The Biomechanical Characteristics of Cranial Sutures Are Altered by Spring Cranioplasty Forces

Abstract

The mechanical properties of the pediatric craniofacial complex allow dissipation of spring cranioplasty forces. Springs do not fully expand in situ and continue to transmit a continuous force until removal. The authors wished to investigate whether ongoing forces altered the biomechanical characteristics of cranial sutures. Thirty New Zealand White rabbits were divided into five groups: spring expansion for 4, 7, and 10 weeks; early spring removal at 4 weeks followed by monitoring for 3 weeks; and a control group (n = 6 each). Cranial expansion was monitored using cephalometry. The left coronal suture then underwent load-displacement testing in a dynamometer. Relapse of cranial expansion was observed following early spring removal (mean, 6 percent; p = 0.017). Cranial suture thickness was significantly correlated to the length of spring insertion. Load displacement curves of sutures in all groups initially exhibited classic viscoelastic behavior. The treatment group developed intrasutural weakening before failure that was not observed in controls. The peak load before failure as a percentage of that observed in controls was 31 percent in the 4-week group (p = 0.001), 35 percent in the 7-week group (p = 0.000), and 45 percent in the 10-week group (p = 0.023). Cranial suture compliance is modified in the presence of continuous spring cranioplasty forces. Thickening of the coronal sutures, which have been expanded in a shear-like manner, increases their three-dimensional surface area and may contribute to the relative lack of relapse observed after early spring removal.