Computerized morphometric analysis of the femoral diaphyseal canal.

The constant increase in the use of hip arthroplasty and the continuous search for the best possible adaptation of the implant to femoral anatomy have led to the development of methods of radiographic analysis that are increasingly precise and reliable. Among these the methods that include the use of traditional radiograms-despite their limits-deserve a place of importance. In fact, these methods offer the advantage of being easy to apply and of allowing for a comparison to be made with pre-existing files. Computer science is useful in this field, in particular, computerized analysis, both morphometric and statistical, of the data acquired by digitizer. The protocol of acquisition and analysis that we applied to x-rays in anteroposterior view allowed for an evaluation to be made of some of the morphologic parameters of 354 femurs (corresponding to 264 patients), relating them with the pathologies that led to hip arthroplasty. The duration of a cementless hip prosthesis strongly depends on primary stability. For this reason, an ever-increasing number of studies tends to make a precise evaluation of the morphology of the joint, in order to obtain excellent contact between bone and prosthetic component. The methods used are essentially radiological, with the use of computerized tomography and stereophotogrammetry. Morphometric studies of the proximal femoral area have in particular considered the width of the medullary canal at various levels; the cervico-diaphyseal angle; the flare index of the femoral canal (relationship between the internal metadiaphyseal diameter and that of the isthmus) and the distance between the rotation center of the femoral head and the diaphyseal axis. The evident absence of proportion between femoral sizes and shape of the medullary canal has led to the search for parameters capable of describing in simple fashion the shape of the femoral diaphyseal canal. A good describer of femoral morphology is the flare index, that allows for classification of the various shapes of the diaphyseal canal in three families: "stove-pipe like", "normal", "champagne glass like". The distinction between these groups is not clear, as the passage from one shape to another is gradual. The idea of obtaining more knowledge on femoral morphology, also to the purpose of determining possible new criteria that may be of help in preoperative planning and in the choice of a model to be implanted, has suggested our study on modifications caused by some of the pathologies that most frequently lead to arthroplasty.