QUANTITATION OF ARTICULAR SURFACE-TOPOGRAPHY AND CARTILAGE THICKNESS IN KNEE JOINTS USING STEREOPHOTOGRAMMETRY

An analytical stereophotogrammetry (SPG) technique has been developed based upon some of the pioneering work of Selvik [Ph.D. thesis, University of Lund, Sweden (1974)] and Huiskes and coworkers [J. Biomechanics 18, 559-570 (1985)], and represents a fundamental step in the construction of biomechanical models of diarthrodial joints. Using this technique, the precise three-dimensional topography of the cartilage surfaces of various diarthrodial joints has been obtained. The system presented in this paper delivers an accuracy of 90-mu-m in the least favorable conditions with 95% coverage using the same calibration method as Huiskes et al. (1985). In addition, a method has been developed, using SPG, to quantitatively map the cartilage thickness over the entire articular surface of a joint with a precision of 134-mu-m (95% coverage). In the present study, our SPG system has been used to quantify the topography, including surface area, of the articular surfaces of the patella, distal femur, tibial plateau, and menisci of the human knee. Furthermore, examples of cartilage thickness maps and corresponding thickness data including coefficient of variation, minimum, maximum, and mean cartilage thickness are also provided for the cartilage surfaces of the knee. These maps illustrate significant variations over the joint surfaces which are important in the determination of the stresses and strains within the cartilage during diarthrodial joint function. In addition, these cartilage surface topographies and thickness data are essential for the development of anatomically accurate finite element models of diarthrodial joints. The geometric data obtained in this study may also be useful for other bioengineering applications such as the determination of joint contact areas [Ateshian et al, ASME Biomech. Symp. 98, 105-108 (1989), Soslowsky et al., ASME Adv. Bioengng 15, 129-130 (1989), Soslowsky et al., Biomechanics of Diarthrodial Joints, pp. 243-268. Springer, NY (1990)] and the development of anatomically accurate artificial joints.