Optimal orientation of the bone tunnels in the anterior cruciate ligament reconstruction

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Although large internal pressure are reported to occur in ligament grafts at bone tunnels, little is known about the optimal bone tunnels in anterior cruciate ligament (ACL) reconstruction. The purpose of this study was to determine the optimal orientation of the bone tunnels in the ACL reconstruction. Optimal orientation is defined to be such that the bending and strain imposed on the graft throughout the range of motion is minimal. First, in the numerical analysis, optimal orientataion of the drill holes was investigated by computer reconstituted three dimensional knee model. Secondly, in the experiment using fresh cadeveric knees, the orientation of drill holes and bending angle of in the grafts were measured by analysing the two dimensional radiografs taken with the specially desined apparatus. The optomal orientation of the drill hole of the femur tilted 20_O laterally in coronal plane and 23_O anteriorly in sagital plane. In the tibia, drill hole should be directed 24_O medially and 50_O anteriorly from the isometric point. Numerically analyzed bening angle corresponded well to the experimental study and the maximal bending angle were 58_O for the femur and 18_O for the tibia respectively. The deformity of the graft in the femoral side is larger than that in the tibial side. Since there is restriction as to the possible orientation of the bone tunnels in femur with current reconstructive procedure, a different drilling system such as inside-out drilling appears to be advantageous to prevent early failure of the graft after ACL reconstruction.