AAOS Scientific Exhibit 71 An Evolving Concept: Individualized, Anatomic ACL Reconstruction in 2017 Humza S. Shaikh, BA Marcio B.V. Albers, MD Elmar Herbst, MD Daniel Guenther, MD Sebastian Irarrázaval, MD Jeremy M. Burnham, MD and Freddie H. Fu, MD, DSc (Hon.), DPs (Hon.) Department of Orthopaedic Surgery, University of Pittsburgh, Pittsburgh, PA, USA Corresponding Author: Freddie H. Fu, MD E - Mail: ffu@upmc.edu NOTES:
The Primary Goal of Individualized Anatomic ACL Reconstructive Surgery: Restoration of the ACL to its native dimensions, collagen orientation, and insertion sites to replicate the individual anatomy as closely as possible. Anatomy of the ACL ▪ Understanding the functional anatomy of the ACL starts with understanding its development during fetal life. In a previous study, 40 fresh fetal knees, 17 to 23 weeks of gestational age were carefully dissected with the aid of stereomicroscope. 6 Once the surrounding synovial membrane was removed, the presence of the two functional bundles, anteromedial (AM) and posterolateral (PL), separated by a clear defined septum was evident. Histology revealed, in the transverse cuts, a well-defined septum that was later proven to be a potential source of CD34+ and CD146+ stem cells, which may contribute to the healing process of the injured ligament. 19 ▪ Although the ACL is referred to as one ligament, it consists of two functional bundles. These two bundles are named for the place where they attach on the tibia. There is an anteromedial (AM) bundle, which inserts more anterior (towards the front) and medial (towards the inside) of the tibia. The posterolateral (PL) bundle inserts most posterior (towards the back) and lateral (towards the outside) of the tibia. 2
▪ When the ACL is carefully dissected away, it becomes much clearer where the AM and PL bundle attach to the femur and tibia. Below you can see the AM and PL bundle attachments on the tibia (left) and femur (right). 7 ▪ On the femur, there are two ridges that outline the insertion of the ACL to the bone. There is one ridge that borders the top of the ACL (the lateral intercondylar ridge) and there is one ridge that forms the border between the AM and PL bundles (the lateral bifurcate ridge). 5 When your ACL is torn off the femur, these two ridges serve as a map to help us to find the location where your ACL used to attach. 3
▪ Regarding the ACL insertion site size variation in the population, one study revealed that intra-operative measurements of the tibial and femoral footprint lengths varied from 12 to 22 mm and 12 to 20 mm, respectively. 16 This large variation in insertion site size suggests that patients with either a very small or very large insertion site may not do well with the standard 10 mm single-bundle ACL reconstruction. An ACL insertion site greater than 18 mm allows for two bundle graft reconstruction or double-bundle reconstruction. If the insertion site is less than 14 mm, there is only space available for a single-bundle procedure. Between 14 – 18 mm, we can perform either double- or single-bundle reconstruction. ▪ A recent study analyzed the area of the tibial footprint of the ACL in 126 patients that had their native insertion sites measured by 3 subsequent slices of both their MRI in sagittal and coronal planes, as well as intra-operatively. 9 The results confirmed the previous findings that there is variation of the native ACL footprints regarding its size, but this can be reliably predicted by the measurements based on the pre-operative MRIs. Also, the shape of the tibial insertion site was previously shown to be predominantly oval, although once again variation is the rule and multiple shapes were subjectively observed. ▪ The objective evaluation of the ACL anatomy, with special attention to nuances that cannot be fully appreciated during gross dissection, were further delineated using 3D laser scanning with a robotic testing system to analyze the dynamic changes of the shape and size of the ACL during different flexion angles and loadings. 8 A total of 8 cadaveric specimens were 4
studied with confirming that the ACL shape is complex, has an isthmus located at approximately the mid-portion between the tibial and femoral insertion sites and that compared to the projected area of the tibial insertion site to different planes, the isthmus measures from 35% to 50% of the tibial insertion site and the femoral insertion site measures 69% of the tibial insertion site. Imaging: Special MRI Planes ▪ Below , the first two views are special views or “cuts” of the MRI that are specifically designed to look directly at the ACL. These special views were developed at the University of Pittsburgh, and very few other places around the world use them to help diagnose ACL tears. The image on the right show a more conventional MRI cut. These views all show an intact anterior cruciate ligament. ▪ Below, an MRI of a torn ACL is shown. 5
Is Anatomic ACL Reconstruction Really Anatomic? “ Evidence to Support the Interpretation and Use of the Anatomic Anterior Cruciate Ligament Reconstruction Checklist ”. van Eck, Fu et al. JBJS Orthopaedic Forum 2013 25 ▪ Published papers on anatomic anterior cruciate ligament (ACL) reconstruction often lack details in the description of the surgical procedure, and there are large variations in anatomic ACL reconstruction techniques. We aimed to develop a validated checklist to be used for anatomic ACL reconstruction. 34 ACL experts ranked 27 terms by importance, creating a list that was then verified by 959 academic orthopaedists. The final checklist underwent preliminary testing for internal consistency, intertester reliability, and validity. Cronbach’s alpha for internal consistency was 0.82, and the intraclass correlation coefficient (ICC) for intertester reliability was 0.65. This large survey-based study on anatomic ACL reconstruction resulted in the development of the Anatomic ACL Reconstruction Checklist. ▪ On the left is a 3D CT scan of a femur of someone with a normal native ACL. The middle picture shows a 3D CT scan after anatomic double-bundle reconstruction. The AM and PL bundle are placed in the same location as the normal knee. The picture on the right shows a 3D CT scan after non-anatomic ACL reconstruction. On the right, the non-anatomically placed ACL is in front (anterior) of and above (superior) where the native AM and PL bundles are. You can still see the normal AM and PL bundle attachment below the non-anatomic placement Biomechanics ▪ Studies over the past 20 years have resoundingly found that the ACL is not isometric and the anatomic DB ACL reconstruction better restores knee kinematics and in situ forces. o One study by Yagi et al. sought to determine whether reconstruction of both bundles better restores native knee kinematics than single bundle reconstruction. 28 Robotic testing in a 6-DOF (degrees of freedom) system was done on 10 fresh-frozen cadaveric knees, split into four groups: ACL intact, deficient, SB ACLR, and anatomic DB ACLR. Knee were tested under two conditions: 134N ATT and simulated pivot shift. This study found that anatomic DB ACLR better restores knee kinematics, especially with regard to rotatory stability. 6
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