ABSTRACT
PURPOSE: To evaluate and compare the spontaneous regeneration repair process in femoral bone defects in 6-week-old rabbits and to compare the healing time periods between different rabbit groups. MATERIALS AND METHODS: Bone defects were created at the femur mid-shaft and an external fixator was applied in 50 rabbits. The periosteum was resected in 10 rabbits (defect size: 15%, 25%) and left untouched in the remaining rabbits. Forty rabbits were divided into four groups according to the percentage of bone defects (15%, 20%, 25%, 30%). Radiographs were taken weekly to evaluate the bone regeneration and union. The bone union time was measured between the osteotomy and the cortico-medullary differentiation by examining radiographs. The healing index was defined as the union time (week) per amount (cm) of bone defect. Eight rabbits, 2 from each groups with the bone defects, were investigated by histopathologic examination. RESULTS: The mean union time was approximately 7.0 to 7.3 weeks. The healing index in groups that had a large percentage of bone defects was less than in groups that had a small percentage of bone defects. The periosteum-resected group did not show bone regeneration. Histopathologic examinations showed intramembranous and atypical endochondral ossifications along the periosteum and typical endochondral ossification at the center of the bone defects. CONCLUSION: Spontaneous bone regeneration may be used in children to fill the bone defect instead of performing an internal bone transport. Spontaneous bone regeneration is useful in cases of mid-shaft bone defects or when the remaining bone fragments are large enough for an external fixation application.