Analysis of the Müller anterolateral femorotibial ligament reconstruction using a computerized knee model

Iliotibial tract tenodesis has been described by Müller as part of the surgical treatment for anterolateral rotatory instability in the ACL deficient knee. The aim of this study was to use a previously described and validated computer model of the knee to calculate the effectiveness of Müller's extraarticular anterolateral femorotibial ligament (ALFTL) graft as a substitute for the ACL or as an adjunct to an intraarticular ACL reconstruction in the ACL deficient knee. This effectiveness was tested by simulating the application of a torque sufficient to create 15 degrees of internal rotation or 5 mm of anterior displacement of the tibia on the femur at 0 degrees, 15 degrees, and 30 degrees of knee flexion. The effects of moving the graft's proximal fixation point 1 cm superior, inferior, and anterior to the current surgical attachment site were examined to determine the amount of permissible surgical error in graft placement. The model predicts that the ALFTL is a useful restraint to internal rotation when it is performed with or without an intraarticular ACL reconstruction. The ALFTL graft took up greater amounts of tension and became more effective at increasing angles of knee flexion. Placement of the ALFTL graft 1 cm anterior to the current surgical attachment site decreases the vector component that lies perpendicular to the long axis of the tibia and consequently reduces resistance to internal rotation. The ALFTL graft at any attachment site was ineffective in resisting pure anterior displacement between 0 degrees and 30 degrees.