Holographic studies on human femur with internal fixations

Abstract

Healing of fractured bones may proceed under conditions of maintained stable contact using internal fixations like plates and screws and intramedullary nails. The effect of these fixators is to reduce (not abolish) fracture mobility. Thus, pain is reduced and the limb is protected from excessive deformation. Internal fixation of fractured bones, therefore, requires a good knowledge of the dynamics of stresses and strains, in order to provide an optimal environment for undisturbed fracture healing.
Pauwels postulated that eccentrically (off-axially) loaded bones have one cortex loaded in tension and the other in compression. The eccentrically loaded bone is subjected to bending stresses, which result in a typical distribution of stresses with the tension coming on the convex side and compression on the concave side of the bone. Pauwels demonstrated its application using an engineering technique called tension band fixation. This postulate has also been proven in vivo using strain gauges by Schatzker.
In this study, double-exposure holographic interferometry (DEHI) was used to determine the dynamics of bending and compression on a human femur with internal fixations under eccentric loading. The advantages of DEHI are the following: it is non-contact, extremely sensitive and a full-field displacement distribution is readily obtained. Three bones were used in this study: a femur without fracture, a femur with fracture stabilized by a plate and screws, and a femur with fracture stabilized by an intramedullary nail.