Critical-Size Defect Ossification: Effect of Leporid Age in a Cranioplasty Model

The ability of the human cranium to ossify full-thickness defects depends on the size of the area and the age of the patient. An adult leporid cranioplasty model is commonly used to study inlay cranioplasty materials; the influence of age on ossification is unknown in this model. The purpose of this study was to determine the effect of age on healing of a rabbit critical-size defect. Nineteen rabbits were divided into 4 groups: group 1 (n = 5) aged 4 months, group 2 (n = 4) aged 8 months, group 3 (n = 5) aged 12 months, and group 4 (n = 5) aged 16 months. A 17 x 17-mm defect was created in the parietal bones with preservation of the underlying dura. Animals underwent micro-computed tomography 4 months postoperatively to determine ossification of the defect. Group 1 defects healed by 28.5% (SD, 12.5%), group 2 defects ossified by 37.2% (SD, 5.7%), group 3 defects closed by 28.2% (SD, 11.9%), and group 4 defects healed by 39.4% (SD, 11.0%). No difference in ossification was found between groups (P = 0.31). Leporids as young as 4 months do not close a 17 x 17-mm defect; ossification is similar to animals as old as 16 months. Rabbits 4 months or older are suitable for a calvarial critical-size defect model.