Abstract
Objective: This study challenges the assumption that pivot shift is abolished once anterior stability is restored in the ACL reconstructed knee. Method: The kinematics of 7 cadaver knees were studied with the Flock-of-Birds, as pivot shift was repeated in intact, ACL deficient, then ACL reconstructed specimens with grafts tensioned at 0, 10, 20, 40 and 60N. All were BPTB grafts in similar positions. Results: Pivot shift is described as a sudden reduction from internal rotation of 8.57 +/− 2.3° at knee flexion of 24.2 +/− 11°; achieved with iliotibial loading of 56.2 +/− 11.5N, 2.26 +/− 0.6Nm valgus load and 1.5 +/− 0.4Nm internal torque. Internal rotation was significantly reduced at 40N (3.2°, p< 0.005) and 60N (2.9°, p=0.001). At maximum tension, all specimens felt stable and pivoted less. This reduction of internal rotation averaged 62%; ranging from 42% (subtle pivot) to 100% (complete abolition). At 90° knee flexion external rotation was reduced with graft tension of 60N, but not significantly (p=0.03). The range of knee flexion during reduction of the pivot shift was not significantly altered. Conclusions: Tensions of grafts that restored anterior stability (40N & 60N) did not always abolish the pivot shift, but significantly reduced it. This may account for complaints of subtle instability despite surgical reconstruction. Grants: DTT Lie was supported by a grant from the Singapore National Medical Research Council.
The abstracts were prepared by Professor Jegan Krishnan. Correspondence should be addressed to him at the Flinders Medical Centre, Bedford Park 5047, Australia.
