Leg extension after anterior cruciate ligament surgery.

Recovery after an anterior cruciate ligament rupture is a long process that can be divided into several phases. This phasing is designed based on knowledge of recovery capacity (/recovery time) and conditions associated with safe and efficient movement. An example is that we first want someone to have a good quality gait pattern and sufficient leg strength/control before starting running, for example.

Yet there is not quite a consensus on treatment protocols when it comes to guiding a VKB rehabilitation. For example, there are doctors and physical therapists who work with treatment protocols in which the view is that open chain exercises (exercises in which the feet have no point of contact with the ground or at least a "fixed point") should not be performed in the first phase of rehabilitation. This is because they could potentially cause laxity (stretching) of the new cruciate ligament or even cause the cruciate ligament to rupture. These statements are largely based on relatively old research (between 1985 and 2000) in which the results are also very questionable in terms of reliability and quality. Despite the fact that many studies have been carried out since that time, which strongly question these earlier conclusions, we have noticed that the image of, for example, leg extension in VKB rehabilitation does not want to change. 

It is frequently mentioned in literature that the strength of the quadriceps musculature is a major predictor of long-term rehabilitation success. In closed chain (where there is a contact point between the foot and a solid surface) different exercises are offered in rehabilitation programs such as squat, leg press, lunges or step up. We also think these are good exercises to include in a knee rehabilitation program. However, it is strange that, while research shows that the quadriceps play an important role in recovery, we should label their isolated loading as dangerous.... 

We briefly put a few facts together; 


  • When your orthopedist has finished his reconstructive work, he will perform the Lachmann test. This is a test in which the function of the VKB is tested with an average force of 150N. 
  • It turns out that the average force for a leg extension between 1-12 repetitions amounts to about 158-396N. 
  • The average force required to rupture the original VKB amounts to about 2000N. After reconstruction, the same kind of tensile strength should eventually be achieved. 
  • The average force on the VKB during a squat/lunge is 100-150N between 0-30 degrees of knee flexion. 
  • What is even more interesting is that the researchers found as mentioned earlier that during a leg extension there was 248N of load on the cruciate ligament at a 15-degree angle. That same measurement was taken during walking and what did they find? At the same 15-degree angle, that produces 355N of resistance on the cruciate ligament.

Of course, we understand that some important factors are needed before starting leg extension exercises. For example, having good motor control of your quadriceps is very important for performing this exercise. Also, having a full ROM in the extension direction is important

In summary, this tells us that, according to current insights, we should not be afraid to use the leg extension in your program after a cruciate ligament reconstruction to regain quadriceps strength. However, we do want to include an important tip to ensure proper quadriceps control in the first phase of rehabilitation and make sure that the ROM (range of motion) is adjusted to your patient's possible restrictions. 

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