Morphometry of proximal humerus end

Little is known about the spatial geometry of the medullary canal of the humerus. This may explain why the humeral prostheses are presently made by means of the graphical techniques used for femural prostheses. Furthermore, no mathematical models have been used to study the shape of the humeral medullary canal. Material and methods. We have calculated, on standard radiographs the values of the flare index and the curvature radius of 70 dried humeri. The curvature radius of the proximal medullary canal of the same humeri was determined applying a mathematical model to the data obtained by means of measures carried out on axial CT scans (by calculating the barycentres of the scans) and on three-dimensional reconstructions. The values obtained were compared with those calculated on radiographs. The results obtained with our technique were then compared with those obtained from data. Results. Our results show that no precise information on the spatial geometry of the humeral medullar canal can be obtained form radiographic studies. We also found that the proximal half of the humeral canal either sharply procurves, though to a mild extent, and then gradually becomes rectilinear, or gradually reaches the largest amount of curvature. On the frontal plane, the upper half of the medullar canal is cranially inward curved and distally outward curved, or vice versa. Conclusions. The results of this study give new information on the spatial geometry of the humeral medullary canal. Hence, while it seems impossible to improve beyond a certain limit the "fill" of the femural canal achieved by custom made prostheses, the typical morphometry of the humeral canal may lead to further improvements of the "fit" between the implant and the canal, compared with the currently available prostheses.