gms | German Medical Science

Objectives: Delayed healing and non-union formation remain a substantial clinical problem. Non-union models in mice are of increasing interest as they allow to study the molecular basis of fracture healing with specific gene-targeted strains and antibodies. Large segmental bone defects have been successfully used to create non-unions in these animals. However, this approach does not resemble the pathophysiology of trauma-induced fractures, because the non-unions are induced by osteotomy. Thus, the aim of the present study was to develop and validate a novel non-union model in mice using periosteal cauterization.

Methods: CD-1 mice with an age of 12- 16 weeks were used. In the periosteal-cauterization group, a 0.6 mm K-wire was insertedinto the femoral canal in a retrograde fashion. Afterwards a transverse mid-shaft fracture was created by using a 3-point-bending device. Subsequently, the fracture site was exposed by a lateral approach and the periosteum was cauterized circumferentially over a distance of 1 mm on each side of the fracture site. In the segmental-defect group, a distally flattened pin was implanted through the intramedullary canal. Afterwards the femur was exposed by a second lateral approach to implant a 6 mm clip ventro-dorsally into the femur. Then, an osteotomy with a gap size of 1.8 mm was created using size-standardized spherical trephines. The femora were analyzed at 2, 5 and 10 weeks after surgery by radiology, biomechanics, µCT, histology and Western blot analysis. Values are expressed as mean ± SEM. Statistical significance: P < 0.05.

Results and Conclusion: The periosteal-cauterization group showed an increased bending stiffness at 2, 5 and 10 weeks (0.48 ± 0.08 vs. 3.58 ± 1.52 N/mm) after surgery when compared to the segmental-defect group. This was associated with an enhanced formation of low and high mineralized bone tissue. X-ray, µCT and histological analyses further revealed a reliable non-union formation in 8 out of 10 femora in the periosteal-cauterization group. In the segmental-defect group, however, radiological analysis revealed an atrophic non-union formation in 10 out of 10 femora. Moreover, Western blot analysis demonstrated an increased expression of bone morphogenetic protein 4 (1.14 ± 0.59 vs. 34.64 ±11.11 pixel intensity 10^4) receptor activator of NF-kappaB ligand (0.57 ± 0.3 vs. 21.62 ± 9.37 pixel intensity 10^4)as well as osteoprotegerin (0.62 ± 0.09 vs. 19.57 ± 6.05 pixel intensity 10^4), indicating an enhanced bone turnover in the periosteal-cauterization group.

Themodel using segmental defects showed a more reliable non-union formation when compared to animals with periosteal cauterization. Hence, this appraoch should be used for the establishment of treatment strategies for non-unions, especially tissue engineering applications. The model of periosteal cauterization, however, may be of particular interest for the evaluation of novel approaches focusing on regenerating injured periosteum in delayed and compromised fracture healing.