The femoral canal fill of two different cementless stem designs : The accuracy of radiographs compared to computed tomographic scanning

In 19 cadaver femora we compared the fill of two types of femoral stems (plastic replica) using computed tomographic (CT) scan with a border detecting computer program and conventional radiographs. In the metaphyseal area the fill of the two types was surprisingly similar. In the diaphysis the straight stem filled significantly more than the proximally anatomic and distally over-reamed stem. Using conventional radiographs the fill measures were from 1.2 to 2.1 times higher than the values of CT scan, depending on the method of calculation. When both anteroposterior and lateral views were used, the fill as measured by radiographs correlated well with the fill as measured using CT scan. When conventional radiographs are used for evaluation of the canal fill, the calculation based on hypothetical rectangular areas at each level seemed to provide the most accurate results.