Anatomic study of the double-bundle of the anterior cruciate ligament with the knee in 90 o flexion

Objective: To anatomically evaluate the femoral origin and tibial insertion of the anteromedial and posterolateral bands of the anterior cruciate ligament. Methods: We studied eight cadaver knees as for the following: in the femur, distance from the center of the anteromedial band to the deep cartilage and the ceiling; also in the femur, distance from the center of the posterolateral band to the deep cartilage, to the inferior cartilage and to the superficial cartilage. In the tibia, we measured the distances between the anterior tibial bone edge to the anterior region of the anteromedial band, to the center of the anteromedial band and to the center of the posterolateral band. We also measured the distance between the center of the posterolateral band to the tibial posterolateral bone and the total length of the anteroposterior tibial insertion of the anterior cruciate ligament. Results: In the femur, the distance from the center of the anteromedial band to the deep cartilage was 6.3 ± 1.4 mm, and 11.2 ± 2 mm to the ceiling. Also in the femur, the distance from the center of the posterolateral band to the deep cartilage was 9 ± 4 mm, to the superficial cartilage 7.6 ± 1.8 mm, and to the inferior cartilage 4.2 ± 0.9 mm. In the tibia, the distance from the anterior tibial bone edge to the anterior region of the anteromedial band was 11.9 ± 2.8 mm, to the center of the anteromedial band 18.8 ± 2.6 mm, and to the center of the posterolateral band 26.5 ± 2.3 mm. The distance from the center of the posterolateral band to the tibial posterior bone edge was 19.6 ± 4 mm and the total length of the anteroposterior tibial insertion of the anterior cruciate ligament was 19.4 ± 1.8 mm. Conclusion: The center of the tibial insertion of the anteromedial band is approximately 20mm distant from the anterior edge of the tibia, while the center of the posterolateral band is approximately 30mm. The distance between the center of the origin of the anteromedial band to the deep cartilage is 6mm, and to the posterior lateral 10mm.

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INTRODUCTION INTRODUCTION INTRODUCTION INTRODUCTION INTRODUCTION
T he incidence of anterior cruciate ligament (ACL) reconstruction is 100,000 cases per year in the United States of America 1 .Every year there are more cases of injury due to the growing number of practitioners in sports activities [2][3][4] .
The reconstruction techniques, focusing on the repair of the anteromedial band, are well established with good results, also with regards to the return to high performance physical activities 5,6 .
Despite the wide use of the reconstruction with a single band, the ACL consists of two bands: the anteromedial (AM) and posterolateral (PL).Proponents of the reconstruction of both bands claim that there is residual instability in the conventional reconstruction, which causes degenerative changes [7][8][9][10][11][12] .Based on the fact that ACL reconstruction is not effective in preventing the progression to osteoarthritis in the operated knee, questions arose about whether the conventional AM band reconstruction is able of keeping the joint healthy, especially in women [13][14][15] .
One of the most discussed questions about the surgical technique of reconstruction is the placement of the tunnels.The papers describe ACL anatomy in anatomical position 16 (extension), whereas surgical position is at 90° flexion 17 .This complicates the interpretation of the anatomy by the surgeon during the operation.
In the classic study by Girgis 16 it has been shown that there is change in the anatomical relationship of the ACL with the flexion movement, but it was analyzed as a single unit, regardless of having two bands.The traditional nomenclature -proximal / distal and anterior / posterioris not easy to apply with the knee at 90°.In order to facilitate anatomical description a specific nomenclature was proposed for analysis at 90° knee flexion.The new nomenclature suggests that, when the knee is at 90°, the anatomic relationships should be called superficial / deep, superior / inferior 17 .
This applies to the femur, as in the case of the tibia there is no change in the anatomical relationship between the two situations.
The objective of this study is to assess the anatomic relationships of the two macroscopic bands of the ACL in its femoral origin in surgical position and in the tibial insertion.

METHODS METHODS METHODS METHODS METHODS
This work was conducted by the Department of Anatomy, Division of Biological Sciences, Federal University of Paraná.Twenty different cadaver knees were dissected in order to study the anatomy in the surgical position, according to the new nomenclature 17 (Figures 1 A and B), and measurements of anatomic structures and relationships in the ACL femoral origin and tibial insertion were performed.
As inclusion criteria, we used only cadaver knees with intact cruciate ligaments (anterior and posterior), without prior arthrotomy.Eight knees met the criteria.The dissection was anterior, with medial parapatellar approach till proper exposure of the cruciate ligaments was achieved 18 .All knees were preserved in formaldehyde (Figure 2).
For comparison of measurements we used 40x12mm needles in marking the specific points and a metallic caliper.The study was conducted with the knee flexed at 90 degrees for measurement of femoral data.
The measurements of the following distances were performed in the femur (Figure 3): 1) from the center of the anteromedial band to the deep cartilage (AM-CP); 2) from the center of the anteromedial band to the intercondyle ceiling (AM-teto); 3) from the center of the posterolateral band to the deep cartilage (PL-CP); 4) from the center of the posterolateral band to the superficial cartilage (PL-CS); and 5) from the center of the posterolateral band to the inferior cartilage (PL CI).
The measurements of the following distances were performed in the tibia (Figure 4): 1) from the anterior edge to the anterior portion of the anteromedial band (AM-AT-A); 2) from the anterior edge to the center of the anteromedial band (AT-AM); 3) from the anterior edge to the center of the posterolateral band (TA-PL); 4) from the posterior edge to the center of the posterolateral band (PL PT); and 5) anteroposterior diameter of the ACL (AP).

RESULTS RESULTS
The measures, means and standard deviations of the femoral origin of the ACL of the two bands are shown in table 1 and the ones from the tibia in table 2.
In the femur the measurements were: AM-CP, 6.3 ± 1.4 mm; AM teto, 11.2 ± 2 mm; PL-CP, 9 ± 4 mm; PL-CI, 4.2 ± 0.9 mm; PL-CS 7.6 ± 1.8 mm.In the tibia we found: AT-AM-A, 11.9 ± 2.8 mm; AT-AM, 18.The restoration of the anatomy of the knee to the nearest normal, with the positioning of the tunnels in the most anatomically possible position, is crucial to the success of ACL reconstruction [19][20][21][22][23] .Most articles study the anatomy of the ACL as a whole, not analyzing the bands separately, which constitutes a limiting factor in studying the placement of tunnels with dual band reconstruction.
We found no anatomical description with the femur at 90° flexion, which is the surgical, though nonanatomical, position.Despite the anatomical analysis of the flexed knee does not have a direct influence on the measures, it facilitates the interpretation of surgical data.
The distance between the center of the femoral origin of the posterolateral (PL) band to the inferior cartilage was 4.2 ± 0.9 mm.Petersen et al. 24 found a value of 4 to 5mm.This shows that the origin of the PL band almost touches the articular cartilage.
Regarding the measure of the distance between the center of the PL band to the region of the deep femoral cartilage, we obtained 9 ± 4 mm.Yasuda et al. 25 reported values of 5 to 8 mm for this lenght.These numbers help as a location parameter of the origin of this band in the knee.It is known that the PL band is more superficial than the anteromedial (AM), because the distance from the AM band to the deep cartilage was 6.3 ± 1.4 mm.Another parameter measured was the distance from the superficial cartilage to the center of the PL band and we found 7.6 ± 1.8 mm.There are no values in the literature to compare with the determination of this measure.In an arthroscopic view these numbers mean that the superficial edge of the ACL would touch an imaginary line that cuts the condyle in half.
The anatomical visualization of the ACL on the tibia is not changed between the surgical position and the classical anatomical one; so it is said that the name of the ACL bands is due to its tibial position.But this is only one way to avoid confusion in the interpretation of the surgical anatomy and does not correspond to reality.
According to Petersen et al. 24 , the insertion of the ACL begins 10 to 14 mm posterior to the anterior border of the tibia and the diameter of the sagittal plane of the ligament varied from 15 to 19 mm.These numbers have clinical relevance in double band reconstructions, as in the realization of the double tibial tunnel it is essential that the size of the tunnels is adapted to the size of the knee.Small knees require more delicate drills to prevent communication between the tunnels, preserving a bone bridge between them.In this work the distance from the anterior edge of the tibia to the anterior portion of the AM band was 11.9 ± 3 mm, similar to that found by Petersen et al. 24 , whereas the antero-posterior diameter was 19.4 ± 2 mm, greater than the one found by them.
The distance obtained from the center of the AM band to the anterior edge of the tibia is an important finding because it can be used as a parameter for the conventional ACL reconstruction; it is known that an error in this position may bring bad results to the ACL reconstruction 26 .In this work the values of this measure was 18.8 ± 3 mm, and Petersen et al. 24 had 13-17mm.
The distance from the center of the PL band to the anterior tibial edge serves as parameter for dual-band reconstructions.We obtained 26.5 ± 2 mm in this study, whilst Petersen et al found 20 25mm 24 .
It is interesting to note that the tibial insertion is long in the antero-posterior plane (19.4 ± 2 mm), the center of the PL band being closer to the posterior edge of the tibia (19.6 ± 4mm) than to the anterior one (26.5 ± 2mm).
In conclusion, the distance from the center of origin of the anteromedial band to the deep cartilage of the femur is approximately 6 mm, and to the posterolateral band 10 mm.The center of the tibial insertion of the anteromedial band is approximately 20 mm from the anterior edge of the tibia, and the posterolateral band 30 mm.The distance between the center of the origin of the posterolateral band to the inferior cartilage is about 5 mm.

Figure 1 Figure 1 Figure 1 Figure 1
Figure 1 Figure 1 Figure 1 Figure 1 Figure 1 -A) anatomical position and anatomical description, B) surgical position and description proposed by Zantop 17

Figure 2 Figure 2 Figure 2 Figure 2 Figure 2 -
Figure 2 Figure 2 Figure 2 Figure 2 Figure 2 -The two ACL bands, when appropriate for anatomical assessment.