Epidemiology of ACL tears

In Singapore, there has been a rise in the number of people being involved in sports over recent years. This has also led to an increase in the incidence of knee injuries.

One of the most common knee injuries is ACL (Anterior Cruciate Ligament) tear, which accounts for more than 50% of sporting knee injuries. In the sporting population, most choose to have their ACL tears surgically managed. This is because ACL tears can lead to instability of the knee with reduced balance capabilities.


Importance of ACL rehabilitation after ACL reconstruction

The length of ACL rehabilitation after a reconstruction surgery is typically 6 to 9 months. Rehabilitation is important, as there will be muscle weakness, knee instability, and reduced balance post-surgery. Moreover, the risk of having a second ACL injury can be 15 times greater during the 1st 12 months after an ACL reconstruction. This has been observed especially in people who return to sporting activities prematurely.

Thus, it is important that you have a structured rehabilitation programme done with a qualified physiotherapist to address these issues.

physiotherapist adjust knee braces on patient


Components of an ACL rehabilitation programme

In the past, ACL rehabilitation protocols were time-based. However, with more research done over the years, ACL rehabilitation protocols have evolved to be more goal-oriented instead. This allows the rehabilitation process to be more patient-centered. Your rehabilitation will be done with the guidance of a physiotherapist, to guide you with each step along the way, looking out for you as you achieve each milestone to progress your rehabilitation safely.

There are typically 4 phases to an ACL rehabilitation programme. Each phase contains a set of milestones to achieve, before moving onto the next phase. This ensures that you can do your rehabilitation in a safe manner that does not put the reconstructed graft under any strain during this crucial period.

During the 1st phase of your rehabilitation, we will focus on getting you to be able to walk with a normal pattern, reduce your swelling, and improve your knee mobility.

In the 2nd phase, we will focus on improving your knee mobility further; achieve better muscle strength, better control of the knee, and attaining a good balance. Running will typically be done in the 3rd phase of ACL rehabilitation after you have achieved certain milestones.

patient running on a treadmill


What are the milestones to be achieved before you start running?

Clinical test
  • Goals
Pain scale (Visual Analog Scale)
  • 2/10 or less
Knee Range
  • Full knee extension
  • At least 95% of knee flexion
Walking Pattern
  • Normal
Swelling/ effusion
  • Not present
  • At least 70% compared to your good leg
Biomechanics when performing a single leg squat
  • No hip adduction/ internal rotation
  • No knee valgus
  • No excessive tibial external rotation
  • 43 Seconds on single leg with eyes opened
  • 9 seconds on single leg with eyes closed
  • Y balance test:
    • At least 90% compared to your good leg
Single leg hop test
  • At least 70% compared to good leg


1. Pain scale of 2/10 or less on a visual analog scale

Running is a vigorous activity that generates a significant amount of loading onto the knee. Your pain has to be well managed before starting to run or it will usually lead to more pain, which might inhibit your progress. Having pain can also cause you to start compensating in your body movements, which can be detrimental to your form in the future if you start to form bad habits when you run.

2. No swelling

This is important because running can generate a significant amount of ground reaction force to your knee. If your knee swells when doing normal activities such as walking, running will only intensify the swelling. This can lead to other issues such as limiting the force production of your knee muscles, reduced knee stability leading to delays in your recovery.

patient in a knee brace


3. Normal walking pattern

If you are unable to achieve a normal walking pattern, it is unlikely that you are able to achieve a normal running pattern as well. When you run with an abnormal pattern, it is very likely that compensatory movements will occur somewhere along with the biomechanics of your body. This can increase the risk of a second ACL injury, or cause strain and pain in other areas of the body.

4. At least 95% range of motion in the knee

Having a good range of your knee will provide sufficient mobility of your quadriceps muscles and kneecap for you to commence running. The required ranges are at least full knee extension (being able to straighten your knee fully), and at least 95% of knee flexion range compared to your other leg.

This is important to ensure that you can move through the range required of the knee to run comfortably. With a limited range when running, it can lead to other issues such as overloading on the kneecap, which can cause pain and dysfunction. This also prevents any compensatory movements in other parts of your body.

5. Sufficient strength of the leg and good trunk control

Sufficient strength of the leg is crucial to ensure the stability of the knee before you start running. Good trunk control is also important because poor trunk control can lead to compensations from the leg, which might put you at risk for an injury.

Typically, the strength of your knee will be compared to the other side. You will need to achieve at least 70% strength compared to your good leg to proceed. This can be done with a Biodex machine.

Alternatively, we can test the strength of your leg with the following set of hurdle requirements:

  • 5 repetitions of single-leg box squats
  • 20 repetitions of single-leg bridges
  • 20 repetitions of single-leg calf raise
  • To maintain 30 seconds of side planks on both sides
  • 10 repetitions of single-leg sit to stand movements

patient doing a body stretch


6. Proper biomechanics

Achieving good strength alone is not sufficient to ensure that you are able to run without the risk of a re-injury. It is also important that you have good form when you perform the above exercises. This is because the improper form can strain the ACL, leading to an increased risk of ACL injury.

Some of the forms associated with a high risk of ACL injuries when performing your knee movements (especially single-leg squats) are:

  • Internal rotation and inward movement of the femur (thigh bone)
  • Inward movement of the knee
  • Excessive external rotation of your shin in relation to the knee
  • Inward rotation of your foot

As such, it is important to have a physiotherapist guide you through your rehabilitation ensuring that you have good form to avoid unnecessary strain to your ACL.

7. Good single leg balance

Having a good balance indicates that your nervous system has a good ability to synchronize the muscular activity of your knee to achieve good dynamic stability. This will reduce the risk of an injury. Typically, you will need to achieve the following results to proceed:

  • 43 seconds of single-leg balance with eyes opened
  • 9 seconds of single-leg balance with eyes closed
  • Y-Balance test: To score a limb symmetry index of 90% on your operated leg, compared to your good leg

With balance testing, individuals might use inefficient techniques to compensate when they lack balance. Thus, it is important to have a physiotherapist monitor your form, and guide you through the balance exercises properly.

8. Good power and stability on single leg hops

After achieving all the above goals, this is the last hurdle you should clear before returning to running. When you run, it is crucial to have good power and stability on your legs. A hop test has its similarities to running, such as pushing off with one leg and also landing on one leg. As such, it is important that you clear this hurdle before you start running.

Due to the high demands of loading on the leg when performing this test, your form is crucial. A physiotherapist will be able to guide you and work with you to ensure that you achieve good form when landing on one leg.

You are required to achieve a distance of at least 70% on the operated leg, compared to the good leg on a single hop. This is usually performed over 3 times, with the average distance taken.

Once you achieve good form in landing, and sufficient power on your leg, the risk of re-injury is lower and you are ready to start running.

patient balancing on ball


ACL Rehabilitation in Heartland Rehab

All of the above milestones will usually be achieved in a reasonable timeframe of 8-16 weeks. The timeframe is usually dependent on your surgeon, as he will assess and allow sufficient healing of your ACL graft before you start running.

A structured ACL rehabilitation with an attentive physiotherapist will go a long way to achieve your goals. It is crucial that milestones are achieved before you progress to more demanding activities. Here at Heartland Rehab, we have a structured programme to allow you to progress your ACL rehabilitation in the most time efficient and safe manner.

Should you have more inquiries, please feel free to contact us immediately.