Mechanical and Physical Properties of Regenerate Bone of Distraction Osteogenesis

Hahn, Soo Bong; Choi, Chong Hyuk; Park, Byeong Mun

Abstract

Distraction osteogenesis techniques have provided more than a clinical treatment of limb length discrepancies and bone deformities. The nature of this mechanical environment and the characteristics of the regenerate bone are not typical of that found elsewhere in the skeleton. The purposes of this study were to investigate the physical and mechanical properties of regenerate bone in different consolidation period (sacrificing at the period of 8, 12, 18, 20, 24, 26 weeks post surgery) and to find out the relationship between both properties. Two ring Ilizarov fixators were applied to the right tibia in 7 large, skeletally mature dogs. A subperiosteal osteotomy of tibia was performed. Postoperatively, after 7 days of latency period, distraction was begun. Distraction of 1mm daily, 3 times per day was continued until radiographic evidence of a 2.5 cm distraction. Sacrifice was at 8, 12, 18, 20, 22, 24, 26 weeks post surgery. Allof the specimens were obtained from regenerate bone and were cutted in the rectangular shape of approximately 8x4x4 mm. Specimens were tested in axial compression and displayed an average modulus of elasticity of 215(sd=184)Mpa, an average yield stress of 3.58(sd=2.54)MPa, an average apparent bone density of 0.399(sd=0.107)g/cc, and an average ash weight density of 0.164(sd=0.084)g/cc. A linear regression of yield stress on modulus of elasticity was significant(p < 0.001) with R-square=0.28, and a slope of 0.007. The radiographic bone densitometry was performed before sacrifice. The results of densitometry of regenerate bone was osteoporotic comparing with those of the opposite tibia which did not be operated in all of the animals. The linear regressions of mechanical properties on physical properties were significant, only 12-34% of the variance in mechanical properties could be explained by the physical properties. In conclusion, based on the observation of the low ash fraction, it would be expected that the relationship between physical properties and mechanical properties may not be strong. This study suggested that the regenerate bone was a composite of bone and non-mineralized tissue until 26 weeks of post surgery. For the more accurate information of material property, testing of real regenerate bone without non-mineralized bone may be necessary.