Reconstruction technique affects femoral tunnel placement in ACL reconstruction

Abstract

Grafts placed too anteriorly on the femur are reportedly a common cause of failure in anterior cruciate ligament reconstruction. Some studies suggest more anatomic femoral tunnel placement improves kinematics. The ability of the transtibial technique and a tibial tunnel-independent technique (placed transfemorally outside-in) to place the guide pin near the center of the femoral attachment of the anterior cruciate ligament was compared in 12 cadavers. After arthroscopic placement of the guide pins, the femur was dissected and the three-dimensional geometry of the femur, anterior cruciate ligament footprint, and positions of each guide pin were measured. The transtibial guide-pin placement was 7.9 +/- 2.2 mm from the center of the footprint (near its anterior border), whereas the independent technique positioned the guide pin 1.9 +/- 1.0 mm from the center. The center of the footprint was within 2 mm of an anteroposterior line through the most posterior border of the femoral cartilage in the notch and a proximodistal line through the proximal margin of the cartilage at the capsular reflection. More accurate placement of the femoral tunnel might reduce the incidence of graft failure and might reduce long-term degeneration observed after reconstruction although both would require clinical confirmation.

Fig. 1

In the independent technique, a two-incision technique was used to place the femoral guide pin transfemorally from the outside-in, independently of the tibial tunnel. The target of the independent guide was placed at the center of the anterior cruciate ligament (ACL), as judged visually by the surgeon.

Fig. 2

A 3-D digitizing stylus (top) was used to generate 3-D models of the femur, including the cartilage border and ACL attachment site (bottom). In this specimen, the independent technique placed the guide pin near the centroid of the ACL, whereas the transtibial technique resulted in placement anterior and proximal to the center of the ACL.

Fig. 3

Position of an anatomic reference point relative to the center of the ACL was measured. The anatomic landmark was defined as the intersection of the most posterior point on the cartilage-bone border and the most proximal point on the cartilage visible in the notch. In addition, the shape and position of the ACL was measured in the sagittal plane (mean ± standard deviation).

Fig. 4

The independent technique placed the guide pin closer to the center of the ACL compared with the transtibial technique (p = 0.000012, mean + standard deviation).

Fig. 5

The transtibial technique placed the guide pin anterior (p = 0.006) and proximal (p = 0.01) to the independent technique. The anatomic reference point, defined as the position of the intersection of an anteroposterior line through the most posterior border of the femoral cartilage and a proximodistal line through the proximal margin of the cartilage at the capsular reflection, was within 2 mm of the center of the ACL.