Adaptation of the cranium to spring cranioplasty forces.

BACKGROUND: During spring-assisted cranioplasty, the spring transmits forces through adjacent cranium. We have previously demonstrated that the ectocranial-endocranial thickness of cranial sutures increases significantly over time in the presence of continuous spring forces. We wished to investigate if cranial bone showed similar adaptational responses.
METHODS: New Zealand white rabbits were randomized into a treatment group [a spring was placed across a posterior frontal suture (PFS) suturectomy and a control group (PFS suturectomy)]. Animals (n = 6) were euthanized from each group at 4, 7, and 10 weeks, respectively. A sham group (n = 6) was euthanized at 10 weeks. Frontal bone thickness was recorded at five reproducible anatomical points on the frontal bone. Histological analysis of the bone architecture was performed.
RESULTS: Frontal bone thickness was significantly greater than controls at all five sites at weeks 7 and 10. There were multiple significant differences between the 4-, 7-, and 10-week groups with each site progressively thickening over time. Histological analysis revealed a uniform increase in thickness of the endocranial and ectocranial cortical bone in the treatment groups.
CONCLUSIONS: Cranial bone adapts to the presence of continuous spring cranioplasty forces by progressively thickening over time. This property is beneficial in craniosynostosis cases with very thin and poor quality bone and may partly explain the observed lack of spring erosion through bone.