Abstract
Introduction Techniques of joint motion study have been limited in value by being cadaveric, or if living, non-weight-bearing, or involving two-dimensional imaging [fluoroscopy]. MRI is attractive in providing no exposure to ionising radiation, and having the potential for analysis in three dimensions. Vertical-access open MRI, designed to allow invasive procedures within the imaging volume of the magnet, can be used to allow assessment of the knee in the standing living subject. A ‘tracking device’ can maintain the same plane of scan despite incremental movements of the joint. This allows imaging of a single slice of the joint throughout the range of knee motion.
Methods A series of studies have been undertaken employing this technique to establish tibio-femoral kinematics in the normal, ACL deficient, and post ACL reconstruction knee. In addition the kinematics of the Lachman’s test have been studied.
Results The sagittal plane results for the mid-medial and mid-lateral compartments of the normal knee show very different patterns of motion of the femur on the tibia during flexion. There is little antero-posterior position change medially but the lateral femur moves a considerable way back on the tibia. This differential motion equates to femoral external rotation [tibial internal rotation] as the knee flexes. The same pattern of movement occurs and to the same magnitude, but with the tibia in a more anterior position throughout. The ACL reconstructed group had very good clinical outcome, and their laxity was reduced. However the pattern of the tibio-femoral motion was same as the ACL deficient knees.
Conclusions Our results question the widely held concepts of femoral ‘roll-back’, mediated by tension in the cruciate ligaments. The implications are potentially very far-reaching for knee arthroplasty technique and design and knee ligament injury and treatment. It may also be possible to explain, as a consequence of normal tibio-femoral motion, a theory of causation of the usual pattern of osteoarthritis affecting the antero-medial part of the tibia.
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.
