Most fractures heal uneventfully but some evolve into nonunions. Autologous bone graft is the gold standard for stimulating healing. However, donor site morbidity, and limited graft supply make alternatives interesting. Bone Morphogenetic Proteins, BMPs, are growth factors involved in bone signaling. They are available in recombinant form for local application in nonunions and stimulate differentiation and proliferation of osteoblasts. However, BMPs also induce osteoclastic activation, which can lead to callus resorption. In this thesis, we hypothesized that concurrent treatment with the bisphosphonate zoledronate (ZOL) could counteract this resorption, leading to superior healing compared to isolated BMP-7 treatment. In studies 1, 2 and 3, the synergistic effect of BMP-7 and zoledronate was investigated in a rat femoral osteotomy model, that untreated is known to heal in only 60 %.

In study 1, autograft was compared with autograft+BMP-7 and autograft+BMP-7+ZOL with the hypothesis that the latter treatment would lead to superior healing compared with the others. All three treatments increased the healing rate from 60 % to 100 %. The autograft group reached half the strength compared with the non-operated controls, while the autograft+BMP-7 and the autograft+BMP-7+ZOL equaled and doubled the strength of the controls respectively.

In study 2, we investigated if allograft+BMP can replace autograft. Allograft and different combinations of allograft, BMP-7 and ZOL were compared with;​ no treatment, autograft and autograft+ZOL with the hypothesis that allograft+BMP-7+ZOL would lead to superior union compared with autograft. Allograft+BMP-7+ZOLtreatment yielded a substantially higher peak force than all other groups.

In study 3, we investigated if the testing method influenced the results of the mechanical tests. BMP-7 and BMP7+ZOL were compared with controls and each other. Calluses were tested both in three-point bending and twisting. All femurs healed. BMP-7+ZOL-treatment led to higher ultimate force and greater stiffness than BMP-7 alone. This difference was most evident in the three-point bending test

In study 4, the Masquelet induced membrane technique, was used to study the healing of a 6 mm rat femoral critical size defect. A synthetic scaffold was compared with BMP-7, BMP-7+scaffold and BMP-7+scaffold+ZOL. We found the combination of BMP-7+scaffold+ZOL to be superior to the other treatments.

In conclusion we could show a synergistic effect by concurrent treatment with BMP-7 and zoledronate in all four studies. This supports the use of the combination, either alone or as a supplement to autograft, allograft or synthetic scaffold in both nonunions and bone defects.