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RESEARCH PAPERS

Precise Measurement of Cat Patellofemoral Joint Surface Geometry With Multistation Digital Photogrammetry

[+] Author and Article Information
J. L. Ronsky, S. K. Boyd

Department of Mechanical Engineering, University of Calgary, 2500 University Drive, N.W., Calgary, T2P 1N4 Canada

D. D. Lichti, M. A. Chapman

Department of Geomatics Engineering, University of Calgary, 2500 University Drive, N.W., Calgary, T2P 1N4 Canada

K. Šalkauskas

Department of Mathematics and Statistics, University of Calgary, 2500 University Drive, N.W., Calgary, T2P 1N4 Canada

J Biomech Eng 121(2), 196-205 (Apr 01, 1999) (10 pages) doi:10.1115/1.2835104 History: Received January 08, 1998; Revised December 01, 1998; Online January 23, 2008

Abstract

Three-dimensional joint models are important tools for investigating mechanisms related to normal and pathological joints. Often these models necessitate accurate three-dimensional joint surface geometric data so that reliable model results can be obtained; however, in models based on small joints, this is often problematic due to limitations of the present techniques. These limitations include insufficient measurement precision, the requirement of contact for the measurement process, and lack of entire joint description. This study presents a new non-contact method for precise determination of entire joint surfaces using multistation digital photogrammetry (MDPG) and is demonstrated by determining the cartilage and subchondral bone surfaces of the cat patellofemoral (PF) joint. The digital camera–lens setup was precisely calibrated using 16 photographs arranged to achieve highly convergent geometry to estimate interior and distortion parameters of the camera–lens setup. Subsequently, six photographs of each joint surface were then acquired for surface measurement. The digital images were directly imported to a computer and newly introduced semi-automatic computer algorithms were used to precisely determine the image coordinates. Finally, a rigorous mathematical procedure named the bundle adjustment was used to determine the three-dimensional coordinates of the joint surfaces and to estimate the precision of the coordinates. These estimations were validated by comparing the MDPG measurements of a cylinder and plane to an analytical model. The joint surfaces were successfully measured using the MDPG method with mean precision estimates in the least favorable coordinate direction being 10.3 μm for subchondral bone and 17.9 μm for cartilage. The difference in measurement precision for bone and cartilage primarily reflects differences in the translucent properties of the surfaces.

Copyright © 1999 by The American Society of Mechanical Engineers
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