BACKGROUND:
Cranioplasty in children is difficult because supply of autologous bone is limited and alloplastic materials are not recommended. To expand available calvarial donor sites, surgeons have used bone-dust produced by high-speed drilling and particulate bone obtained with a hand-driven brace and bit. While particulate bone has been shown clinically to heal cranial defects, bone-dust has demonstrated variable success. The purpose of this study was to compare the efficacy of bone-dust verses cranial particulate bone for inlay cranioplasty.
METHODS:
A critical-size (17mm x 17mm) full-thickness defect was made in the parietal bone of 17 adult male New Zealand White Rabbits. Animals were divided into three groups. Group I (n=5) control defects were left open. Group II (n=6) defects were filled with bone-dust. Group III (n=6) was treated with particulate bone graft. Bone-dust and particulate graft were obtained from the frontal bone using a high-speed burr or Hudson brace and D’Errico bit, respectively. To determine ossification of the critical-size defects, computed tomography (CT) was conducted 8 and 16 weeks following cranioplasty. In order to assess the possible importance of particle size, the average volume of each piece of bone-dust and particulate graft was determined by measuring the dimensions of 50 particles of each material with a micrometer.
RESULTS:
Eight weeks postoperatively, control Group I healed 19.2% (+/-5.1) of the cranial defect, Group II ossified 39.5% (+/-11.2) of the area, and Group III showed 80.0% (+/-12.5) ossification. At the completion of the study 16 weeks postoperatively the critical-size defect in Group I healed 47.3% (+/-7.8), Group II ossified 50.1% (+/- 9.4), and Group III defects were 98.6% (+/-1.8) closed. Group III had significantly greater ossification compared to Group I or II (p=0.01). There was no difference in ossification between Groups I and II (p=0.7). Mean particle volume for bone-dust was 7.2 X 10³ μm³ (range, 100.0 to 8.0 x10³ μm³), the smallest dimension was thickness (mean= 2.0μ) (range, 1.0 to 6.0 μ) (p=0.0001). Particulate bone pieces had a larger volume of 2.6 X10⁶ μm³ (range, 4.8 X 10⁵ to 9.0 X 10⁶ μm³), the smallest dimension was thickness (mean= 20.0 μ) (range, 17.0 to 28.0 μ) (p=0.0001).
CONCLUSIONS:
Particulate bone graft successfully heals full-thickness cranial defects, in contrast to bone-dust which shows no efficacy compared to non-treated controls. Thus, particulate bone, and not bone-dust, should be used clinically for inlay cranioplasty. The difference in efficacy between particulate bone graft and bone-dust may be related to particle size; bone-dust is small enough to be digested by macrophages. In addition, bone-dust is subjected to thermal injury from the high-speed burr used for harvesting, unlike particulate graft, which is obtained with a hand-driven brace and bit.