Radiomorphometry and biomechanical assessment of recombinant human bone morphogenetic protein 2 and polymer in rabbit radius ostectomy model

The study objective was to determine the mechanical integrity and radiopacity of regenerated bone within critical‐sized defects (CSDs) in radii of rabbits using recombinant human bone morphogenetic protein 2 (rhBMP‐2) with a porous, biodegradable poly(D,L‐lactic acid) (PDLLA) carrier (designated PLA). Twenty millimeter, unilateral radial ostectomies were created in 96 skeletally mature New Zealand white rabbits. The rabbits were randomly assigned to six treatment groups with two euthanasia periods. Treatment groups included unfilled defect (n = 8), segmental autograft (n = 8), PLA + 0 μg rhBMP‐2 (n = 8), PLA + 17 μg rhBMP‐2 (n = 8), PLA + 35 μg rhBMP‐2 (n = 8), and PLA + 70 μg rhBMP‐2 (n = 8). The radiopacity was significantly greater for the 35‐ and 70‐μg rhBMP‐2 groups at 4 weeks compared to unfilled controls, PLA only, and 17‐μg rhBMP‐2 groups and equivalent to the autograft. At 8 weeks all groups receiving rhBMP‐2 were equivalent to the autograft and significantly greater than unfilled defects and PLA alone. Similarly, the biomechanical analysis indicated significantly greater torque at failure for the 35‐μg rhBMP‐2 group compared to all other groups at 4 weeks. By 8 weeks all groups receiving rhBMP‐2 and autograft had significantly greater torque than unfilled controls and PLA alone. These radiomorphometric and biomechanical results indicate PLA may be a suitable carrier for rhBMP‐2 used for skeletal regeneration. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 43: 365–373, 1998