Femoral insertions of the anteromedial and posterolateral bundles of the anterior cruciate ligament: morphometry and arthroscopic orientation models for double-bundle bone tunnel placement--a cadaver study.

PURPOSE

The purpose of this study was to analyze the femoral insertions of the anteromedial (AM) and posterolateral (PL) bundles of the anterior cruciate ligament (ACL) and to develop arthroscopic orientation models for double-bundle (DB) bone tunnel placement.

METHODS

The femoral insertions of the AM and PL bundles were dissected in 50 human cadaveric knees, documented on digital photographs, and quantified with a digital image analysis system.

RESULTS

The insertion areas of both bundles were significantly larger in men (53 mm(2) for AM and 45 mm(2) for PL) than in women (39 mm(2) for AM and 39 mm(2) for PL), and the average ACL insertion area was significantly larger in left knees than in right knees. According to the "femoral center angle model," the centers of the AM and PL bundles were horizontally aligned when the femoral shaft axis was lifted 12 degrees from the horizontal plane or when the knee was flexed to 102 degrees . In this position the center of the AM bundle was 3 to 4 mm "lower" (arthroscopic terminology) to the over-the-top position, and the distance of the PL bundle to the "shallow" articular cartilage of the lateral femoral condyle was 6 mm. According to the "modified femoral clock wall model," the average centers of the AM and PL bundles were both aligned at 1 o'clock for a left knee and at 11 o'clock for a right knee in 102 degrees of knee flexion.

CONCLUSIONS

The average femoral insertion areas of the ACL and the AM and PL bundles were significantly larger in men compared with women and in left knees compared with right knees. According to the femoral center angle model, the AM and PL insertions are aligned horizontally in an average of 102 degrees of knee flexion, resulting in one commuted time for the AM and PL bundles in the modified femoral clock wall model. Both models support reproducible and reliable arthroscopic AM and PL bone tunnel placement. With regard to a mean anatomic anteroposterior length of the femoral ACL insertion of 14 to 15 mm, adequate DB bone tunnel placement should be possible in most cases.

CLINICAL RELEVANCE

This study provides an anatomic description of the femoral AM and PL insertions including gender differences, landmarks, and arthroscopic orientation models for DB bone tunnel placement.