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    Automated anterior drawer test for ACL assessment - GNRB Rotab

    The GNRB Rotab was created for doctors’ whose intention was to study the anterior cruciate ligament with more precision than the GNRB. The option indeed measures the medial rotation that occurs on the tibia while applying an anterior translation. This medical device permits the analysis of the ACL and its posterior-lateral bundle.

    GNRB Rotab video - Anterior cruciate ligament (ACL) assessment with medial rotation

    GNRB Rotab - Automated Anterior Drawer Test for ACL analysis with consideration of 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.

    Example of an anterior cruciate ligament test using the GNRB Rotab

    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.

    Why is the GNRB Rotab arthrometer more accurate than any other arthrometer?

    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.

    Graph Results of two patients

    Graph Results of two patients

    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.

    How to run a test on the anterior cruciate ligament (ACL) with the GNRB Rotab

    GNRB Rotab - Patient Positioning Tutorial

    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.

    1) Position the patient of the GNRB Rotab

    Patient positioning is the first step to run tests on the anterior cruciate ligament (ACL) of the patient. His leg should be in a 30-40° flexion for optimal anterior cruciate ligament (PCL) testing. This can easily be done with a LDA® Couch which is an accessory especially designed for our products and patient comfort.

    Patient positioning is the first step to run tests of the anterior cruciate ligament (ACL) of the patient. First, two separate marks shall be placed with a pencil on the apex of the patella and the anterior tibial tuberosity. The leg of the patient shall then be placed on the GNRB with the mark of the apex of the patella being located in the hole of the knee cup. The objective here is to block the patella against the femur so that when tests are run, the femur/patella stay locked in position while the tibia undergoes anterior translation. Following this, the foot is to be locked in the Rotab boot which is equipped with a sensor calculating the medial rotation resulting from the anterior drawer test induced by the GNRB. A displacement sensor is then placed on the anterior tibial tuberosity to measure the tibial translation.

    2) Run the tests

    Once patient positioning is achieved, a patient file is to be created on the computer that is provided with the GNRB and the tests shall begin. As soon as a push force is chosen (134, 150, 200 N...), the user can choose to run the tests:

    The cup located under the calf starts applying the force on the tibia leading to an anterior translation. When the chosen force is detected, the cup under the calf stops and goes back to its initial position. This ultimately makes the displacement sensor move upwards/downwards calculating the displacement of the tibia against the force applied. Additionally, the Rotab boot also measures the Medial Rotation resulting from the anterior tibial translation. The data collected is then stored in a table chart with a graph.

    Repeat this on the other knee.

    3) Results:

    When the tests are done, the user will find in the results tab the data collected from these tests. They are under the form of a graph showing the compliance curves (=opposite of the stiffness curves) accompanied by a table chart showing the numerical values.

    GNRB main characteristics for optimal ACL assessment

    • Device using LDA® Method applying anterior anterior tibial translation (Lachman's Test) for anterior cruciate ligament and knee. stability objective evaluation.
    • Dynamic and none-invasive tests.
    • Medial rotation calculus.
    • Automatic tibial displacement differential and compliance curves slope differential calculation.
    • Registration of the patellar fixation force and patient foot / Base of the machine distance for reproducibility.
    • Delivery with PC and LDA® Software.
    • Thrust force from 1 to 200 N.
    • Patient data automatically saved, results exportable as xls. files, pdf. format for great communication.
    • Dimensions : 845 x 270 x 400mm / 15kg.

    GNRB additionnal options

    • 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.