The elastic modulus of fetal cranial bone: A first step towards an understanding of the biomechanics of fetal head molding

Abstract

Fetal head molding is the change in shape of the fetal head due to forces of labor. The biomechanics of this process are poorly understood. To understand it better, classical engineering structural analysis is being applied to analyze the process. A fundamental part of this analysis is to describe the mechanical properties of the constituent materials, a knowledge which has been lacking for fetal cranial bone.As a first step toward defining the mechanical properties, 86 specimens of fetal cranial bone obtained from specimens ranging in estimated gestational age from 25 to 40 weeks were tested in three-point bending. In addition, 12 specimens from a 6-yr-old calvarium were tested for comparative purposes. The data indicate that the elastic modulus is highly sensitive to gestational age and fiber orientation. Elastic modulus values for specimens with parallel fiber orientation are in the range of 1.65 x 103 MPa for preterm bone to 3.86 x 103 MPa for term bone. The results are discussed with respect to the limitations of the test method. Finally, clinical inferences are made.