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Technical Briefs

# A New Device for Measuring Knee Rotational Kinematics Using Magnetic Resonance Imaging

[+] Author and Article Information
R. Dana Carpenter1

Department of Radiology, University of California at San Francisco, Suite 203, 1700 4th Street, San Francisco, CA 94158

Sandra J. Shefelbine, Jesus Lozano, Julio Carballido-Gamio, Sharmila Majumdar

Department of Radiology, University of California at San Francisco, Suite 203, 1700 4th Street, San Francisco, CA 94158

C. Benjamin Ma

Department of Orthopaedic Surgery, University of California at San Francisco, San Francisco, CA 94158

1

Corresponding author.

J. Med. Devices 2(4), 044501 (Nov 07, 2008) (5 pages) doi:10.1115/1.2976029 History: Received June 11, 2007; Revised July 16, 2008; Published November 07, 2008

## Abstract

There are few commonly used clinical techniques to quantify the rotational stability and joint contact kinematics in knees in vivo. A magnetic-resonance-imaging-compatible device capable of applying axial and torsional loads to the foot was developed and used to measure in vivo knee kinematics in 14 healthy volunteers. The device was used to apply an internal torque and an axial compressive load at the foot, with the thigh held in place. Sagittal scans were made of the knee with and without an applied internal torque, and three-dimensional geometric representations of the knee joint were constructed from the images. Repeat scans of four volunteers were performed to assess precision, and phantom scans were performed to assess accuracy. Rotational measurements had a root mean square error of 0.1 deg, and precision errors for repeat measurements were 1.6 deg for internal tibial rotation, 0.3–1.1 mm for contact centroid translations, and $24.5 mm2$ for a contact area. Results indicated that the device induced significant internal tibial rotation with respect to the femur and significant translation of the medial and lateral contact centroids. A preliminary study on five anterior cruciate ligament (ACL)-deficient patients did not detect any rotational difference between ACL-deficient and contralateral knees under an isolated internal torque. This method is able to calculate rotations and centroid translations out of the scan plane and has potential applications in investigating the effects of knee injury and recovery of function.

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Copyright © 2008 by American Society of Mechanical Engineers
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## Figures

Figure 1

Experimental setup and rotational device. Top: The MRI-compatible rotational device applies an internal torque and an axial compressive load to the foot while the femur is held in place. The axial weight is attached to the rotational device via a loading strap that passes underneath the patient and applies an axial load to the foot. The torsional weight induces internal rotation via the rotational device. The surface coil is attached to the medial and lateral sides of the knee using a medical tape. Bottom left: photograph of the rotational device. Bottom right: schematic of the rotational device and load directions.

Figure 2

Coordinate systems used for the analysis of knee kinematics. Spheres were fit to the posterior aspects of the femoral condyles, and the line connecting them was used as the ML axis (left). The ML axis of the tibia was defined by connecting the two most posterior points on the medial and lateral sides of the tibial plateau (right).

Figure 3

Analysis of the cartilage-on-cartilage contact area. Left: Points along the contact region were defined on sagittal slices. Right: All points were connected with a set of triangles to compute the 3D contact area and centroid locations.

Figure 4

MR images of rotational phantom. The axis connecting the sphere centers (left) was used to define the ML axis of the “femur” in the phantom. The axis connecting the most posterior points of the test tubes (right) was used to define the ML axis of the tibia in the phantom.

Figure 5

In a representative subject with 3 deg internal tibial rotation, the lateral contact centroid moved 2.6 mm in the posterior direction, and the medial contact centroid moved 0.2 mm in the posterior direction

## Errata

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