Nasal Dorsal Augmentation with Freeze-Dried Allograft Bone: 10-Year Comprehensive Review: Correction.

T authors report the first case of freeze-dried bone graft for nasal surgery. Their cases exhibited an initial loss of measured projection. At 6 months, however, projection persisted, with an average of 87 percent at 6 months. Two pathways of graft survival are hypothesized: (1) bone induction involving vascularization by stem cell conversion to eventual osteoblastic bone proliferation, and (2) preservation of the graft as an unaltered “alloimplant. ” To the authors’ credit, their experiment was a bold attempt to test the efficacy of freeze-dried bone without the usual adjunct of bone morphogenetic protein to enhance osteoinduction. Ten patients showed 100 percent maintenance of projection at 1 to 3 years, an impressive percentage considering the known history of freeze-dried grafts in the literature1 when bone morphogenetic protein is not used. Their use of positron emission tomographic scans to evaluate vascularization can probably be justified. They provide a detailed analysis of their rationale. Their assertion that osteoinduction can occur without bony contact is probably valid—animals given supraperiosteal hydroxyapatite acid/bone morphogenetic protein implants animals show bone ingrowth.2 Most importantly, their hypothesis that some grafts may survive as an alloimplant is credible. Good evidence for it is the biopsy specimen at 2 years of one patient showing that the graft showed no change whatsoever over time, appearing similar to a new freeze-dried allograft when purchased. One question is prompted, however: if the freeze-dried graft is in effect an alloimplant, is it subject to the potential problem implants have in terms of exposure when under thin skin? My main concerns are as follows: first, the suggestion that osteoinduction was enhanced by bone morphogenetic protein remaining in the freezedried allograft is weak. In analyzing freeze-dried specimens, Li et al.3 found no discernible bone morphogenetic protein. Second, vascularization may not be the best criterion with which to establish that graft survival was accomplished by osteoinduction. Even unadulterated allografts undergo vascularization before resorption.4 The method preferred by orthopedists to determine whether allograft incorporation has occurred is computed tomography. Ideally, one would like to see an actual fusion between the graft and nasal bone to declare that bone induction has occurred. Therefore, the lack of fusion noted in the given case example may be stronger evidence in favor of the alloimplant phenomenon than osteoinduction. Third, a minor point that does not relate to the hypothesis of the article is that the patient in Figure 9 did not need much augmentation. At most, temporalis fascia would have been my choice. Fourth, although unavoidable, the sparseness of long-tem follow-up is problematic. Only two patients were seen at 3 years. Ultimately, we will want to know the range of retention values for freeze-dried grafts. Some of them could be undergoing long-term slow resorption as allografts tend to do. It takes many years before ultimate absorption is seen in some irradiated cartilage allografts.5 The same may turn out to be the case for freeze-dried allografts, but possibly not. Furthermore, the standard material is autogenous cartilage, which invariably shows a retention rate well over 95 percent. In sum, the authors have bravely developed a method to avoid the unpleasant donor-site morbidity associated with autogenous rib grafts. To me, their data suggest that if the freeze-dried graft follows an osteoinduction pathway it may, without bone morphogenetic protein, undergo late resorption. However, their data also support the ingenious hypothesis that it can act as an alloimplant that can be permanent. As such, it might be beneficial to encourage an avascular approach, which presumably favors alloimplant induction, by placing the allograft supraperiosteally and not screwing to nasal bone. Future follow-up by the authors will answer some of these questions. They were