Femoral Tunnels' Length Changes with Knee Flexion Angle in Anatomical Anterior Cruciate Ligament Reconstruction

OBJECTIVE The objective of our study was to evaluate the effect that knee flexion angle while femoral tunnels are being drilled may have on the length of these tunnels, in anatomical reconstruction of the anterior cruciate ligament. METHODS We measured the lengths of anteromedial and posterolateral tunnels for the anterior cruciate ligament in 20 unpaired anatomical knee specimens (10 right and 10 left knees), all with the cartilage and cruciate ligaments intact. Tunnels were drilled with the knees flexed at 90°, 110° and 130°, through the accessory anteromedial portal, with a 2.5 mm drill. The statistical analysis was done by means of Friedman's variance analysis and the Mann-Whitney U test. RESULTS The mean anteromedial femoral tunnel lengths measured with the knees flexed at 90°, 110° and 130° were 33.7 (± 3.72) mm, 37.4 (± 2.93) mm and 38.8 (± 3.31) mm, respectively. For the posterolateral femoral tunnel lengths, the results were 32.1 (± 4.24) mm, 37.3 (± 4.85) mm and 38.4 (± 2.51) mm, respectively. Friedman's variance analysis showed that there was a significant difference between the lengths of the tunnels drilled with 90° and 110° of flexion angle, but showed that there was no significant difference between the tunnels drilled with flexion of 110° and 130° (P < 0.05). CONCLUSIONS It is possible to drill the femoral tunnels through the accessory anteromedial tunnel with the knee flexed at 110° in such a way as to produce a tunnel of sufficient length for a good bone-graft interface.