ACL TEST - MEDIAL ROTATION

The GNRB Rotab is nowadays the most precise arthrometer capable of objectively evaluating knee stability because of the dynamic tests it does. It is also the only one able to evaluate the medial rotation resulting from anterior translation. User friendliness, reproducibility and precision are words that best describe the GNRB Rotab.

The medial rotation evaluation added to the LDA® Method for ACL analysis is an integral part of the GNRB Rotab and it is what makes the GNRB Rotab the greatest innovation for functional analysis of the ACL instability. The results provided after running tests are shown under the form of a graph with compliance curves (=opposite of the stiffness curves) accompanied by a table chart. This makes the tests easy to understand and to reproduce.

Graph 1 shows the results obtained after performing tests on both knees of a same patient with the GNRB Rotab. The graph shows the compliance curves (=opposite of stiffness curves) obtained after applying several forces on the tibia of the patient to perform (anterior tibial translation with consideration of medial rotation).

This is called a dynamic analysis because calculation of the displacements of the tibia is done while applying different forces which put the anterior cruciate ligament under stress. Therefore, the bigger the displacement differential, the higher the chances of an ACL tear.

In comparison, other arthrometers (Laximeters)  collect data at a certain force which can be described as a static evaluation. Consequently, it is against this background that Genourob created the GNRB, the first automated tibial translation arthrometer for dynamic assessment of the anterior cruciate ligament that collects data while  applying various forces on the knee.

Click on the title below to learn more about dynamic assessment of the ACL.

The two graphs below show the results obtained on the knees of two different patients having suffered from knee ligament injuries after a GNRB test. The green curves show the test results of the healthy knees whereas the red curves show the results of the pathological knees.

As 134 N became the international reference force for assessing the ACL thanks to the KT1000, the GNRB Rotab provides the displacement for this given force. However, we can see that the displacements at this point are the same for both patients. This is problematic, as a false ACL diagnosis would be put forward. Yet, it is exactly here that the GNRB shows innovation & precision as an additional diagnosis may be performed through the analysis of the slope of the curves.

In fact, we can determine that Patient 1 has a stable knee while Patient 2 is unstable. Why?

Because on the graph of patient 1, the ACL compliance curves (=opposite of stiffness curves) are parallel and on the graph of patient 2 the ACL compliance curves (=opposite of stiffness curves) diverge.

Consequently, this shows that patient 1 has two stable knees with a slight side-to-side difference in laxity, which remains the same. However, patient 2 clearly shows signs of an increasing side-to-side difference in laxity correlated with the increase of force applied on the knees, hence the diagnosis of an unstable knee.

This example purely states the efficiency of running dynamics tests against static tests on the knee. Considering the slope differential between both compliance (=opposite of stiffness) curves on behalf of the displacement differential between both knees ultimately leads to a much more accurate analysis of the state of the ACL present in the knee.

The GNRB is therefore nowadays the most advanced arthrometer (Laximeter) for evaluating the state of the anterior cruciate ligament following knee injuries. Besides, it is also the only device capable of assessing ACL laxity after surgery without any risk thanks to its controlled tibial translation. 

Doctors are thus able to follow the behaviour of the ACL graft over time, which is the key to guarantee knee stability. Today's surgical techniques indeed require a lot of time of recovering therefore making the GNRB indispensable during anterior cruciate ligament rehabilitation (ACL Rehab).

If you are curious in knowing how a test is performed, click on the title below to see a video of a GNRB Rotab test.

To run a precise diagnosis on the ACL of a patient using Genourob's GNRB Rotab, it is required to follow these steps:

1) Position the patient on the GNRB Rotab.

2) Run the tests on both legs.

3) Read the results on the graph and its table chart.

• Over time, Genourob created several options that could be added to the GNRB such as the PCL option. Initially, this arthrometer was created for anterior cruciate ligament objective assessment by applying anterior tibial translation.

• GNRB PCL is also available and was created to analyze the PCL by applying posterior tibial translation.

• The last main option available is the GNRB Radio: This option was designed to analyze the anterior cruciate ligament associated with X-ray technology. This device is indeed made of materials especially adapted to X-technology.

• Finally, other remaining accessories available are the LDA®Couch which provides the patient with great comfort and is specially designed for our products, the LDA®Trolley for storage of the GNRB and the printer for printing the results.