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Notes: Abstract The purpose of this study was to evaluate the influence of the graft positioning on the clinical outcome and magnetic resonance imaging (MRI) signal of the graft following anterior cruciate ligament (ACL) reconstruction using the central one-third of the patellar tendon. Twentytwo patients with a chronic anterior instability underwent a modified Marshall-MacIntosh procedure, while 27 with a subacute torn ACL had an ACL reconstruction using a free bone-patellar tendon-bone graft. The patients were retrospectively reviewed with a 1.8-year average followup (1–3 years). The clinical result was evaluated through the comparative range of motion and the residual laxity as measured with the KT 1000 arthrometer. The roentgenographic analysis was performed from anteroposterior (AP) and mediolateral (ML) views, made first on one-leg standing with the knee at 30° of flexion, and secondly at “zero” extension with active quadriceps contraction. Lines were drawn to visualise the location of the tibial and femoral tunnels in relation to the tibial plateaus and the intercondylar roof represented by Blumensaat's line. The analysis of the lateral MRI views of the graft allowed discrimination between homogenous and heterogenous graft signals. On lateral roentgenograms of normal knees, it was found that Blumensaat's line crossed the surface of the medial tibial plateau at 30%±9% of its sagittal width (20%–40% range), demonstrating the variability of intercondylar roof inclination. The range of motion was normal in 34 patients (group I), 9 patients had a flexion deficit (group II), and 6 exhibited an extension deficit (group III). The residual laxity was similar in each group (P〉0.05). When comparing group III to group I, patients from the former group had a tibial tunnel significantly more anterior with regard to Blumensaat's line (P=0.02). In group III, all patients exhibited a heterogenous MRI graft signal (P〈0.05). and the angle between the intra-articular part of the graft and the tibial tunnel was higher (P〈0.001). These findings were not observed in group II where the location only of the femoral tunnel seemed to influence the flexion deficit (P〈0.05). This study demonstrated that the location of the tibial tunnel with regard to the intercondylar roof, when the knee is at “zero” extension, was the most relevant parameter in control of the extension deficit resulting from a graft impingement. No relation was found between the tibial tunnel location with regard to the tibial plateaus and the mobility deficit. Also, graft impingement was always associated with a heterogenous graft MRI signal. When reconstructing the ACL, care must be taken when inserting the K-wire aimed to guide the tibial drill to obtain a proper position with regard to the roof of the intercondylar notch. The K-wire location must be checked at “zero” extension. Intraoperative X-rays may help.