The triangle between the anterior and posterior cruciate ligaments: an arthroscopic anatomy study

The goal of anterior cruciate ligament (ACL) reconstruction is to place the graft in closest proximity to the native ACL anatomy. This study aims to examine the angular relation between intact anterior and posterior cruciate ligaments (PCL) from an arthroscopic perspective.

Forty patients (20 male, 20 female) with a mean age of 35.12 (range: 18-40) years that underwent knee arthroscopy for reasons other than ACL rupture were included in the study. Following diagnostic examination and repair of the primary pathology, the triangle between ACL and PCL was seen at different flexion degrees of the knee joint (120, 90, 60, and 30°) through standard anterolateral (AL) and anteromedial (AM) portals. The narrow top angle of the triangle between the long intersecting axes of ACL and PCL was measured using recorded images by 3 blind observers.

The average ACL-PCL angle was 61°, (standard deviation±2°) at 90°of knee flexion. The angles were narrower when viewed through the AM portal. The degree of the angles was not affected by age, sex, body mass index (BMI), or the side (right or left) on which the procedure was performed. There was good-to-excellent intra- and interobserver reliability.

The angular relation between intact ACL and PCL has the potential to provide a better view of the anatomy during arthroscopic ACL surgery. To perform better anatomic reconstructions, it is important to create a 60° angle between the ACL graft and PCL (as viewed through AL portal) at 90°of knee flexion.