The effects of limb alignment on anterior cruciate ligament graft tunnel positions estimated from plain radiographs

The aims of this study were (1) to evaluate the femoral tunnel position after anatomic double-bundle and nonanatomic single-bundle reconstruction; (2) to evaluate the influence of rotation of the femur caused by limb malalignment on measurements of the position of the femoral ACL tunnel aperture relative to Blumensaat's line.

3D CT scans were performed in 5 patients after anatomic double-bundle reconstruction and 5 patients after nonanatomic single-bundle reconstruction. Digitally reconstructed lateral radiographs were generated from the 3D CT scans to determine the tunnel position on the femur along and perpendicular to Blumensaat's line. The femur was then rotated to simulate internal/external and varus/valgus rotations from 0° to 15° in 5° increments. At each rotated bone position, tunnel position relative to Blumensaat's line was calculated and the difference from the lateral radiograph was calculated.

After double-bundle reconstruction, the AM tunnel was located at 31.5 (±5.0) % along Blumensaat's line and 29.7 (±13.6) % perpendicular to Blumensaat's line, and the PL tunnel at 36.2 (±12.9) % along Blumensaat's line and 34.2 (±7.6) % perpendicular to Blumensaat's line. Valgus greater than 10° significantly affected the assessment of tunnel position (P = 0.043). After nonanatomic single-bundle reconstruction, the tunnel position was 35.4 (±15.0) % along Blumensaat's line and -2.7 (±19.4) % perpendicular to Blumensaat's line. Internal rotation of more than 10° significantly affected the assessment of tunnel position (P = 0.043).

Tunnel position after anatomic double-bundle reconstruction and nonanatomic single-bundle reconstruction can be determined on lateral radiographs. However, valgus and internal rotation of more than 10° can introduce significant errors in tunnel position estimates.

Case series, Level IV.