Optimal Femoral Tunnel Positioning in Posterior Cruciate Ligament Reconstruction Using Outside-in Drilling

PurposeThe goal of our study was to determine the precise femoral drill guide placement during reconstruction of the anterolateral bundle (ALB) of the posterior cruciate ligament (PCL) femoral footprint that would produce a minimum tunnel length of 25 mm, a maximum graft/femoral tunnel angle of 50°, and a minimum distance of 10 mm between the femoral socket and the subchondral bone of the weight-bearing surface of the medial femoral condyle.MethodsUsing computer navigation, we used synthetic replicas of human femora to create a series of virtual femoral sockets. We then measured the bone tunnel length, angle of the femoral socket relative to the PCL footprint, and distance from the subchondral bone of the weight-bearing surface of the medial femoral condyle to the femoral socket at a series of guide pin sleeve positions. We positioned the guide pin using the following angle combinations: −20°, −10°, 0°, 10°, 20°, 30°, 40°, 50°, and 60° to a line perpendicular to the femoral axis in the coronal plane and −15°, 0°, 15°, 30°, 45°, and 60° to a line parallel to the transepicondylar axis in the axial plane. Using linear regression models, we determined the precise drill guide placement angles that would produce the optimal tunnel length, graft/femoral tunnel angle, and distance to the subchondral bone margin.ResultsThe results were consistent between small, medium, and large femora. We found that the optimal drilling angles for anatomic reconstruction of the femoral footprint of the ALB of the PCL were 0° to a line perpendicular to the femoral axis in the coronal plane and 15° to a line parallel to the transepicondylar axis in the horizontal or axial plane.ConclusionsDuring outside-in drilling for PCL reconstruction, holding the guide pin sleeve at a position 0° to a line perpendicular to the femoral axis in the coronal plane and 15° to a line parallel to the transepicondylar axis in the horizontal or axial plane results in optimal bone tunnel length, graft/tunnel angle, and distance between the femoral socket and the subchondral bone of the weight-bearing surface of the medial femoral condyle.Clinical RelevanceWe describe a precise femoral tunnel drill guide placement during outside-in PCL reconstruction that ensures an optimal femoral socket with a minimum bone tunnel length of 25 mm, maximum graft/femoral tunnel angle of 50°, and minimum distance of 10 mm between the subchondral bone of the weight-bearing surface of the medial femoral condyle and the femoral socket.