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Small variability associated with identifying and locating anatomical landmarks on the knee has the potential to affect the joint coordinate systems and reported kinematic descriptions. The objectives of this study were to develop an approach to quantify the effect of landmark location variability on both tibiofemoral and patellofemoral kinematics and to identify the critical landmarks and associated degrees of freedom that most affected the kinematic measures. The commonly used three-cylindric open-chain kinematic description utilized measured rigid body kinematics from a cadaveric specimen during simulated gait. A probabilistic analysis was performed with 11 anatomical landmarks to predict the variability in each kinematic. The model predicted the absolute kinematic bounds and offset kinematic bounds, emphasizing profile shape, for each kinematic over the gait cycle, as well as the range of motion. Standard deviations of up to 2 mm were assumed for the anatomical landmark locations and resulted in significant variability in clinically relevant absolute kinematic parameters of up to 6.58 and 4.4 mm for tibiofemoral and 7.68 and 6.5 mm for patellofemoral kinematics. The location of the femoral epicondylar prominences had the greatest effect on both the tibiofemoral and patellofemoral kinematic descriptions. A quantitative understanding of the potential changes in kinematic description caused by anatomical landmark variability is important not only to the accuracy of kinematic gait studies and the evaluation of total knee arthroplasty implant performance, but also may impact component placement decisionmaking in computer-assisted surgery. ß

Understanding the differences in knee kinematic descriptions is important for comparing data from different laboratories and observing small but important changes within a set of knees. The purpose of this study was to identify how differences in fixed body femoral coordinate systems affect the described tibiofemoral and patellofemoral kinematics for cadaveric knee studies with no hip present. Different methods for describing kinematics were evaluated on a set of seven cadaveric knees during walking in a dynamic knee simulator. Three anatomical landmark coordinate systems, a partial helical axis, and an experimental setup-based system were examined. The results showed that flexion-extension was insensitive to differences in the kinematic systems tested, internal-external rotation was similar for most femoral coordinate systems although there were changes in absolute position, varus-valgus was the most sensitive to variations in flexion axis direction, and anterior-posterior motion was most sensitive to femoral origin location. Femoral coordinate systems that define the sagittal plane using anatomical landmarks and locate the flexion axis perpendicular to the femur's mechanical axis in the frontal plane were typically similar and described kinematics most consistently.

The technique of vacuum shadowing small objects and the advantages of this method in light photography are detailed. The ultra-thin metal-carbon films thus prepared show greater contrast and resolution than acetate peel replicas.Two main problems arise in the photography of small objects. First, with curved surfaces the depth of field may not be sufficient for perfect focus to be attained over the entire object. Second, the relief of the object may be so slight as to result in insufficient contrast for good photographic reproduction.The first problem has been largely solved by the technique of cellulose acetate peels, a method familiar to most geologists. The second problem, that of increasing contrast, has been examined in a number of ways; Dollar (1948), for example, described a technique for use in studying low relief on etched or abraded rock surfaces. He accentuated topographic contrast by filling cavities in the rock surface with a suitable pigment, which, in the process of making a peel, adhered to the cellulose acetate. Other techniques to improve contrast have been described by Triebel (1947) andFournier (1956) ; none of these methods, however, is completely satisfactory. A further difficulty arises from the effect of light scattering by the acetate film at higher magnifications, which seriously affects the quality of the photographs.The method described below is based on a technique commonly used in electron microscopy, but which has not, as far as the authors know, been used in light photography. Initially, a peel is made of the object to be studied. With hard objects such as sand grains, it is possible to obtain very clean surfaces by repeated replication (the early replicas being discarded) which frees the surface of relatively loose material. The peel is then placed in a vacuum evaporator with a pressure of about 10' 4 mm. of mercury, and a heavy metal such as chromium is vaporized at an angle (usually 45 degrees) upon the peel. Such shadowing results in a metal film which is thickest on surfaces perpendicular to the direction of shadowing, and lightest on surfaces parallel to that direction. Carbon is then vaporized perpendicularly upon the film to give it added strength. Finally the peel is removed with acetone, leaving a very fine metal-carbon film which has a thickness of less than 200 angstroms and is, of course, transparent. The film may be picked up on a very fine GEOL. MAG. VOL. 101 NO. 4 .

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