UTOLOGOUS bone grafts from the iliac crest are used commonly in spinal, orthopedic, and plastic proce- dures. These grafts are the gold standard in estab- lishing fusion or filling bone gaps during craniofacial re- construction. They are also the material of choice in the repair of large bone defects resulting from trauma or tumor resection. Standard iliac bone graft harvesting pro- cedures include harvesting of tricortical crest for grafts providing structural support, bicortical subcrestal window to fill bone gaps in the oral and maxillofacial areas, and unicortical bone from the anterior or posterior aspect of the ilium. 17,23,32 A review of the literature pertaining to iliac crest bone graft harvesting reveals major complication rates ranging from 5.8% (in a retrospective evaluation of 414 consecu- tive cases) to 8.6% (after 243 bone grafts from various sites, 90% from the iliac crest). 2,33 Large full-thickness iliac rim defects can be associated with significant post- operative complications including vascular injuries, deep infections at the donor site, neurological injuries, deep hematoma formation requiring surgical intervention, and iliac wing fractures. 2,33 Other complications include signif- icant long-term pain and cosmetic deformities. 9,16,27,29 Perhaps the most dramatic complication associated with harvesting of the full-thickness and tricortical iliac crest bone grafts is herniation of the abdominal contents through the donor site defect. Although this is a relatively rare complication, there have been more than 20 reported cases. 8,11,19,25,26 Associated complications, including incar- ceration, volvulus, and strangulation of the small bowel, have also been described. 4,17 Regeneration of the donor site defect is desirable to facilitate reharvesting of bone in patients requiring exten- sive reconstruction or multiple grafting of the same lesion. There have been reported advantages of decreased post- operative pain associated with reconstruction of the iliac crest donor site. 12,13,27,29,30 Lemperle, et al., 18 investigated the concept of protected bone regeneration in a canine model by using titanium mesh to prevent the ingress of soft tissue into the bone healing site. The protected site facilitated bone healing by preserving the space, thereby allowing the unimpeded regeneration of healing bone. Moed, et al., 22 investigated the potential for reharvesting of iliac crest cancellous bone after using the hinged-door harvesting method and concluded that cancellous bone was available for reharvesting 24 months after the initial grafting procedure. A similar study in dogs by Montgom- ery and Moed 23 revealed that the cancellous bone of the J Neurosurg (Spine 4) 97:456–459, 2002 456 Use of a resorbable sheet in iliac crest reconstruction in a sheep model G. BRYAN CORNWALL, PH.D., P.ENG., DONNA L. WHEELER, PH.D., KEVIN A. THOMAS, PH.D., WILLIAM R. T AYLOR, M.D., AND A. SIMON TURNER, B.V.SC., M.S., DIPL. A.C.V.S. MacroPore Biosurgery, Inc., San Diego, California; Colorado State University, Fort Collins, Colorado; and University of California San Diego, California Object. Iliac crest bone graft harvesting can result in major complications, the rates of which range from approximate- ly 6 to 8%. The objective of this study was to evaluate the postoperative regeneration of iliac crest donor defects in an ani- mal model after harvesting a full-thickness tricortical graft. Methods. In skeletally mature sheep, a tricortical iliac crest graft was harvested. The graft sites were allowed to heal unprotected or protected with the resorbable polylactic acid sheet material, MacroPore OS Protective Sheeting. After 6 months of healing, the sites were assessed by examination of undecalcified histological sections. Histomorphometric mea- surements of the original defect area, the area of new bone within the defect site, and the percentage of defect filled with new bone were quantified for both control and protected groups. In all histological sections, new bone growth within the defect sites appeared normal, with no observed excessive inflammatory cells. The developing bone tissue appeared to be remodeling normally. For the unprotected sites, the area of new bone averaged 16.3 mm 2 ( 7.2 mm 2 ), and the percentage of the defect area filled with bone averaged 10.7% ( 6.5%). In the protected sites, the area of new bone averaged 64.8 mm 2 ( 11.6 mm 2 ) and the percentage of the defect area filled with bone averaged 25.9% ( 1.6%). Both differences in area of new bone growth and percentage of defect area filled were statistically significant. Literature review has indicated that regeneration of donor site defects is desirable. Conclusions. Based on the results of the present study, MacroPore resorbable Protective Sheeting can improve bone regeneration significantly within the donor site following tricortical iliac crest graft harvesting. KEY WORDS • bioabsorbable implant • graft • iliac crest A J. Neurosurg: Spine / Volume 97 / November, 2002 Abbreviation used in this paper: ETOH = ethyl alcohol.