Comparison of radiographic images. A new method for analysis of very small movements.

A new method, shift comparisoN, for comparing 2 radiographic images is described. The method may be used for many purposes, but is particularly suitable for detecting small provoked motions between skeletal parts. Defective union in fractures or osteotomies is easily diagnosed by such a comparison. Films are exposed before and during the application of force to one of the fragments. By examining the films in the Shift Comparator small movements caused by the force may be detected. The technique has also been used for measuring the development of stability of union of tibial fractures by determining th deflection of the fracture caused by a bending moment.