Postoperative evaluation of femoral tunnel position in ACL reconstruction: plain radiography versus computed tomography

Inaccurate femoral tunnel placement has been identified as one of the most frequent errors in failed anterior cruciate ligament reconstructions. Most surgeons evaluate the femoral tunnel position on plain radiographs but in a lot of cases it is difficult to detect the femoral tunnel. The goal of this study was to compare plain digital radiographs and multiplanar computed tomography (CT) scans for the evaluation of femoral tunnel position. We examined 50 patients 24-60 months postoperatively, following an arthroscopically-assisted anterior cruciate ligament reconstruction with central third bone-patellar tendon-bone graft. Endobutton fixation was used on the femoral side and titanium interference screws on the tibial side. Standard antero-posterior and lateral X-rays and a CT scan were obtained from each patient. Sagittal and frontal reconstructions of the CT scan were used for the evaluation. We measured the height of the center of the tunnel in the notch in the frontal plane, and the position of the tunnel along Blumensaat's line (BL) in the lateral plane. Measurements are reported as percentages of total notch height and of the length of BL. On plain X-rays the tunnel was invisible in 46 cases in the anterior-posterior plane and in eight cases on the lateral plane. The average position in the frontal plane was 89.8%, and in the lateral plane 38.6%. In the CT scans, measurements were able to be done in 48 patients. The frontal-plane position averaged 90.5% and the lateral-plane position 34.1%. Pearson's correlation coefficient for the values in the lateral plane for CT and X-rays was low at 0.22, with p>0.05. In our group of 50 patients we were able to detect the femoral tunnel on both plains of standard X-rays in only four patients, whereas it was possible to take accurate measurements in 48 patients on reconstructed CT scans. We advocate the use of CT technology for the evaluation of femoral position whenever precise measurements are needed.