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Research Papers

# Quasi-Steady-State Displacement Response of Whole Human Cadaveric Knees in a MRI Scanner

[+] Author and Article Information
K. J. Martin

Biomedical Engineering Program, University of California, One Shields Avenue, Davis, CA 95616

C. P. Neu

Department of Orthopaedic Surgery, University of California at Davis Medical Center, 2315 Stockton Boulevard, Sacramento, CA 95817

M. L. Hull1

Biomedical Engineering Program, and Department of Mechanical Engineering,  University of California, One Shields Avenue, Davis, CA 95616mlhull@ucdavis.edu

1

Corresponding author.

J Biomech Eng 131(8), 081004 (Jun 19, 2009) (7 pages) doi:10.1115/1.2978986 History: Received March 19, 2007; Revised May 15, 2008; Published June 19, 2009

## Abstract

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.

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## Figures

Figure 1

Electropneumatic apparatus with top and side of frame removed for clarity. The apparatus frame fits within the 58-cm-diameter bore of a clinical MRI scanner.

Figure 2

Diagram of plastic version of 4DOF adjustable attachment device with components in non-neutral positions. The aluminum version of the device had the same dimensions but did not have compartments encasing Delrin spheres surrounded by silicone gel and had a pin fixed to the end of the hinge, which was collinear with the vector from the center of rotation of the plastic device to the single sphere at its end, which was used to fix the device, and thus specimen, to the loading apparatus. M-L and A-P translations were achieved by sliding slotted plates relative to the first plate, which was attached to the distal end of the tibia. F-E and V-V rotations were achieved by revolving the hinge and pivot block, respectively, about the two axes of the universal joint.

Figure 3

Apparatus with knee aligned to 10 deg of flexion. The top and side of the frame are removed for clarity.

Figure 4

Example displacement response for a cadaveric knee specimen cyclically loaded in compression to 1500 N. While displacement continues to change once quasi-steady state is achieved (at 276 cycles for this particular specimen), this change is less than the change allowed by the slope criterion required by the CDTR technique.

Figure 5

Example images in the sagittal plane of a specimen depicting undeformed (b) and deformed (c) states of cartilage of the knee taken from the region of interest shown in the original unloaded cartilage image (a). Solid arrows denote an area of observable deformation. Deformation analysis cannot be performed between these two images because 3D registration of the cartilage volume is required to account for any out-of-plane cartilage displacement. A 3D registration was not performed because CDTR has not yet been adapted for use with a clinical scanner and therefore could not be applied to establish and track tag lines over a 3D volume.

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