Measuring three-dimensional knee kinematics under torsional loading

Excessive knee joint laxity is often used as an indicator of joint disease or injury. Clinical assessment devices are currently limited to anterior-posterior drawer measurements, while tools used to measure movement in the remaining degrees of freedom are either invasive or prone to soft tissue artefact. The objective of this work was, therefore, to develop a methodology whereby in vivo knee joint kinematics could be measured in three dimensions under torsional loading while still maintaining a non-invasive procedure. A device designed to administer a subject-normalized torque in the transverse plane of the knee was securely fastened to the outer frame of an open magnetic resonance imaging (MRI) magnet. Low resolution 3D T1-weighted images (6.25 mm slice thickness) were generated by the 0.2 Tesla MRI scanner in less than 3 min while the joint was under load. The 3D image volume was then shape-matched to a high resolution image volume (1.56 mm slice thickness) scanned in a no-load position. Three-dimensional rotations and translations of the tibia with respect to the femur were calculated by comparing the transformation matrices before and after torque was applied. Results from six subjects showed that this technique was repeatable over five trials with the knee in extended and flexed positions. Differences in range of rotation were shown between subjects and between knee positions, suggesting that this methodology has sufficient utility for further application in clinical studies.