Functional anatomy of the anterior cruciate ligament and a rationale for reconstruction

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.