The load-displacement characteristics of neonatal rat cranial sutures

Objective: Recently several centers have attempted to distract the cranio-facial skeleton in infants with craniosynostosis. To effectively achieve this goal, we must first understand the normal sutural response to tensile forces. The objective of this study was to determine the load-displacement characteristics of neonatal rat sutures. Methods: Thirty cranial sutures were harvested from 1-week-old Wistar rats (10 each coronal, posterior frontal, and sagittal). The width of the harvested bone-suture-bone construct was standardized to 4 mm. The specimens, kept moist, were mounted fresh and distracted at 10 μm/sec until rupture using a Vitrodyne V1000 universal tester. Standard load-displacement curves were constructed. The stiffness, defined as tensile force/change in suture length, and the ultimate stress, defined as tensile force at suture rupture/cross sectional area, were calculated. Results: These sutures demonstrated classical viscoelastic behavior. During the elastic phase, they elongated approximately 1 μm for every 1 g of force (10⁴ N/m). The ultimate tensile stress was epproximately 4 MN/m². The estimated mean elastic modulus was 10 megapascals. The posterior frontal sutures were significantly less stiff then the other two sutures (Kruskal-Wallis nonparametric analysis of variance, p = .0023). The difference in the ultimate stress was also significant (p = .0201). Conclusions: This study provides data regarding the basic mechanical behavior of neonatal cranial sutures in a mammalian system.