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Health, Knee pain

ACL Injury: Strengthening and Rehab Rules

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acl mechanismInjured your ACL? Strengthening and rehabilitating the right way after ACL injury means less arthritis, faster return to sport and a more stable knee – So why wouldn’t you?

First and foremost, an ACL injury needs to be confirmed and then you need to ask yourself: Do you really need surgery?

Most likely, you won’t need surgery unless you are a high-level athlete or want to return to pivoting and high demand sports – the above post explains this in more detail and will help explain your options.


Why does a knee need to be strengthened following ACL injury?

acl anatomuThe ACL is right in the middle of the knee and prevents the tibia sliding forward on the femur and prevents excessive rotation. It is one of the four main  ligaments in the knee that give passive stability

So, simply, if you have an ACL injury – you have less passive stability in the knee and need to make up for this. This is done by improving the active stabilizers – Your muscles.

This is the same whether you have done a partial or full rupture – If partial, you need to unload the ACL and support the knee while it is healing. If you have ruptured it, then you need to replace this loss with increased muscle supports.


Why hamstrings are your savior:

hamstrings action in protecting the aclTo better understand a few of the below rules of rehab, it is important to know about the role of the hamstrings. The ACL works to prevent your tibia (the shin bone) sliding forward, when landing, kicking, twisting etc. Luckily the hamstring also does a similar job – they travel down the


ACL Injury Rehab Rules:

1. Closed-chain before open-chain exercises

Why: First of all a quick explanation of open and closed chain exercises for those of you who don’t yet know:

open and closed chainOpen chain: Simply, your hand or foot is free to move in the air while doing open chain exercises – the chain is not continuous. Such as bench press, biceps curls, and hamstring curls.

Closed chain: This is when your hands or feet and planted, in constant contact with a surface. Such as a push-up, squat or leg press.

A study investigating the tensile forces placed on the ACL during a range of exercises found that there is significantly less force through the ACL during weight-bearing (closed chain) exercises when compared to open chain exercises – hence unloading the ACL and putting less forward pull on the tibia.

For example:

  • 0 Newtons of ACL loading during barbell squat, leg press, wall squat, front or side lunge (closed chain)
  • 59 Newtons of ACL loading during single leg squat (closed chain)
  • Seated knee extension (open chain): 396 newtons

The exception of this is seated knee flexion (hamstring curl) this is an open chain exercise but produces 0 ACL loading – this is because as discussed earlier, the hamstrings support the ACL by holding the tibia back in place.

It has also been shown that closed chain exercises recruit important stabilizing muscle groups of the hip which play a big part in knee alignment and proprioception.

hamstirngs squat2. Lean forward at the hips

Why: Because the hamstrings originate from your sitting bones (ischial tuberosities) at the back of your pelvis – If you tilt forward at the pelvis more as shown here it acts to lengthen out the hamstrings. Thus increasing hamstring tension. As we now know that the hamstrings are important in stabilizing an ACL deficient or injured knee – this is what we want! So don’t try to keep your body straight up and down (it is pretty hard to squat like that anyway). Actually, the optimal forward trunk tilt was shown to be 30 degrees as this increases hamstring muscle activity and force – Ideal!

Don’t stretch your hammies

3. Balance it out: Don’t stretch your hamstrings or idolize your quads

Why: Your quadriceps and hamstrings play a tug-of-war on the knee – the quads pulling the tibia forward (increasing ACL tension) and the hamstrings pull the tibia backward (decreasing ACL tension). You need to make sure there is a balance here by making sure your hamstrings stay tight and strong and when strengthening your quads – only do this in closed chain exercises in order to get co-activation of the hamstrings and hip stabilizers.

4. Keep your heels down

Squatting with your heels off the ground causes 3 times more ACL loading compared to squatting with your heels flat – so when possible (ie if you haven’t got incredibly tight calves) keep your heels flat on the ground. This is because having the heels raised up increases how far forward the knees go during a squat. As your knees go further forward the top of the tibia/ shin bone slopes down more – increasing the force on the ACL.

Note: This also applies to your shoes – If your wear shoes with big fat cushioned heels when working out – this can increase the shear force on your knee also.

5. Do not do resisted knee extensions

This is a pet hate of mine as it puts a huge amount of force through the the ACL and increases anterior tibial shear. The reason for this is because as an open chain exercise, it is working the quadriceps muscles in near-isolation, pulling the tibia forward and increasing ACL strain – Not what we want.

There are a lot of other exercises that would be far better to do such as leg presses, various forms of squats, lunges etc – these all have better co-contraction of knee stabilisers and importantly the hamstrings, leading to great ACL protection. When you are stronger and healing nicely it is important to do sports specific and functional rehab and so open chain exercises will be needed to have a strong knee – your Physio can progress you and guide you on to this as every knee is different.


For more specific information and data on ACL tensile forces during exercises, see this great paper by Escamilla et al.

Thanks for reading and good luck strengthening your knee!

Remember this is just a guideline to help your achieve your best and nothing is better than getting hands on input from your local Physio.

Health, Knee pain

ACL tear – Do you really need surgery?

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ACL tear non contact
When can I play again? Do I need surgery? These are the questions emotionally asked after anterior cruciate ligament injury. In this post i am going to answer these questions and more!

Torn your ACL and now wondering, do you really need surgery? The simple answer is: No – Only if you are a high level athlete, wish to return to pivoting/high demand sports OR have an unstable knee.

In this first post we will explore the difference in outcomes between surgery and conservative treatment and what that means for you: 

How do you know if you have an ACL tear?

If you heard a pop, snap or tear, the injury should be suspected as a ACL tear until proven otherwise. You may have felt something pop out or move  in the knee, this is sometimes confused for patella/knee cap dislocation but is most often an ACL tear.

You may or may not also feel clicking and locking which would indicate meniscal damage. Meniscal injury occurs in at least 40% of all meniscal tears(1).

Swelling will occur within an hour of injury, if swelling occurs a few hours later it points more towards meniscal tear.

But it is always best to get it thoroughly assessed by your local Sports Physiotherapist – It is not worth relying on Doctor Google or hoping it will go away!

Brief anatomy:

acl anatomuThe knee is formed by three bones, making up two joints. One joint is where the patella (knee cap) glides on the femur as you bend your knee. The other is formed by the tibia and the femur – This is the main joint that the ACL is in the middle of.

There are four main ligament that connect the femur and the tibia together and form this large hinge-like joint. These are the medial collateral(MCL), lateral collateral(LCL), anterior cruciate(ACL) and posterior cruciate(PCL) ligaments.

The ACL is right in the middle of the knee and prevents the tibia sliding forward on the femur and prevents excessive rotation.

Between the smooth articular surfaces of the tibia and femur and the menisci – the lateral and medial meniscus act as the shock absorber of the knee to prevent body injury, absorb shock and offer a smooth, rounded surface to move on.

Causes of ACL tear:

ACL injuries occur when the bones of the leg twist in opposite directions under full body weight, either during contact, or non-contact:

Non-contact ACL injury makes up about 70% of all ACL injuries, The two main mechanisms of non-contact injury are:

  • acl mechanismHigh impact jump-landing with a under-flexed (too straight) knee or valgus position (knee going laterally)







  • acl non contact 2Forceful rotation of the knee with the foot planted on the ground. This often happens when turning, side-stepping, pivoting etc.






acl tear contact

Contact ACL injuries:

The other 30% of ACL tears are due to contact and so are more random and due to a less preventable mechanism – There are often just plain unlucky.





Risk factors for ACL injury:

  • Poor sports specific conditioning
  • Muscle imbalance – The main one here is a low hamstrings-to-quadriceps strength ratio
  • Poor technique and awkward body movement
  • Poor neuromuscular coordination and balance

Risk factors that are hard to change:

  • Female gender
  • Joint laxity
  • Reduced ACL size and strength
  • Increased female sex hormones



In the USA alone, about 250 000 ACL injuries occur annually. This translates into a 1 in 3000 chance that a member of the general population will injure their ACL.(2)

And over half of these injuries are full ruptures of the ACL!

So that means an estimated 175 000 ACL reconstructions costing over US$2 billion each year.(3) That is a huge cost – especially if extrapolated world-wide! Unfortunately I can’t get a number on this but I’m sure you can appreciate that it is absolutely gargantuan.

This represents a huge financial cost for the health system AND for you with nearly half of ACL injuries undergoing surgery!

So imagine if it was found that there was no significant difference in outcome between surgery and conservative rehab?

Conservative rehab Vs Surgery – What are the outcomes? 

Re-Injury rate after reconstruction:

One of the big concerns following surgery is re-injuring the ACL or surrounding structures (e.g. meniscus or cartilage) upon returning to sport. This is because the re-injury rate IS HIGH – studies looking into this have found it can vary from 2.3% to 13%.(4) The reason for the reasonably large range here is because it does depend on the sport or activity that the player returns to.

The re-injury rate is in the higher spectrum if playing a pivoting sport. The re-injury rate is 12% when playing a pivoting sport such as rugby and football/soccer – This is an unacceptably high rate giving an almost 1 in 8 chance of re-injury!

Risk of Osteoarthritis:

Often patients are recommended surgery so that the risk of osteoarthritis (OA) is reduced, but this is simply not true.

The rate of return to sport, treatment method or how much loading the knee takes in the years after injury are not the main factors contributing to OA – The initial injury itself is the important factor contributing to OA. This is due to bleeding within and inflammation of the joint after injury that, although your symptoms resolve gradually (pain, limited range etc) and tears can be repaired surgically, trigger a remodeling process. This chronic remodeling triggered in the cartilage and other tissues in the joint leads to OA in the majority of cases.(7)

This results in roughly half of all ACL inured knees showing OA after 10 years and nearly 100% after 15-20 years.

Some studies have actually found that following re-construction there is more OA. Kessler et al 2008 found that although there was better knee stability after a re-con, there was significantly more OA when compared to conservative treatment (42% vs 25%).(6)

It is also worth mentioning that sports participation itself – without prior injury moderately increases the risk of hip or knee OA.

Conclusion: There is NO evidence to suggest that ACL repair prevents future arthritis.

So when is surgery called for?

People who SHOULD under-go reconstruction are those that:

  • Have on-going symptomatic instability, eg knee giving out
  • Are elite athletes


  • Wish to return to high-risk sports (pivoting sports)

The main reason for ACL reconstruction is to give an athlete a stable knee – So do not rush off to the surgeon if you do not have an unstable knee!

Follow this link for great information on:


Please Like, Share and Comment to let me know how you go and check out the below link to check your hip stability! Your hip controls the knee so this is very important!



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