Effects of extremity positioning on radiographic evaluation of femoral tunnel location with digitally reconstructed femoral lateral radiographs after anterior cruciate ligament reconstruction

BACKGROUND Radiographic imaging is a valuable tool in clinical practice for quick anatomical assessment. We aimed to radiographically assess (A) the anterior cruciate ligament (ACL) graft tunnel location after anatomic single-bundle (SB) reconstruction and (B) the effects of extremity positioning on the localization of the orifice of the tunnel in the distal femur in comparison with Blumensaat's line (BL). METHODS Three-dimensional computed tomography (3D CT) scan examinations of 22 knees of 22 subjects were evaluated. The 3D CT scan data was used to digitally reconstruct the true lateral radiographs. Graft tunnel location on the distal femoral shaft along the Blumensaat's line and perpendicular to it were assessed on these radiographs. The femur was digitally rotated to simulate varus, valgus, internal rotation and external rotation in 5-degree increments from 0 to 20-degree. At each incremental rotated position of the femur, position of the ACL graft tunnel was calculated relative to BL and the difference from the true lateral x-ray was estimated. RESULTS The position of the tunnel in the distal femur was 30.6 (±4.4) % along BL and 33.1 (±5.4) % perpendicular to BL. Ten and more degree of external, internal, valgus and varus rotations significantly affected the estimates of tunnel position (P < 0.05). CONCLUSIONS Femoral tunnel location can be reliably estimated from lateral radiographs after anatomic SB ACL reconstruction. Although, ten or more degree of rotations can introduce significant inaccuracies in tunnel location estimates, our study suggests that BL is overall reliable for assessing location of the distal femoral tunnel. LEVEL OF EVIDENCE Level 2b (Retrospective Cohort Study).