Radiographic landmarks for tunnel positioning in double-bundle ACL reconstructions

Abstract

The purpose of this study was to establish quantitative and qualitative radiographic landmarks for identifying the femoral and tibial attachment sites of the AM and PL bundles of the native ACL and to assess the reproducibility of identification of these landmarks using intraclass correlation coefficients. It was hypothesized that the radiographic positions of the AM and PL bundles could be defined in relation to anatomic landmarks and radiographic reference lines. The femoral and tibial attachment sites of the AM and PL bundles on twelve cadaveric knees were labeled with radio-opaque markers. The positions of the AM and PL bundle attachment sites were quantified on radiographs by three independent examiners. On the lateral femoral view, the AM bundle was located at 21.6±5.6% of the sagittal diameter of the femur drawn along Blumensaat's line and 14.2±7.7% distal to the notch roof along the maximum notch height. The PL bundle was located at 28.9±4.6% of the sagittal diameter and 42.3±6.0% of the notch height. The knee flexion angle at which the AM and PL bundle attachment sites were horizontally oriented was 115±7.1°. On the tibial AP view, the AM and PL bundles were located at 44.2±3.4 and 50.1±2.1%, respectively, from the medial aspect of the tibia along its coronal diameter. On the lateral view, the distances from the AM and PL bundles to the anterior tibial margin measured along the tibial sagittal diameter were 36.3±3.8 and 51.0±4.0%, respectively. The center of the PL bundle attachment was located almost precisely at the center of the tibial plateau in both the coronal and sagittal planes. This study defines the radiographic locations of the femoral and tibial bundle attachment sites of the native ACL and a reliable and transferrable protocol for identifying these sites on radiographs in relation to surrounding landmarks and digitally projected reference lines. In addition, it was found that the femoral attachments of the AM and PL bundles were horizontally aligned at 115° of knee flexion and the PL bundle tibial attachment was located essentially at the center of the tibia.