Volume Maintenance of Onlay Bone Grafts in the Craniofacial Skeleton: Micro-architecture versus Embryologic Origin

Abstract

The superior volume maintenance of membranous over endochondral bone has been shown in several studies and provides the basis for its preferred clinical use as an onlay grafting material in the craniofacial skeleton. The scientific rationale for this seeming embryologic advantage, however, has never been proven. Our hypothesis is that the pattern of onlay bone graft resorption is primarily determined by a graft's micro-architecture (relative cortical and cancellous composition) rather than its embryologic origin (membranous versus endochondral). Twenty-five adult New Zealand, White rabbits were used for this study. Eight animals were killed at 3 weeks, eight animals at 8 weeks, and nine animals at 16 weeks. Three graft types were placed onto each rabbit cranium: cortical bone graft of membranous origin and cortical and cancellous bone graft of endochondral origin. Fluorochrome markers were injected into all living rabbits at 1, 6, and 14 weeks. Microcomputed tomography scanning was performed on all of the bone grafts to determine postsacrifice volumes and to obtain detailed information regarding the bone graft's trabecular architecture. In addition, specimens were examined histologically. Volume analysis showed a statistically greater resorption rate in the cancellous endochondral bone graft than in either the endochondral or membranous cortical bone grafts (p < 0.05) for all time points. In addition there was no significant difference in the resorption rates between the endochondral and membranous cortical bone grafts. A post-test power analysis (alpha = 5 percent) of the volume data comparing the two types of cortical bone grafts showed that a difference in resorption of 8.9 percent would be detected with a 90-percent probability. Previous studies, which have shown a seeming superiority of membranous over endochondral bone grafts, used composite grafts composed of both cortical and cancellous portions. By separating these components, we have shown that cortical bone grafts maintain their volumes significantly better than cancellous bone grafts. In addition, we found no statistical difference in the resorption rates between the two cortical onlay bone grafts of different embryologic origins, a finding that has never been previously published. From our results, we believe cortical bone to be a superior onlay grafting material, independent of its embryologic origin. We believe these results challenge the currently accepted theories of bone graft dynamics and may lead to a change in the way clinicians approach bone graft selections for craniofacial surgery.

Autogenous Versus Composite Graft for the Augmentation of Anterior Maxilla Prior to Implant Placement – A Comparative Study.

“…Furthermore, membranous cortical grafts revascularization is more rapid than endochondral bone grafts.Therefore, embryological origin of donor bone is important factor for a successful recovery period. 13,14,15 Hising P etal 16 stated that from the time of implant placement and irrespective of loading time, a survival rate of 80.5% for the individual implants was estimated. In most patients (73%), Bio-Oss was mixed with autogenous bone from the chin.…”

The efficacy of biodegradable mesh as a fixation device for support of autogenous onlay bone grafts: a radiographic and histomorphometric analysis

“…Rosenthal and Buchman (2003) demonstrated that inlay bone grafts exhibit increased volumes with time, in contrast to onlay bone grafts which resorb with time .ln addition these authors ( Rosenthal & Buchman ,2003) have also shown that when the bone grafts are placed as an inlay, there is no significant advantage of cortical bone grafts over PBCM grafts with regard to bone graft volume maintenance. However, when bone grafts are placed as an onlay, the cortical bone graft maintained a higher bone volume (Ozaki and Buchman, 1998).It is also clear in the literature (animal studies and clinical trials) that inlay bone grafts maintain greater bone volume when compared to onlay grafts (Ozaki and Buchman, 1998).…”

“…In another study using a rabbit model, Ozaki and Buchman (1998) applied cancellous endochondral bone grafts on the calvarium of the rabbits, as an onlay graft, without a fixation deviee. They found that such a bone graft retained 8.1 % of its original volume at 8 weeks and only 2.1 % at 16 weeks.…”

Initial treatment of alveolar gaps in cases of labio-maxillary-palatal clefts

“…A study led by Osaki 16 showed that the embryonic origin of the graft had no influence on the quality of osteointegration. Cancellous bone brings the best results in grafts serving to fill space.…”

“…Surgeons most frequently employ cancellous bone to restore alveolar clefts. The prompt revascularization of cancellous bone and its rich supply of stem cells stimulate rapid integration at the site of the graft 4,9,16 .…”