gms | German Medical Science

Introduction: During the last years a considerable number of different mouse models have been established to study the molecular mechanisms of bone healing. However, the different models are not well characterized. Therefore, the aim of the study was to analyze the influence of an open osteotomy versus open fracture on the mechanims of bone healing.

Material and methods: Forty CD-1 mice were used. The right femora of twenty mice were stabilized with an intramedullary screw after creating a fracture using a blunt guillotine. In another twenty mice, the femora were stabilized after performing an osteotomy with a Gigly saw. Bone healing was studied using radiological (mCT; n=8), biomechanical (n=16), histomorphometric (n=16) and protein biochemical analysis (n=8) at 2 and 5 weeks after stabilization.

Results: Histological analysis of the total callus area showed a significantly reduced amount of bone tissue (2,5±0,5mm² vs. 4,6±0,7mm²; p<0,04) and an increased amount of cartilage tissue (3,7±0,4mm² vs. 2,2±0,5 mm²; p<0,04) after osteotomy at 2 weeks compared to fracture. At 5 weeks cartilaginous tissue was still found increased with a significantly larger callus size after osteotomy (7,8±0,9mm² vs. 4,6±0,7mm²; p<0,02), indicating a delay in bone remodeling.

Accordingly, the radiological analyses showed a significantly reduced amount of newly formed bone tissue after osteotomy compared to fracture (bone volume/tissue volume: 21.9±0,4% vs. 29,5±2,5%; p<0,02).

Biomechanical analysis showed a significantly reduced bending stiffness after osteotomy at 2 (0,5±0,1% vs. 6,0±1,9%; p<0,01) and 5 weeks (13,2±2,0% vs. 56,2±13,0%; p<0,01).

Western blot analysis showed an increased expression of the angiogenic growth factors CYR61 and VEGF after osteotomy.

Conclusion: We herein demonstrate that an open osteotomy induces a marked delay of bone healing despite the comparable soft tissue trauma and stabilization technique, most probably due to periostal damage. This should be considered in future studies analyzing the mechanisms of bone healing.