Leg extension after VKB reconstruction

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 of this is that we first want someone to have a quality gait pattern and sufficient strength/control over the legs before starting running, for example.

Yet there is not quite a consensus on treatment protocols when it comes to guiding a VKB rehabilitation. Some physicians and physiotherapists work with treatment protocols in which the vision is that open chain exercises (exercises in which the feet have no contact with the ground or at least a 'fixed point') should not be performed in the first phase of the rehabilitation. These exercises can cause laxity (stretching) of the new cruciate ligament or can even cause the cruciate ligament to tear. These statements are largely based on relatively old research (between 1985 and 2000) where the results are also very doubtful when it comes to reliability and quality. Despite the fact that after this time, many studies have been conducted that strongly doubt the conclusions drawn earlier, we notice that nowadays the image of, for example, a leg extension in UKB rehabilitation is not very willing to change. 

The literature often mentions that the strength of the quadriceps muscle is a great predictor for the success of the rehabilitation in the long run. 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 the 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 the recovery, we should consider the isolated use of it as dangerous. 

We briefly put some 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 appears that the average strength in a leg extension between 1-12 repetitions equates to approximately 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 found 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 does it show? At the same 15-degree angle, that produces 355N of resistance on the cruciate ligament.

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

Summarizing, this tells us; that according to the current insights, we don't have to be afraid to use the leg extension in your program after a cruciate ligament reconstruction to make the quadriceps stronger again. However, we would like to give an important tip to make sure that in the first phase of the rehabilitation, you have a good quadriceps control and that the ROM (range of motion) is adjusted to the possible restrictions of your patient. 

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