Frontonasal suture expansion in the rabbit using titanium screws.

PURPOSE

This study investigated the ability to use titanium screws to provide stable skeletal points in the growing craniofacial region of the rabbit for suture expansion. These screws provided sites for direct application of external forces to alter growth and anatomic form.

MATERIAL AND METHODS

Twenty-one rabbits (30 days old) were divided into three groups: control (n = 9), experimental (n = 9, and sham (n = 3). Four four-holed AO/ASIF commercially pure titanium craniofacial plates were contoured into an L-shape with a 90 degree angle at the midpoint. The plates were placed bilaterally in the frontal and nasal bone sites and secured with 2.0-mm diameter, 4-mm long, commercially pure titanium screws in both the sham and experimental groups. After 4 week of healing, a spring mechanism with a distraction force of 55 g was activated between ipsilateral plates and across the frontonasal sutures bilaterally in the experimental group for 5 weeks. No force was applied between the plates in the sham group. A preliminary evaluation of the bone-implant interface and the changes in the suture was done histologically. Morphologic changes were measured using cephalometric radiographs and direct anatomic measurements.

RESULTS

The experimental group showed a significant increase in growth across the frontonasal suture in comparison with the sham group (P < .05). In addition, an increase in the length of the nasal and frontal bones in the expanded group was observed in comparison with the control and sham groups (P < .05). Histologically, a mixture of woven and lamellar bone was seen in the suture region and lamellar bone was seen in the screw-bone interface.

CONCLUSION

This study indicates that titanium screws in the developing rabbit skull can provide stable sites for the direct application of external forces, producing secondary changes in skeletal morphology. This laboratory models provides a useful system for the further study of growth modification using such external mechanical forces.