Expander elements in craniofacial surgery: An experimental study in rabbits

With the inception of craniofacial surgery elaborate surgical procedures we re introduced for the treatment of craniosynostosis. Recently the use of im plantable springs to aid simple strip craniectomies for these conditions ha s been described. Having shown the feasibility of using springs for dynamic skull reshaping, several questions remain to be answered. all of them abou t how to control the spring action clinically. One of the most important qu estions concerns force. The purpose of this study was to evaluate experimen tally the effect of two springs of different strengths on the growth of rab bit calvaria after strip craniectomy. Thirty-two 6-week-old rabbits were ra ndomised into one of four groups: sham-operation where only amalgam markers were inserted after subperiostal dissection: strip craniectomy of the: sag ittal suture. no expansion: strip craniectomy of the sagittal suture and in sertion of an expander element made of titanium molybdenum alloy (TMA): and strip craniectomy sagittal suture and insertion of an expander element mad e of stainless steel (SS). SS springs delivered a range of forces from 2.42 -2.18 N. whereas the TMA expander elements delivered a range from 1.39-1.09 N. The parietal bone marker separation after 12 weeks was 4.9 mm in the TM A group and 7.4 mm in the SS group. This resulted in a significant increase of the calvarian height compared with control groups. Histological examina tion showed intramembranous bone formation in the bone gap in all groups.