Background and purpose Metaphyseal fractures heal in a rapid fashion that is different from the bone shaft healing process. Animal studies have focused on diaphyseal fractures. We investigated the metaphyseal fracture-healing process in rabbits.Animals and methods 60 rabbits (divided into 12 groups) underwent proximal tibial osteotomy, anatomical reduction, and fixation with screws. After surgery, the proximal tibiae were harvested at different time points for histology.Results No obvious osteonecrosis or bone resorption were found 2 weeks after surgery. From day 5 to week 5, woven bone or new trabeculae formed. From week 2, remodeling into lamellar bone started and reached a peak at week 6. These 3 stages overlapped. Histomorphometry showed that the structure changed as a unimodal curve.Interpretation The healing process of metaphyseal fractures appears to differ from the commonly studied healing process in diaphyseal fractures. It is rapid, and can be divided into 4 histological stages: cellular activation and differentiation, formation of woven bone, transformation of woven bone into lamellar bone, and further remodeling.

Simvastatin, as one of the HMG-CoA reductase inhibitors for lowering lipids, has been demonstrated its potential benefit in bone formation, which was, however, conflicting and inconclusive in vivo studies. Thus, we performed this study to assess the in vivo effects of simvastatin on bone formation. Six-week old rats were administered with simvastatin (20 mg/kg/d) or vehicle for 6 or 9 weeks. All animals were sacrificed one day after the final administration. The left femora were removed for the measurement of bone histomorphometry and bone mineral density (BMD).Compared to the control groups, on both 6th week and 9th week, bone mineral density and bone histomorphometry detected no significant differences in bone mass and microarchitecture in simvastatin treatment group, as well as bone formatin/resorption parameters. These results indicate that simvastatin had no positive effect or impact on bone in rats administered with high dose simvastatin (20 mg/kg/d) for 6 or 9 weeks.