Quadriceps/anterior cruciate graft interaction. An in vitro study of joint kinematics and anterior cruciate ligament graft tension.

The Oxford Rig, a device that simulates active knee extension during stance, was used to study the effects of quadriceps force on AP tibial displacement and axial tibial rotation in vitro. Human anatomic specimen knees were tested with the anterior cruciate ligament (ACL) intact, sectioned, and reconstructed. Patellar tendon grafts used in the ACL-reconstructed state were attached distally to a load cell, allowing direct measurement of graft tension. Both ACL status and quadriceps force had significant effects on anterior tibial displacement, limits of AP displacement, axial tibial rotation, and graft tension, as shown by analysis of variance. Anterior cruciate ligament sectioning led to anterior tibial displacement in the absence of quadriceps force, whereas ACL reconstruction led to posterior tibial displacement. In the ACL-intact, quadriceps-stabilized state, anterior displacement of the tibia was observed between 95 degrees flexion and full extension, with a maximum displacement (3.5 +/- 0.2 mm) between 30 degrees and 45 degrees flexion. After ACL sectioning, anterior tibial displacement resulting from quadriceps force was accentuated relative to the intact state by as much as 4.5 mm +/- 0.9 mm at 20 degrees and 25 degrees flexion. Anterior tibial displacement in the ACL-intact and reconstructed specimens was similar when quadriceps force was present. In the quadriceps-stabilized state, graft tension increased between 5 degrees and 80 degrees flexion. The maximum increase in graft tension due to quadriceps force was at 35 degrees flexion.