Roentgenographic measurement study for locating femoral insertion site of anterior cruciate ligament: a cadaveric study with X-Caliper

The purpose of this study was to determine the relationships of the anterior cruciate ligament (ACL) femoral insertion site with femoral bony landmarks and develop a new method of location. Sixteen unpaired normal Chinese human cadaveric knees were used. Femoral insertion sites of the ACL were marked with metal wires. Four pairs of bony landmarks were selected: anatomical axis of distal femur (A) and parallel tangent of posterior condyles (B); tangent of anterior condyles parallel to landmark A (C) and landmark B; Blumensaat’s line (D) and parallel tangent of distal condyles (E); and tangent of posterior condyles (F) and parallel tangent of anterior condyles (G). The X-Caliper was used to measure the distance between the centre of the insertion site and each pair of bony landmarks. The ratio of distances to each pair of bony landmark was calculated. Clock position of the ACL femoral footprint was measured on anteroposterior (AP) roentgenograms at 90 degree flexion. The centre of the ACL footprint was found at 65.3% ± 1.1% between A and B, 78.1% ± 1.0% between B and C, 38.3% ± 2.7% between D and E, and 43.1% ± 4.6% between F and G. The distances to bony landmarks A, B, D, and E have smaller variations. Blumensaat’s line and the anatomical axis of the distal femur were regarded as more useful and made location of the insertion site more precise. A parallelogram made up of these two bony landmarks can be used. On AP roentgenograms, the centre of the femoral footprint should be moved to lower than the 10:00 o’clock (2:00) position.