What is the Role of Force in Correcting Scaphocephaly Through Spring-Mediated Cranial Vault Expansion for Sagittal Craniosynostosis?

Abstract

Spring-mediated cranial vault expansion (SMC) may enable less invasive treatment of sagittal craniosynostosis than conventional methods. The influence of spring characteristics such as force, length, and quantity on cranial vault outcomes are not well understood. Using in vivo and ex vivo models, we evaluate the interaction between spring force, length, and quantity on correction of scaphocephalic deformity in patients undergoing SMC. The authors retrospectively studied subjects with isolated sagittal craniosynostosis who underwent SMC between 2011 and 2019. The primary outcome measure of in vivo analysis was head shape determined by cephalic index (CI). Ex vivo experimentation analyzed the impact of spring length, bend, and thickness on resultant force. Eighty-nine subjects underwent SMC at median 3.4 months with median preoperative CI 69% (interquartile range: 66, 71%). Twenty-six and 63 subjects underwent SMC with 2 and 3 springs, with mean total force 20.1 and 27.6 N, respectively (P < 0.001).Postoperative CI increased from 71% to 74% and 68% to 77% in subjects undergoing 2- and 3-spring cranioplasty at the 6-month timepoint, respectively (P < 0.001). Total spring force correlated to increased change in CI (P < 0.002). Spring length was inversely related to transverse cranial expansion at Postoperative day 1, however, directly related at 1 and 3 months (P < 0.001). Ex vivo modeling of spring length was inversely related to spring force regardless of spring number (P < 0.0001). Ex vivo analysis demonstrated greater resultant force when utilizing wider, thicker springs independent of spring arm length and degree of compression. A dynamic relationship among spring characteristics including length, bend, thickness, and quantity appear to influence SMC outcomes.