The failure rate after anterior cruciate ligament (ACL) reconstruction performed by expert surgeons is estimated to be in the range of 10-15%, and only 60% of patients undergoing this surgery are able to resume sporting activities comparable to those they engaged in prior to the traumatic incident. Incorrect femoral tunnel placement is one of the main causes of failed ACL reconstruction and this must be remembered when undertaking revision surgery. There are various possible errors that can be committed and, to plan revision surgery correctly, it is fundamental to study the position of the existing femoral tunnel(s) both on classic anteroposterior and lateral plain radiographs and on computed tomography scans with frontal, sagittal, and coronal sections, and also using three-dimensional reconstruction. In-depth anatomical knowledge and familiarity with the various possible surgical techniques are also mandatory for a successful surgical outcome. Fig. 5. The dotted line indicates the area under which the femoral insertion point of the new ligament (asterisk) is located.

<p><strong>Aim</strong> <br />To evaluate tunnel positioning on radiographs in singlebundle (SB) and double-bundle (DB) anterior cruciate ligament<br />(ACL) reconstruction, to evaluate if measurement is accurate and reproducible.<br /><strong>Methods<br /></strong> Radiographs of 30 SB and 30 DB ACL reconstruction were reviewed by two examiners who measured tunnel positioning with the quadrant method on the femur (a=depth, b=height) and the Amis and Jakob method on the tibia. Intra- and inter-observer reliability were evaluated with intra-class correlation coefficient (ICC).<br /><strong>Results</strong> <br />A radiographic analysis was completed in all patients in a SB-group and in 27 in a DB-group (p>0.05). Intra-observer reliability was almost perfect on femoral (ICC: a=0.85, b=0.83) and tibial (ICC=0.87) side in the SB-group. In the DB-group, it was almost perfect for tibial anteromedial (AM) and posterolateral (PL) bundles (ICC: AM=0.84, PL=0.81) and for femoral PL bundle (ICC: a=0.83, b=0.82), and substantial for femoral AM bundle (ICC: a=0.78, b=0.74). Inter-observer reliability was almost perfect on tibial (ICC=0.81) and femoral (ICC: a=0.81, b=0.87) side in the SB-group, and substantial on tibial (ICC: AM=0.71, PL=0.77) and femoral (ICC: AM a=0.73, b=0.78; PL a=0.74, b=0.76) side in the DB-group. Standard deviation (SD) was low (±9%) with respect to the centre of tunnel(s).<br /><strong>Conclusion</strong> <br />The quadrant method and the Amis and Jakob method are accurate and reproducible measurement methods. Also, as SD<br />was low, an outside-in approach with a front-entry guide, which is free-hand positioned, can be postulated as a reliable method to locate the femoral tunnel in SB reconstruction and the AM bundle in DB reconstruction.</p>