An Automated System for Design and Analysis of Total Hip Implants: A Method of Modeling the Proximal Endosteal Canal Using 3-D CT Data

The clinical success of Total Hip Arthroplasty is enhanced by matching hip implant geometry to femoral geometry. Traditionally, the shapes of hip implant designs have been based on data collected from patient populations using X-ray, CT Scan, digitized sliced bone, and other physical methods. The morphology of interest and the frame of reference often vary across researchers and the resulting numeric data are difficult to use in a Computer Aided Design package to build an implant model. This goal of this thesis was to develop procedures and automated programs for the design and evaluation of femoral hip implants using CT data. The procedures bridge the gap between patient specific custom prosthesis design and the so-called averaged femur implant designs. By automating the measurement, orientation and averaging of any user selected grouping of femora, these programs allow construction of an average femur template for small subsets of a population or populations. The programs allow grouping of femora using either dimensional attributes and/or patient attributes such as pathology, ethnic background, etc. The average femur template created for each group can then be used as the design boundary for a discrete implant size. Additional functionality is also provided for comparing average femur templates to their constitutive femora and for comparison of average femur templates against each other. To illustrate that the goals of this theses were realized, an example of the use of the system for a population of 192 Japanese is included in this thesis. The criteria for evaluation of the average femur templates was the gap or interference of the template to that of each constitutive femur along the medial and lateral endosteal contours. Testing 24 template sizes, the average of the worst fitting template to femur combination for each size resulted in a gap or interference of less than 2mm in the metaphysis and less than 4mm proximally