Variations in sagittal locations of anterior cruciate ligament tibial footprints and their association with radiographic landmarks: a human cadaveric study

BACKGROUND This cadaveric study aimed to demonstrate variation of the anterior cruciate ligament (ACL) tibial attachment in the sagittal plane, and to analyze the radiographic landmarks which predict the sagittal location of the ACL tibial attachment. METHODS In 20 cadaveric knees, native ACLs were removed and the centers of the ACL tibial and femoral attachments were marked with metal pins. Full extension lateral radiographs were then obtained in each cadaveric knee. Using the full extension lateral radiographs, the sagittal location of the ACL tibial footprint center was estimated as a percentage in the Amis and Jakob's line. Several radiographic landmarks including the geometry of Blumensaat's line and the apex of the tibial eminence were measured. Then, the relationship between the variation of the sagittal location of the ACL tibial footprint and several radiographic landmarks were analyzed using Pearson's correlation analysis. RESULTS The average sagittal position of the native ACL tibial footprint was 40.9% (range: 38.0-45.0%). The line connecting the centers of the ACL footprint was nearly parallel to Blumensaat's line, with an average angle of 1.7° (range: 0-4.1°). In addition, the distance from the point where Blumensaat's line meets the tibial articular surface to the center of the ACL tibial footprint was almost consistent, at 7.6 mm on average (range: 6.4-8.7 mm). The correlation analysis revealed that the geometry of Blumensaat's line was significantly correlated with the sagittal location of the ACL tibial footprint. CONCLUSION The radiographic landmark that showed a significant correlation with the ACL tibial footprint in the full extension lateral radiographs was Blumensaat's line.