Transport Disc Distraction Osteogenesis for the Reconstruction of a Calvarial Defect

Purpose: Reconstruction of bone defects is possible through distraction osteogenesis using small bone transport discs. The aim of this study was to evaluate the usability of transport disc distraction osteogenesis (TDDO) in the reconstruction of skull defects in an animal experiment. Methods: Eleven mongrel female dogs were used. Craniectomy (33 x 15 mm) was performed on both sides of the parietal bone symmetrically. On the experimental site, the 7 x 15-mm transport bone disc was used for TDDO. The control site was left in the defect state. An external distraction device was used. The latency period was 5 days, the rate of distraction was 1 mm/d, and distraction was done for 26 days. After a 6-month consolidation period, a computed tomographic scan was performed. The area of regenerated bone was measured from the computed tomographic scan. The hardness was checked on the regenerated bone and the normal bone. A histologic examination of the regenerated bone was done. Result: Eight cases were included in the evaluation, and 3 cases were excluded because they showed early escape of the distraction device. The mean (SD) area of the regenerated bone was 57.1% (26.3) in the experimental site and 41.8% (21.3) in the control site, which was not a statistically significant difference (P > 0.05). The mean (SD) hardness was 0.50 (0.17) MPa in the experiment site and 0.55 (0.29) MPa in the normal calvarial bone; the difference was not statistically significant (P > 0.05). On histologic examination, membranous ossification was found in the regenerated bone in the experimental site. Conclusions: Transport disc distraction osteogenesis can induce new bone formation with hardness comparable to that of a normal bone. However, the amount of regenerated bone is not sufficient to allow TDDO to be substituted for conventional autogenous bone grafts.