Kinematic Analysis of the Indirect Femoral Insertion of the Anterior Cruciate Ligament: Implications for Anatomic Femoral Tunnel Placement

Purpose: To determine the effect of debriding the indirect insertion component of the femoral anterior cruciate ligament (ACL) attachment on tibiofemoral kinematics when compared with the intact knee. Methods: Knee kinematics were measured in 9 cadaveric knees with the ACL intact, after indirect insertion debridement, and after ACL transection. Three loading conditions were used: (1) a 134-N anterior tibial load, (2) a combined 10-Nm valgus and 5-Nm internal tibial torque, and (3) a simulated robotic pivot shift. Anterior tibial translation (ATT) was recorded in response to anterior and combined loads at 0 degrees, 15 degrees, 30 degrees, 45 degrees, 60 degrees, and 90 degrees of flexion. Posterior tibial translation and external tibial rotation were recorded during the simulated pivot shift. Results: With an anterior load, indirect insertion debridement increased ATT by 0.37 +/- 0.24 mm at 0 degrees (P = .002) and by 0.16 +/- 0.19 mm at 15 degrees (P = .033; increases < 1 mm in all specimens). ACL transection increased ATT in response to an anterior load (P = .0001) with maximum effect at 15 degrees compared with the intact and debrided states (11.26 +/- 1.15 mm and 11.04 +/- 1.08 mm, respectively). With a combined load, indirect insertion debridement increased ATT by 0.17 +/- 0.11 mm at 0 degrees (P = .001; increases < 0.3 mm in all specimens) with no effect at other angles. ACL transection increased ATT in response to a combined load (P = .001) with maximum effect at 15 degrees (4.45 +/- 0.85 mm v ACL intact and 4.44 +/- 0.84 mm v debrided indirect insertion). In the ACL intact condition, the pivot shift produced 1.29 +/- 1.34 mm of posterior tibial translation and 1.54 +/- 1.61 degrees of external tibial rotation, as compared with 1.28 +/- 1.34 mm and 1.54 +/- 1.47 degrees, respectively, after debridement (P = .68 and P = .99, respectively) and 12.79 +/- 3.22 mm and 17.60 +/- 4.30 degrees, respectively, after ACL transection (P = .0001). Conclusions: The indirect femoral ACL insertion contributes minimally to restraint of tibial translation and rotation.