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Patient Specific Instrumentation in ACL reconstruction1437The shortcoming of the current surgical techniques is resembled by the high prevalence of femoral tunnel malposition. It has been recognized before that a one size fits all approach is not the way to go in ACL reconstruction.18 Using the current available techniques that rely on the intra-operative identification of anatomical landmarks and ACL remnants, an accurate, true anatomic femoral tunnel position is not easily achieved. With the use of PSI we aim to provide a patient specific true anatomic ACL reconstruction that does not rely on the experience of the surgeon. When both the femoral and tibial tunnel are positioned at the native origin and insertion sites, the graft can resemble the native ACL more closely. From a practical point of view, we have chosen to aim for the center of the femoral footprint of the ACL which was regarded as the midpoint between the anteromedial (AM) and posterolateral (PL) bundle of the ACL. The advantage of the PSI design as described here, is that the surgeon has ultimate control over the entire femoral tunnel position. This means that a point toward the AM bundle can be selected as well. Also, control over tunnel position can be of great benefit in the case of revision surgery. In this way, tunnel collision can be prevented through accurate preoperative planning of the tunnel. The selected point in this experiment is not representative for clinical use as mid-bundle techniques potentially have a higher graft re-rupture rate.22 The aim of our study was limited to determining the accuracy of the patient specific aiming guide; in other words, can we achieve a planned tunnel position. The scope of this study did not involve the amount of coverage of the ACL footprint. However we hypothesize that recreation of native anatomy will improve outcome after ACL reconstruction. The footprint of the ACL has been shown to vary in size from 60mm2 to 130mm2, of which about half of it being reserved for each bundle.18 An average hamstrings graft of 8mm in diameter can cover an area of about 50mm2 (A= π r2) which increases to about 80mm2when a 10 mm graft is harvested. More recent studies by Smigelski have shown that the ACL may in fact be more ribbon shaped27 and ACL reconstruction techniques have been proposed to reconstruct the ACL using a ribbon shaped graft.6 On the other hand, some authors advocate the reconstruction of the isometric, direct fibers of the ACL using the I.D.E.A.L. technique.19 Ideally, if we strive for patient specific ACL reconstruction, Mark Zee.indd 143 03-01-2024 08:56