Diversity of proximal femoral medullary canal.

To analyze the endosteal dimensions of the proximal femoral medullary canal, we studied 50 cadaver femora using computed tomography and a border detection method from 20 mm above the lesser trochanter, the osteotomy level, down to the isthmus. We documented the presence of a dense calcar septum in 96% of femora studied. In addition to mediolateral, anteroposterior, and neck-oriented dimensions, we calculated canal flare indices (CFIs) between the osteotomy level and the isthmus and metaphyseal canal flare indices (MCFIs) between the osteotomy level and the level 20 mm below the lesser trochanter midpoint to describe the shape of the endosteal cavity. With respect to the canal opening, the anteroposterior and mediolateral planes parallelled each other over the entire region as indicated by the high correlation (r = .7, P < .001) between the CFIs in these directions. The prediction of one dimension from another was unreliable in the metaphyseal region, where bone ingrowth is supposed to occur in a femoral prosthesis. The MCFI seemed to be the best parameter to distinguish the various types of proximal femoral canal shapes. We have described the variability of the proximal femoral endosteal dimensions in detail and find that the wide variation in the shape and size of the proximal femoral medullary canal means that it is almost impossible to achieve 100% cortical contact with the stem, especially in the metaphysis.