The use of bone grafts and alloplastic materials in cranioplasty.

Trephination dates from prehistoric neolithic times (10,000-7000 B.C.) and is the oldest operation known. Cranioplasty with bone allografts dates from the Stone Age Celts. Through the millennia, generations of surgeons have tried bone autografts, allografts, and rarely xenografts for cranioplasty but abandoned these in favor of alloplastic metals and plastics, most recently methylmethacrylate. Disillusionment with bone cranioplasty has followed the recurrent experience that orthotopic transplantation of bone to skull is almost invariably accompanied by a striking propensity for resorption. Resorption coupled to new bone formation is the usual process of remodeling. A unique acellular nonosteoclastic resorption, antedating invasion of the graft by osteoprogenitor cells and unrelated to the remodeling, characterizes the initial response of bone placed in a skull bed. This previously undescribed resorption in the skull likely represents passive diffusion of mineral from an altered matrix (calciolysis) and varies directly with the degree the graft is denatured by processing. There is the least amount of resorption in the fresh autograft and the most in autoclaved or chemically treated frozen or freeze-dried grafts. Remodeling of this diminished template occurs centripetally from skull defect margins through osteoconductive mechanisms only. Marrow-poor skull with thin diploe provides few osteoprogenitor cells that slowly, incompletely remodel the reduced graft over years.

Toward uniformity in evaluating results of lumbar spine operations. A paradigm applied to posterior lumbar interbody fusions.

Criteria for evaluating the results of treating lumbar spinal disorders vary widely. Comparative analyses of outcome among different therapy protocols are compromised by the diversity among the groups studied, as well as by the varying methods of measuring success. A rating scale is proposed based on the economic and functional status of the patient before and after treatment; anatomic results can be correlated. Application of this method to 34 patients who had undergone posterior lumbar interbody fusion showed a favorable response in 85% with a fusion incidence of 94%. This rating scale is easily applicable and can delineate pre- and postoperative conditions of patients on a semiquantitative basis. A more universal acceptance of common criteria for judging the outcome of lumbar spinal operations will facilitate comparisons among various methods of treatment.

Quantitative comparisons of healing in cranial fresh autografts, frozen autografts and processed autografts, and allografts in canine skull defects.

Adult dog skull defects larger than 17 mm do not spontaneously heal. A quest for a potentially viable, cosmetically, mechanically, and technically acceptable template for human cranial reconstruction prompted a comparison of processed autogeneic and allogeneic bone implants with a fresh autograft control in the dog. Quantitative reproducible observations demonstrated that fresh calvarial bone autografts were superior to the nonviable implants in volume percent defect filled, mm2 new cortical bone, mm2 new and old cortical bone, and cortical bone porosity. Frozen autografts achieved 75%, antigen-extracted, autolyzed, partially demineralized auto- and allografts, 50% of the overall efficiency of fresh autografts. Fresh cancellous bone added to allografts did not improve long-term repair. Remodeling of all grafts appeared consistent with osteoconductive invasion by peripheral host endosteal and diploic elements; host external periosteum and dura contributed less. Central osteoinductive recruitment of mesenchymal cells from muscle or dura seemed not to occur in the adult dog. Partially demineralized dog calvarial grafts were resorbed without acting as a template for new bone formation. Surface demineralization, antigen extraction, and autolytic digestion of autografts and allografts, with or without fresh iliac bone, did not improve calvarial bone regeneration in adult dogs.

Composite autogeneic human cranioplasty: frozen skull supplemented with fresh iliac corticocancellous bone.

Skull totally exteriorized during craniotomy becomes nonviable. Resorption of the reimplanted cranial section occurs variably according to its treatment, the properties of the recipient bed, and the metabolic conditions of the host. Neurosurgeons commonly deep freeze autogeneic skull for preservation before delayed autogeneic cranioplasty. Aseptic necrosis commonly follows replacement of the autograft in its former cranial bed. This clinical study of six patients represents an attempt to block this destructive resorption by supplementing the frozen autograft with fresh corticocancellous autogeneic ilium. Observations of these patients ranging in age from 12 to 52 years support the following conclusions: (a) Osteogenesis was not enhanced by the addition of fresh corticocancellous bone to the frozen autoimplant. (b) The period of time that the autoimplant was frozen did not influence its subsequent biological behavior after cranioplasty. (c) Sterilization with ethylene oxide and in one case additional gamma irradiation did not impair the quality of the implant compared to those not sterilized. (d) Resorption occurred in both frozen and fresh but devitalized autogeneic skull. (e) Autogeneic skull is repaired by osteoconduction rather than by inducing competent perivascular stem cells to become osteogenic. (f) Freezing of autogeneic skull for preservation is practical, acceptable, but suboptimal from the perspectives of cerebral protection and cosmetic reconstruction. (g) The supplementation of the frozen autoimplant with fresh corticocancellous bone increases operating time and patient discomfort without affording additional benefit.

Clinical utility of allogeneic skull discs in human craniotomy.

One hundred fifteen burr hole defects were filled with sterilized human cadaver skull in 45 patients ranging in age between 10 and 88 years. One to 6 allogeneic skull discs per patient were placed in all areas of the calvaria. The length of postoperative observation ranges between 6 months and 5 years. No instances of infection, resorption, or rejection have occurred. Discs became incorporated and were osteoconductive, with new bone formed by "creeping substitution." In contrast to frozen autogeneic skull, these allogeneic discs were not resorbed. Allogeneic skull may be used safely and effectively to fill small discontinuity defects in the human calvaria.

Human bone morphogenetic protein (hBMP).

Human bone morphogenetic protein (hBMP) was chemically extracted from demineralized gelatinized cortical bone matrix by means of a CaCl2 X urea inorganic-organic solvent mixture, differential precipitation in guanidine hydrochloride, and preparative gel electrophoresis. hBMP is isolated in quantities of 1 mg/kg of wet weight of fresh bone, and has the amino-acid composition of an acidic polypeptide. The mol wt is 17 to 18 k-Da (kilodaltons). Implants of the isolated 17-kDa protein are very rapidly adsorbed and produce a smaller volume of bone than protein fractions consisting of 24-, 17-, and 14-kDa proteins. Since the isolated 24- and 14-kDA components lack hBMP activity, the kinetics of the bone morphogenetic processes including the function of other proteins as carrier molecules, await investigation.

Superior osteogenesis in transplanted allogeneic canine skull following chemical sterilization.

Sterilization of allogeneic bone increases the availability of this tissue for supplanting skeletal defects and effecting fusions. The optimal sterilant destroys micro-organisms, preserves the physical and chemical integrity of bone and possibly even reduces immunogenicity. Cortical bone of skull heals slowly and is variably resorbed. Of 36 dogs, spontaneous regeneration in 72 paired 20 mm defects was constant but always incomplete, and restored only about one third of the cross-sectional area of the defect at six months. The repair in defects replaced with canine allogeneic bony disc, sterilized with ethylene oxide (n = 9), gamma irradiation (n = 7), or methanol/chloroform/iodoacetic acid (n = 7) and then lyophilizedd, was compared with repair in defects filled with aseptically procured lyophilized only (n = 23) discs from the same donor. Criteria for evaluation of implants at six months included volume of defect filled, radiodensity, extent of fusion around circumference, revascularization, and remodeling. Bony discs sterilized with methanol/chloroform/iodoacetic acid remodeled at a superior rate (p less than 0.01). Radiation sterilization resulted in diminished density and inferentially reduced protection of the brain (p less than 0.025). Ethylene oxide, lyophilized implants, and implants lyophilized only produced comparable repair. Whereas an acceptable cranioplasty was achieved in 86% of methanol/chloroform/iodoacetic acid, lyophilize implants, all other alloimplants served an osteoconductive function with a successful repair occurring in 56% to 58%.