Title:
A simple evaluation of anterior cruciate ligament femoral tunnel position: the inclination angle and femoral tunnel angle.

Abstract:
Postoperative determination of tunnel position after anterior cruciate ligament (ACL) reconstruction can be challenging.
The femoral tunnel angle and inclination angle are reliable methods for evaluating tunnel position after ACL reconstruction while aiding in determining whether an ACL reconstruction falls outside an anatomic range as defined on 3-dimensional (3D) computed tomography (CT).
Cohort study (diagnosis); Level of evidence, 3.
Fifty patients were included who received single-bundle ACL reconstructions with postoperative flexion weightbearing radiographs, magnetic resonance imaging (MRI), and CT scans. Femoral tunnel angles were determined from posterior-to-anterior postoperative radiographs, and inclination angles were determined from sagittal MRI. The ACL reconstructions were grouped by surgical technique, transtibial (TT) or tibial tunnel independent (TTI), and as either falling inside or outside an anatomic range on 3D CT.
Patients with tunnel positions within an anatomic range, as previously defined, had a larger femoral tunnel angle (39.3° ± 4.2°) and smaller inclination angle (49.5° ± 2.7°) than patients who fell outside an anatomic range (17.2° ± 12.5° and 62.3° ± 7.8°, respectively) (P < .001). Patients in the TTI group had a larger femoral tunnel angle (37.6° ± 9.30°) and smaller inclination angle (51.8° ± 6.5°) than those in the TT group (14.2° ± 9.3° and 63.5° ± 7.2°, respectively) (P < .001). Posterior-to-anterior femoral tunnel position was negatively correlated with femoral tunnel angle (P < .001, r = .78) and positively correlated with inclination angle (P < .001, r = .74). Based on a receiver operating characteristic (ROC) curve, a femoral tunnel angle of 32.7° (100% sensitivity and 85% specificity) and inclination angle of 55° (100% sensitivity and 87.5% specificity) were determined to distinguish ACL reconstructions that fell either within or outside an anatomic range on 3D CT.
Femoral tunnel angle and inclination angle can be reliably determined from both posterior-to-anterior radiographs and sagittal MRI and provide a useful metric for characterizing femoral tunnel position.