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    Automated anterior drawer test for ACL assessment - GNRB

    The anterior cruciate ligament (ACL) was for GENOUROB the first knee ligament intended to be studied using the GNRB. This arthrometer (aka. laximeter) has quickly become the reference in the orthopaedic field for studying the state of the ACL by applying an automated Lachman Test.

    GNRB Video - Anterior cruciate ligament (ACL) assessment

    GNRB - Automated lachman test for ACL assessment

    Presently, the GNRB device provides the best precision in regards of knee ACL laxity assessement as it is the only arthrometer (aka. laximeter) able to objectively evaluate knee stability because of the dynamic tests it runs.

    While designing this tool, user friendliness was for us one of the major aspects that had to be taken into account. This consequently lead to many parameters and sensors being considered in order to guide the users while running dynamic tests. Thanks to these parameters and sensors, precise test reproducibility is now one of the top attributes the GNRB has to offer among many other.

    Further-more, the LDA® Method, which is an integral part of the GNRB, is perhaps what makes this device leader in the field of ACL analysis. The results given after a test are shown under the form of compliance curves (=opposite of the stiffness curves) accompanied by a table chart that generate sensible data to practitionner.

    This makes the tests easy-to-understand, to reproduce and it allows an evaluation with accurate figures of ACL laxity & knee stability.

    Example of an anterior cruciate ligament assessment using the GNRB

    Graph 1

    Graph 1

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

    The green curve represents the data collected on the healthy knee while the red curve represents the pathological knee.

    This is called "dynamic analysis" because calculation of the displacements of the tibia is done while applying different forces that put the anterior cruciate ligament under stress (from 0 to 200N for example) to enable the drawing of compliance curves (=opposite of stiffness curves). As a result, the bigger the side-to-side differential, the higher the chances of an anterior cruciate ligament tear.

    In comparison, other arthrometers  only collect data at a certain force (134 N for example). This is called "static analysis".

    It is thus against this background that Genourob innovated while conceptualizing the GNRB, the first automated tibial translation arthrometer for dynamic assessment of the anterior cruciate ligament.

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

    Here is an example to answer this question : 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 is the international reference force for assessing the ACL thanks to the KT1000, let us compare the displacement differential between both knees of both patients at this force.

    We can see here that the side-to-side displacement differential at 134 N is the same for both patients (1.5 mm). This should indicate that both patients are not suffering from a torn ACL. However, it not the case. The GNRB indeed shows innovation & precision in this exact situation as it provide an additional diagnosis method: 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.

    This indeed shows that patient 1 has two stable knees with a slight side-to-side difference in laxity that remains the same eventhough the force applied on the knee increases. This indicates a stable knee. However, patient 2 clearly shows an increasing side-to-side difference in laxity correlated with the increase of the force applied on the knees, hence the objective 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 in the knee.

    The consequently places the GNRB as the most advanced arthrometer for evaluating the state of the anterior cruciate ligament. Besides, it is also the only device capable of assessing ACL laxity very after surgery without any risk thanks to its controlled tibial translation (maximum forces applied can be chosen: 89, 100, 134, 150, 200 Newtons). 

    Doctors are thus able to follow the behaviour of the ACL graft over the months following the surgery, which is key to increasing the probability of gaining 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 test.

    How to run tests on the anterior cruciate ligament (ACL) with the GNRB

    GNRB - Patient Positioning Tutorial

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

    1) Position the patient on the GNRB.

    2) Run the tests on both legs.

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

    1) Position the patient on the GNRB

    Patient positioning is the first step to run tests on 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 to avoid any vertical movements and a displacement sensor in placed on the anterior tibial tuberosity.

    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. 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 tibial translation (Lachman's Test) for ACL and knee stability objective evaluation.
    • Dynamic and none-invasive tests.
    • 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

    • Over time, Genourob created several options that could be added to the GNRB such as the PCL option dedicated to analyzing the knee cruciate ligament, the posterior cruciate ligament (PCL).
    • GNRB Rotab is also available and was created to analyze the ACL with more precision by taking into account the calculation of the medial rotation that occurs when applying anterior tibial translation.
    • The last main option available is the GNRB Radio: This option was designed to analyze the ACL associated with X-ray technology. The GNRB Radio 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.