The Anteromedial Portal for Anterior Cruciate Ligament Reconstruction




Introduction


The correct placement of the femoral tunnel is very essential for the success of the anterior cruciate ligament (ACL) reconstruction. The transtibial drilling of the femoral tunnel has been very much popularized because of its simplicity and good visualization. However, there is evidence that drilling the femoral tunnel through the tibial tunnel can result in a nonanatomical placement of the graft in the femur.


Drilling the femoral tunnel more laterally at the medial surface of the lateral femoral condyle (LFC) (2 or 10 o’clock) has been proposed for better functional results, especially to avoid not only the anterior drawer but also the pathological rotation of the tibia. It was shown the tension curve of grafts in the 9 o’clock position is similar to the characteristic pattern of the normal ACL’s tension curve. To reach this position (centered at 2 or 10 o’clock with the lowest point near 9 or 3 o’clock), the anteromedial portal is essential.


Thus the anteromedial portal has become more and more attractive, and a large number of orthopaedic surgeons prefer this portal.




Advantages


The advantages of this technique are as follows:




  • It allows for easy manipulation of the instruments to drill the tunnel in any position at the medial side of the LFC without considering the placement of the tibial tunnel.



  • The femoral and tibial tunnels are drilled separately. Thus one can choose the desired placement of the femoral tunnel without considering the placement of the tibial tunnel.



  • There is no risk of enlarging the tibial tunnel posteriorly, which can lead to poor fit and stabilization of the graft in the tunnel.



  • By using bone–patellar tendon–bone (BPTB) graft, there is no divergence when placing the interference screw.



  • In double-bundle ACL reconstruction, it is easier to choose the two entry points.



  • The drilling can be performed with the knee flexed to 120 degrees. In this position, the 10-o’clock and also the 9-o’clock position can easily be reached without the risk of a blowout fracture of the dorsal corticalis of the femoral condyle.



  • The correct rotation of the graft insertion toward the long femur axis (important to restore the anteromedial and posterolateral bundle using BPTB graft) is easily found because it is parallel to the tibia plateau in the 120-degree flexion position.





Advantages


The advantages of this technique are as follows:




  • It allows for easy manipulation of the instruments to drill the tunnel in any position at the medial side of the LFC without considering the placement of the tibial tunnel.



  • The femoral and tibial tunnels are drilled separately. Thus one can choose the desired placement of the femoral tunnel without considering the placement of the tibial tunnel.



  • There is no risk of enlarging the tibial tunnel posteriorly, which can lead to poor fit and stabilization of the graft in the tunnel.



  • By using bone–patellar tendon–bone (BPTB) graft, there is no divergence when placing the interference screw.



  • In double-bundle ACL reconstruction, it is easier to choose the two entry points.



  • The drilling can be performed with the knee flexed to 120 degrees. In this position, the 10-o’clock and also the 9-o’clock position can easily be reached without the risk of a blowout fracture of the dorsal corticalis of the femoral condyle.



  • The correct rotation of the graft insertion toward the long femur axis (important to restore the anteromedial and posterolateral bundle using BPTB graft) is easily found because it is parallel to the tibia plateau in the 120-degree flexion position.





Technique


The technique is as follows:




  • Place the anterolateral portal for the arthroscope 2–3 cm higher than the tibial plateau between the lateral distal border of the patella and the LFC. Place the anteromedial portal 1 cm higher than the tibial plateau and very close to the medial border of the patellar tendon.



  • Resect the ligamentum mucosum and, if needed, pieces of infrapatellar fat for better visualization. In 90 degrees of flexion, débride the posterior surface of the medial side of the LFC from soft tissues. The posterior margin of the notch must be clearly identified to ensure an over-the-top position. This identification is very important, so place the femoral tunnel as far posteriorly as desired. Introduce a femoral guide (6-mm offset for an 8-mm hamstring graft or 7-mm offset for a 10-mm BPTB graft) through the medial portal.



  • Slowly flex the knee to 120 degrees, and check for good visualization. Sometimes higher fluid pressure is demanded, or parts of the fat pad need to be removed to have good visualization of the femoral footprint of the ACL. The center of the femoral tunnel is the center of the ACL footprint at 10 o’clock in the left knee and 2 o’clock in the right knee. Drill a 2.5-mm guidewire through the LFC with the knee in 120 degrees of flexion; the drill exits from the skin at the lateral side of the femur ( Fig. 42.1 ).




    Fig. 42.1


    Drilling a guidewire from the anteromedial portal through the lateral femoral condyle. The drill exits from the skin at the lateral side of the femur.



  • In this position (120 degrees of flexion), the drill should be aligned parallel to the tibial plateau. Thus a dorsal blowout fracture is surely avoided.



  • If you are certain that the guidewire is in the correct position, overdrill the guidewire with a reamer in the chosen depth.



  • If you are not sure about the correct position, the placement of the guidewire should be controlled fluoroscopically (recommended for all arthroscopic procedures ) as follows:



  • Change the drilling machine and fix it at that end of the wire that exits through the skin. Withdraw the Kirschner wire (K wire) until its inner end is flush with the bone level of the LFC. Now the ending of the K wire marks the estimated center of ACL insertion ( Fig. 42.2 ).




    Fig. 42.2


    Withdraw the K wire (A) until its end is flush with the wall of the lateral condyle (B) .



  • Under fluoroscopic control in strictly lateral projection, superimpose both femoral condyles on the monitor ( Fig. 42.3 ).




    Fig. 42.3


    Fluoroscopic control in lateral projection.



  • Measure the position of the end of the K wire using the quadrant method ( Fig. 42.4 ).




    Fig. 42.4


    Quadrant method: Taking a strictly lateral radiograph, superimposing both condyles, quartering the sagittal diameter, and quartering the notch height. The center of the anterior cruciate ligament insertion is located in the distal corner of the most superoposterior quadrant (arrow) .



  • It is not necessary to perform an additional fluoroscopic tunnel view because the quadrant method determines the position of the end of the K wire in the anteroposterior direction as well ( Fig. 42.5 ).




    Fig. 42.5


    Example of different K wire positions in true lateral projection (left) and in Frick’s projection (right) . The endings of the K wires are even with the bony surface of the condyle. Under this condition a constant relation exists between the measurements in the sagittal plane and the position of the end of the K wire in the frontal plane. The position in craniocaudal direction in the lateral view corresponds to the clockwise position in the tunnel view. For instance, a positioning at 25% of the height of the notch in the lateral view leads to the 1:30 clock position in the anteroposterior view (left knee). A drill hole that is positioned at 0% of the height of the notch in lateral projection would be in the high-noon position in Frick’s projection.



  • Overdrill the K wire if its position is correct; if not, replace the K wire and repeat the fluoroscopy ( Fig. 42.6 ).


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Aug 21, 2017 | Posted by in ORTHOPEDIC | Comments Off on The Anteromedial Portal for Anterior Cruciate Ligament Reconstruction

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