have to decide in which direction you are going to turn to avoid a tackle. At the last moment you suddenly shift to the opposite side. Your foot is still stuck in the ground while your body already moves sideways and turns at an enormous speed. You hear a pop and immediately you feel pain in your knee. This is an example of a non-contact injury.

Non-contact injuries account for about 70% of all anterior cruciate ligament sprains. Twisting your knee or landing awkwardly from a jump are the prime mechanism of injuries. Hyperextending your knee (bending the knee the wrong way by more than 10 degrees causing it to gap at the back) and Sudden deceleration: coming to an abrupt stop whilst the foot is firmly planted, are also causing factors in the event of a sprain.

Contact Injuries account for about 30% of ACL injuries. Usually a blow to the side of the knee when the foot is firmly planted to the ground e.g. with studs or spikes which forces the shin bone too far inwards or backwards.

Women are more vulnerable to get Knee Ligament injuries
Women are 3 times more likely to suffer from an Anterior Cruciate Ligament knee injury. This is thought to be due to a combination of factors including hormone levels, ligament structure, pelvis angle, hamstring flexibility and size of the ligament itself.

ACL injury,

What happens to the ACL on a cellular level

A ligament sprain is a form of overstretching of the ligament. There are several classifications for ligament sprains depending on the severity (Degree or Grade 1, 2 or 3). The fibrous band is like a pulley, which prevents the joint moving into extreme ranges. But when the force is too big for the ligament to resist, the fibers will tear. Over stretching the Anterior Cruciate ligament will result in tears & a sprain of your ligament. It is very important to know and understand the difference and implications thereof. In the case of a tear, you may hear a snap or tearing sound.

The collagen fibers tear like a tension cable when overloaded, the fibers unravel. On a cellular level, injury will cause a split along the sheath of the ligament (a membrane that gives the ligament its nutrients – disruption of normal sustenance). In turn, inflammation causes swelling, pain and loss of function of the ligament, leaving the knee to buckle forwards. The swelling along the sheath contributes to loss of space around the ligament that restricts the normal slide of the ligament. Mucoid degeneration and fibrinoid necrosis indicate ligament tears (a type of cell death).

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How bad is it?

Grade 1 ACL sprain (mild)

Small amount of fibers torn, some discomfort and pain. The ligament only has a slight stretch. No swelling or much pain, but you may run into troubles if the cycle repeats itself again. Recurrence of micro tears in the ligament could lead to more severe tears. You will have no loss of function or range of movement of your knee, but may be painful at some point during the movement. You will be able to continue playing.

Symptoms of a grade 1 Sprain

  • Light stretch, no tear
  • About 5/10 pain on the VAS scale
  • Slightly swelling
  • Mild tenderness over the area
  • No instability/giving way of the knee
  • No discolouration
  • Pain at end of range (at the end of straightening or bending your knee)

Medical treatment
You will need to consult with a Physio to establish the extent of damage and accurate diagnosis. Physio treatment of a Gr 1 ACL sprain is very successful.

What you should do during this time

  • Rest from any activity that causes your pain
  • Ice your knee

Recovery Time
Grade 1 – 2 to 4 weeks. An ACL sprain heals within a few weeks (anything between 2-4 weeks). However, the collagen fibers only align after 6 weeks (maximal ligament strength), so it is advisable to not return to sport too soon.

Grade II ACL Sprain (moderate)

Partial tear with some swelling and bruising. Pain level increases quite a bit from a grade I, and moving the knee will not occur without pain. It may feel uncomfortable to bend or straighten the knee and your knee may feel unstable and like it wants to “give way”.

20% to 80% of the fibers torn. You will not be able to put weight through the leg. Even if you try to continue playing, you will have considerable amount of pain and limping. The pain will not allow you to straighten your knee or lift your leg forward (knee to chest).

Grade II ACL sprain symptoms

  • 80% of the ligament fibers tear
  • Swelling common
  • Bruising (discolouration)
  • Intense pain
  • Difficulty bending or straightening (flexing and extending) the knee
  • Difficulty rotating (twisting your knee)
  • Feeling of instability (giving way) when full weight bearing on injured side
  • Fearful balancing on one leg
  • You won’t be able to climb stairs
  • Pain through range- hyperextending, going down on your haunches.

Medical treatment
Contact us A.S.A.P. The faster we have a look at it before the swelling and bleeding sets in, the better. You have to consult with a Physio to establish the extent of damage and determine the most appropriate course of action. We can successfully restore your ligament without any surgical intervention.

  • Use a  weight-bearing brace or supportive strapping. This aids in avoiding overuse of the ligament and puts some pressure on the ligament to ease the pain.
  • Physiotherapy management during this grade is the same as a grade I, although progression will be slightly slower.
  • Comprehensive rehabilitation program addressing all the stages of recovery
  • Expect return to activity to be no sooner than 6 weeks.

Recovery Time
Grade 2 – 6 to 8 weeks (With early treatment, we try to get you jogging at 6 weeks)

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Grade III ACL sprain (severe)

Complete tear. Swelling and discolouration (bleeding under the skin) is visible. The knee feels like it wants to give way completely. Bearing full weight is nearly impossible. Bleeding and swelling will definitely be present.

The main concern with a Gr 3 tear, is the ligament’s ability to stabilize the knee joint,  if the ligament tears into two separate flaps, there is no way the ligament can ‘heal’ or reattach without surgery. A Sonar or Diagnostic Ultrasound will show the full extent of the damage. Surgery is the best option to reconnect the separated segments of the torn muscle.

Often there will be no pain, but the disfigurement is quite obvious, since all the fibers are torn. It is important to know that there could be other structures involved with such an injury, but we will discuss this in more detail with our differential diagnosis later.

Grade III ACL sprain symptoms

  • Complete ligament rupture
  • Swelling
  • Bleeding under skin (red and blue discolouration)
  • Unstable joint
  • Can’t bear full weight on affected side- 1 leg standing
  • Feeling of knee wanting to give way
  • Either no pain, or severe pain that subsides quickly
  • This injury usually increase the risk of other structures getting injured as well
  • Laxity and giving way forward with no resistance in the knee (buckling)
  • Climbing downstairs will be agonizing

Most ACL tears are complete, as a partial tear is quite unlikely and rarely happens.

Medical treatment
Contact us immediately! The faster we have a look at it before the swelling and bleeding sets in, the better.
You have to consult with a Physio to establish the extent of damage and determine the most appropriate course of action.

What you should do during this time:

  • You will be on crutches for up to 6 weeks, during which you will wear a hinged brace
  • It is essential to see your physiotherapist for full rehabilitation of the knee, as it will become a very unstable joint if left with no treatment.

Recovery Time
Will depend on conservative or surgery treatment option. Conservative may be more than 8 weeks with intensive rehab.

If you have completely ruptured your medial collateral ligament, surgery is indicated and may take 4 – 6 months to full recovery.

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Test your Anterior Cruciate Ligament

Stand on one leg

  • Do a small squat (bend the knee slowly)
  • You will either feel pain at the front of your knee, or you won’t want to stand on one leg, depending on the severity of your sprain
  • With a complete rupture, you won’t be able to put weight on your affected knee alone without it completely feeling like it wants to give way.


  • Stand on a step
  • Step down with the affected leg staying on the step
  • Your knee will feel like it wants to give way forwards and down
  • Pain inside the knee joint is an indication of a sprain during these tests


  • Stand on your affected leg
  • Bend it slightly
  • Twist your body towards your knee
  • Then twist your body away from the knee
  • Again, your knee would want to give way forwards with a sprain (buckle)

Extension test

  • Stand with your affected leg on a small step
  • Draw your toes up, so only your heel is touching the step
  • Let your knee straighten as much as it can
  • Pulse your knee
  • If there is a sprain it would feel like there is too much flexibility backwards

Forward translation of the knee (Anterior drawer test)

When you sit on a chair where your knee is facing directly forward, bent at a 90 degree angle. Relax your leg in this position. You can even put your foot on a little step. Place both your thumbs at the back of your knee (over your calf muscles) and hold your shin bone with your remaining fingers. Gently and slowly slide your Tibia (Shin bone) forward. If you feel that same pain, then you may have sprained your Anterior cruciate ligament. If there is no resistance and your tibia just slides off without the movement being stopped, your may have completely ruptured the ACL. It’s important to note that a complete rupture of the ACL is much less painful than a sprain.

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Physical Examination

Physiotherapists will be able to accurately diagnose an ACL tear and diagnose other injured structures even without any expensive scans. We will perform these tests during your assessment with the physiotherapist. There are mainly three tests we use to determine an ACL sprain, such as: Lachman Test, Anterior Drawer Test, Pivot Shift test.


X-rays can be helpful to exclude fractures of the patella, Femur, Tibia or Fibula, but will not show a ACL ligament tear. This is usually the test most emergency rooms opt for, when there are no fractures diagnosed, they conclude that the ‘knee ligaments’ are torn, it still doesn’t tell us much. Get to your physio, so they can test each ligament individually to get a more conclusive diagnosis.

However, children have softer bone. The anchor of the ligament tears away from the bone easier, resulting in an avulsion fracture, visible on x-ray. It’s essential to make sure there no fractures if we suspect an ACL injury in a child before proceeding with further tests.


The golden standard (best in the industry) to diagnose an ACL tear would be via MRI, then CT scan. MRI has the advantage of providing a clear image of all the anatomic structures of the knee. An MRI can diagnose ACL injuries with an accuracy of 95%. It will also reveal any related meniscal tears, chondral injuries, or bone bruises. However, it is a very expensive test. An orthopedic surgeon will perform this test.

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If you have limited funds, but you would like to confirm it with a scan, we will advise you to take a sonar or Diagnostic Ultrasound at a reputable Musculoskeletal Sonographer. In this case, the ACL itself won’t be visible on the scan, but the trauma in the structures around the ACL will lead us to assume an injury to the ACL, after which we may refer for further testing to confirm, such as MRI or CT scans.

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ACL Surgery

Only Grade 3 ligament tears, where there is complete rupture of the ligament, the torn sections aren’t unable to re-attach by itself. Surgery is your best option, Arthroscopy is the way to go due to its minimal invasive technique. An ACL can’t be sutured back together, so the surgeon uses a technique called tissue graft. They harvest the hamstrings or the adductors to create an artificial tendon attached to the femur, which is like a scaffolding for the ligament to grow on. This allows the body’s natural form of healing to take place. In the case of a complete ACL rupture, there are usually other structures involved, like the medial meniscus, thus an arthroscopic procedure allows the surgeon to investigate and repair these structures at the same time.

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ACL injury

Problems we see with the ACL

Getting back to sport too soon: Not going through with the whole rehabilitation process can be detrimental to your ACL. If you load it too much, too soon, the ligament will not be able to withstand the forces being put on it and could sustain a re-rupture, which starts the whole process right from the beginning, this time with even more scar tissue to begin with. This can become a recurrent problem and weakens the ligament to the extent of your knee being completely unstable.

Generic braces: Only allows compression but doesn’t restrict certain ranges which is needed to protect the ACL. It merely provides a false sense of stability of the knee, even though the ligament might be severely injured.

Waiting too long to come for physio due to the false sense of support the swelling provides. Swelling makes it more difficult to assess and diagnose the knee completely. (See excerpt of swelling in the knee at general knee ligament injuries)

Not attending to your injury apart from physiotherapy: Your physiotherapist will give you a home program you need to tend to. We only see you an hour maybe twice a week. The rest of the time, it is your responsibility to do what is needed in order for complete healing to occur.

It’s safer to know the extent of the damage and to be able to do something about it rather than assuming “my knee feels fine”.

What makes it worse?

  • Climbing down stairs
  • Squats
  • Jumping lunges
  • Downhill running
  • Getting out of the car
  • Kicking
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Physio treatment for a ACL tear- rehabilitation and goals

Grade 1 Anterior Cruciate Ligament sprain:

Phase 1 (Week 1)


  • Reduce swelling
  • Get the knee to fully extend (straighten)
  • To get the knee flexed (bent) more than 90 degrees
  • Start pain free strengthening exercises


  • Pain free Passive stretches of the quads and hamstring muscles
  • Static quad and hamstring strengthening exercises
  • Isometric quad, hamstring, glute and calf exercises.
  • Examples: calf raises, quads contractions on pillow, theraband resistance exercises- but come see us for a more specific exercise protocol and put us to the test!
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Phase 2 (Week 1-2)


  • Get rid of swelling completely
  • Restore full range of motion (ROM)
  • Start jogging


  • Dynamic strengthening exercises introduced here
  • Examples: knee flexions, extensions, step ups, half squats, single leg calf raises, bridging exercises

Phase 3 (Week 2-4)


  • Regain full strength
  • Maintain Full ROM
  • Introduce sport specific exercises/ exercises that allow you to get back to your daily activities completely like driving, climbing stairs and running


  • Adding more load/weight to activities
  • Increasing the speed and agility of movements
  • Examples: weighted squats, leg presses, plyometrics, sideways running drills, cycling stationary bike
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Phase 4 (Week 3-6)


  • Maintaining full ROM, strength, agility, speed
  • Adding endurance
  • Performance based when dealing with a sports person (full time training and competition based)


  • Finally hopping, bouncing or jumping activities can be included here

Grade 2 or 3 Anterior Cruciate Ligament tear:

Phase 1 (Week 1 – 4)


  • Control swelling
  • Maintain full extension of knee
  • Gain range to more than 90 degrees flexion
  • Introduce strengthening exercises
  • Maintain fitness (best suggestion would be a stationary bike).


  • Non weight bearing week 1-2 (use crutches)
  • Partial weight bearing week 3-4
  • Full weight bearing week 4 onwards
  • Wear a brace that is set at 30 degrees
  • Stretching, strengthening and mobility exercises in the brace (knee extension should not be more than 30 degrees)
  • Examples of exercises: static quads, hamstrings, calf raises, hip abductions
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Phase 2 (Week 4 – 6)


  • Completely eliminate swelling
  • Full weight bearing
  • Full ROM
  • Injured leg as strong as uninjured leg


  • Week 5: Knee brace set to 60 degrees
  • Week 6: Remove knee brace (other knee support can help at this time for compression, for example a knee guard, only to support knee during this transition phase for a week, no longer than that because we don’t want the knee to become dependent on external support)
  • Examples of exercises: Quads and hamstring stretches, along with static and isometric quad exercises: leg presses, hamstring curls, step ups, calf raises. Upper body strength and endurance should remain and general fitness kept by swimming or stationary bike. No breaststroke though!

Phase 3 (Week 6 – 10)- post surgery


  • Full ROM
  • Strength
  • Light jogging
  • Sport specific exercises at week 10
  • Full activities of daily living (walking, driving, getting in and out of bed without pain)


  • Light jogging after week 6
  • Sideways running after week 8
  • Plyometrics, hopping, jumping, agility, speed by week 10. We need to challenge the knee here and get you into full sport function, at the same or even better level than you were before. A good test here would be for you to do a burpee or jumping squat until fatigued.
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Phase 4 (Week 3-6)


  • Maintaining full ROM, strength, agility, speed
  • Adding endurance
  • Performance based when dealing with a sports person (full time training and competition based)


  • Finally hopping, bouncing or jumping activities can be included here
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Other Causes of Pain in the front of the knee

  • Knee or patellar dislocations- weakness and laxity of your knee joint
  • Meniscal injuries– catching during twisting of your knee
  • Collateral ligaments injury– pain mostly inside or outside of the knee rather than front (inside or outside ligaments)
  • Posterolateral corner of the knee- pain more behind the knee
  • Patellar dislocation or fracture- pain on full weight bearing and inability to walk
  • Femoral, tibial or fibular fractures– deep pain that throbs even when not walking on that leg
  • Bursitis– pain just below or above your kneecap, an irritated and swollen fluid filled sack.
  • Fat pad impingement– pinching of adipose tissue
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