QUADRICEPS ANTERIOR CRUCIATE GRAFT INTERACTION - AN IN-VITRO STUDY OFJOINT KINEMATICS AND ANTERIOR CRUCIATE LIGAMENT GRAFT TENSION

The Oxford Rig, a device that simulates active knee extension during s tance, was used to study the effects of quadriceps force-on AP tibial displacement and axial tibial rotation in vitro. Human anatomic specim en 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 di rect measurement of graft tension. Both ACL status and quadriceps forc e had significant effects on anterior tibial displacement, limits of A P displacement, axial tibial rotation, and graft tension, as shown by analysis of variance. Anterior cruciate ligament sectioning led to ant erior tibial displacement in the absence of quadriceps force, whereas ACL reconstruction led to posterior tibial displacement. In the ACL-in tact, quadriceps-stabilized state, anterior displacement of the tibia was observed between 95-degrees flexion and full extension, with a max imum displacement (3.5 +/- 0.2 mm) between 30-degrees and 45-degrees f lexion. After ACL sectioning, anterior tibial displacement resulting f rom quadriceps force was accentuated relative to the intact state by a s much as 4.5 mm +/- 0.9 mm at 20-degrees and 25-degrees flexion. Ante rior tibial displacement in the ACL-intact and reconstructed specimens was similar when quadriceps force was present. In the quadriceps-stab ilized state, graft tension increased between 5-degrees and 80-degrees flexion. The maximum increase in graft tension due to quadriceps forc e was at 35-degrees flexion.