Abstract
Introduction In-vivo study by MRI has contributed to the understanding of knee kinematics for prosthetic design and the impact of knee pathology. The aim of this study was to compare the characteristics of knee motion exhibited by the tibio-femoral contact footprint and centre of the femoral posterior condyles over the tibial plateau during the flexion arc.
Methods Twelve subjects (five males, ages 19 to 42 years) with a unilateral anterior cruciate ligament (ACL) injury performed a supine leg press against a 15 kg load. Sagittal MR images recorded the motion from 0° to 90° flexion of both knees. The tibio-femoral contact points and the position of the posterior condylar centres were measured against the reference of the tibial plateau, at 15° intervals, for both the healthy knee and the ACL injured knee.
Results The tibio-femoral contact points in the healthy knee began anteriorly on the tibial plateau, and progressed posteriorly during the flexion arc. From 0° to 30° the footprints of the medial and lateral compartments are almost parallel. Onward from 30°, the lateral condyle moved further posteriorly than the medial condyle. In the ACL injured knee the footprint was more posterior on the tibial plateau, particularly on the lateral condyle, suggesting the axis of rotation of the knee had shifted medially due to ACL loss. The posterior condylar centres in the healthy knee were positioned over the centre of the tibial plateau in knee extension. The medial condylar centre remained central during the flexion arc, whereas the lateral condylar centre moved back over the tibial plateau. In the ACL injured knee the posterior condylar centres were more posterior than the healthy knees from 0° to 15°, but from 30° to 90° are not significantly different to the healthy knee. The difference in the position of the posterior condylar centres in the ACL injured knee between 0° and 15° indicates the effect of ACL deficiency on the governing axis of the knee in extension, as evidenced clinically by the pivot shift.
Conclusions The tibio-femoral contact patterns describe events at the articular surface whereas posterior condylar centres reflect the movement of the axis of rotation at the knee; two characteristics of knee kinematics. The altered action of the ACL injured knee at the tibio-femoral interface has implications for the development of wear changes in the chronic ACL injured knee.
In relation to the conduct of this study, one or more of the authors is in receipt of a research grant from a non-commercial source.
The abstracts were prepared by Mr Jerzy Sikorski. Correspondence should be addressed to him at the Australian Orthopaedic Association, Ground Floor, William Bland Centre, 229 Macquarie Street, Sydney NSW 2000, Australia.
