Summary

“Anatomic” ACL reconstruction is defined as the functional restoration of the native ACL. To reproduce native ACL anatomy in the surgery, considering the femoral ACL footprint’s long axis is important. The mean angle between axis of shaft and the long axis of femoral ACL footprint are approximately 29 degrees. However, there exists a lot of variation in the femoral ACL footprint’s long axis.

Abstract

Background

Although, numerous studies about ACL anatomy have been published, not many studies have been mentioned to the angle of the long axis of the femoral ACL footprint. To reproduce native ACL anatomy in the surgery, considering the femoral ACL footprint’s long axis is important.

Materials And Methods

Thirty non-paired formalin fixed Japanese cadaveric knees were used (16 males, 14 females, median age 78.9, range 53-94). Knees with severe osteoarthritic changes were not included in this study. All surrounding muscles, and other soft tissues around the knee were resected before ACL dissection. Anteromedial (AM) and posterolateral (PL) bundles were identified according to the difference in tension patterns during complete knee range of motion. As reported by Mochizuki et al., there existed a fold between the mid-substance insertion site and the fan-like extension fibers, and the fold could be detected macroscopically. Following the identification of the AM and PL bundles of mid-substance fibers, the mid-substance and the fan-like extension fibers were divided in the AM and PL bundles and stained with ink. We defined the line passing through the center of AM and PL bundles as the long axis of the ACL. The center point of each of four areas (mid-substance insertion of AM and PL, fan-like extension fibers of AM and PL) and the angle between ACL’s long axis and knee bony morphology were calculated using Image J software (National Institute of Health).

Results

The mean angle between axis of femoral shaft and the long axis of ACL mid-substance insertion was 28.8±12.2 degrees (range 7.8-64.6). The mean angle between axis of femoral shaft and the long axis of whole ACL insertion was 29.4±12.0 degrees (range 8.4-64.6). The mean angle between Blumensaat’s line and the long axis of mid-substance was 54.2±13.5 degrees (range 30.1-80.6). The mean angle between Blumensaat’s line and the long axis of whole ACL was 54.6±12.2 degrees (range 32.4-80.6).

Discussion

“Anatomic” ACL reconstruction is defined as the functional restoration of the ACL to its native dimensions, collagen orientation, and insertion sites. It is well known that ACL composed of AM and PL bundles, and they have a twisted structure. In this study, it was found that there exist wide variations on the long axis of the ACL. To perform accurate anatomic ACL reconstruction like double bundle ACL reconstruction or rectangular BPTB ACL reconstruction, it should take into consideration to reproduce native ACL footprint’s long axis angle.

Conclusion

The mean angle between axis of femoral shaft and the long axis of femoral ACL footprint are approximately 29 degrees. There exists wide variation in the femoral ACL footprint’s long axis.