Morphometric Analysis of the Tibial Attachment Shape of the Anterior Cruciate Ligament and Its Relationship With the Location of the Anterior Horn of the Lateral Meniscus

Abstract

Background: The success of anterior cruciate ligament (ACL) reconstruction relies on the accurate replication of the native ACL anatomy, including attachment shapes. The tibial attachment of the ACL exhibits significant shape variations with elliptical, C, and triangular shapes, highlighting the need for objective classification methods and additional information to identify individual anatomic variations.

Hypothesis: The location of the attachment of the anterior horn of the lateral meniscus (AHLM) may determine the shape of the ACL attachment.

Study design: Cross-sectional study; Level of evidence, 3.

Methods: The study used 25 knees from 17 Japanese cadavers for macroscopic anatomic examination and quantitative analysis. The shape of the ACL attachment was quantified using principal component analysis with elliptical Fourier descriptors, whereas the AHLM location was quantified by measuring its mediolateral and anteroposterior positions on the superior surface of the tibia. Reliability was assessed statistically.

Results: The shape of the tibial attachment of the ACL varied among individuals and was classified as elliptical, C-shaped, or triangular. Scatterplots of the principal components of the ACL attachment shape showed overlapping regions of elliptical, C-shaped, and triangular ACL attachments, indicating that a C-shaped attachment is intermediate between elliptical and triangular attachments. The location of the AHLM attachment also varied, with areas in the anterolateral, anteromedial, or posteromedial region. The ACL shape and AHLM location were related, with elliptical, C-shaped, and triangular ACL attachments corresponding to anterolateral, anteromedial, and posteromedial AHLM attachments, respectively.

Conclusion: The AHLM attachment location influences the shape of the ACL attachment. Information on the location of the AHLM attachment can aid in predicting the shape of the ACL attachment during ACL reconstruction, potentially improving footprint coverage.

Keywords: anatomy; anterior cruciate ligament; lateral meniscus.

Figure 1.

Assessment methods of anatomic structures. (A) Type classification and principal component analysis were performed to evaluate the shape of the anterior cruciate ligament (ACL) attachment. (B) To evaluate the location of the anterior horn of the lateral meniscus (AHLM) attachment, coordinates (horizontal axis [Lat] and vertical axis [Ant] values) of the AHLM tip were measured on the superior surface of the tibia. LM, lateral meniscus. See text for details.

Figure 2.

Anatomic variation of the tibial side of anterior cruciate ligament (ACL) and anterior horn of the lateral meniscus (AHLM) attachments. The superior side of the tibia is observed from the superior aspect. (A) Elliptical ACL attachment area with anterolaterally located AHLM attachment. (B) C-shaped ACL attachment area with medially located AHLM attachment. (C) Triangular ACL attachment area with posteromedially located AHLM attachment. The transverse ligament (intermeniscal ligament) was observed in this sample (see Appendix Figure A1, available online). LM, lateral meniscus.

Figure 3.

Shape of the anterior cruciate ligament (ACL) attachment and location of the anterior horn of the lateral meniscus (AHLM) attachment of all 25 specimens. The ACL attachment area is shown in yellow, the leading edge of the AHLM is shown with both arrow curves, and the AHLM tip is shown with arrowheads. For the left knee specimens, mirrored images are presented (No. 2, 3, 5, 8, 10, 12, 14, 16, 19, 25). Sample numbers correspond to those in Table 1.

Figure 4.

Reconstructed contours of the principal components (PCs) of the anterior cruciate ligament (ACL) attachment shape. The mean shape of the ACL attachments in 25 samples was slightly wider at the anterior portion than at the posterior portion, with a concave lateral border and convex medial border. PC1 is considered to reflect the intensity of the expansion/contraction of the overall width of the attachment area and the concave shape of the lateral edge, such that higher PC1 values are closer to an elliptical or triangular shape and lower values to the C shape. PC2 is thought to reflect the intensity of the reduction and expansion of the width of the anterior portion and the concavity of the lateral edge, such that higher PC2 values are closer to an elliptical shape and lower values are closer to a triangular or C shape. The contributions of PC1, PC2, and PC3 to the shape of the ACL attachment were 41.4%, 27.9%, and 13.4%, respectively.

Figure 5.

Scatterplots of PC1 and PC2 of the anterior cruciate ligament attachment shape. The results of the type classification by observer 1 are overlaid. Each type did not form a distinct cluster in the coordinate plane, and the regions of each type overlapped. The overlap between the elliptical and C shapes, and between the C and triangular shapes was particularly pronounced, indicating that the C shape is intermediate between the elliptical and triangular shapes. PC, principal component.

Figure 6.

Scatterplots of the location of anterior horn of the lateral meniscus (AHLM) attachments. (A) The location of the AHLM attachment exhibited interindividual variability, and its possible range was the anterolateral, anteromedial, or posteromedial area of the anterior intercondylar region. (B) Expansion of the rectangular area in panel A, overlaid with the shape classification of anterior cruciate ligament (ACL) attachments. Individuals with anterior, medial, and posteromedial AHLM attachments tended to have elliptical, C, and triangular shapes in their ACL attachments, respectively. Ant, vertical axis; Lat, horizontal axis.

Figure 7.

Morphological relationship between the shape of the anterior cruciate ligament (ACL) attachment and anterior horn of the lateral meniscus (AHLM) attachment location. The tibial sides of the ACL and AHLM both occupy the anterior intercondylar region, and the location of the AHLM attachment would determine the shape of the ACL attachment. Consequently, the AHLM attachment anterolateral, anteromedial, and posteromedial locations correspond to the ACL attachment elliptical, C, and triangular shapes, respectively. Information on the AHLM attachment location may be useful in predicting the ACL attachment shape during ACL reconstruction.