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ABSTRACT
Many surgeons use cancellous or corticocancellous allogeneic bone grafts to augment spinal arthrodeses. The efficacy of onlay freeze-dried cortical allografts for posterior spinal fusions has been questioned in the past. In this report, freeze-dried, crushed cortical bone allograft was used as the sole fusion material in 32 consecutive posterior spinal fusions for idiopathic adolescent scoliosis. Absence of clinical or radiographic pseudarthrosis in all patients at an average follow up of 34 months suggests that freeze-dried, crushed cortical bone allograft is a suitable material for augmentation of the fusion mass during posterior spinal fusion with segmental instrumentation.
The potential benefits of allogeneic bone graft in spinal arthrodesis have been well-described.1"9 The use of freeze-dried bone allografts is supported by their ready availability, absence of donor site morbidity, decreased operative time and blood loss, low infection transmission potential, and excellent osteoinduction.10"13 While numerous investigators have advocated the use of bone allografts in spinal arthrodesis, questions still remain regarding the optimal harvesting technique, method of preparation, and role of the immune response and histocompatibility during graft incorporation.1,8,13-22 Multiple factors, including the surgical technique of spinal arthrodesis or the type of instrumentation used, can influence graft incorporation, thus confounding the data. Likewise, methods of preparation of bone allografts appear important, as allografts sterilized in ethylene oxide gas have shown high pseudarthrosis rates in the cervical, thoracic, and lumbar spine.23,24
To date, most literature pertaining to allograft augmentation in spinal arthrodesis deals with cancellous or corticocancellous bone graft.1,4-8,11 The porous architecture of cancellous grafts permits more rapid revascularization and incorporation compared with cortical bone graft.2,13,15 The relative merits of cortical allograft are more controversial. Some authors have suggested that freeze-dried onlay cortical plate allografts placed under tension do not incorporate well, especially if used to augment posterior cervical fusions.25
On the other hand, cortical allograft may possess some qualities superior to cancellous allograft. Urist and Dawson2 noted comparable fusion rates between iliac autograft and autolyzed antigenextracted allogeneic cortical bone slabs for inter-transverse process arthrodeses in the lumbar spine. Spence et al26,27 reported that freeze-dried cortical allograft chips were superior to cancellous allografts for healing of bone cysts. A freeze-dried cortical allograft has fewer osteocytes and therefore has lower antigenicity than a freeze-dried cancellous or rresh-fjozen allograft.11,13,16,18
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