Review Question - QID 1100

All of the given responses are true except for Answer 4, because an excessively anterior femoral tunnel does not cause interference screw divergence.

Anterior placement of the femoral tunnel is the most common surgical error during arthroscopic ACL reconstruction. Errors in surgical technique are one of the most common reasons for graft failure in patients who present with recurrent instability after ACL reconstruction. Technical shortcomings that result in graft failure after primary reconstruction include nonanatomic tunnel placement, graft impingement, improper tensioning of the graft, inadequate fixation of the graft in bony tunnels, graft material problems, and the failure to address insufficiency of the secondary stabilizers of the knee during ACL reconstruction.

The papers by Allen and Harner et al stress the importance of determining the cause of failure prior to revision surgery. It is estimated that 70% to 80% of graft failures are caused by malpositioned tunnels. The consequences of nonanatomic tunnel placement are well described in the literature.

Sommer et al note that inappropriate positioning of either the tibial or femoral tunnels results in excessive changes in graft length as the knee moves through its functional range of motion and can effect clinical results. Because biologic ACL grafts can only accommodate small changes in length before undergoing plastic deformation, a mal-positioned graft may result in either capturing of the knee or lengthening of the graft over time; this results in either a loss of motion or recurrent instability, respectively. Improper femoral tunnel placement is most often caused by the failure to adequately visualize the most posterior aspect of the notch (the “over-the-top” position). Because the femoral attachment of the ACL is closer to the center of rotation of the knee, small errors in femoral tunnel placement may have deleterious effects on knee kinematics.