The absence of osseous consolidation of a fracture for 9 or more months with no potential to heal is defined as nonunion. Both for the patient and from a socioeconomic point of view, nonunions represent a major problem. Hypertrophic, vital nonunions are distinguished from atrophic avital ones. Risk factors for a delayed fracture healing are insufficient immobilisation, poor adaptation of the fracture surfaces or residual instability, interposition of soft tissue within the fracture gap, as well as circulation disturbances and infections. The incidence of nonunions after fractures of the long bones lies between 2.6 and 16% depending on the surgical technique used. In human and animal studies, a positive effect of parathyroid hormone (PTH) on fracture healing has been shown. PTH has a direct stimulatory effect on osteoblasts and osteoclasts. In addition, it appears to influence the effect of osseous growth factors. In this prospective study, 32 patients with nonunions were treated with teriparatide to investigate the effects of PTH on fracture healing. Definitive healing of the nonunions following PTH treatment could be observed in 95% of the cases.

The comparative investigation of a highly nanoporous bone grafting material (NanoBone S, NBS) and a sintered hydroxyapatite ceramic (Cerabone, CB) aimed to show the influence of the structure of the material on osteoinductivity.NBS consists of synthetic nanocrystalline hydroxyapatite embedded in a porous silica gel matrix. Its specific surface amounts 206 m2/g in contrast to CB with a specific surface of 0.4 m2/g.The biomaterials were implanted in the neck region of 18 sheep and left there for the periods of 6, 12 and 26 weeks. In each case granulate was implanted superficially into the trapezius muscle and into the subcutaneous adipose tissue respectively. The samples were analysed by micro-CT, histochemistry, immunohistochemistry and histomorphometry. In the case of NBS ossicles had developed. An intensive remodelling process was verifiable. The bone formation in CB was marginal.As a basic phenomenon in NBS, the substitution of the original SiO2 gel matrix by organic molecules forming an organic matrix around the embedded hydroxyapatite seams to be the key event causing these results.

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