Split Cranial Bone Grafting in Children Younger Than 3 Years Old: Debunking a Surgical Myth

Autologous bone grafts are the sine qua non in pediatric cranioplasty.1–4 They are preferred over alloplastic materials because of their high biocompatibility and strength profiles; commensurate expansion with the rapidly growing brain; and their ability to promote osteoconduction, osteoinduction, and osteogenesis.5,6 Furthermore, the use of alloplastic materials is inherently associated with higher rates of infection and extrusion, especially when there is direct communication with the paranasal sinuses.7–9 In the first year of life, the osteogenic potential of the dura allows smaller cranial defects to be left open; however, the bone derived from dural regeneration tends to be uneven and unpredictable in thickness and irregular in contour. In addition, larger defects tend not to fully reossify, thus necessitating coverage with a graft.10 Common sources of autologous bone for grafting of the craniofacial skeleton include the cranium, ribs, and iliac crest, but the cranium is uniquely suited for this purpose because of its favorable cross-sectional anatomy and its ability to recapitulate the native bone in both form and function. It exists as a tripartite structure consisting of a resilient inner and outer cortex separated by an intervening diploic space. The diploic space is filled with soft cancellous bone that facilitates splitting of the cranium into separate bone fragments that are similar in size, shape, and contour. These bone fragments can then be used as grafts in the reconstruction of the cranial vault, essentially doubling the amount of autologous bone available.11 As a semirigid material, split cranial bone is easily contoured in young patients and fundamentally “replaces like with like.” A recurring theme in the literature is that cranial bone is too thin for splitting in both infants and children younger than 3 years.1,12–14 The prevailing concept is that the inner and outer table of the cranium cannot be separated before formation of the diploe—a statement often repeated in textbooks.15,16 As a result, particulate bone grafting is often touted as the procedure of choice in these young patients, given its relative ease of harvest, minimal morbidity, and ability to reossify larger calvarial defects because of the underlying dural osteogenic potential.1,10,17 Although particulate bone grafting may be a useful technique in certain situations, it does not afford the structural integrity or resistance to resorption often called for in cranial vault reconstruction. Split cranial bone grafting is used exclusively in our practice at the University of Michigan. Our experience with split cranial bone grafting has led us to revisit the common dictum that cranial bone cannot be split before 3 years of age, because we routinely perform this technique in patients as young as 2 months. The impetus for reporting our experience with splitting cranial bone in pediatric cranioplasty patients is from a question on the 2012 Plastic Surgery In-Service Examination. The question asked the examinee to identify the most appropriate material for reconstruction of a 12-cm2 cranial defect in a 21-month-old child who had previously undergone a cranial vault remodeling procedure. Both particulate bone and split calvaria were offered as possible answers, but particulate bone was considered the most correct, citing that cranial bone is difficult to split before the age of 4 years. We found this explanation to be at great odds with our experience. For the past 17 years, the senior author (S.R.B.) has assigned the task of splitting cranial bone to the residents in all of his pediatric cranioplasties. Despite several recent publications demonstrating that cranial bone can indeed be split in children younger than 3 years,18,19 the application of this powerful technique in infants and children has regrettably become ingrained in craniofacial surgery as a surgical myth, on par with the prohibition of the use of epinephrine in the finger. In this study, we demonstrate the technique of splitting cranial bone in children younger than 3 years.