Introduction
Over the last decade, anatomical anterior cruciate ligament (ACL) reconstruction that restores the original size and location of the ACL insertion is widely performed. Anatomical studies have been performed to know the position of the ACL insertion, and the ACL can be divided into two parts: the anteromedial and posterolateral bundles, which have different functions with different lengths and force-change patterns. Some biomechanical studies showed that anatomical double-bundle (DB) ACL reconstruction achieved equal knee kinematics to those of the intact knee with stability of tibial anterior translation and rotation. Accordingly, anatomical DB ACL reconstruction is a widely used procedure. Therefore femoral tunnel position in anatomical ACL reconstruction is considered to be one of the most important factors influencing knee kinematics and clinical results. To accurately know the location of an anatomical ACL insertion is very important.
Macroscopic Anatomy of the Anterior Cruciate Ligament
The long axis of the femoral insertion of the ACL is tilted slightly forward from the vertical line of the lateral femoral condyle and is in continuity from the posterior femoral cortex. The femoral insertion of the ACL was investigated by several previous studies, which reported its size and area. The common consensus is that the presence of the lateral intercondylar ridge is the better known of the landmarks to identify the ACL insertion. The ridge—the so-called resident’s ridge, as coined by William Clancy Jr.—is a bony ridge in the medial wall of the lateral femoral condyle that exists throughout the ACL insertion from proximal to distal, reaching the articular cartilage. Although it is also a common recognition that the ACL attaches posteriorly to the lateral intercondylar ridge, the area of insertion remains controversial, as previously described ( Table 48.1 ). In this chapter, the shallow position along the Blumensaat line is defined as anterior and the deep position is defined as posterior, with the knee flexed at 90 degrees. For the area, some authors showed a large insertion area that extends backward to the articular cartilage margin ; on the other hand, some authors showed a relatively narrow insertion area. In particular, Śmigielski et al. reported that the average width of ACL was only 3.54 mm. For the shape, Girgis et al. described that the femoral ACL insertion had a straight anterior side and convex posterior side, and some researchers showed that the shape of the femoral ACL insertion was more oval. Other researchers observed the area and size of the femoral ACL insertion with removed surface membrane and described the femoral ACL insertion as being more oval and narrow with standing off from the posterior cartilage margin. In addition, the shape of the ACL insertion was described as having a ribbon-like appearance. We also investigated the femoral ACL insertion macroscopically. The femoral insertion area was narrow and oval shaped, and the average length of the long axis was 17.7 ± 2.7 mm (range, 12–20 mm). They were some distance away from the posterior cartilage border, and the average distance from the posterior margin of the ACL insertion and the posterior cartilage border was 7.8 ± 1.2 mm. Therefore the area of the femoral ACL insertion was considered narrow, and it was some distance away from the posterior cartilage border.
| Anterior Cruciate Ligament Insertion | Relationship Between Anterior Cruciate Ligament and Posterior Cartilage ∗ | ||||
|---|---|---|---|---|---|
| Literature | Study Design | Length (mm ± SD) | Width (mm ± SD) | Area (mm 2 ± SD) | |
| Girgis et al. (1975) | Macroscopic | 23 | — | — | Separate |
| Odensten and Gillquist (1985) | Macroscopic | 18 ± 2 | 11 ± 2 | 150 † | Close |
| Amis and Dawkins (1991) | Macroscopic | — | — | — | Close |
| Muneta et al. (1997) | Macroscopic | 16.0 ± 2.8 | 8.3 ± 2.8 | 93.3 ± 34.1 | — |
| Harner et al. (1999) | Macroscopic | — | — | 113 ± 27 | Close |
| Yasuda et al. (2004) | Macroscopic | — | — | — | Separate |
| Colombet et al. (2006) | Macroscopic | 18.3 ± 2.3 | 10.3 ± 2.7 | 148 † | Close |
| Takahashi et al. (2006) | Macroscopic Radiographical | AM 11.3 ± 1.6 PL 11.0 ± 1.7 | AM 7.5 ± 1.3 PL 7.6 ± 1.0 | AM 66.9 ± 2.3 PL 66.4 ± 2.3 | Separate |
| Mochizuki et al. (2006) | Macroscopic | AM 9.2 ± 0.7 PL 6.0 ± 0.8 | 4.7 ± 0.6 | 65 † | Separate |
| Ferretti et al. (2007) | Macroscopic Arthroscopic 3D laser digitizer | 17.2 ± 1.2 | 9.9 ± 0.8 | 196.8 ± 23.1 | Close |
| Siebold et al. (2008) | Macroscopic | AM 7 ± 1 PL 7 ± 2 | AM 7 ± 1 PL 7 ± 1 | AM 44 ± 13 PL 40 ± 11 | Separate |
| Hara et al. (2009) | Macroscopic | — | — | — | Separate |
| Iwahashi et al. (2010) | Microscopic 3D Volume-rendered CT | 17.4 ± 0.9 | 8.0 ± 0.5 | 128.3 ± 10.5 | Close |
| Kopf et al. (2011) | Arthroscopic | AM 9.2 ± 1.2 PL 7.1 ± 1.1 | AM 8.9 ± 0.9 PL 6.9 ± 1.0 | 102.7 † | — |
| Sasaki et al. (2012) | Macroscopic Microscopic | 17.7 ± 2.7 | 4.6 ± 0.7 5.3 ± 1.1 | Separate | |
| S´migielski et al. (2014) | Macroscopic | 16.0 | 3.54 | 56.6 | Separate |
∗ Judgment from figure or measurement value of paper.
Macroscopic Anatomy of the Anterior Cruciate Ligament
The long axis of the femoral insertion of the ACL is tilted slightly forward from the vertical line of the lateral femoral condyle and is in continuity from the posterior femoral cortex. The femoral insertion of the ACL was investigated by several previous studies, which reported its size and area. The common consensus is that the presence of the lateral intercondylar ridge is the better known of the landmarks to identify the ACL insertion. The ridge—the so-called resident’s ridge, as coined by William Clancy Jr.—is a bony ridge in the medial wall of the lateral femoral condyle that exists throughout the ACL insertion from proximal to distal, reaching the articular cartilage. Although it is also a common recognition that the ACL attaches posteriorly to the lateral intercondylar ridge, the area of insertion remains controversial, as previously described ( Table 48.1 ). In this chapter, the shallow position along the Blumensaat line is defined as anterior and the deep position is defined as posterior, with the knee flexed at 90 degrees. For the area, some authors showed a large insertion area that extends backward to the articular cartilage margin ; on the other hand, some authors showed a relatively narrow insertion area. In particular, Śmigielski et al. reported that the average width of ACL was only 3.54 mm. For the shape, Girgis et al. described that the femoral ACL insertion had a straight anterior side and convex posterior side, and some researchers showed that the shape of the femoral ACL insertion was more oval. Other researchers observed the area and size of the femoral ACL insertion with removed surface membrane and described the femoral ACL insertion as being more oval and narrow with standing off from the posterior cartilage margin. In addition, the shape of the ACL insertion was described as having a ribbon-like appearance. We also investigated the femoral ACL insertion macroscopically. The femoral insertion area was narrow and oval shaped, and the average length of the long axis was 17.7 ± 2.7 mm (range, 12–20 mm). They were some distance away from the posterior cartilage border, and the average distance from the posterior margin of the ACL insertion and the posterior cartilage border was 7.8 ± 1.2 mm. Therefore the area of the femoral ACL insertion was considered narrow, and it was some distance away from the posterior cartilage border.
| Anterior Cruciate Ligament Insertion | Relationship Between Anterior Cruciate Ligament and Posterior Cartilage ∗ | ||||
|---|---|---|---|---|---|
| Literature | Study Design | Length (mm ± SD) | Width (mm ± SD) | Area (mm 2 ± SD) | |
| Girgis et al. (1975) | Macroscopic | 23 | — | — | Separate |
| Odensten and Gillquist (1985) | Macroscopic | 18 ± 2 | 11 ± 2 | 150 † | Close |
| Amis and Dawkins (1991) | Macroscopic | — | — | — | Close |
| Muneta et al. (1997) | Macroscopic | 16.0 ± 2.8 | 8.3 ± 2.8 | 93.3 ± 34.1 | — |
| Harner et al. (1999) | Macroscopic | — | — | 113 ± 27 | Close |
| Yasuda et al. (2004) | Macroscopic | — | — | — | Separate |
| Colombet et al. (2006) | Macroscopic | 18.3 ± 2.3 | 10.3 ± 2.7 | 148 † | Close |
| Takahashi et al. (2006) | Macroscopic Radiographical | AM 11.3 ± 1.6 PL 11.0 ± 1.7 | AM 7.5 ± 1.3 PL 7.6 ± 1.0 | AM 66.9 ± 2.3 PL 66.4 ± 2.3 | Separate |
| Mochizuki et al. (2006) | Macroscopic | AM 9.2 ± 0.7 PL 6.0 ± 0.8 | 4.7 ± 0.6 | 65 † | Separate |
| Ferretti et al. (2007) | Macroscopic Arthroscopic 3D laser digitizer | 17.2 ± 1.2 | 9.9 ± 0.8 | 196.8 ± 23.1 | Close |
| Siebold et al. (2008) | Macroscopic | AM 7 ± 1 PL 7 ± 2 | AM 7 ± 1 PL 7 ± 1 | AM 44 ± 13 PL 40 ± 11 | Separate |
| Hara et al. (2009) | Macroscopic | — | — | — | Separate |
| Iwahashi et al. (2010) | Microscopic 3D Volume-rendered CT | 17.4 ± 0.9 | 8.0 ± 0.5 | 128.3 ± 10.5 | Close |
| Kopf et al. (2011) | Arthroscopic | AM 9.2 ± 1.2 PL 7.1 ± 1.1 | AM 8.9 ± 0.9 PL 6.9 ± 1.0 | 102.7 † | — |
| Sasaki et al. (2012) | Macroscopic Microscopic | 17.7 ± 2.7 | 4.6 ± 0.7 5.3 ± 1.1 | Separate | |
| S´migielski et al. (2014) | Macroscopic | 16.0 | 3.54 | 56.6 | Separate |
∗ Judgment from figure or measurement value of paper.
Microscopic Anatomy of the Anterior Cruciate Ligament
The differences of macroscopic observation may confuse surgeons when deciding the femoral tunnel positions during ACL reconstruction. Therefore microscopical investigation is needed to better understand the femoral insertion.
Iwahashi et al. investigated the ACL insertion microscopically and described the direct insertion as constituting ligaments, noncalcified fibrocartilage, calcified fibrocartilage, and bone located in the depression between the lateral intercondylar ridge and the articular cartilage border, whereas the indirect insertion constitutes ligaments and bone extending posteriorly in contact with the margin of the articular cartilage. Meanwhile, in our study, the ACL insertion was located between the lateral intercondylar ridge and the posterior cartilage margin by hematoxylin-eosin (H&E) staining ( Fig. 48.1A ). However, the direct insertion was positioned at the central region of the ACL insertion (see Fig. 48.1B ) and was not continuous to the posterior cartilage. Another bony ridge, the lateral intercondylar posterior ridge (see Fig. 48.1A , black arrow ), was positioned at the posterior margin of the direct insertion. In the direct insertion, the chondrocytes were observed in noncalcified and calcified fibrocartilage layers (see Fig. 48.1C ). The depth of the calcified fibrocartilage and bone layer (CFB) of the direct insertion was thick, and the average was 0.8 ± 0.3 mm. On the other hand, at the marginal region of the ACL insertions, there was an indirect insertion in which ligaments were directly anchored to bone (see Fig. 48.1D and E ) and the Sharpey-like fibers were observed in this area (see Fig. 48.1E ). The indirect insertion was positioned posterior to the lateral intercondylar posterior ridge. Posterior to the ACL insertion, ligaments looked as if they were continuous to the posterior cartilage. In azan staining, all collagen fibers were stained and the cartilage layer and ligaments appeared continuous to the posterior cartilage ( Fig. 48.2A ). However, in alcian blue staining, an unstained area between the direct insertion and posterior cartilage border presented, and calcified and noncalcified cartilage layers were positioned a few millimeters away from the posterior cartilage border (see Fig. 48.2B ). Under a polarizing microscope, the direct insertion exhibited a four-layered structure ( Fig. 48.3A ); on the other hand, the indirect insertion did not have a four-layered structure (see Fig. 48.3B ). In addition, the posterior ACL fibers and fibers of the ACL membrane gained entrance into the posterior cartilage (see Fig. 48.3C ).
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