Purpose: To define the positions of the attachments of the anteromedial (AM) and posterolateral (PL) bundles of the anterior cruciate ligament (ACL).
Methods: The shape and positions of the femoral and tibial attachments of the 2 bundles relative to bony landmarks were measured in 7 fresh-frozen, unpaired cadaveric knees by 6 independent observers. Metallic marker beads were then inserted into the defined anatomic points, and plain radiographs of the specimens were taken. We used the line described by Amis and Jakob on the tibia and the grid prepared by Bernard et al. for the femur to define AM and PL bundle attachment positions.
Results: In the cadaveric specimens, referencing the position of the AM bundle tibial attachment from the retro-eminence ridge (RER) resulted in the least interobserver error. On tibial radiographs, the distance between the posterior tibial cortex and the perpendicular projection of the center of the AM bundle attachment onto Amis and Jakob's line was 35.6 +/- 5.1 mm. The ratio of this distance to the length of Amis and Jakob's line (from the anterior cortex) was 36% +/- 3.8% (and 52% +/- 3.4% for the center of the PL bundle). On the femur, the center of the AM bundle was situated at 26.4% +/- 2.6%, and the center of the PL bundle at 32.3% +/- 3.9%, along the length of Blumensaat's line.
Conclusions: The RER provides an easily identifiable and accurate reference point that can be used clinically. On a lateral radiograph, the positions of the tibial attachments can be referenced to Amis and Jakob's line. This method, different from Blumensaat's line, is independent of knee flexion.
Clinical relevance: This study details anatomically and radiologically the positions of the attachments of the AM and PL bundles of the ACL. This could assist with accurate tunnel placement in reconstruction surgery and provide reference data for postoperative radiographic evaluation.