Relaxin does not rescue coronal suture fusion in craniosynostotic rabbits

Objectives: Craniosynostosis affects 1 in 2000 to 3000 live births and may result in craniofacial and neural growth disturbances. Histological data have shown that thick collagenous bundles are present in the sutural ligament, which may tether the osteogenic fronts, resulting in premature fusion. The hormone relaxin has been shown to disrupt collagen fiber organization, possibly preventing craniosynostosis by relaxing the sutural ligament and allowing osteogenic fronts to separate normally and stay patent. This study tested this hypothesis with a rabbit model of delayed-onset coronal suture synostosis. Methods: A total of 18 New Zealand White rabbits with craniosynostosis were randomly assigned to one of three groups: sham control, protein control (BSA), relaxin treatment. After initial diagnosis, sham surgery, BSA, or relaxin was delivered to the fusing coronal suture in a slow-release (56-day) collagen vehicle. Longitudinal radiographs and body weights were collected at 10, 25, 42, and 84 days of age, and sutures were harvested for histology. Results: Relaxin-treated animals had more disorganized intrasuture content than control groups. These specimens also appeared to have relatively wider sutures ectocranially. There were no significant differences in relaxin-treated animals for all craniofacial growth measures, or suture separation compared with controls. Conclusions: These data do not support our initial hypothesis that the use of relaxin may rescue sutures destined to undergo premature suture fusion. These findings suggest that collagen fiber arrangement may not be important for suture fusion. This protein therapy would not be clinically useful for craniosynostosis.