Figure 7.41 PP head bearing surface feature curve profiles of a selected curve from all specimens have smaller correlation coefficient values compared with other correlation coefficients. Thus, generally, it is better to use other dimensions such as the radii of the minimum best-fit circles and the widths of the PP head as the defining sizes of the finger joint replacement designs.
Suppose that the radii of the best-fit circles in the PP head are used in the finger joint prosthesis design. From the database we find that the radii of the best-fit circles range from 2.5 to 4.5 mm, which is considered as the anatomical range of all finger joints for people ingeneral. Therefore, the final design can be categorized into several groups based on the dimensions of the radii of the best-fit circles.
7.6.2 Generalized finger joint surface reconstruction
Owing to the complexity of the finger joint geometry, a great deal of data is required to construct a model of the articulating surface of a finger joint. Several problems are involved in this process: first, the huge amount of data will require much space to store the information, which is generally not desired; second, there will be strong information redundancy in the database, which will hinder the application of the database. To resolve this, we apply an NURBS-based information model that uses control points and Bernstein polynomials to represent complex curves and surfaces.
Control points on the feature curves of the finger joint surface are extracted and a database stores the control points. Data from the database can then be accessed by commercial CAD software packages to reconstruct the finger joint bearing surfaces.
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