Disclaimer: The information contained within the Grand Rounds Archive is intended for use by doctors and other health care professionals. These documents were prepared by resident physicians for presentation and discussion at a conference held at Baylor College of Medicine in Houston, Texas. No guarantees are made with respect to accuracy or timeliness of this material. This material should not be used as a basis for treatment decisions, and is not a substitute for professional consultation and/or peer-reviewed medical literature. Free Bone Grafts INTRODUCTION: There are many different types of bone grafts used for reconstructive surgery and the choice of graft depends on multiple factors, such as the extent of the defect or wound, the added operative time, donor site morbidity, and overall patient performance status. The three general categories of grafts are: (1) free bone grafts, (2) free grafts placed in contact with vascularized muscle flap, and (3) fully vascularized bone flap. Free bone grafts involve bone only, with no vascular pedicle, soft tissue, or muscle component. Free grafts can be divided into autograft, such as calvarial, rib, and iliac bone; or allograft, which includes irradiated, freeze dried, and demineralized bone from a donor patient. The autograft, however, is less desirable because of significant resorption, loss of function, and fibrosis reaction. Free bone grafts placed in contact with a vascularized muscle flap have the theoretical advantage of increased survival, but have the disadvantage of an added procedure. The vascularized bone flap has the best survival and function because the native blood supply remains in direct contact with the graft. Calvarium bone pedicled to temporalis muscle and vessels, rib attached to intercostal muscle and vessels, and iliac crest pedicled to internal oblique muscle and vessels are common choices in reconstruction. Although survival and function are greatly improved, the procedure is much more extensive and technically challenging. MEMBRANOUS VS. ENDOCHONDRAL BONE GRAFTS There are two basic types of bone with respect to embryologic formation, and some debate exists as to which is preferable for grafting. Membranous bones include the flat bones of the cranium, face, and mandible (the mandible has some endochondral component with Meckel's cartilage origin). These bones form by intramembranous ossification in which embryonic mesenchymal cells differentiate directly into osteoblasts that synthesize a collagenous osteoid. The osteoid then becomes hard bone after undergoing mineralization by calcium phosphate. Endochondral bones are the long bones of the skeleton (including iliac and rib) as well as the petrous, occipital, ethmoid, mastoid, and sphenoid. These bones form by endochondral ossification whereby cartilage growth occurs at an epiphyseal surface which is then replaced by osteoid that eventually becomes mineralized. Controversy exists as to which type of bone has less resorption, but the literature points to membranous bone as the graft with greatest survival. Smith and Abramson (1974) used a rabbit animal model to study the survival of calvarial versus iliac bone grafts placed both subperiosteally and subcutaneously. They found that after 1 year the calvarial grafts retained their original thickness and had been completely replaced by new bone. The iliac (endochondral) bone, however, had undergone 75% resorption with only a thin shell of cortical bone and scant marrow remaining. Zins and Whitaker (1983) studied zygomatic and calvarial versus iliac grafts in rabbits and monkeys and found, after 20 weeks, that the membranous bone grafts (zygomatic, calvarial) had 20% resorption and the endochondral (iliac) graft had 65 to 88% resorption. Although there are many theories as to why the difference in resorption occurs, Kusiak's work (1985) provided objective data that demonstrated improved vascularization of the membranous grafts and thus enhanced survival. FREE BONE GRAFT SITES Of the endochondral bones, rib and iliac crest are the most commonly used free grafts. Rib grafts have an advantage in that they have a similar contour to skull, they can be shaped easily to fit many defects, long (14cm) grafts can be harvested to bridge large defects, and regeneration occurs at the donor site if periosteum is left intact. The disadvantages are the possibility of pneumothorax, postoperative pain, second scar, and resorption. Iliac crest grafts provide an abundant supply of cancellous bone, and inner or outer cortex may provide appropriate contour. The disadvantages include limited supply of cortical bone, postoperative pain and hematoma, acetabular injury, fascia lata clicking, and pain with paresthesias if injury to lateral femoral cutaneous nerve occurs. The most common membranous bone graft is the calvarial graft. This bone graft has minimal donor site pain and its harvest can typically be incorporated into incisions made for the primary reconstruction (i.e. bicoronal incision). The donor site defect can often be hidden by the hair, has a useful gradual curvature, and minimal resorption occurs. The disadvantages of calvarial grafts include the risk of epidural hematoma from damage to the sagittal or other dural sinuses, dural tears, limited shaping because of bone rigidity, and limited amount of cancellous bone. The risks of intracranial complications and donor site deformity can be minimized by using split calvarial instead of full thickness bone grafts. The skull as a donor site has further advantages in that skull chips or shavings as well as bone dust can be harvested to fill certain defects that do not require a formal graft, or can be used to augment a bone graft. CONCLUSION The source of bone graft appears to be the most important factor when choosing a graft for reconstruction. Membranous and endochondral factors such as resorption must be considered for long term outcome, and donor site and technical aspects of the actual harvest are important issues to consider. The ideal recipient site should provide good blood supply adequate bony contact, and the graft should be secured to minimize mobility. Case Presentation A 47-year-old male was brought to BTGH after a self-inflicted gunshot wound to the oral cavity with a .22-caliber rifle. He denied loss of consciousness and was alert and oriented upon presentation. Physical exam demonstrated ecchymoses and swelling over the left malar and periorbital region. Visual and extraocular movements were intact and an exit wound was identified lateral to the orbital rim. An infraorbital rim stepoff and comminuted zygomatic arch fracture were present, and intraoral exam revealed a defect in the left buccal mucosa. Cranial nerve exam was significant for a moderate weakness in the lower division of the facial nerve. Facial x-ray series confirmed an orbital rim and trimalar fracture with a comminuted zygomatic arch, and CT scanning concurred with these findings while also revealing an orbital floor defect. The patient underwent transconjunctival orbital exploration with teflon repair of the floor and microplate oper reduction internal fixation of the orbital rims. Reconstruction of the left zygomatic arch was performed using a split calvarial bone graft. Bibliography Dingman RO. Use of iliac bone in the repair of facial and cranial defects. Plast Reconstr Surg 1950;6:170-175. Gruss JS, MacKinnon SE. Complex maxillary fractures: role of buttress reconstruction and immediate bone grafts. Plast Reconstr Surg 1986;78:9-21. Gruss JS, Mackinnon SE, Kassel EE. Role of primary bone grafting in complex craniomaxillofacial trauma. Plast Reconstr Surg 1985;75:17-24. Jackson IT, Pellett C, Smith JM. Skull as a bone graft donor site. Ann Plast Surg 1983;11:527-532. Khouri RK, Basem K, Reddi H. Tissue transformation into bone in vivo. JAMA 1991;266:1953-1955. Kusiak JF, Zins JE, Whitaker LA. Early revascularization of membranous bone. Plast Reconstr Surg 1985;76:510-514. Longacre JJ, deStefano GA. Reconstruction of extensive defects of the skull with split rib grafts. Plast Reconstr Surg 1957;19:186-190. Luyten FP, Cunningham NS, Ma S, et al. Purification and partial amino acid sequence of osteogenin, a protein initiating bone differentiation. J Biol Chem 1989;264:1528-1534. Manson PN, Crawley WA, Yaremchuk MJ, et al. Midface fractures: advantages of immediate extended open reduction and bone grafting. Plast Reconstr Surg 1985;76(1):1-10. Mark DE, Hollinger JO, Hastings C Jr, et al. Repair of calvarial non-unions by osteogenin, a bone-inductive protein. Plast Reconstr Surg 1990;86:623-630. McCarthy JG. In: McCarthy JG, editor. Plastic Surgery, volume 2. Boston: WB Saunders Company, 1990. Petroff MR, Burgess LP, Anonsen CK, et al. Cranial bone grafts for post-traumatic facial defects. Laryngoscope 1987;97:1249-1253. Sampath TK, Muthukumaran N, Reddi AH. Isolation of osteogenin, an extracellular matrix-associated, bone-inductive protein, by heparin affinity chromatography. Proc Natl Acad Sci USA 1987;84:7109-113. Shehadi SI. Skull reconstruction with bone dust. Br J Surg 1970;23:227-230. Smith JD, Abramson M. Membranous vs. endochondral bone autografts. Arch Otolaryngol 1974;99:203-205. Tessier P. Autogenous bone grafts taken from the calvarium for facial and cranial applications. Clin Plast Surg 1982;9:531-540. Urist MR, DeLange RJ, Finerman GAM. Bone cell differentiation and growth factors. Science 1984;220:680-686. Zins JE, Whitaker LA. Membranous versus endochondral bone: implications for craniofacial reconstruction. Plast Reconstr Surg 1983;72:778-784. Grand Rounds Archive | Department Home page BCM Public | BCM Intranet | Privacy Notices | Contact BCM | BCM Site Map | ©2001-2006 Baylor College of Medicine
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