Acute knee injuries can result in damage to different structures within the knee, including ligaments, meniscus, cartilage and bone. In this piece we’re discussing Anterior Cruciate Ligament (ACL) injury, however a lot of the rehabilitation principles discussed later can be applied to any acute knee injury.

ACL injury generally requires more specific and long-term rehabilitation when compared to other knee injuries as it can result in instability, knee stiffness, impaired muscle function, and may lead to further tissue injury.

Although these injuries are commonly treated with surgery, in some cases people are able to recover without it. The need for surgery may depend on the level of activity that someone is wants to return to, the presence of other injuries (such as meniscus tears), and the level of improvement achieved with conservative or pre-surgical management. 


The pre-surgical management of ACL injuries has come to be known as “Prehabilitation” or “Prehab”, and is a very important aspect of management following an ACL injury. The improvement gained during prehab may help someone decide whether or not surgery will be required in his or her situation. 

Perhaps more importantly, when surgery is required, 6 weeks of prehab has been shown to significantly improve post op outcomes, and increase the chance of returning to pre-injury level of activity or sport 

Rehabilitation and prehabilitation 

Rehabilitation (post op) and prehabilitation will broadly speaking have similar objectives, such as: 

  • Swelling/inflammation management 
  • Restoration of knee range of motion (in particular extension or straightening the knee) 
  • Improving general lower limb strength (with specific focus on quadriceps and hamstring)
  • Progression to more challenging/global strength while also building neuromuscular control of the knee
  • Graduated return to running, plyometric type exercise, agility, sport-specific activities, and restoring load tolerance (conditioning).

Whilst objectives are similar prehab periods (~6 weeks is recommended prior to surgery) will typically be shorter than the extensive rehab required post op (usually 9-12 month supervised rehab before return to sport) as such prehab may not extend to more dynamic phases listed above.

Important components of rehab/prehab

Rehabilitation programs should all have a focus on building strength, stability and increasing the capacity of the knee to tolerate certain activities; however the type, intensity, frequency, speed and progression of the exercises needs to be specific to each person. 

There are a number of different types of exercise that are essential to include in some capacity in knee rehabilitation/prehabilitation programs. Whilst these have been listed separately below, during rehab these exercises or phases will typically overlap. 


  • Global lower limb strength needs to be restored pre/post ACLR
  • Specific focus on quads/hamstring strength – failure to restore strength here may indicate greater risk of reinjury
  • Strength exercises may be split into hip driven strength, and knee driven strength
  • Exercises will include both isolated strengthening exercise and larger more functional exercise.


  • Exercises with a focus on balance and control through movement 


  • Involves jumping and landing exercises, which work on the body’s ability to create and absorb force and can help to build coordination and power.
  • Essential for return to any activities that involve any running, jumping or agility 

Return to Running drills

  • Drilling to restore specific characteristics (leg stiffness, coordination, technique etc) required for return to running
  • Graduated exposure to build load tolerance and running conditioning

Agility and sport specific exercise

  • This component will vary depending on specific requirements of the individuals sport or activity


  • For the individual to return to sport whole body conditioning needs to be considered specific to the requirements of the sport
  • Poor performance on fitness metrics can in itself be a risk factor for future injury


Monitoring progress – when am I ready to play?

A variety of testing procedures can be used to assess progress and readiness to return to play. Typically these will assess for restoration of strength, proprioception, power and agility.

Whilst there are rationales for a number of different testing procedures (and not necessarily a consensus on the best) The Limb Symmetry Index (LSI) is a commonly used outcome measure.

The LSI is a ratio comparing the performance of the effected and unaffected leg with an aim of achieving >90% when comparing the testing scores of both sides. Testing involves assessing the strength of the quadriceps and hamstrings in isolation, as well as utilising a combination of single leg hop tests. 

Typically during the later phases of rehabilitation the physio will guide the individual back into graduated and controlled participation in the training of their specific sport. This in itself provides indication of readiness as the individual is able to gradually increase participation as directed, and usually is not given the all clear to return to match play until they have completed a certain number of training sessions at full participation.

Last but maybe most important is the individuals own perception of readiness or confidence. Simply put if the individual doesn’t feel confident in their readiness to return then they’re not ready.

Management after return to play  

I’m back playing sport now is my rehab finished?

 Whilst your formal rehab period might be over, certain components of your rehab program should probably be continued indefinitely. Unfortunately the biggest risk factor for injuring your ACL is previous ACL injury (even if it’s on the other leg).

This suggests that whilst participating in sport ongoing work should be put into possible injury preventative exercise that involve a combination or strength, balance and plyometric exercises.

Whilst injury prevention programs may vary for each individual and their sport there are some quick and easy to perform routines that only take 10-15 minutes to complete and can easily replace a ‘normal’ warm-up routine prior to sport or activity. Evidence has shown that they can lead to improvements in balance, 20m sprint, vertical jump and agility and have been shown to reduce knee injury risk by 50% in certain populations. 

I got back to sport but then had a break and now want to get back into it

Return to sport after extended period away is actually where we see the most injuries occur. The addition of prior ACL injury actually increases injury risk! We highly recommend anyone in this scenario consider a “top up” 6-12 week program consisting of similar elements to late stage ACLR rehab to ensure readiness to get back into it.

If you’re in this category or have had other knee injuries that might require similar have a look at our “knee top up program”. 

Additionally any other queries regarding ACL injuries, surgery, injury prevention or other types of knee injury just get in touch!

Written by Physiotherapist Patrick Gillingham