Do expansile cranial springs erode through the cranium?

UNLABELLED: Expansile cranial springs are used in selected cases of craniosynostosis. The spring exerts moderate force against the relatively thin skull. We investigated whether the spring erodes through the bone and the clinical significance of any erosion relative to the cranial expansion achieved.

METHODS

New Zealand white rabbits (n = 10) underwent sagittal suturectomy and spring insertion. Amalgam markers were placed perpendicular to the expected direction of suture erosion. A control group (n = 10) underwent suturectomy. Radiological evaluation was performed for 7 weeks to check for migration of the spring foot.

RESULTS

The mean cranial thickness was 1.4 mm at the site of spring insertion. This compared with 1.8 mm in 7 children undergoing spring cranioplasty. The mean spring force was 9.4 N. In sagittal synostosis, the mean spring force used is 7 to 10 N.The cranial width increased 11.02 mm in the spring treatment group compared with 0.23 mm in the control group (P < 0.001). Spring erosion occurred in 4 (20%) of the 20 spring ends. Mean spring erosion for the treatment group was 0.18 mm. This was 3.2% of the mean increase in cranial width. The maximum percentage spring erosion versus cranial expansion in an individual rabbit was 14.17%. There was no statistical difference in cranial expansion between the rabbits in whom bone erosion did and did not occur.

CONCLUSIONS

The degree of spring force required to effectively expand the cranium may cause bone erosion in some individuals. This degree of spring erosion was of minimal clinical significance in this animal model.