Bone healing of critical size defects of the rat femur after the application of bone marrow aspirate and two different rh-BMP7 concentrations

It is known that the application of growth factors can enhance fracture healing in defect fractures. The role of bone marrow aspirate (BMA) in combination with BMP-7 and the dosage of rh BMP-7 are still under discussion. Our hypothesis was that the combination of rh-BMP-7 with BMA can heal bone defects more effectively than rh-BMP-7 alone. Twenty-eight rats obtained a 5 mm critical size defect in the diaphysis of the right femur which was stabilized by a plate. Rh-BMP-7 was applied at 10 and 200 A mu g either with collagen or together with collagen and BMA. Collagen only and collagen with BMA served as control groups. Blood flow was assessed by laser Doppler flowmetry in regular time intervals until euthanasia. Callus formation and bone density were measured by micro-computed tomography and biomechanical stability was evaluated by torsional testing at 4 weeks, postoperatively. Blood flow increased at the operated side after surgery until the second postoperative week independent of treatment. Animals treated with high dose BMP-7 showed significantly (p = 0.001) increased mechanical stiffness independent of BMA treatment. Failure loads were lowest for the two control groups (p = 0.001). The reduction of the BMP-7 dose led to less callus tissue and lower biomechanical stability. BMA did not show significant influence on bone healing. The combination of an rhBMP-7 dose that would be equivalent to a dose used clinically in humans with bone marrow aspirate does not heal a critical bone defect more effectively than the same rhBMP-7 dose alone.