Related knowledge
The commonly used methods to preserve autologous cranial bone are in vivo preservation and in vitro preservation. In vivo preservation: autologous cranial bone is mostly subcutaneously preserved, i.e., autologous cranial valves were preserved under the abdominal wall, femoral skin or epicranial aponeurosis. As required, cranial valves are transplanted back for repair of cranial defects. In vitro preservation: free cranial valves were soaked in ethanol, chlorhexidine, glycerol, and povidone iodine to maintain their aseptic condition. Other preservation methods include cryopreservation[6-7], irradiation, and ethylene oxide sterilization. As for irradiation preservation, a 25 Gy of irradiation dose can kill all bacteria and this method can maintain the bioactivity of cranial valve the same as fresh bone, as determined by pathological examination. Optical examination of pathological sections showed that the cranial valves in vivo preserved for more than 2 years remained the basic normal bone structure; in contrast, all osteocytes of in vitro preserved cranial valves died after alcohol soaking, but the normal bone structure constructed by organics and calcium salt is not destroyed.
Periosteum is a dense connective tissue membrane and covers bone surface. It contains abundant vessels, nerves and osteoblasts. Periosteum promotes bone growth and regeneration. Childhood periosteal osteoblasts can consistently produce new bone tissue to thicken bone, and periostal osteoblasts contribute to fracture healing and bone regeneration. Excessive stripping of periosteum during surgery would hinder bone nutrition providing and regeneration, which influences fracture healing and even causes osseous necrosis. A study[8] reported that cultured and cryopreserved periosteal cells can give rise to bone and cartilage tissue after directly injected into a subcutaneous site in athymic mice. Cranial periosteum has been shown to exhibit the potential to regenerate and promote the formation of new bone[9]. The cranial valve with periosteum embedded subperitoneally can obtain nutrition from subcutaneous blood capillaries and adjacent tissue fluid, thereby to maintain the bioactivity of periosteal osteoblasts and prolong the lifespan of bone valve.
Bias or shortcomings
All 100 patients succeed in repair of cranial defects by cranial valves with periosteum, with no hydrops beneath the scalp or infection. They felt uncomfortable because of foreign substance, but their daily life was not greatly influenced. There was no obvious appearance difference between surgical and contralateral sides. Six months later, of 56 patients receiving brain CT examination, 30 showed no obvious absorption of cranial valve with periosteum but clear bone edge, the remaining 26 showed vague edge of cranial valve with periosteum. The healing of the cranial valve edge was negatively correlated with patients’ age. In the present study, two patients complained of osseous geloses in the abdominal part 9 months after removal of cranial valve with periosteum and had them taken out. This demonstrates that periosteum acclimates subcutaneous environment and survives, and following removal of cranial valve with periosteum, periosteal osteoblasts subcutaneously divide, proliferate and then give rise to rigid osseous tissue. More cases should be included to make a longer period of follow-up.
Clinical significance
Results from this study demonstrate that cranial valve with periosteum embedded subperitoneally can maintain its shape, size, and bioactivity for long time and provide data, imaging and time evidence for clinical surgery. Such a cranial repair material exhibits advantages over other cranial repair materials[10-11]. Autologous cranial valves are the cranial bone from defect region, and they fully anastomose cranial defect region in shape and size, with no need of trimming. In addition, easy operation, short surgical time, few infections, reliable postoperative fixation, good appearance, and no aesthetic compromises are satisfactory. More importantly, normal physiological curves recovered and normal cranial cavity structure maintained promote local hemodynamic recovery, and thereby contribute to postoperative recovery of neurological functions[12].
