Quasi-steady-state displacement response of whole human cadaveric knees in a MRI scanner.

It is important to determine the three-dimensional nonuniform deformation of articular cartilage in its native environment. A new magnetic resonance imaging (MRI)-based technique (cartilage deformation by tag registration (CDTR)) has been developed, which can determine such deformations provided that the compressive load-displacement response of the knee reaches a quasi-steady state during cyclic loading. The objectives of this study were (1) to design and construct an apparatus to cyclically compress human cadaveric knees to physiological loads in a MRI scanner, (2) to determine the number of load cycles required to reach a quasi-steady-state load-displacement response for cyclic loading of human cadaveric knees, and (3) to collect sample MR images of undeformed and deformed states of tibiofemoral cartilage free of artifact while using the apparatus within a MRI scanner. An electropneumatic MRI-compatible apparatus was constructed to fit in a clinical MRI scanner, and a slope criterion was defined to indicate the point at which a quasi-steady-state load-displacement response, which would allow the use of CDTR, occurred during cyclic loading of a human knee. The average number of cycles required to reach a quasi-steady-state load-displacement response according to the slope criterion defined herein for three cadaveric knee joints was 356+/-69. This indicates that human knee joint specimens can be cyclically loaded such that deformation is repeatable according to MRI requirements of CDTR. Sample images of tibiofemoral cartilage were obtained for a single knee joint. These images demonstrate the usefulness of the apparatus in a MRI scanner. Thus the results of this study are a crucial step toward developing a MRI-based method to determine the deformations of articular cartilage in whole human cadaveric knees.