In thirty-three normal cadaver knees from adults (mean age, twenty-nine
years), the average length of the anterior cruciate ligament was 31 +/- 3
millimeters and the angle between the ligament and the long axis of the
femur was 28 +/- 4 degrees with the knee at 90 degrees of flexion. We could
find no macroscopic or microscopic evidence of discrete subdivisions of the
anterior cruciate ligament. We studied the functional importance of the
positions of the attachments of the anterior cruciate ligament. The
distance between the central points of the normal attachment areas on the
tibia and on the femur was found to be isometric during flexion and
extension. The so-called over-the-top position on the femur was the least
favorable of the positions that we tested, since it resulted in an average
elongation of the ligament of ten millimeters with the knee in full
extension as compared with full flexion. On the basis of the results in the
present study, we suggest some basic principles for a standardized
replacement operation for a deficient anterior cruciate ligament.