The effect of intra-operative knee flexion angle on determination of graft location in the anatomic double-bundle anterior cruciate ligament reconstruction

Graft tunnel placement is the factor with most influence on the outcome of double-bundle anterior cruciate ligament (ACL) reconstruction. However the final decision for the graft location has to be decided subjectively under arthroscopy, and can be misplaced due to the effect of the knee flexion angle. The displacement of the estimated placement by surgeons from the ACL anatomical attachment is due to the knee’s differing knee flexion angle. Eight cadaveric knees and an electromagnetic position recording system were employed. After digitizing the anatomical location of AM and PL bundle center, four experienced surgeons estimated the graft placement repeatedly at 70°, 90° and 110° of knee flexion. The displacements between these two positions were calculated and analyzed separately in antero-posterior and disto-proximal directions. The displacements of the estimated AM bundle placements were 4.7 ± 3.4 mm at 70°, 4.3 ± 2.2 mm at 90°, and 6.0 ± 2.6 mm at 110°, while those of the PL bundle were 4.0 ± 2.2 mm at 70°, 3.4 ± 1.9 mm at 90°, and 4.2 ± 2.5 mm at 110°. The best results were obtained at 90° of knee flexion. Additionally, the estimated placements for both AM and PL bundle were located more distally as the flexion angle increased. Our results imply that the knee should be set at 90° when determining the graft placement in double-bundle reconstruction to prevent misplacement of the graft usually in a disto-proximal direction.