Acetabular morphology and resurfacing design

The bony surfaces of 18 archaeological hemipelves were scanned using a 3D l aser surface scanner and CyDir(TM) software on a Silicon Graphics workstati on. The acetabular area was selected and point data from the approximately spherical bone surface saved. These data were input to a MATLAB routine tha t calculated the radius and centre of the best-fit sphere. The goodness of fit was estimated using the mean and standard deviation of the distance of the bone surface points from the sphere surface. Eight points, at approxima tely equal distances around the acetabular rim, were selected with referenc e to bony landmarks. A plane containing three of these points served as an orientation reference plane. The vectors joining the eight rim points to th e centre of the best-fit sphere were found. The angles between these Vector s and the normal to the reference plane were calculated. Paired angles were summed to give the angle subtended by the acetabular rim in four direction s. The overall mean angle was 158 degrees (range of mean angles 145 degrees -173 degrees). The largest individual angles, some exceeding 180 degrees, were in the superior-inferior direction, while the mean angle in the anteri or-posterior direction, i.e. that controlling flexion-extension, was 152 de grees. Males had larger subtended angles than females, although the differe nce was not statistically significant. Simulated reaming increased all angl es by approximately 10 degrees. The subtended angles are important paramete rs in the design of the acetabular component of a hip replacement and parti cularly important in resurfacing hip replacement when the volume available is tightly constrained. (C) 2000 Elsevier Science Ltd. All rights reserved.